SYSTEM AND METHOD FOR DETERMINING DATA RATE
A hierarchical communication system is described in which two wireless local area networks exhibiting substantially different characteristics are employed to link inherently portable or mobile computer devices. A series of radio base stations make up a infrastructure network. The infrastructure network and at least one portable computer device make up the first local area network. The communication on the first local area network is accomplished by spread spectrum frequency hopping communication A second local area network allows for radio communication between a portable computer device and peripheral devices with built-in transceivers utilized by the portable computer device. The communication in each local area network is controlled by a reservation access communication protocol. The communication protocol facilitates frequency hopping synchronization and supports adaptive data rate selection based upon the quality of communication on the communication channel. The communication protocol prevents interference between communication on the first local area network and communication on the second local area network. In a premises LAN, a series of radio base stations and a backbone LAN make up an infrastructure network. The infrastructure network and at least one mobile computing device make up a higher-power LAN, utilizing a frequency hopping protocol. A lower-power LAN allows for radio communication between a mobile computing device and -peripheral devices, utilizing a single-frequency spread spectrum protocol. A vehicular LAN provides for short-range communication between a vehicle terminal and a portable terminal. When out of direct RF range of the premises LAN, the vehicle terminal maintains indirect communication when necessary with the premises LAN via one of several alternate RF channels. A microprocessor, located inside radio units which participate in multiple LAN'"'"'s, selects the appropriate protocol, frequency band and power level for communicating through the network.
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- 1-82. -82. (canceled)
- 83. A method of determining data rate in a direct sequence spread spectrum system, the method comprising:
receiving a signal that was transmitted at a particular data rate, wherein the particular data rate is one of a plurality of data rates and is unknown when received;
processing the signal according to a first data rate, thereby generating a signal corresponding to a sequence of bits; and
determining the particular data rate according to the sequence of bits.
- View Dependent Claims (84, 85, 86, 87, 88, 89)
- 90. A system for determining data rate in a direct sequence spread spectrum system, the system comprising:
one or more circuits for receiving a signal that was transmitted at a particular data rate, wherein the particular data rate is one of a plurality of data rates and is unknown when received;
wherein the one or more circuits process the signal according to a first data rate, thereby generating a signal corresponding to a sequence of bits; and
wherein the one or more circuits determine the particular data rate according to the sequence of bits.
- View Dependent Claims (91, 92, 93, 94, 95, 96)
- 97. A system for determining data rate in a direct sequence spread spectrum system, the system comprising:
at least one processor for receiving a signal that was transmitted at a particular data rate, wherein the particular data rate is one of a plurality of data rates and is unknown when received;
wherein the at least one processor processes the signal according to a first data rate, thereby generating a signal corresponding to a sequence of bits; and
wherein the at least one processor determines the particular data rate according to the sequence of bits.
- View Dependent Claims (98, 99, 100, 101, 102, 103)
- 104. A method of determining data rate in a communication system, the method comprising:
receiving a direct sequence spread spectrum signal that was transmitted at a particular data rate, wherein the particular data rate is unknown to the receiver, wherein the particular data rate is one of a high data rate and a low data rate, and wherein the high data rate is a binary multiple of the low data rate;
processing the direct sequence spread spectrum signal according to the high data rate, thereby generating a despread signal corresponding to a sequence of bits;
determining the particular data rate according to an occurrence of repetition in the sequence of bits; and
initiating proper decoding mechanisms for the particular data rate.
- View Dependent Claims (105)
- 106. A system for determining data rate in a communication system, the system comprising:
one or more circuits for receiving a direct sequence spread spectrum signal that was transmitted at a particular data rate, wherein the particular data rate is unknown to the receiver, wherein the particular data rate is one of a high data rate and a low data rate, and wherein the high data rate is a binary multiple of the low data rate;
said one or more circuits for processing the direct sequence spread spectrum signal according to the high data rate, thereby generating a despread signal corresponding to a sequence of bits;
said one or more circuits for determining the particular data rate according to an occurrence of repetition in the sequence of bits; and
said one or more circuits for initiating proper decoding mechanisms for the particular data rate.
- View Dependent Claims (107)
This application is a continuation in part of U.S. Application Serial Nos: a) Ser. No. 08/279,148, filed Jul. 22, 1994 (Attorney Docket Nos. 10082US11; DN37998XD); b) Ser. No. 07/876,629, filed Apr. 30, 1992 (Attorney Docket Nos. 92P275; DN36837D); and c) Ser. No. 08/267,758, filed Jul. 5, 1994 (Attorney Docket Nos. 10554US02; DN37613A).
The application U.S. Ser. No. 08/279,148 is a continuation-in-part of: PCT Application Serial No. PCT/US94/05037 filed May 6, 1994 (Attorney Docket Nos. 10082WO08; DN37998XAX); U.S. application Ser. No. 08/205,639 filed Mar. 4, 1994 (Attorney Docket Nos. DN37139XXA; 10458US03); and U.S. application Ser. No. 08/275,821, filed Jun. 10, 1994 (Attorney Docket Nos. 10082US10; DN37998XC).
PCT Application Serial No. PCT/US94/05037 is based on U.S. application Ser. No. 08/198,404, filed Feb. 22, 1994 (Attorney Docket Nos. 10082US07; DN37998XA), which is itself a continuation of U.S. application Ser. No. 08/198,452, filed Feb. 18, 1994 (Attorney Docket Nos. 10082US06; DN37998X), which is in turn a continuation-in-part of U.S. application Ser. No. 08/168,478, filed Dec. 16, 1993 (Attorney Docket Nos. 10092US06; DN37998E), and PCT Application Serial No. PCT/US93/12628 filed Dec. 23, 1993 (Attorney Docket Nos. DN37967C and 10082WO01). The application U.S. Ser. No. 08/168,478 is a continuation-in-part of U.S. application Ser. No. 08/147,377 filed Nov. 3, 1993 (Attorney Docket No. DN37998D), which is a continuation-in-part of U.S. application Ser. No. 08/101,254 filed Aug. 3, 1993 (Attorney Docket No. DN37998C), which is itself a continuation-in-part of U.S. application Ser. No. 08/085,662 filed Jun. 29, 1993 (Attorney Docket No. DN37998B), which is itself a continuation-in-part of U.S. application Ser. No. 08/076,340 filed Jun. 11, 1993 (Attorney Docket No. DN37998A), which is in turn a continuation-in-part of U.S. application Ser. No. 08/062,457, filed May 11, 1993 (Attorney Docket No. DN37998).
PCT Application Serial No. PCT/US93/12628 is based on pending U.S. application Ser. No. 08/027,140 filed Mar. 5, 1993 (Attorney Docket Nos. DN37967B; 10082US05), which is itself a continuation-in-part of U.S. application Ser. No. 07/997,693 filed Dec. 23, 1992 (Attorney Docket Nos. DN37967A; 10005US02), now abandoned, which is a continuation-in-part of U.S. application Ser. No. 07/982,292 filed Nov. 27, 1992 (Attorney Docket Nos. DN37967; 92 P 837), now abandoned, which is itself a continuation-in-part of U.S. application Ser. No. 07/700,704 filed May 14, 1991 (Attorney Docket Nos. DN37834X; 91P383), now abandoned, which is itself a continuation-in-part of U.S. application Ser. No. 07/699,818 filed May 13, 1991 (Attorney Docket Nos. DN37834; 91P862), now abandoned.
The application U.S. Ser. No. 08/205,639 is a continuation-in-part of U.S. application Ser. No. 07/735,128 filed Jul. 22, 1991 (Attorney Docket Nos. DN37139XX; 91P326), which is itself a continuation-in-part of U.S. application Ser. No. 07/467,096 filed Jan. 18, 1990 (Attorney Docket Nos. DN37139), now U.S. Pat. No. 5,052,020.
U.S. application Ser. No. 08/062,457 is a continuation in part of U.S. Ser. No. 07/876,776, filed Apr. 28, 1992 (Attorney Docket Nos. 92P334; DN36649XZB), which is itself a continuation in part of U.S. Ser. No. 07/854,115, filed Mar. 18, 1992 (Attorney Docket Nos. 92P241; DN36649XZA), which is in turn a continuation in part of U.S. Ser. No. 07/558,895, filed Jul. 25, 1990 (Attorney Docket Nos. 91P387; DN36649XZ). U.S. Ser. No. 07/558,895 is a continuation in part of U.S. Ser. No. 07/529,353, filed May 25, 1990 (Attorney Docket Nos. 91P869; DN36649XY), which is itself a continuation in part of U.S. Ser. No. 07/347,602, filed May 3, 1989 (Attorney Docket Nos. 91P386; DN36649XX), which is itself a continuation of U.S. Ser. No. 07/345,771, filed May 2, 1989 (Attorney Docket Nos. 91P844; DN36649Y), which is itself a continuation of U.S. Ser. No. 07/345,200, filed Apr. 28, 1989 (Attorney Docket Nos. 91P423; DN36649X), which is itself a continuation of U.S. Ser. No. 07/305,302, filed Jan. 31, 1989 (Attorney Docket Nos. 91P422; DN36649).
The application U.S. Ser. No. 07/876,629 is also a continuation in part of U.S. Ser. No. 07/854,115, filed Mar. 18, 1992 (Attorney Docket No. DN36649XZA), with its parentage as listed above.
The application U.S. Ser. No. 08/267,758 is a continuation in part of U.S. Ser. No. 07/748,150, filed Aug. 21, 1991 (Attorney Docket Nos. 10554US01; DN37613), now issued as U.S. Pat. No. 5,349,678 on Sep. 20, 1994.
The above referenced applications, PCT Application No. PCT/US92/08610 filed Oct. 1, 1992, as published under International Publication No. WO 93/07691 on Apr. 15, 1993, together with U.S. Pat. No. 5,070,536, by Mahany et al., U.S. Pat. No. 4,924,426, by Sojka, and U.S. Pat. No. 4,910,794, by Mahany, are incorporated herein by reference In their entirety, including drawings and appendices, and hereby are made a part of this application.
Also incorporated herein by reference in their entirety, including drawings and appendices, are Mahany U.S. Pat. No. 5,696,903 issued Dec. 9, 1997, and Mahany, et al., U.S. Pat. No. 5,657,317 issued Aug. 12, 1997, and U.S. Pat. No. 5,790,536 issued Aug. 4, 1998.
The present invention relates generally to communication networks having a plurality of wired and/or wireless access servers configured to provide remote processing and data storage. More specifically, this invention relates to the intelligent migration of programs and data through a wireless and hardwired communication network comprised of a plurality of access servers, computers and peripherals.
Multiple radio base station networks have been developed to overcome a variety of problems with single radio base station networks such as spanning physical radio wave penetration barriers, wasted transmission power by portable computing devices, etc. However, multiple radio base station networks have their own inherent problems. For example, in a multiple base station network employing a single shared channel, each base station transmission is prone to collision with neighboring base station transmissions in the overlapping coverage areas between the base stations. Therefore, it often proves undesirable for each base station to use a single or common communication channel.
In contradistinction, to facilitate the roaming of portable or mobile devices from one coverage area to another, use of a common communication channel for all of the base stations is convenient. A roaming device may easily move between coverage areas without loss of connectivity to the network.
Such exemplary competing commonality factors have resulted in tradeoff decisions in network design. These factors become even more significant when implementing a frequency hopping spread spectrum network. Frequency hopping is a desirable transmission technique because of its ability to combat frequency selective fading, avoid narrowband interference, and provide multiple communications channels.
Again, however, changing operating parameters between coverage areas creates difficulties for the roaming devices which move therebetween. In particular, when different communication parameters are used, a portable or mobile device roaming into a new base station coverage area is not able to communicate with the new base station without obtaining and synchronizing to the new parameters. This causes communication backlog in the network.
Computer terminals and peripheral devices are widely used. Many types of computer terminals exist which vary greatly in terms of function, power and speed. Many different types of peripheral devices also exist, such as printers, modems, graphics scanners, text scanners, code readers, magnetic card readers, external monitors, voice command interfaces, external storage devices, and so on.
To communicate with such peripheral devices, portable computers have been adapted to use RF (Radio Frequency) and infrared communication. Such configurations, however, do not always provide for efficient communication. For example, a portable computer device may be mounted in a delivery truck and a driver may desire to transmit data to, or receive data from, a host computer or peripheral device at a remote warehouse location. While permitting such transmissions, wide area networks (WANs) only provide point-to-point communications, use a narrow bandwidth, and often exhibit heavy communication traffic. Moreover, WANs require relatively higher transmission power—a negative factor in the ever increasing need for power savings associated with portable transceiving devices. As a result, WANs are generally slow and expensive, and simply do not provide an effective overall solution.
The need for portable, or otherwise mobile, devices has led to smaller, lower power designs. Portable computer terminals have achieved such size and power reductions by decreasing local processing and storage resources. In contrast, application programs are growing in size and functionality, requiring more and more processing and storage resources to operate. As a result, portable computer terminals have been effectively disabled from independently performing many needed tasks. Others have been stretched to a nearly unacceptable limit of portability, battery life and processing and storage ability.
To address such needed tasks, remote processing and storage techniques are currently being used. For example, stationary remote host computers having superior processing and storage capability are often connected via a WAN network to a mobile computer terminal. In such configurations, whenever the mobile terminal desires access to data, it sends a request across the WAN for such data. Similarly, when it desires remote processing, the mobile computer terminal formulates a request which is sent to the host computer over the WAN. However, the mobile terminal is still required to use the relatively expensive and delayed services provided by the WAN for each such request, which often prove unacceptable for a given task.
Similarly, the relaying of communications through even lower power radio networks is required in many multi-hop radio environments. Repetitive requests and associated delivery of data, program or processing resources from a source (e.g., a mobile computer terminal) to a destination (e.g., a host computer) takes its toll on overall network performance.
Thus, there is a need for a wireless communication network that provides efficient distribution and utilization of network resources in support of portable and otherwise mobile computer devices.
Yet another object of the invention is to provide a method and apparatus wherein collisions are minimized in overlapping coverage areas by utilizing uncommon communication channel characteristics in a multiple base station network, while still providing seamless communication for roaming devices by informing roaming devices of the nature of the neighboring base station communication channel characteristics.
A still further object of the present invention is to provide a hierarchical communications system for providing an efficient communication pathway for data and programming objects.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
The present invention solves many of the foregoing problems in a variety of embodiments. The network of the present invention has a plurality of computing devices at least one of which is a mobile terminal device configured with a wireless transceiver. The network comprises a plurality of access devices arranged in a spanning tree configuration to support communications among the plurality of computing devices, and at least one of the plurality of access devices is configured to selectively intercept, store and forward requested data, thereby reducing traffic on the communication network. Further, at least one of the plurality of access devices may be configured to selectively intercept and store requested processing resources for future processing, again reducing traffic on the communication network. The processing resources stored may be, for example, those that perform the function of decoding signals representative of two-dimensional images captured by a two-dimensional code reading device. In addition, at least one of said plurality of access devices may be configured to selectively intercept, store and forward requested program code, once again reducing traffic on the communication network.
Before storing requested data, processing resources, or program code, an access device may consider a number of factors including the cost of re-obtaining the requested data, processing resources, or program code, the frequency that the data, processing resources, or program code is requested, the amount of its available storage capacity, and the size of the data, processing resources, or program code.
The access device may selectively delete stored data, etc. and may consider the factors listed above before doing so.
In another embodiment, a communication network of the present invention has a mobile terminal device configured with a wireless transceiver. The communication network also comprises a data source and a plurality of access devices. The plurality of access devices are arranged to provide a communication pathway between the mobile terminal device and the computing device. Moreover, at least one of said plurality of access devices is configured to monitor communication traffic through that access devices, and to selectively store for future forwarding requested data so as to shorten the communication pathway from the data to the mobile terminal device.
In yet another embodiment of the present invention, a communication network contains at least one two-dimensional code reading device configured with a first wireless transceiver. The network also comprises a plurality of access devices arranged to maintain wireless communication with the code reading device. Further, at least one of the plurality of access devices comprising a second wireless transceiver for receiving signals representative of two-dimensional images captured by a two-dimensional code reading device, and a code processing circuit for decoding the received signal.
In another embodiment, in a communication network having at least one two-dimensional code reading device configured with a first wireless transceiver, a processing device comprises a second wireless transceiver for receiving signals representative of two-dimensional images captured by a two-dimensional code reading device. The processing device also comprises a code processing circuit for decoding the signals received from the two-dimensional code reading device. The code processing circuit delivers to the two-dimensional code reading device via the second wireless transceiver an indication of successful image decoding.
The processing device may further comprise an image database for storing signals representative of two-dimensional images. Such images are used by the processing circuit for comparison with recieved signals so as to aid in the code identification process. A decode algorithm might also be used, either alone or in combination with attempted identification through image database comparison.
In another embodiment, a communication network operates between a premises and a vehicle which comprising a data source located (at the premises) and a terminal device (within the vehicle). A first communication link exists between the data source and the terminal device. In addition, a vehicular network is included which comprises a portable computing device and the terminal device which communicate via a second wireless communication link. The terminal device is configured to store data delivered from the data source, and, upon communication from the portable computing device, selectively forwarding the stored data to the portable computing device.
Moreover, in some configurations, the terminal device also monitors the flow of data to the portable computing device, and, based on such monitoring, said terminal device selectively migrates data into local storage. Similarly, in other configurations, the terminal device also monitors the flow of program code to the portable computing device, and, based on such monitoring, said terminal device selectively migrates program code into local storage. In yet other configurations, the terminal device monitors processing requests from the portable computing device, and, based on such monitoring, said terminal device selectively migrates programming resources into local storage.
The premises LAN consists of an infrastructure network comprising radio base stations, i.e., wireless access points 15, and a data base server 16 which may be part of a more extensive, wired LAN (not shown). Herein, base stations which participate in routing and relaying data throughout the communication network are referred to as “access points.” If they also participate in the storage or migration of data and program code or in local processing, the base stations are referred to herein as “access servers.” As will become apparent below, an access point may be modified with additional circuitry and/or programming resources to become an access server. Additionally, access servers and access points are both referred to herein as “access devices.”
The access points 15 may communicate with each other via hard-wired links, such as Ethernet, RS232, etc., or via wireless (radio frequency) links. A plurality of roaming terminal devices, such as a roaming computing device 20, participate in the premises LAN of the hierarchical communication network 10 to exchange information with: 1) other roaming computing devices; 2) the data base server 16; 3) other devices which might be associated with data base server 16 (not shown); and 4) any other devices accessible via the premises LAN (not shown). A roaming computing device can be, for example, a hand-held computer terminal or vehicle mounted computer terminal (vehicle terminal).
In most circumstances, the premises LAN provides a rather optimal solution to the communication needs of a given network. However, in some circumstances, to serve a variety of particular communication needs, the premises LAN does not offer the optimal solution. Instead of relying on the premises LAN for such communications, when and where beneficial, alternate LANs are spontaneously created by (or with) network devices, such as the roaming computing device 20, within the hierarchical communication system 10. Such spontaneously created LANs are referred to herein as spontaneous LANs. After the immediate benefits end, i.e., a task has been completed, or if the participants of the spontaneous LAN move out of range of each other, the spontaneous LAN terminates operation.
An exemplary spontaneous LAN involves the use of peripheral devices as illustrated in
Although a spontaneous LAN may operate completely independent of the premises LAN, it is more likely that there will be some degree of coordination between the two. For example, while participating in the peripheral LAN, the roaming computing device 20 may terminate participation in the premises LAN, and vice versa. Alternately, the roaming computing device 20 may only service the peripheral LAN when specific participation on the premises LAN is not required, or vice versa. Moreover, the roaming computing device 20 may attempt to service each peripheral LAN as necessary in a balanced time-sharing fashion, placing little priority upon either LAN. Thus, based on the protocols and hardware selected, a spontaneous LAN can be configured so as to exist hierarchically above, below, at the same level, or independent of the premises LAN.
In generally, to design a given LAN configuration, only the characteristics of that LAN are considered for optimization purposes. However, in the hierarchical communication system of the present invention, the operation of other LANs must also be taken into account. For example, because of the roaming computing devices participation in both the premises and peripheral LANs, the requirements and operation of the premises LAN must be taken into consideration when defining the peripheral LAN, and vice versa. Thus, the hierarchical communication system of the present invention provides a series of tightly coupled radio LANs and WANs with radio transceiver and communication protocol designs which take into consideration such factors as cost, weight, power conservation, channel loading, response times, interference, communication flow, etc., as modified by a primary factor of multiple participation.
The peripheral LAN replaces hard-wired connection between a roaming computing device and associated peripherals. In a typical configuration, a peripheral LAN will consist of one or more peripherals slaved to a single master roaming computing device, although multiple master roaming computing devices are possible. Peripheral devices may be printers, code scanners, magnetic card readers, input stylus, etc.
Each of the peripheral devices 22 has a built-in radio transceiver to communicate with the roaming computing devices 20. The roaming computing devices 20 are configured with built-in radio transceivers capable of communicating on both the peripheral and premises LAN. The access points 15 may be configured with radio transceivers only capable of communicating in the premises LAN. In alternate embodiments, as described below, the access points 15 might instead be configured to participate on both the premises and peripheral LANs.
In particular, the peripheral LAN is intended to provide communications between two or more devices operating within near proximity, e.g., distances of a few tens of feet. The majority of constituents of the peripheral LAN are generally devices that do not require access to resources outside their immediate group, or which can suffice with indirect access through devices which participate outside their immediate peripheral LAN group. In contradistinction, the premises LAN is intended to provide communications between relatively many devices operating across great distances throughout a building.
The characteristics of the peripheral LAN permit the use of radio transceivers of lower cost, lower power consumption, and generally more simplistic operation than permitted by the premises LAN. However, the operation of the peripheral LAN is adapted for integration with the premises LAN so that a radio transceiver and protocol designed for operation on the premises LAN includes features which allow concurrent or sequentially concurrent operation on the peripheral LAN. For example, by selecting similar communication hardware characteristics and integrating protocols, communication within the premises and peripheral LANs may be achieved with a single radio transceiver.
In one embodiment, radio communication through the premises LAN, i.e., among the access points 15 and the roaming computing device 20, utilizes relatively higher-power spread-spectrum frequency-hopping communication with a reservation access protocol. The reservation access protocol facilitates frequency-hopping and supports adaptive data rate selection. Adaptive data rate selection is based upon the quality of communication on the premises LAN radio channel. Radio communication through the peripheral LAN utilizes a relatively lower-power single frequency communication also with a reservation access protocol. As more fully described below, the coordinated use of reservation access protocols in the peripheral and premises LANs maximize information flow while minimizing conflicts between devices participating in the two LANs.
Two peripheral LANs 40 and 41 allow for wireless communication between each mobile computing device 35 and 36 and its respective peripheral devices 43, 44 and 45 when the mobile computing device is not communicating on the premises LAN 37. Specifically, the peripheral LAN 40 consists of the mobile computing device 35 and the peripheral device 43, while the peripheral LAN 41 consists of the mobile computing device 36 and the two peripheral devices 44 and 45.
The access points 56, 58 and 59 can support multiple mobile computing devices. For example, the access point 56 uses a frequency-hopping communication protocol for maintaining communication with mobile computing devices 61 and 62. Moreover, each of the mobile computing devices may roam out of range of the access point with which they have been communicating and into the range of an access point with which they will at least temporarily communicate. Together, the host computer 55 and the access points 56, 57, 58 and 59 and mobile computing devices 61, 62, 64, 65 and 66 constitute a premises LAN.
More particularly, each access point operates with a different set of communication parameters. For example, each access point may use a different frequency hopping sequence. Additionally, different access points may not employ a common master clock and will not be synchronized so as to have the frequency hopping sequences start at the same time.
Mobile computing devices 61, 62, 64, 65 and 66 are capable of roaming into the vicinity of any of the access points 56, 58 and 59 and connecting thereto. For example, mobile computing device 62 may roam into the coverage area of access point 58, disconnecting from access point 56 and connecting to access point 58, without losing connectivity with the premises LAN.
Each mobile computing device 61, 62, 64, 65 and 66 also participates with associated peripherals in a peripheral LAN. Each peripheral LAN is made up of the master device and its slave device. Similarly, as illustrated, the access point 57 is shown as a direct participant in not only the premises LAN but also in the peripheral LAN. The access point 57 may either have limited or full participation in the premises LAN. For example, the access point 57 may be configured as a mobile computing device with the full RF capability of transmission in both the premises and peripheral LANs. Instead, however, participation in the premises LAN may be limited to communicating through the hard-wired link, effectively dedicating the access point 57 to the task of servicing peripherals.
Although the use of a plurality of built-in radio transceivers could be used so as to permit simultaneous participation by a single device, factors of cost, size, power and weight make it desirable to only build-in a single radio transceiver capable of multiple participation. Furthermore, even where a plurality of radio transceivers are built-in, simultaneous participation may not be possible depending upon the potential transmission interference between transceivers. In fact, full simultaneous participation may not be desirable at least from a processing standpoint when one transceiver, servicing one LAN, always or usually takes precedence over the other. Justification for such precedence generally exists in a premises LAN over a peripheral LAN.
For example, communication flow in most premises LANs must be fast, efficient and rather robust when considering the multitude of participants that operate thereon. In the peripheral LAN, however, response times and other transmission related delays are generally more acceptable—even adding extra seconds to a peripheral printer'"'"'s print time will usually not bother the user. Thus, in such communication environments, it may be desirable to design the transmitters and associated protocols so that the premises LAN takes precedence over the peripheral LAN. This may yield a communication system where fully simultaneous participation in both the premises and peripheral LANs does not exist.
In communication environments wherein fully simultaneous participation does not exist or is not desired, transmitter circuitry might be shared for participation in both the premises and peripheral LANs. Similarly, in such environments, the communication protocol for the peripheral LAN can be tightly coupled with the protocol for the premises LAN, i.e., integrated protocols, so as to accommodate multiple participation. Moreover, one protocol might be designed to take precedence over the other. For example, the premises LAN protocol might be designed so as to minimize participation or response time in the peripheral LAN. As described in more detail below, such transceiver and protocol analysis also takes place when considering additional multiple participation in the vehicular LAN and WAN environments.
As was shown in
The Time Division Multiple Access slots may also be located at different points within the access interval. Positioning the Time Division Multiple Access slots allow for various systemic advantages. Referring now to
Referring now to
Location of the Time Division Multiple Access slots 2305 at the position shown in
In the access interval 2300 configuration shown in
Referring now to
The configurations shown in
In one embodiment of the Access Interval structure, all message transmissions use standard high-level data link control (“HDLC”) data framing. Each message is delimited by High-Level Data Link Control Flags, consisting of the binary string 01111110, at the beginning of the message. A preamble, consisting of a known data pattern, precedes the initial FLAG. This preamble is used to attain clock and bit synchronization prior to start of data. Receiver antenna selection is also made during the preamble for antenna diversity. A CRC for error detection immediately precedes the ending FLAG. Data is NRZ-I (differentially) encoded to improve data clock recovery. High-Level Data Link Control NRZ-I data is run-length-limited to six consecutive bits of the same state. Alternatively, a shift register scrambler could be applied instead of differential encoding to obtain sufficient transitions for clock recovery. Data frames may be concatenated, with two or more frames sent during the same transmission, with a single FLAG separating them. An example of this is SYNC, followed by a HELLO or Reservation Poll (SYNC, HELLO and Reservation Poll are discussed more fully below).
While much of the following discussion centers on the use of frequency hopping in the premises LAN, the Access Interval structure of the present invention is also suitable for single channel and direct sequence spread spectrum systems. The consistent timing of channel access, and the relative freedom from collisions due to channel contention, provide desirable benefits in systems that support portable, battery powered devices regardless of modulation type or channelization. Functions that are unique to frequency hopping may be omitted if other channelization approaches are used.
The Access Interval is a building block. The length of the Access Interval can be optimized based on network layer packet size, expected mix of Bandwidth on Demand (“BWOD”) and Scheduled Access traffic, expected velocities of devices within the NET, acceptable duration of channel outages, latency or delay for scheduled services, etc. The preferred Access Interval duration of 20 ms (and maximum packet length of 256 Bytes at 1 MBIT/sec) represents a value chosen for systems with device velocities up to 15 MPH, and a mix between Bandwidth On Demand and scheduled service traffic.
Within a frequency hopping network, one or more Access Intervals may be used during each dwell in a frequency hopping system. A dwell is the length of time (d) each frequency in the hopping sequence is occupied by the system. For example,
In a frequency hopping operation, the Access Interval 200 of
- 1. Address of the Control Point device.
- 2. Identification of the Hopping Sequence, and index of the current frequency within the hop table.
- 3. Identification of the hop rate, number of Access Intervals per hop, and Access Intervals before next hop.
- 4. A timing character for synchronization of device local clocks to the NET clock contained within the Control Point device.
- 5. Status field indicating reduced SYNC transmissions due to low NET activity (Priority SYNC Indicator).
- 6. Status field indicating if the Access Interval will contain a broadcast message to all devices within the NET.
- 7. Status field indicating premises or spontaneous LAN operation.
- 8. The SYNC field information is optionally encrypted using a block encryption algorithm, with a key provided by the network user. A random character is added to each SYNC message to provide scrambling.
However, there are two circumstances during which a SYNC message is not transmitted: 1) co-channel interference; and 2) low NET utilization. With regard to co-channel interference, before issuing a SYNC message, the Control Point device performs channel monitoring for a brief interval. If the Received Signal Strength Indicator (RSSI) level indicates an ON channel signal greater than the system defer threshold, then the Access Interval is skipped. Alternatively, a strong ON channel signal may dictate a reduction in Control Point device power to limit the interference distance of the net for the duration of the Access Interval. A system defer threshold 30 dB above the receiver sensitivity is a preferred choice. Communication within the NET is deferred for the duration of the Access Interval if SYNC is not transmitted due to co-channel interference.
In times of low system utilization, SYNC and Reservation Poll messages are reduced to every third Access Interval. The SYNC message includes a status field indicating this mode of operation. This allows devices to access the NET, even during Access Intervals where SYNC is skipped, by using an Implicit Idle Sense algorithm. If the hopping sequence is 79 frequencies in length as shown in
It should be noted that SYNC messages are preceded by dead time, which must be allocated to account for timing uncertainty between NET clocks and local clocks within NET constituents. In frequency hopping systems, the dead time must also include frequency switching time for the RF modem.
The Reservation Poll frame 203 immediately follows the SYNC header 201. The two messages are concatenated High-Level Data Link Control frames separated by one or more Flags. The reservation poll provides NET constituents an opportunity to gain access to the media. It includes:
- 1. A field specifying one or more access slots.
- 2. A field specifying a probability factor between 0 and 1.
- 3. A list of addresses for which the access points has pending messages in queue.
- 4. Allocation of Time Division Multiple Access slots for scheduled services by address.
- 5. Control Point device Transmitted Power level for SYNC and Reservation Polls.
The number of access slots, n, and the access probability factor, p, are used by the Control Point device to manage contention on the channel. They may each be increased or decreased from Access Interval to Access Interval to optimize access opportunity versus overhead.
If the NET is lightly loaded, the pending message list is short, and the NET is not subject to significant interference from other nearby NETs, the control point device will generally specify a single slot 501 as shown in
In cases when the transmission density is higher, n multiple reservation slots will be specified, generally with a probability factor p of 1. In this case a device will randomly choose one of n slots for transmission of their Request for Poll. The slotted reservation approach is particularly appropriate in instances where many NETs are operating in near proximity, since it diminishes reliance on listen before talk (“LBT”) (explained more fully below). The number of slots n is determined by a slot allocation algorithm that allocates additional slots as system loading increases.
In cases where NET loading is extreme, the Control Point may indicate a number of slots, e.g., not more than 6, and a probability less than 1. This will cause some number of devices to defer responding with a Request for Poll in any of the slots. This prevents the control point device from introducing the overhead of a large number of slots in response to heavy demand for communications, by dictating that some units back off until demand diminishes.
A pending message list is included in the Reservation Poll. The pending message list includes the addresses of devices for which the Control Point device has messages in queue. Devices receiving their address may contend for the channel by responding with a Request For Poll (RFP) in the slot response phase.
Devices with transmission requirements respond in slots with a Request for Poll. This message type includes the addresses of the Control Point device and requesting device, the type and length of the message it has to transmit, and a field that identifies the type of device. Devices that detect their address in the pending message list also contend for access in this manner.
As mentioned above, devices may be Type 1, Type 2, or Type 3. Type 1 devices are those which require critical battery management. These may be in a power saving, non-operational mode much of the time, only occasionally “waking” to receive sufficient numbers of SYNC and Reservation Poll messages to maintain connectivity to the NET. Type 2 devices are those that are typically powered up and monitoring the NET at all times. Type 3 units are devices that will remain awake for a window period following their last transmission in anticipation of a response. Other device types employing different power management schemes may be added.
Slot responses are subject to collision in both the single and multiple slot cases. Collisions may occur when two or more devices attempt to send Request for Polls in the same slot. However, if the signal strength of one device is significantly stronger than the others, it is likely to capture the slot, and be serviced as if it were the only responding unit.
The Control Point device may or may not be able to detect collisions by detecting evidence of recovered clock or data in a slot, or by detecting an increase in RF energy in the receiver (using the Received Signal Strength Indicator, (“RSSI”)) corresponding to the slot interval. Collision detection is used in the slot allocation algorithm for determining addition or deletion of slots in upcoming Reservation Polls.
As an optional feature to improve collision detection in the multiple slot case, devices that respond in later slots may transmit the addresses of devices they detect in earlier slots as part of their Request for Poll. Request for Polls which result in collisions at the Control Point device often are captured at other remote devices, since the spatial relationship between devices that created the collision at the base does not exist for other device locations within the NET. The duration of the response slots must be increased slightly to provide this capability.
If the Control Point device receives one or more valid Request for Polls following a Reservation Poll, it issues a Reservation Resolution (“RR”) Poll and places the addresses of the identified devices in a polling queue. The Reservation Resolution message also serves as a poll of the first unit in the queue. Addresses from previous Access Intervals and addresses of intended recipients of outbound messages are also in the queue.
If the Polling Queue is empty, then no valid Request for Polls were received or collision detected and no Reservation Resolution poll is issued. If within this scenario a collision is detected, a CLEAR message indicating an Explicit Idle Sense (explained more fully below) is transmitted containing a reduced probability factor to allow colliding units to immediately reattempt NET access.
Outbound messages obtained through the network infrastructure may result in recipient addresses being prioritized in the queue, that is, if the recipients are active devices—Type 2 devices or Type 3 devices whose awake window has not expired. This eliminates the need for channel contention for many outbound messages, improving efficiency. Messages for Type 1 devices are buffered, and the recipient address is placed in the pending message list for the next Access Interval.
Generally the queue is polled on a first in first out (FIFO) basis. The polling order is:
a. Addresses of active units with outbound messages.
b. Addresses from previous Access Intervals
c. Addresses from the current Access Interval
Since propagation characteristics vary with time and operating frequency, it is counterproductive to attempt retries if Poll responses are not received. If a response to a Poll is not received, the next address in the queue is polled after a short response time-out period. Addresses of unsuccessful Polls remain in the queue for Polling during the next Access Interval. Addresses are aged, so that after several unsuccessful Polls they are dropped from the queue. Addresses linked to outbound messages are added to the pending message list. Devices with inbound requirements must re-enter the queue through the next reservation phase.
Data is transferred in fragments. A maximum fragment payload of 256 bytes is used in the preferred implementation. If transfer of network packets larger than of 256 bytes is required, two or more fragments are transferred. Fragments may be any length up to the maximum, eliminating the inefficiency that results when messages that are not integer multiples of the fragment length are transmitted in systems that employ fixed sizes.
The sequence for transferring data from a remote device to the control point device is illustrated in
Following successful receipt of the first fragment, the Control Point device sends a second poll 705, which both acknowledges the first fragment, and initiates transmission of the second. The length parameter is decremented to reflect that the time required for completion of the message transfer is reduced. A second fragment 707 is transmitted in response, and also contains a decremented length field. Following receipt of the second fragment 707, the Control Point device sends a third poll 709. This pattern is continued until a final fragment 711 containing an End of Data (EOD) indication is received. In
If for some reason a fragment is not successfully received, the next poll from the Control Point device would indicate a REJECT, and request re-transmission of the same fragment. The length field would remain fixed at the previous value, prolonging reservation of the channel for the duration of the message. After a fragment is transmitted more than once without successful reception, the Control Point device may suspend attempts to communicate with the device based upon a retry limit, and begin polling of the next address in the queue.
A flow chart depicting how inbound messages are received during an access interval is shown in
Outbound messages are transmitted in a similar fashion as inbound messages, with the Control Point and device roles largely reversed as illustrated in
All terminating ACK or CLEAR messages contain fields to aid in synchronization of new units to the NET. The content of these fields is identical to that in the SYNC message, except that the timing character is deleted. Synchronization is discussed more fully below.
Broadcast Messages intended for groups of addresses, or all addresses within a NET may be transmitted during the sessions period. Broadcast messages are not individually acknowledged. These messages may be communicated at intervals over the course of several Access Intervals to provide reliable communication. Messages such as SYNC and Reservation Polls are specialized broadcast messages, with dedicated bandwidth in the Access Interval structure.
Security of payload data is left to the higher protocol layers. Application programs resident in portable/mobile devices may employ encryption or other means of providing protection against undesired use of transmitted data.
Portable/mobile devices may employ transmitter power control during the sessions period to reduce potential interference with other NETs that may occasionally be on the same or adjacent channels. These devices will use Received Signal Strength Indicator readings from outbound messages to determine if transmitter power may be reduced for their inbound transmission. Because of the need to maintain channel reservations and Listen Before Talk capabilities, the Control Point device does not use transmitter power control. Since Control Point devices are generally part of an installed system infrastructure, they are likely to be physically separated from devices operating in other NETs. They are therefore less likely to cause interference to devices in other NETs than portable devices, which may operate in proximity to devices in other NETs.
Often, control point devices will empty the polling queue before the conclusion of the access interval. Two mechanisms within the Access Control Protocol, Explicit and Implicit Idle Sense, are provided to improve bandwidth utilization. These supplemental access mechanisms often provide means for devices that failed to gain reservations during the reservation phase to gain access to the NET within the Access Interval. To assume an Explicit or Implicit Idle Sense, a device must have detected a valid SYNC and Reservation Poll in the current Access Interval.
The incorporation of a probability factor p≠0 in the final (terminating) ACK or CLEAR from the control point device provides the function of an Explicit Idle Sense (mentioned above). Devices with transmission requirements solicit Request for Polls using the same rules normally used for a single slot Reservation Poll. Successfully identified addresses are placed in the polling queue, and are polled immediately or in the next Access Interval depending on the time remaining in the current Access Interval. The p factor for Explicit Idle Sense is subject to the same optimization algorithm as the Reservation Poll probability.
Communication of channel reservations, in the form of the length fields in Polls and Message Fragments is useful to units seeking to access the NET through Explicit Idle Sense. Reservations allow devices to predictably power down during the period that another device has reserved the NET to conserve battery power, without loosing the ability to gain access to the NET.
Implicit Idle Sense provides an additional means of channel access. An Implicit Idle Sense is assumed whenever a device detects a quiet interval period greater than or equal to the duration of a Poll plus the maximum fragment length after a channel reservation has expired. Detection based upon simple physical metrics, such as a change in Received Signal Strength Indicator or lack of receiver clock recovery during the quiet interval, are preferred methods of ascertaining channel activity. Algorithms based upon these types of indicators are generally less likely to provide a false indication of an inactive channel than those that require successful decoding of transmissions to determine channel activity. False invocation of an Implicit Idle Sense is the only mechanism by which data transmissions are subject to collision within the NET. Thus, the Implicit Algorithm must be conservative.
Quiet interval sensing may begin at the following times within the Access Interval:
- a. Any time after the last reservation slot following a Reservation Poll;
- b. Any time after a terminating ACK or CLEAR indicating an Explicit Idle Sense;
- c. Following an unsuccessful response to a single Slot Reservation Poll; or
- d. Any time prior to reserved Time Division Multiple Access time slots at the end of the Access Interval.
It is preferable that devices detecting a quiet interval use a p persistent algorithm for channel access to avoid collisions. The probability factor for Implicit Idle Sense Access will generally be less than or equal to the factor in Explicit Idle Sense.
A device must receive the SYNC and Reservation Polls at the beginning of an Access Interval to use Implicit Idle Sense. The Reservation Poll provides indication of guaranteed bandwidth allocation to scheduled services at the end of the Access Interval, which may shorten the period available for Bandwidth On Demand communications.
Devices requiring scheduled services must contend for the channel in the same fashion as those requiring Bandwidth On Demand access. When polled, these initiating devices will initiate a connection request that indicates the number of inbound and outbound Time Division Multiple Access slots required for communication, and the address of the target device with which communication is desired. The network infrastructure will then attempt to establish the connection to the target device. Once the connection is established, the Control Point device will signal the allocation of slots to the initiating device. Time Division Multiple Access slots are relinquished by transmitting a disconnect message to the control point device in the Time Division Multiple Access slot until the disconnect is confirmed in the next Reservation Poll.
The transmission requirements of speech and slow scan video (scheduled services) are similar. In one embodiment, Time Division Multiple Access slots are allocated as multiples of 160 bits payload at 1 MBIT/sec, plus overhead for a total of 300 μs. For 10 ms access intervals, acceptable voice communication can be obtained by allocating 1 Time Division Multiple Access slot each for inbound and outbound communication per access interval. For 20 ms access intervals, two slots each way are required. A system employing 10 ms access intervals at 100 hops per second may improve transmission quality by using two or three slots each Access Interval and sending information redundantly over two or three access intervals using interleaved block codes. Scheduled transmissions are generally not subject to processing or validation by the control point device, and are passed through from source to destination. Use of interleaved error correction coding or other measures to improve reliability are transparent to the NET.
The selection of certain system parameters are important when considering scheduled services. As an example, since speech is quantized over the duration of the access interval and transmitted as a burst, the length of the access interval translates directly into a transport delay perceptible to the recipient of that speech. In real time voice communications, delays longer than 20 ms are perceptible, and delays longer than 30 ms may be unacceptable. This is particularly the case where the premises LAN is interconnected with the public switched telephone network (“PSTN”), which introduces its own delays. Two way services such as voice communications are the most sensitive to transport delay because delay impacts the interaction of the communicating parties. One way services are less sensitive to transport delay. One way services are good candidates for interleaving or other forms of redundant transmission.
Similarly, the selection of hop rate is important, as hop rate determines the duration of outages that may occur. If one or more frequencies in the hop sequence are subject to interference, for instance, scheduled transmissions during those hops will be disrupted. In a system that hops slowly, detrimental outages of hundreds of milliseconds will occur resulting in poor transmission quality. Occasional losses of smaller durations, e.g., 10 ms or 20 ms, are generally less perceptible, indicating that faster hop rates are desirable if the NET is to offer real time voice transport.
Scheduled service intervals may also be used for data transport on a scheduled or priority basis. Telemetry, data logging, print spooling, modem replacement, or other functions are possible. For these activities, a few Time Division Multiple Access slots scheduled for example every fourth, eighth, or sixteenth Al are necessary.
Because of multipath and dispersion issues with 2.4 GHz transmission at relatively high data rates, the ability of the NET to adaptively switch between two or more data rates is desirable.
In one embodiment, implementation of data rate switching may be accomplished by selecting a standard rate of communications, e.g., 250 KBPS and high rate of communications of 1 Mbit/sec. Messages that contain system status information, including SYNC, Reservation Polls, Reservation Resolution Polls (Request for Polls), Polls, ACKs and CLEARS are transmitted at the standard rate. These messages are generally short, and the time required for transmission is largely determined by hardware overhead, e.g., transmitter receiver switching time. The incremental overhead introduced by transmitting these messages at the lower rate is therefore small in comparison to the total length of an access interval. The reliability of reception of these messages will increase, which will eliminate unnecessary retries in some instances where fragments are received successfully, but acknowledgements or polls are missed.
A test pattern at the higher data rate is inserted in each Poll (not in Reservation Polls, however). The Poll recipient evaluates signal quality based on the high data rate test pattern, Received Signal Strength Indicator, and other parameters to determine whether to transmit a fragment at the high rate or the low rate. Fragment lengths are selected such that high and low rate maximum fragment lengths are the same duration. In other words, a fragment at the low rate conveys approximately ¼ the payload of a fragment for the case where the data rate is four time greater. This method is generally suitable for transaction oriented communications, which frequently require short message transmissions. Alternatively, the length field in Polls and messages can be used to allow different fragment lengths for the two data rates while still providing channel reservation information to other devices in the NET. This method also provides for forward migration. As modulation and demodulation methods improve, newer products can be added to old networks by upgrading Control Points devices. Both new and old devices share the ability to communicate at a common low data rate.
An alternate embodiment uses signaling messages such as SYNC, Reservation Polls, Request for Polls, etc., at the higher rate with fallback operation to the standard rate for the communications sessions only SYNC and Reservation Polls at the high rate constitute a high data rate test message. The Request for Poll response to the Reservation Poll at the high rate may include a field indicating that sessions communications should take place at the fallback, standard rate. Signal quality measures such as signal strength and clock jitter are appropriate. Data rate selection information is included with the device address in the polling queue. When the device is polled, it will be polled at the rate indicated in the Request for Poll. Channel reservation information in the Reservation Resolution Poll will indicate the reservation duration based upon the data rate indicated.
In this alternate embodiment, the fact that SYNC and Reservation Polls must be detectable at the high data rate prioritizes access to the NET for those devices that have acceptable connectivity during the current access interval. This general approach has desirable characteristics in a frequency hopping system, as the propagation characteristics between devices may change significantly as the NET changes from frequency to frequency within the hopping sequence, or over several Access Intervals during the dwell time on a single frequency. Reduction in data rate in this system is primarily intended to remedy the data smearing (inter-symbol interference) effects of dispersion due to excess delay, rather than temporary poor signal to noise ratio due to frequency selective fading. Devices that receive high data is rate transmissions with acceptable signal strength but high jitter are likely to be experiencing the effect of dispersion.
The concept of allowing Polls and message fragments to occur at either a high or low data rate could create difficulties for other NET constituents that need to be able to monitor the channel for reservation information. Two embodiments for solving this problem are the use of auto-discriminating receivers or the use of fixed data rate headers for system communications.
Auto discrimination requires the receiver to process messages sent at either data rate, without necessarily having prior knowledge of the rate.
Given a high rate of 1 MBIT/SEC, and a low Rate of 250 KBPS, i.e., one being a binary multiple of the other, it is possible to devise preambles that can be received at either rate. Consider that 01 and 110 sent at the low rate correspond to 00001111 and 111111110000 at the high rate. These preambles are transmitted continuously before the transmission of the High-Level Data Link Control FLAG character at the correct data rate indicating the start of a message. In this example, a preamble of 20 bits of 01 at the low rate indicates operation at the high rate. A preamble of 30 bits of 110 indicates operation at the low rate. A receiver tuned to either rate is capable of receiving both types of preambles and initiating the proper decoding mechanisms for the intended rate of transmission.
This general technique, with appropriate selection of preamble content, is applicable to binary modulation schemes, for example, a frequency modulated system where a common frequency deviation value is used for both data rates. It is also applicable to systems where switching occurs between binary and multilevel modulation, such as disclosed in pending U.S. application Ser. No. 07/910,865, filed Jul. 6, 1992.
Referring now to
With auto-discrimination, it is possible to change data rates on a per-poll basis, thereby adjusting for channel temporal dynamics. Since all devices in the NET have auto discrimination capabilities, and channel reservation information is included in message headers as a length field, the bandwidth reservation features of the NET are preserved. The maximum fragment duration may be maintained at a fixed value, meaning that low data rate fragments convey less data than their high rate counterparts, or may be scaled in the ratio of the data rates to allow consistent fragment data payloads.
An alternative to auto-discrimination is the use of headers to communicate system information. This embodiment is less preferred, but may be appropriate if economics, size, or power constraints dictate a simpler design than that required for auto-discrimination. In this embodiment, any transmission at the lower data rate is preceded by a header at the high data rate that conveys NET management information, i.e., channel reservation status. Devices other than those directly involved in polling or fragment transmission need only monitor at the high rate for channel reservation information. The header at the high rate and the following transmission at the low rate are concatenated High-Level Data Link Control frames, with an appropriate preamble for low rate clock recovery synchronization in-between.
For the communicating devices, the header can serve the additional purpose of acting as a test pattern at the high rate. For example, if a device is polled at the low rate, but successfully decodes the high rate header with adequate signal quality, it may indicate back to the polling unit to poll again at the high rate.
In a premises LAN as discussed in reference to
The basic method for communication of status information regarding the premises LAN is the HELLO message. HELLO messages are sent routinely, but relatively infrequently, for example, every 90 Access Intervals. The HELLO transmission interval is tied to the Priority SYNC interval, so that the HELLO interval corresponds to Access Intervals where SYNC is transmitted if the network is lightly utilized.
In an alternate embodiment, HELLOs could be inserted as a broadcast message at the beginning of the Sessions period.
HELLO messages may also contain information regarding pending changes in the local NET. If the local NET is changing Access Interval durations or hop sequences, for instance, changes may be communicated in several consecutive HELLOs so that the information is reliably communicated to all NET constituents, permitting all devices to make the change in coordinated fashion. Further discussion of HELLO message content is provided below.
For purposes of channel management in the Access Interval structure, the maximum transmission duration by a device should be limited to the time that the device moving at a maximum expected velocity can traverse ¼ wavelength of the maximum carrier frequency. The duration may be further reduced to compensate for link bit error rate characteristics or expected duration or frequency of interference bursts. A maximum transmission duration of 2.5 ms is suitable for 1 MBIT/SEC transmission, with a device velocity of 15 mph, in a multiple NET environment.
Use of spatial or polarization antenna selection diversity is also desirable in indoor propagation environments. First, the receiving unit makes an antenna diversity decision during the preamble portion of each transmission. The antenna used for reception for each device address is then recorded in memory so that the correct antenna will be used for response messages to each address. While diversity selection is only valid for a short time, it is not necessary to age this information, because antenna selection is equi-probable even after diversity information is no longer valid.
The Access Interval structure of the present invention also inherently provides routine channel sounding for each hop. This is important in a frequency hopping system, as channel conditions will vary considerably from frequency to frequency within the hopping sequence. NET constituents must, in most cases, be able to receive SYNC and Reservation Poll transmissions from the Control Point device to attempt inbound access in an Access Interval. This provides a positive indication that the device is not experiencing a channel outage, allowing power saving and eliminating possible channel contention. Channel sounding does not need to be employed during periods where the NET is not busy since contention is unlikely in this situation.
Channel sounding for Outbound messages is accomplished through a Request for Poll/Poll cycle where handshaking messages with short time out periods must be successfully communicated before longer message transmissions may be attempted.
As discussed above with regard to
The access points 15 may be interconnected via industry standard wired LANs, such as IEEE 802.3 Ethernet, or IEEE 802.5 Token Ring. Access points may be added to an existing LAN without the need to install additional LAN cable. Alternatively, it may be desirable to install access points on dedicated LAN segments to maximize performance of both the radio network and other collocated computer devices.
Access points within the premises LAN provide Control Point functions for individual NETs. NETs employ different hopping sequences to minimize potential interference between NETs. Regulatory restrictions generally preclude synchronization of multiple NETs to a single master clock, requiring that individual NETs operate independently from one another. The lack of the ability to coordinate timing or frequency usage between NETs introduces the potential for collisions between independent NETs with overlapping coverage areas.
Since NETs are not synchronized, different NETs that use the same hopping sequence are likely to interfere during periods where oscillator drift causes them to be temporarily synchronized. At other times, they may only interfere due to imperfect channelization. For example, for a worst case 100 ppm frequency error between two NETs using the same 79 frequency sequence at one Access Interval per hop and 50 hops per second, NETs will partially or fully overlap for a duration of 10 minutes every 4.3 hours. Typically the frequency error will be 25% to 50% of the worst case, leading to longer overlap periods occurring less frequently.
NETs using the same hopping sequence must be physically isolated from one another to reduce interference to an acceptable level. Extensive hopping sequence reuse generally requires site engineering and optimization of access point placement. Using more hopping sequences reduces the need for critical system engineering during installation. Fifteen hopping sequences is a preferred number for hopping sequence reuse, allowing simplified installation and minimal coordination.
NETs that use different hopping sequences will also temporarily synchronize in timing relationships that cause mutual co-channel interference on common channel frequencies. Since the number of channels that must be used in a sequence is a significant fraction of the total number of channels available, all sequences will share some number of frequencies in common. When sequences are time aligned so that a common frequency is used simultaneously, interference can occur. Optimization of sets of sequences for low cross correlation is necessary to prevent various time alignments of sequences from having more than one or two frequencies in common.
Optimization of hopping sequences for multiple NETs must also include analysis of imperfect channelization. The performance characteristics of the RF modems may not, for economic or power consumption reasons, provide sufficient transmitter spectral containment, receiver dynamic range, or receiver selectivity to guarantee that devices operating on different frequencies in proximity to one another will not interfere. In selecting hopping sequences for desirable cross correlation properties, adjacent and alternate adjacent channel interference must be considered. Protocol retry mechanisms for fragments lost to adjacent channel interference or limited dynamic range may be randomized to prevent continued disruption of communications in the affected NET.
Often in campus environments where systems must provide coverage in several buildings, the cost of wiring LAN cable between access points is prohibitive. To establish connectivity between access points in an premises LAN, it may be necessary to provide wireless links between groups of access points connected to separate LAN segments.
In one embodiment, the access points 1203 and 1205 may be configured in a wireless point to point mode, wherein one access point serves as a control point device while the others operate in a slaved mode dedicated to point to point data transfer. Slave access points are configured to operate as portable/mobile devices, and forward communications to master bases by sending Request for Polls during reservation opportunities or Implicit Idle Sense periods. Because of the potential high traffic of point to point links, separate NETs may be allocated for this purpose, with a master communicating with one or more slave units. Master units may also communicate with other portable/mobile devices. The COST weighing (discussed below) in a slave'"'"'s HELLO transmission is preferably set to a high value, to force portable/mobile devices which can connect to another NET to do so.
In another embodiment, it may also be desirable to support wireless access points. Wireless access points serve as control points, but are not connected to the infrastructure through a LAN cable. As is illustrated in
Wireless access points operate as slave devices to master access points which are connected to the wired infrastructure. The wired and wireless access points share the same hopping sequence, and are synchronized as a common NET. Because they are not connected to the Infrastructure, wireless access points must be used as store and forward devices. Each transmission to a wireless base must be retransmitted to the intended destination device, doubling the number of transmissions occurring in the NET. Wireless access points are preferably used for supplementing coverage area of the premises LAN. For example, a wireless access point might provide spot coverage of isolated “dead spots” where data traffic is limited or where providing a wired LAN connection is difficult. Wireless access points may also serve as emergency spares to provide coverage in the event of a failure of a primary access point. In this role, the wireless access point may be either permanently installed in selected locations, or stored in a maintenance area and quickly positioned and connected to AC or battery power to provide communications while repairs are made to the primary wired access point. Moreover, permanently installed wireless access points might also be used for redundancy, i.e., to monitor an associated access point and to take over when a break-down is detected.
The preferred wireless access point embodiment uses interleaved access intervals. The parent wired access point and secondary wireless access point coordinate Access Intervals, the wired access point deferring every third or sixth access interval to the wireless base. Since the wired access point transmits priority SYNC messages every third Access Interval, the wireless access point may routinely be allocated one of the two intervening Access Intervals for priority SYNC communications with devices that are attached to it. Communication between the wired and wireless access points may occur during Access Intervals initiated by either access point. Wireless access points may also communicate with devices during an Access Interval using Implicit or Explicit Idle Sense.
This embodiment provides predictable access for devices attached to the wireless NET, and allows the same power management algorithms to be used regardless of whether the access point is wired or wireless. The wireless access point may transmit its own priority SYNC and HELLO messages. Also, devices seeking communications with the wireless access point will automatically be synchronized with the wired base as well, allowing immediate improved access to the network if their mobility has put them within range of the wired base.
Because of the constraint of sharing bandwidth with a wired access point, connectivity of wireless access points is normally limited to one per wired access point. However, in cases where system loading is predictably and consistently light, multiple wireless access points could share a single wired base, e.g., each transmitting in turn in the Access Intervals between the Wired Base Priority SYNC Access Intervals.
Wireless access points are capable of supporting scheduled traffic. However, since each transmission to a wireless access point must be forwarded, scheduled transmissions through wireless access points use twice the bandwidth as those through wired access points. In other words, twice the number of Time Division Multiple Access slots must be allocated. To avoid introducing excessive delay, communications must be forwarded during the same Access Interval that they are received, or shorter Access Intervals must be used. Scheduled traffic slot assignments must be common to all wireless bases operating within a single NET.
Wireless access points require reliable communication with their wired counterparts. This dictates smaller coverage contours for wireless access points. If a wired access point provides 80,000 square feet of coverage area, a wireless base can be predicted to provide only an additional forty percent coverage improvement, due to overlap with the wired access point. Frequently, access points are mounted at ceiling level, providing a relatively clearer transmission path between access points than exists between bases and portable/mobile devices located in more obstructed areas near the floor. With careful site engineering and installation, a wireless access point can provide somewhat better than the forty percent predicted improvement, but still less than the coverage of an additional wired base.
As discussed above, HELLO messages are used to communicate NET and premises LAN status messages. They facilitate load leveling and roaming within the premises LAN and allow sequence maintenance to improve security and performance within the NET. HELLO messages occur periodically in Access Intervals that contain priority SYNC messages. HELLOs are sent periodically relative to the sequence length, for instance, every 90 Access Intervals. HELLOs, like SYNC information, are optionally encrypted to provide greater security.
Each HELLO message includes a field for COST. COST is a measure of the access point to handle additional traffic. A device determining which of two or more access points having adequate signal strength to register which will select the base with the lowest COST factor.
The base computes COST on the basis of how many devices are attached to the NET, the degree of bandwidth utilization, whether the base is wired or wireless, the number of frequencies experiencing consistent interference within the sequence, and the quality of the connection the base has within the premises LAN.
Simply put, communication of neighbors'"'"' information permits each access point to advise its associated portable/mobile devices (i.e., those having common communication parameters) on how to capture HELLO messages from neighboring access points having different communication parameters. Such communication parameters may include, for example, hopping sequences, spreading codes, or channel frequencies.
For example, neighbors'"'"' information transmission is appropriate in any case where the system uses more than a single channel. For instance, in a direct sequence architecture, a single spreading code is often used. Capacity can be added to such a network by employing different spreading codes at each access point. The neighbors'"'"' information included in the HELLO message from a given access point would include the spreading sequences of access points providing coverage in adjacent coverage areas. Likewise, in a multiple frequency channelized system, HELLO messages would include the channel frequencies of adjacent access points.
In addition to facilitating roaming, communication of neighbors'"'"' information may also facilitate the initial selection of an access point by a portable/mobile device attaching to the premises LAN for the first time.
Access point HELLO messages may also facilitate adaptive access point transmitter power control. For example, each access point HELLO transmission could specify the transmitter power level being used by the access point. If a given attached portable/mobile device notes that the current access point transmitter power level is unnecessarily high (creating the possibility of interference with other access points), the portable/mobile unit could send a message to the access point indicating as such, and the access point could adjust the transmitter power level accordingly.
HELLO messages also enable communication of information indicating to all devices that certain changes in the NET are required. For example, the NET may switch hopping sequences periodically to improve security, or to avoid interference sources that consistently interfere with one or two frequencies within a given sequence. Interference may result from outside sources, or from other NETS. Changes to the NET are communicated over the course of several HELLO messages (with a countdown) before the change occurs, so that all devices are likely to be aware of changes and synchronize at the instant of change.
In addition, if encryption is used, the encryption key may be periodically changed in HELLOs. Like hopping sequence changes, KEY changes are sent over several HELLOs, and are encrypted using the existing key until the change goes into effect.
As mentioned above, roaming portable and mobile computing devices operating in the premises LAN will routinely move between access point coverage areas. At the maximum device velocity and expected coverage area per access point, a mobile device may be expected to cross a NET coverage contour in several seconds. Because of the use of multiple, non-synchronized frequency hopping NETs, it is more difficult to provide for simple hand-off between access points than it would be in a system that used cellular techniques with a single frequency per cell. The premises LAN makes special provisions for roaming by transmitting coarse frequency hopping synchronization information in HELLO messages.
The premises LAN uses a spanning tree algorithm to maintain current information regarding the general location of mobile devices within the network. When a device changes registration from one NET Control Point to another, routing information is updated throughout the infrastructure. Wired access points may broadcast spanning tree updates to attached wireless access points.
In the premises LAN, roaming portable and mobile devices initially select and register with an access point Control Point on the basis of link quality, i.e., signal quality, signal strength and COST information transmitted within HELLO messages. A device will remain attached to a particular access point until the link quality degrades below an acceptable level, then it will attempt to determine if an alternative NET is available. Different device operating scenarios dictate different roaming strategies, discussed below.
An idle device monitors SYNC and HELLO messages from the Control Point device to maintain NET connectivity. Type is 2 devices do not employ power management, and always maintain their receivers in an active state. They monitor all SYNC messages. Type 1 and Type 3 devices typically employ power management, operating in standby or sleep modes of operation for many Access Intervals before activating their receivers for monitoring SYNC and HELLO messages. Control Points are guaranteed to send Priority SYNC frames every third Access Interval. HELLOs occur every 30th Priority SYNC frame. Power managed devices employ sleep algorithms synchronized to wake for the minimum period necessary to guarantee receipt of priority SYNC, HELLO, and Pending Message transmissions before resuming SLEEP.
Type 2 devices are typically operated from high capacity vehicular power systems, which eliminates the need for power management. These devices may travel at velocities near the maximum system design specification, dictating more frequent roaming. Type 2 devices will initiate a search for an alternative NET if SYNC messages are consistently received at signal strengths below a Roaming Threshold or if reception errors are consistently detected. Because of the effects of frequency selective fading, signal strength information is averaged over the course of several hops within the hopping sequence.
If roaming is indicated, the device initiates a Roaming Algorithm, using Neighbors'"'"' information from the most recent HELLO to attempt synchronization with another candidate NET. If SYNC is not detected within 6 hops, another candidate from the Neighbors list will be selected, and the process repeated. Once SYNC is attained on an alternative NET, the device will monitor signal strength and data errors for several hops to determine link quality. If link quality is acceptable, the device will continue monitoring until a HELLO is received. If COST is acceptable, it will then register with the new NET. The Control Point device will update the spanning tree over the wired backbone (or by RF if a wireless base). If link quality or COST is unacceptable, another candidate from the Neighbors list is selected and the process repeated. This continues until an acceptable connection is established. If a connection cannot be established, the device must return to the original NET or employ the initial acquisition algorithm.
Type 2 devices also have the option of monitoring other NETs before degradation of their NET connection. They may do so by monitoring their own NET for the SYNC and pending message list transmissions, then scanning other candidate NETs during the Sessions period of their NET. Other type devices may do so less frequently.
Type 1 and Type 3 devices may sleep extensively when idle, preferably activating every nine Access Intervals to resynchronize and check pending messages. Successful reception of at least one SYNC during three monitoring periods is necessary to maintain fine synchronization to the NET clock. Failure to receive two of three SYNC frames, or receipt of two or three SYNC messages with poor signal strength are possible indications of the need to further test link quality by remaining active for several consecutive SYNC transmissions. If signal strength or data errors over several hops indicates that link quality is poor, or if a received HELLO message indicates high COST, the roaming algorithm is initiated, and alternative NETs are evaluated, as in the case of Type 2 devices.
Some battery powered devices may sleep for periods of time more than nine Access Intervals. For example, devices with extremely limited battery capacity may sleep between HELLOs, or several HELLO periods, after which they must remain active for several consecutive Access Intervals to regain fine synchronization and assess whether to initiate roaming.
A Type 1, Type 2, or Type 3 device that has inbound message requirements immediately activates its receiver and waits for a SYNC and subsequent Reservation Opportunities.
A device that does not detect SYNC messages over the course of six Access Intervals immediately initiates the Roaming Algorithm.
Outbound messages for devices that have changed coverage areas, but which have not yet registered with a new Control Point device, are problematic. For example, in the premises LAN, messages will be forwarded to the access point that the device had previously been attached to. The access point may attempt to poll the device during one or more Access Intervals, then transmit the unit address in the pending message list periodically for several seconds before disregarding it. Once the unit attaches to a base, the message must be transferred from the previous access point for delivery to the unit. All of these activities require transmission bandwidth on either the backbone or RF media, waste processing resources within the premise LAN, and result in delayed delivery.
As this premises LAN embodiment is designed, the network has no means of distinguishing messages it cannot deliver due to roaming from messages that should be retried due to signal propagation characteristics, interference, or sleeping devices. For this reason, the roaming algorithm may be designed to allow devices to quickly detect that they have lost connectivity within their current NET, and re-attach to a more favorably located access point.
Some improvement in delivering pending messages to roaming terminals can be obtained by routinely propagating pending message lists over the wired backbone. When a device attaches to an access point, that base is able to immediately ascertain that the device has a pending message, and initiate forwarding of the message for delivery to the device.
In the preferred frequency hopping embodiment of the present invention, the hopping sequence consists of 3m±1 frequencies, where m is an integer. 79 frequencies are preferred. This embodiment will support hopping rates of 100, 50 hops per second at 1 Access Interval per dwell, 25 hops per second at 2 frames per dwell, and 12.5 hops per second at 4 frames per dwell. Other rates can be supported for other Access Interval Durations. For example, if the Access Interval is optimized to 25 ms, hop rates of 80, 40, 20, and 10 hops per second would be supported.
All devices within the NET may have one or more hopping tables that contain potential hopping sequences that may be used. Up to 64 sequences may be stored in each device. Each sequence has an identifier, and each frequency in each sequence has an index. The sequence identifier and index are communicated in the SYNC transmission.
All SYNC transmissions may be block encrypted to prevent unauthorized devices from readily acquiring hopping synchronization information. To facilitate encryption, the encryption key may initially be factory set to a universal value in all devices. Users would then have the option of changing this key, by providing a new key to each device in the system. This may be accomplished through keyboard entry or other secure means. Keys may also be changed through the NET.
To facilitate hopping management, a hopping control portion of a protocol controller will download a hopping table to a radio modem, and will signal the radio modem when to hop. This approach consolidates timing functions in the protocol controller, while not requiring the controller to be concerned with conveying frequency selection data to the modem each hop.
The NET may switch hopping sequences periodically to improve security, or to avoid interference sources that consistently interfere with one or two frequencies within a given sequence. As mentioned above, changes to the NET are communicated over the course of several HELLO messages before the change occurs so that all devices are likely to be aware of changes.
Initial synchronization requires devices to ascertain the hopping sequence, the hop rate, and the specific frequency from the hopping sequence currently in use. Synchronization information is contained in two types of routine messages. The SYNC field at the beginning of an Access Interval contains synchronization information including the hopping sequence, the index of the current frequency within the sequence, the number of Access Intervals per hop, and the length of the Access Interval. It also contains a timing character that communicates the NET master clock to all listening devices. Termination messages in the Sessions period, ACK and CLEAR, contain the same information, but do not contain the timing character.
The simplest method for attaining synchronization is to Camp—select a quiet frequency that is likely to be within a sequence in use—and listen for valid synchronization information. If a SYNC message is detected, the listening device immediately has both coarse and fine synchronization, and can begin the registration process.
If SYNC is not detected, but a termination message is, then the device has acquired coarse synchronization. The particulars of the hopping sequence are known, but the boundaries of the dwells are not. To acquire fine synchronization, it begins hopping at the indicated hopping rate, listening for SYNC. If SYNC is not detected after a reasonable number of hops, preferably 12 or 15, the device reverts to camping.
The worst case scenario for synchronization is to synchronize to a single NET that is idle. Given a 79 frequency hopping sequence, one Access Interval per hop, and SYNC transmissions every third Access Interval if the NET is idle, it may take nine cycle times to guarantee that a SYNC transmission will be detected with 99.5% probability. At 50 hops per second, synchronization could require as long as 14 seconds. At 100 hops per second, 7 seconds is required.
At 2 Access Intervals per hop, a SYNC transmission is guaranteed to occur every frequency over 2 cycles of the hopping sequence. Six cycles are required for 99.5% probability of acquisition, corresponding to 19 seconds at 25 hops per second.
At 4 Access Intervals per hop, at least one SYNC is guaranteed to occur each hop. Three cycles of the hopping sequence are required for 99.5% acquisition probability. At 12.5 hops per second, this also requires 19 seconds.
This illustrates the advantage of scalability. A device that uses an acquisition algorithm suitable for 2 or 4 Access Intervals per hop will also acquire a NET that hops at 1 Access Interval per hop. The algorithm may be as follows:
- 1. The device scans candidate frequencies until it finds one with no Received Signal Strength Indicator indication.
- 2. The device remains on the frequency for 6.32 seconds 2 Access Interval/hop@25 Hops/second×2, or 4 Access Intervalfirstname.lastname@example.org hops/second×1, or until it detects a SYNC message or a valid termination message.
- 3. If SYNC is detected, the device synchronizes its internal clock to the SYNC, and begins hopping with the NET for the next 11 hops. It may attempt registration after detecting valid SYNC and any Reservation Opportunity. If synchronization is not verified by detection of SYNC within the 11 hops, the acquisition algorithm is reinitialized.
- 4. If a message termination (either an ACK or CLEAR) is detected, the device immediately hops to the next frequency in the sequence and waits for the SYNC. It is coarsely synchronized to the NET but has a timing offset from the NET clock.
When the next SYNC is received, the device synchronizes its clock to the NET clock and initiates registration. If SYNC is not received within a dwell time, the device hops to the next frequency in sequence. This continues until SYNC is attained, or until 15 hops have passed without receiving SYNC, after which the acquisition sequence is restarted.
- 5. If coarse acquisition is not obtained within 6.3 seconds, the device selects another frequency and repeats the process beginning with step 2.
Camping provides a worst case acquisition performance that is perceptibly slow to the human user of a portable device. The preferred approach has the receiver scan all potential frequencies in ascending order, at 125 μsec increments. When the highest frequency is reached, the search begins again at the lowest frequency. The 125 μs sampling rate is much faster than the 250 μsec channel switching time specification of the RF modem. This is possible because the overall switching time specification applies to worst case frequency switching intervals, i.e., from the highest to the lowest operating frequency. By switching a single channel at a time, switching may be maintained over frequency intervals very near a synthesizer phase detectors'"'"' phase lock range, allowing nearly instantaneous frequency switching. The change from highest to lowest frequency at the end of the scan requires the standard 250 μsec.
The 125 μsec monitoring interval allows 85 μs to ascertain if receive clock has been detected prior to switching to the next frequency. The monitoring interval should be selected to be non-periodic with respect to the access interval. For example, the 125 μsec interval allows the entire hopping sequence to be scanned 2(n+1) times in a 20 ms access interval.
If clock is recovered at any frequency, the receiver remains on frequency for a Reservation Opportunity and initiates channel access through the procedure described above. The scanning approach is less deterministic in terms of acquisition probability than camping, but the search time required for 99.5% acquisition probability is about 80 Access Intervals, or three times faster than that for camping.
A hybrid approach that scans only three or four consecutive frequencies incorporates the deterministic aspects of camping with some of the improved performance of the scanning algorithm. For scanning over a small number of frequencies an up/down scan is preferred, i.e., 1,2,3,2,1,2,3 since all frequency changes can be accomplished at the faster switching rate. The end frequencies are visited less often than those in the center. The number of frequencies used, e.g., 3 or 4, is selected so that all can be scanned during the preamble duration of a minimum length transmission.
All devices are required to have unique 48 bit global addresses. Local 16 bit addresses will be assigned for reduced overhead in communications. Local addresses will not be assigned to devices whose global addresses are not on an authentication list maintained in each access point and routinely updated over the infrastructure.
Once a device has attained synchronization, it must register with the control point to be connected with the NET. It initiates this by sending a Request for Poll indicating a registration request, and including its global address. The control point will register the device, and provide a short. Network Address as an outbound message. The Control point will generate the short address if it is a single NET, or exchange the global address for a short Network Address with a Network Address Server if the NET is part of a larger infrastructured network of a premises LAN.
Once a device is synchronized to a NET, it must periodically update its local clock to the NET clock communicated in the SYNC message. The SYNC message contains a character designated as the SYNC character that transfers the NET clock synchronization. This may be the beginning or ending FLAG in the SYNC message, or a specific character within the message.
The maximum expected frequency error between NET and device local clocks is 100 parts per million. To maintain a 50 μs maximum clock error, the local device clock must be re-synchronized at 500 ms intervals. At 20 ms per access interval, a non-sleeping device has up to 26 SYNC opportunities within that period in which to re-synchronize and maintain required accuracy.
As mentioned above, it is desirable that battery powered devices have the capability to sleep, or power off, for extended periods of time to conserve power. The term sleeping terminal in this instance may refer to a device that powers down its radio communication hardware to save power while maintaining other functions in an operational state, or a device that power manages those functions as well. In the power managed state, the device must maintain its hop clock so that full acquisition is not required every time power management is invoked.
Devices that must sleep to manage their power consumption use Priority SYNC Messages to maintain synchronization. Priority SYNC Messages occur every three Access Intervals. In times of low NET activity, non-priority SYNC messages are omitted. By coordinating power management with Priority SYNC Messages, power managed devices can be guaranteed to wake up for Access Intervals where SYNCs will be present, even if the NET activity is low during the sleep period.
A sleeping device with no transmission requirements may sleep for eight 20 ms access intervals, and wake only for the SYNC and Reservation Poll at the beginning of the ninth Access Interval to monitor pending messages before returning to the sleep state, for a duty cycle of less than 5%. This provides three opportunities to synchronize to the NET clock within a 540 ms window. A flow chart depicting the a device sleeping for several access intervals is shown in
Devices may also sleep for longer periods of time, at the risk of losing fine synchronization. They may compensate by advancing their local clocks to account for the maximum timing uncertainty. For example, a terminal could sleep for 5 seconds without re-synchronizing by waking up 500 microseconds before it expects an Access Interval to begin, and successfully receive SYNC messages. This technique is valid for extended periods of time, up to the point where the maximum timing error approaches 50% of an Access Interval. A flow chart depicting the a device sleeping for several seconds is shown in
A power managed device that requires communication during a sleep period may immediately wake and attempt access to the NET at the next available Reservation Opportunity.
A device requiring communications may be able to register with one of several NETs operating in its vicinity, with transmissions occurring on many frequencies simultaneously. A good strategy is to synchronize to a NET that provides an acceptable communication link, then monitor HELLO messages to determine other candidate NETs before attaching to a particular NET by registering with the control point device.
As described above, a spontaneous wireless local area network or spontaneous LAN is one that is established for a limited time for a specific purpose, and which does not use the premises LAN to facilitate communications between devices or provide access to outside resources. Use of spontaneous LAN allows portable devices to share information, files, data, etc., in environments where communication via the premises LAN is not economically justifiable or physically possible. A spontaneous LAN capability also allows portable/mobile devices to have an equally portable network. Peripheral and vehicular LANs are examples of such spontaneous LANs.
Requirements for spontaneous LAN differ from an infrastructured premises LAN in several significant areas. The number of devices in a spontaneous LAN is likely to be smaller than the number that a single NET in a premises LAN must be capable of supporting. In addition, coverage areas for spontaneous LANs are typically smaller than coverage areas for an access point participating in the premises LAN. In a spontaneous LAN, communication often takes place over relatively short distances, where devices are within line of sight of each other.
In an premises LAN, the majority of communications are likely to involve accessing communication network resources. For example, portable devices with limited processing capabilities, memory, and power supplies are able to access large databases or powerful computing engines connected to the AC power grid. Access points within the premises LAN are well suited to the role of Control Points for managing synchronization and media access within each NET.
In a spontaneous LAN, however, communications are limited to exchanges with spontaneous NET constituents. Additionally, NET constituents may potentially leave at any time, making it difficult to assign control point responsibilities to a single device. A shared mechanism for synchronization and media access is preferable in most cases.
In a spontaneous LAN, battery power limitations may preclude assignment of a single device as a control point. The routine transmission of SYNC and access control messages places a significant power drain on a portable, battery powered device. Also, the control point architecture dictates that transmissions intended for devices other than the control point be stored and forwarded to the destination device, further increasing battery drain, and reducing system throughput.
Moreover, the use of scheduled transmission in a premises LAN is likely to differ from use in a spontaneous LAN. For example, unlike the premises LAN, in the spontaneous LAN, applications such as massaging and two way a voice communications may only occasionally be used, whereas video transmission and telemetry exchange may be prevalent.
To promote compatibility and integration with the premises LAN, operational differences required by multiple participating devices should be minimized. For example, selecting relatively close frequency bands for each LAN aids in the design of a multiple LAN transceiver, reducing circuitry, cost, power, weight and size while increasing reliability. Similarly, selecting communication protocols so that the spontaneous LAN protocol constitutes a subset or superset of premises LAN may enable a given device to more effectively communication in both LANs, while minimizing both the overall protocol complexity and potentially limited memory and processing power.
Use of frequency hopping is desirable in premises LAN because of its ability to mitigate the effects of interference and frequency selective fading. In the case of the latter, frequency hopping allows systems to be installed with less fade margin than single frequency systems with otherwise identical radio modem characteristics, providing improved coverage.
The potentially smaller coverage area requirement of spontaneous LANs, however, allows single frequency operation to be considered for some applications, e.g., such as a peripheral LAN. Regulatory structures are in place in some countries to allow single frequency operation in the same bands as frequency hopping systems, providing that single frequency devices operate at reduced power levels. The lower transmit power of single frequency operation and elimination of periodic channel switching are desirable methods of reducing battery drain. The choice of single frequency or frequency hopped operation is dictated by the coverage requirements of the network, and may be left as an option to device users.
As noted earlier, the basic Access Interval structure is suited to single frequency operation as well as to frequency hopping. SYNC messages in a single frequency system substitute a single frequency indication in the hopping sequence identifier field.
A spontaneous LAN comes into existence when two or more devices establish communications, and ceases when its population falls to less than two. Before a spontaneous LAN can be established, at least two devices must agree upon a set of operating parameters for the network. Such agreement may be pre-programmed else exchanged and acknowledged prior to establishing the spontaneous LAN. Once the spontaneous LAN is established, other devices coming into the network must be able to obtain the operating parameters and acquire access.
More specifically, to establish a spontaneous LAN, a computing device must first identify at least one other network device with which spontaneous LAN communication is desired. To identify another network device, the computing device may play an active or passive role. In an active role, the computing device periodically broadcasts a request to form spontaneous LAN with either a specific network device or, more likely, with a specific type of network device. If a network device fitting the description of the request happens to be in range or happens into range and is available, it responds to the periodic requests to bind with the computing device, establishing the spontaneous LAN. Alternately, the network device may take a passive role in establishing the spontaneous LAN. In a passive role, the computing device merely listens for a request to form a spontaneous LAN transmitted by the appropriate network device. Once such a network device comes into range, the computing device responds to bind with the network device, establishing the spontaneous LAN.
The choice of whether a device should take a passive or active role is a matter of design choice. For example, in one embodiment where peripheral devices have access to AC power, the roaming computer terminals take a passive role, while the peripheral devices take a more active role. Similarly, in another embodiment where a vehicle terminal has access to a relatively larger battery source, an active role is taken when attempting to form a spontaneous LAN, i.e., a vehicular LAN, with a hand-held computing device.
Binding, a process carried out pursuant to a binding protocol stored in each network device, may be a very simple process such as might exist when creating a spontaneous LANs that operates on a single frequency channel. Under such a scenario, a simple acknowledge handshake between the computing terminal and the other network device may be sufficient to establish a spontaneous LAN pursuant to commonly stored, pre-programmed operating parameters. However, more complex binding schemes may also be implemented so as to support correspondingly more complex spontaneous LANs as proves necessary. An example of a more complex binding scheme is described below.
It is desirable in some large spontaneous LANs for one device to be designated as a fully functional control point, providing identical NET operation to a single NET in the premises LAN. Providing that all devices share a hopping table and encryption key, the designated device would initiate control point activities, and other devices would synchronize to the designated unit. A device with greater battery capacity, or one that can be temporarily connected to AC power is best suited to the dedicated control point function. This architecture is applicable to Client-Server applications (where the server assumes the control point function), or to other applications where a single device is the predominant source or destination of communications. A portable device used as a dedicated control point is required to have additional programming and memory capacity to manage reservation based media access, pending message lists, and scheduled service slot allocations.
In embodiments where communication requirements of a spontaneous LAN are largely peer to peer, there may be no overwhelming candidate for a dedicated Control Point. Thus, in such cases, the Control Point function is either distributed among some or all the devices within the spontaneous LAN. In such scenarios, the interleaved Access Interval approach used for wireless access points is employed. Initially, control point responsibilities are determined during the binding process. Users may designate or redesignate a Control Point device when several candidates are available.
For spontaneous LANS, access intervals may be simplified to reduce power consumption, program storage and processing power requirements for portable devices used as control points. Control Point devices transmit SYNC, pending message lists, and Time Division Multiple Access slot reservations normally, but only use the single slot reservation Poll (Idle Sense Multiple Access). The reservation poll contains a field indicating reduced control point functionality. This places other devices in a point-to-point communication mode, using the Implicit Idle Sense Algorithm. The probability factor p communicated in the reservation poll is used for the Implicit Idle Sense algorithm. Control point devices may use the deferred SYNC mechanism for light system loading, transmitting Priority SYNC every third Access Interval to further decrease their transmission requirements. Control point devices must monitor the reservation slot for messages addressed to them, but may sleep afterwards.
Request for Polls initiated under Implicit Idle Sense use point-to-point addressing, indicating the address of the destination device directly, rather than the control point device. This eliminates the need for the Control Point device to store and forward transmissions within the spontaneous LAN. The device detecting its address in a Request for Poll begins a session, after employing the Implicit Idle Sense algorithm, by Polling the source address identified in the Request for Poll. The terminating ACK and CLEAR messages contain an Explicit Idle Sense probability factor equal to that in the original reservation poll.
To allow for power managed devices, the Control Point device maintains a pending message list. Devices that have been unable to establish communication with a sleeping device initiate a session with the Control Point device to register the pending message. Upon becoming active, the sleeping device will initiate a Poll to the device originating the pending message. The Control Point device will eliminate the pending message indication by aging, or by receipt of communication from the destination device clearing the pending message. Control point devices are not required to store pending messages, only addresses. As mentioned above, HELLO messages are broadcast to indicate changes in NET parameters. HELLO messages may be omitted to simplify the Control Point function in spontaneous LANs.
Devices are assigned local addresses upon registration with the Control Point device. Devices may communicate an alias that identifies the device user to other users to the Control Point device where it is stored in an address table. The address table may be obtained by other network constituents by querying the Control Point device. A peripheral LAN is a type of spontaneous LAN which serves as a short range interconnect between a portable or mobile computing device (MCD) and peripheral devices.
Designers of portable products are constantly challenged with reducing size, weight, and power consumption of these devices, while at the same time increasing their functionality and improving user ergonomics. Functions that may be used infrequently, or which are too large to fit within the constraints of good ergonomic design may be provided in peripheral devices, including printers, measurement and data acquisition-units, optical scanners, etc. When cabled or otherwise physically connected to a portable product, these peripherals often encumber the user, preventing freedom of movement or mobility. This becomes more problematic when use of more than one peripheral is required.
A second consideration for portable product design is communication docking. A communication dock is a device that holsters or houses a portable unit, and provides for communication interconnection for such tasks as program downloading, data uploading, or communication with large printers, such as those used for printing full sized invoices in vehicular applications. Communication docking of a portable unit may also involve power supply sharing and/or charging.
The requirement for communication docking capability forces newer portable product designs to be mechanically compatible with older docking schemes, or may require that new docks, or adapters, be developed for each new generation of portable device. Product specific docking approaches eliminate compatibility between devices manufactured by different suppliers. This has hindered development of uniform standards for Electronic Data Interchange between portable devices and fixed computing systems.
Physical connection between a portable device with a peripheral or communication dock also hinders user efficiency. Peripheral devices are generally attached with cable. If a peripheral is small enough to be carried or worn on a belt, the mobility of the user may be maintained. If a user must carry a hand-held portable device that is connected to a belt mounted peripheral the assembly cannot be set down while a task that requires movement to a location several feet away is undertaken unless the portable device and peripheral are disconnected. Likewise, connection to peripherals too large to be portable requires the user to frequently connect and disconnect the device and the peripheral.
Use of wireless peripheral LAN interconnection greatly simplifies the task of portable devices communicating with peripherals. In doing so, wireless connectivity allows improved ergonomics in portable product design, flexibility in interconnection to one or more peripherals, freedom of movement over a radius of operation, forward and backward compatibility between portable units and peripherals, and potential communications among products manufactured by different vendors.
Constituents within a peripheral LAN generally number six or fewer devices. One roaming computing device and one or two peripherals comprise a typical configuration. Operating range is typically less than fifty feet.
Because the computing devices generally control the operation of peripheral devices, in a peripheral LAN a master/slave type protocol is appropriate. Moreover, roaming computing devices serving as master are well suited to the role of Control Points for managing synchronization and media access within each peripheral LAN. All peripheral communications are slaved to the master.
In a peripheral LAN, roaming mobile or portable computing devices and wireless peripherals may all operate from battery power. Operating cycles between charging dictate use of power management techniques.
Although all participants in a peripheral LAN might also be configured to directly participate in the premises LAN, the trade-offs in cost, power usage and added complexity often times weighs against such configuration. Even so, participants within a peripheral LAN can be expected to function in a hierarchical manner, through a multiple participating device, with the premises LAN. Thus, the use of a much simpler, lower-power transceiver and associated protocol may be used in the peripheral LAN.
As previously described, a roaming computing device serving as a master device may itself be simultaneously attempting to participate in other networks such as the premises or vehicular LANs. Considerable benefits arise if the radio and processing hardware that supports operation within the wireless network can also support such operation. For example, a device that is capable of frequency hopping is inherently suited to single frequency operation. If it can adjust transmitter power level and data rate to be compatible with the requirements of the peripherals LAN, it can function in both systems. The major benefits of common transceiver hardware across LANs include smaller product size, improved ergonomics, and lower cost.
Specifically, in one embodiment, radio communication on the premises LAN, as described herein, takes place using radio transceivers capable of performing frequency-hopping. To communicate on a peripheral LAN, such transceivers could also utilize frequency-hopping at a lower power. However, such transceivers are relatively expensive in comparison to a lower power, narrow-band, single frequency transceivers. Because of the cost differential, it proves desirable to use the single frequency transceivers for all peripheral devices which will not participate in the premises LAN. Therefore, the more expensive, frequency-hopping transceivers which are fitted into roaming computing devices are further designed to stop hopping and lock into the frequency of the single frequency transceiver, allowing the establishment of peripheral LANs.
Instead of frequency hopping, the peripheral LAN may also use narrow-band, single frequency communication, further simplifying the radio transceiver design for commonality. In another embodiment of the peripheral LAN transceivers, operation using one of a plurality of single frequency channels is provided. Thus, to overcome interference on one channel, the transceiver might select from the remaining of the plurality an alternate, single operating frequency with lesser channel interference. To accommodate the plurality of single frequency channels, the peripheral LAN transceivers may either communicate an upcoming frequency change so that corresponding peripheral LAN participants can also change frequency, or the transceivers may be configured to use frequency synthesis techniques to determine which of the plurality a current transmission happens to be.
The Access Interval structure is also an appropriate choice for peripheral LAN operations. In one embodiment, to provide for simplicity and tighter integration, the Access Interval for the peripheral LAN is a subset of the Access Interval used in the premises LAN. HELLO messages, Implicit Idle Sense, Data Rate Switching, and scheduled services are not implemented. Peripheral devices normally sleep, activate their receivers for SYNC transmissions from the participating master device, and resume sleeping if no pending messages are indicated and they have no inbound transmission requirements. Access Intervals occur at regular intervals, allowing for power management. Access Intervals may be skipped if the master has other priority tasks to complete.
To initialize the peripheral LAN, a device desiring initialization, a master device, selects a single operating frequency by scanning the available frequencies for one with no activity. A typical master device might be a roaming computing device desiring access to a local peripheral. Default values for other parameters, including Access Interval duration, are contained within each participant'"'"'s memory. Such parameters may be pre-adjusted in each participant to yield specific performance characteristics in the peripheral LAN.
Once a master device identifies a single frequency, slaves, which are generally peripherals, are brought into the peripheral LAN through a process called binding. Binding is initiated by the master device by invoking a binding program contained therein. Slaves, such as peripherals, are generally programmed to enter a receptive state when idle. Thus, in one embodiment, the master device accomplishes binding by transmitting Access Intervals of known duration sequentially on a series of four frequencies spread throughout the available frequency range. The specific frequencies and Access Interval durations used are stored as parameters in all potential participating devices. A 250 KBPS transfer rate is appropriate in some embodiments of the peripheral LAN, reflecting a balance between performance and complexity in peripheral devices.
A slave, e.g., a peripheral, responds to the binding attempts by the master device on a given frequency until the slave successfully receives and establishes communication with the master device. If they do not establish communication after four Access Intervals, the slave switches to the next frequency for four Access Interval periods. Once communication is established, the slave registers with the master and obtains the master device'"'"'s selected operating frequency and related communication parameters. When all slave devices have been bound, the master terminates the binding program and normal operation at the selected single frequency may begin.
During the premises LAN Access Interval, the peripheral LAN master device monitors the premises LAN control point for SYNC 1503 reservation poll 1505 and exchanges inbound and outbound message according to the normal rules of the access protocol. The master switches to the peripheral LAN frequency, and transmits its own SYNC frame 1507 during the session period 1509 of its parent control point allowing communication with its peripherals. The peripheral LAN Access Interval is generally shorter than the premises LAN Access Interval, so that it does not extend beyond the premises LAN Access Interval boundary. At the end of the peripheral LAN Access Interval 1501, the master switches to the premises LAN frequency for the next SYNC 1503.
The secondary SYNC 1507 may only be transmitted if the peripheral LAN master is not busy communicating through the premises LAN. If a communication session is occurring, the master must defer SYNC, preventing communication with its peripherals during that Access Interval. The master must also defer SYNC if the current frequency in the LAN is prone to interference from the peripheral LAN frequency, i.e., they are the same frequency or adjacent frequencies. If two consecutive SYNCs are deferred, peripherals will activate their receivers continuously for a period of time, allowing the master to transmit during any Access Interval. This approach is also applicable when the master roams between frequency hopping NETs. Since NETs are not synchronized to one another, the devices in the peripheral LAN adjust Access Interval boundaries each time the master roams. If peripherals do not detect SYNC within a time-out period, they may duty cycle their reception to conserve battery power.
Access points transmit HELLO messages to devices in their coverage area. These HELLO messages communicate to roaming computing devices the cost of connection through the access point, addresses of neighboring access points, and the cost of connection through these neighboring access points. This information allows roaming computing devices to determine the lowest cost connection available and to connect to the access point with the lowest cost.
In addition, access point HELLO message may include communication parameters of neighboring access points, such as frequency hopping sequences and indices, spread spectrum spreading codes, or FM carrier channel frequencies. This information allows roaming computing devices to roam and change access point connections without going through a full acquisition phase of the new access point'"'"'s parameters.
Roaming computing devices initially select and register with an access point control point on the basis of link quality: signal strength and cost information transmitted within HELLO messages. A device will remain attached to a particular access point until the link quality degrades below an acceptable level; then it will attempt to determine if an alternative access point connection is available. The device initiates a roaming algorithm, using neighbors information from the most recent HELLO message to attempt connection with another candidate access point. If connection fails, another candidate from the neighbors list will be selected, and the process repeated. Once connection is made with an alternative access point, the device will monitor signal strength and data errors to determine link quality. If link quality is acceptable, the device will continue monitoring until a HELLO message is received. If the cost is acceptable, it will register with the new access point, and the access point will update the spanning tree over the infrastructure. If link quality or cost is unacceptable, another candidate from the neighbors list is selected and the process repeated. This continues until an acceptable connection is established. If one cannot be established, the device must return to the original access point connection or employ the initial acquisition algorithm.
The host computer 3011 provides the terminal 3007 with remote database storage, access and processing. However, the terminal 3007 also provides for local processing within its architecture to minimize the need to access the remote host computer 3011. For example, the terminal 3007 may store a local database for local processing. Similarly, the terminal 3007 may run a variety of application programs which never, occasionally or often need access to the remote host computer 3011.
Many of the devices found in the illustrative network are battery powered and therefore must conservatively utilize their radio transceivers. For example, the hand-held computer terminal 3007 receives its power from either an enclosed battery or a forklift battery (not shown) via a communication dock within the forklift 3014. Similarly, the code reader 3009 operates on portable battery power as may the printer 3013. The arrangement of the communication network, communication protocols used, and data rate and power level adjustments help to optimize battery conservation without substantially degrading network performance.
In the illustrated embodiment shown in
Because roaming computing devices, such as the hand-held computer terminal 3007, cannot be directly hard-wired to the backbone LAN 3019, they are fitted with RF transceivers. To guarantee that such a network device can directly communicate on the premises LAN with at least one of the access points 3015 and 3017, the fitted transceiver is selected to yield approximately the same transmission power as do the access points 3015 and 3017. However, not all roaming network devices require a direct RF link to the access points 3015 and 3017, and some may not require any link at all. Instead, with such devices, communication exchange is generally localized to a small area and, as such, only requires the use of relatively lower power, short range transceivers. The devices which participate in such localized, shorter range communication form spontaneous LANs.
For example, the desire by a roaming terminal to access peripheral devices such as the printer 3013 and modem 3023, results in the roaming terminal establishing a peripheral LAN with the peripheral devices. Similarly, a peripheral LAN might be established when needed to maintain local communication between a code scanner 3009 and the terminal 3007. In an exemplary embodiment, the printer 3013 are located in a warehouse dock with the sole assignment of printing out forms based on the code information gathered from boxes delivered to the dock. In particular, as soon as the code reader gathers information, it relays the information along a peripheral LAN to the terminal 3007. Upon receipt, the terminal 3007 communicates via the premises LAN to the host computer 3011 to gather related information regarding a given box. Upon receipt of the related information, the terminal 3007 determines that printing is desired with the printer 3013 located at the dock. When the forklift 3014 enters the vicinity of the dock, the terminal 3007 establishes a peripheral LAN with the printer 3013 which begins printing the collected code information.
To carry out the previous communication exchange, the printer 3013 and code reader 3009 are fitted with a lower power peripheral LAN transceivers for short range communication. The computer terminal 3007 transceiver is not only capable of peripheral LAN communication, but also with the capability of maintaining premises LAN communication. In an alternate exchange however, the code reader 3009 might be configured to participate on both LANs, so that the code reader 3009 participates in the premises LAN to request associated code information from the host computer 3011. In such a configuration, either the code reader 3009 or terminal 3007 could act as the control point of the peripheral LAN. Alternately, both could share the task.
With capability to participate in the peripheral LAN only, the code reader 3009, or any other peripheral LAN participant, might still gain access to the premises LAN indirectly through the terminal 3007 acting as a relaying device. For example, to reach the host computer 3011, the code reader 3609 first transmits to the computer terminal 3007 via the peripheral LAN. Upon receipt, the computer terminal 3007 relays the transmission to one of the access points 3015 and 3017 for forwarding to the host 3011. Communication from the host 3011 to the code reader 3009 is accomplished via the same pathway.
It is also possible for any two devices with no access to the premises LAN to communicate to each other. For example, the modem 3023 could receive data and directly transmit it for printing to the printer 3013 via a peripheral LAN established between the two. Similarly, the code reader 3009 might choose to directly communicate code signals through a peripheral LAN to other network devices via the modem 3023.
In an alternate configuration, a peripheral LAN access point 3021 is provided which may be directly connected to the backbone LAN 3019 (as shown), acting as a direct access point to the backbone LAN 3019, or indirectly connected via the access points 3015 and 3017. The peripheral LAN access point 3021 is positioned in the vicinity of other peripheral LAN devices and thereafter becomes a control point participant. Thus, peripheral LAN communication flowing to or from the premises LAN avoids high power radio transmissions altogether. However, it can be appreciated that a stationary peripheral LAN access point may not always be an option when all of the peripheral LAN participants are mobile. In such cases, a high power transmission to reach the premises LAN may be required.
Prior to making a delivery, the truck enters a docking area for loading. As goods are loaded into the truck, the information regarding the goods is down-loaded into the storage terminal 3031 via the terminal 3007 or code reader 3009 (
As information regarding a good is received and stored, the storage terminal 3031 might also request further information regarding any or all of the goods via the peripheral LAN'"'"'s link to the host computer 3011 through the premises LAN. More likely however, the storage terminal 3031 if appropriately configured would participate on the premises LAN to communicate directly with the host computer 3011 to retrieve such information.
The peripheral LAN access point 3021 if located on the dock could provide a direct low power peripheral LAN connection to the backbone LAN 3019 and to the host computer 3011. Specifically, in one embodiment, the access point 3021 is located on the dock and comprises a low power (“short hop”) radio operating in a frequency hopping mode over a 902-928 MHz frequency band. However, the access point 3021 can instead be configured to communicate using, for example, infrared, UHF, 2.4 GHz or 902 MHz spread spectrum direct sequence frequencies.
Once fully loaded and prior to leaving the dock, the storage device 3031 may generate a printout of the information relating to the loaded goods via a peripheral LAN established with the printer 3013 on the dock. In addition, the information may be transmitted via the peripheral LAN modem 3023 to a given destination site.
As illustrated in
Upon reaching the destination, the storage terminal 3031 may participate in any in range peripheral and premises LAN at the delivery site dock. Specifically, as specific goods are unloaded, they are scanned for delivery verification, preventing delivery of unwanted goods. The driver is also informed if goods that should have been delivered are still in the truck. As this process takes place, a report can also be generated via a peripheral or premises LAN printer at the destination dock for receipt signature. Similarly, the peripheral LAN modem on the destination dock can relay the delivery information back to the host computer 3011 for billing information or gather additional information needed, avoiding use of the radio WAN.
If the truck 3033 is used for service purposes, the truck 3033 leaves the dock in the morning with the addresses and directions of the service destinations, technical manuals, and service notes which have been selectively downloaded from the host computer 3011 via either the premises or peripheral LAN to the storage terminal 3031 which may be configured with a hard drive and substantial processing power. Upon pulling out of range, the storage terminal 3031 and the computer terminal 3007 automatically form an independent, detached vehicular LAN. Alternately, the terminals 3007 and 3031 may have previously formed the vehicular LAN before leaving dock. In one embodiment, the vehicular LAN operates using frequency hopping protocol much the same as that of the premises LAN, with the storage terminal 3031 acting much like the premises LAN access points. Thus, the radio transceiver circuitry for the premises LAN participation may also be used for the vehicular LAN and, as detailed above, a peripheral LAN. Similarly, if the radio WAN chosen has similar characteristics, it may to be incorporated into a single radio transceiver.
At each service address, the driver collects information using the terminal 3007 either as the data is collected, if within vehicular LAN transmission range of the storage terminal 3031, or as soon as the terminal 3007 comes within range. Any stored information within storage terminal 3031 may be requested via the vehicular LAN by the hand-held terminal 3007. Information not stored within the vehicular LAN may be communicated via a radio WAN as described above.
Referring again to
Corresponding information to the code data must be retrieved from the host computer 3011. The collected code information and retrieved corresponding information can be displayed on the terminal 3007. After viewing for verification, the information can be printed on the printer 3058. Because of this data flow requirement, the computer terminal 3007 is selected as the peripheral LAN device which must also carry the responsibility of communicating with the premises LAN.
If during collection, the operator decides to power down the computer terminal 3007 because it is not needed, the peripheral LAN becomes detached from the premises LAN. Although it might be possible for the detached peripheral LAN to function, all communication with the host computer 3011 through the premises LAN is placed in a queue awaiting reattachment. As soon as the detached peripheral LAN comes within range of an attached peripheral LAN device, i.e., a device attached to the premises LAN, the queued communications are relayed to the host. It should be clear from this description that the peripheral LAN may roam in relation to a device attached to the premises LAN (“premises LAN device”). Similarly, the premises LAN device may roam in relation to the peripheral LAN. The roaming constitutes a relative positioning. Moreover, whenever a peripheral LAN and a master device move out of range of each other, the peripheral LAN may either poll for or scan for another master device for attachment. The master device may constitute a premises LAN device, yet need not be.
To avoid detachment when the terminal 3007 is powered down, the code reader 3009 may be designated as a backup to the terminal 3007 for performing the higher power communication with the premises LAN. As described in more detail below in reference to
In addition, if the computer terminal 3007 reaches a predetermined low battery threshold level, the terminal 3007 will attempt to pass the burden of providing premises LAN access to other peripheral LAN backup devices. If no backup device exists in the current peripheral LAN, the computer terminal 3007 may refuse all high power transmissions to the premises LAN. Alternatively, the computer terminal 3007 may either refuse predetermined select types of requests, or prompt the operator before performing any transmission to the premises LAN. However, the computer terminal 3007 may still listen to the communications from the premises LAN and inform peripheral LAN members of waiting messages.
The housing 3067 may optionally include a cigarette lighter power input cable 3077 to power the printer 3069, and recharge the battery of the terminal 3073 via the dock 3071. The housing 3067 may also optionally include a wide area network radio to permit communication with a remote warehouse or station 3079. In addition, the housing 3067 may also be configured to include the functionality of the storage terminal 3031 discussed above with respect to
The peripheral LAN embodiments of
Once information regarding a particular pick-up has been stored, either in the terminal or storage terminal, the driver may download the stored data using the WAN radio to the premises LAN host computer at the remote warehouse or station 3079 so that the information may be used to pre-schedule further routing of the goods before the driver even arrives. Because WAN communication is costly, however, the information may instead be automatically transferred wirelessly to the premises LAN host once the driver comes into range of the premises LAN, as discussed above with respect to
Once the host computer has the information regarding the goods picked up by the driver(s), the host can download the data via RF or the docking system 3081 to any number of terminals 3073 used by warehouse personnel who unload the trucks. While unloading, these personnel can, for example, use a terminal 3073 and a code reader 3075 to build containers for further distribution of the goods to various destinations. Specifically, as a container is unloaded, the label previously placed on the container by the driver is scanned by the code reader 3075, and destination information is displayed on the terminal 3073. The box may then be taken to and loaded into the container headed for the same destination. Each container may also have a label which can be scanned to verify the destination of that particular container.
In particular, the transceiver 3110 contains a radio unit 3112 which attaches to an attached antenna 3113. The radio unit 3112 used in peripheral LAN slave devices need only provide reliable low power transmissions, and are designed to conserve cost, weight and size. Potential peripheral LAN master devices not only require the ability to communicate with peripheral LAN slave devices, but also require higher power radios to also communicate with the premises LAN. Thus, potential peripheral LAN master devices and other non-peripheral LAN slave devices might contain two radio units 3112 or two transceivers 3110—one serving the premises LAN and the other serving the peripheral LAN—else only contain a single radio unit to service both networks.
In embodiments where cost and additional weight is not an issue, a dual radio unit configuration for potential peripheral LAN master devices may provide several advantages. For example, simultaneous transceiver operation is possible by choosing a different operating band for each radio. In such embodiments, a 2.4 GHz radio is included for premises LAN communication while a 27 MHz radio supports the peripheral LAN. Peripheral LAN slave devices receive only the 27 MHz radio, while the non-potential peripheral LAN participants from the premises LAN are fitted with only the 2.4 GHz radios. Potential peripheral LAN master devices receive both radios. The low power 27 MHz peripheral LAN radio is capable of reliably transferring information at a range of approximately 40 to 100 feet asynchronously at 19.2 KBPS. An additional benefit of using the 27 MHz frequency is that it is an unlicensed frequency band. The 2.4 GHz radio provides sufficient power (up to 1 Watt) to communicate with other premises LAN devices. Another benefit of choosing 2.4 GHz or 27 MHz bands is that neither require FCC licensing. Many different frequency choices could also be made such as the 900 MHz band, UHF, etc. Alternatively, infrared communication may be used in situations where line of sight may be achieved between devices on the network.
In embodiments where cost and additional weight are at issue, a single radio unit configuration is used for potential peripheral LAN master devices. Specifically, in such embodiments, a dual mode 2.4 GHz radio supports both the peripheral LAN and premises LANs. In a peripheral LAN mode, the 2.4 GHz radio operates at a single frequency, low power level (sub-milliwatt) to support peripheral LAN communication at relatively close distances 20-30 feet). In a high power (up to 1 Watt) or main mode, the 2.4 GHz radio provides for frequency-hopping communication over relatively long distance communication connectivity with the premises LAN. Although all network devices might be fitted with such a dual mode radio, only peripheral LAN master devices use both modes. Peripheral LAN slave devices would only use the low power mode while all other premises LAN devices would use only the high power mode. Because of this, to save cost, peripheral LAN slave devices are fitted with a single mode radio operating in the peripheral LAN mode. Non-peripheral LAN participants are also fitted with a single mode (main mode) radio unit for cost savings.
Connected between the radio unit 3112 and an interface 3110, a microprocessor 3120 controls the information flow between through the transceiver 3110. Specifically, the interface 3115 connects the transceiver 3110 to a selected computer terminal, a peripheral device or other network device. Many different interfaces 3115 are used and the choice will depend upon the connection port of the device to which the transceiver 3110 will be attached. Virtually any type of interface 3110 could be adapted for use with the transceiver 3110 of the present invention. Common industry interface standards include RS-232, RS-422, RS-485, 10BAS2 Ethernet, 10BASE5 Ethernet, 10BASE-T Ethernet, fiber optics, IBM 4/16 Token Ring, V.11, V.24, V.35, Apple Localtalk and telephone interfaces. In addition, via the interface 3115, the microprocessor 3120 maintains a radio independent, interface protocol with the attached network device, isolating the attached device from the variations in radios being used.
The microprocessor 3120 also controls the radio unit 3112 to accommodate communication with the either the premises LAN, the peripheral LAN, or both (for dual mode radios). Moreover, the same radio might also be used for vehicular LAN and radio WAN communication as described above. For example, a radio located in a vehicle or in a hand held terminal can be configured to communicate not only within a local network, but might also be capable of receiving paging messages.
More specifically, in a main mode transceiver, the microprocessor 3120 utilizes a premises LAN protocol to communicate with the premises LAN. Similarly, in a peripheral LAN mode transceiver, the microprocessor 3120 operates pursuant to a peripheral LAN protocol to communicate in the peripheral LAN. In the dual mode transceiver, the microprocessor 3120 manages the use of and potential conflicts between both the premises and peripheral LAN protocols. Detail regarding the premises and peripheral LAN protocols can be found in reference to
In addition, as directed by the corresponding communication protocol, the microprocessor 3120 controls the power consumption of the radio 3112, itself and the interface 3115 for power conservation. This is accomplished in two ways. First, the peripheral LAN and premises protocols are designed to provide for a low power mode or sleep mode during periods when no communication involving the subject transmitter is desired as described below in relation to
In order to insure that the proper device is receiving the information transmitted, each device is assigned a unique address. Specifically, the transceiver 3110 can either have a unique address of its own or can use the unique address of the device to which it is attached. The unique address of the transceiver can either be one selected by the operator or system designer or one which is permanently assigned at the factory such as an IEEE address. The address 3121 of the particular transceiver 3110 is stored with the microprocessor 3120.
In the illustrated embodiments of
Several alternate channel access strategies have been developed for carrier sense multiple access (CSMA) systems and include 1-persistent, non-persistent and p-persistent. Such strategies or variations thereof could easily be adapted to work with the present invention.
The slave device uses a binding protocol (discussed below with regard to
Alternatively, the slave may have data for transfer to the master. If so, the slave indicates as such to the master by transmitting a message during the time period 3217 and then executes a backoff algorithm to determine how long it must wait before transmitting the data. The slave determines from the backoff algorithm that it must wait the time period 3227 before transmitting the data during the time period 3221. The slave devices use the backoff algorithm in an attempt to avoid the collision of data with that from other slave devices which are also trying to communicate with the master. The backoff algorithm is discussed more fully above in reference to
The idle sense messages of the master may also aid in scheduling communication between two slave devices. For example, if a first slave device has data for transfer to a second slave device, the first slave sends a message to the master during the time period 3209 requesting communication with the second slave. The master then broadcasts the request during the next idle sense message. Because the second slave is monitoring the idle sense message, the second slave receives the request and stays activated at the end of the idle sense message in order to receive the communication. Likewise, because the first slave is also monitoring the idle sense message, it too receives the request and stays activated during the time period 3215 to send the communication.
Communication between the master and slave devices is the same as that discussed above in reference to
The slave device thereafter initiates a binding protocol to attempt to regain synchronization with the master. While two time periods 3241 and 3245 are shown, the slave may initiate such a protocol after any number of unsuccessful attempts to locate an idle sense message. With this protocol, the slave stays active for a time period 3247, which is equal to the time period from one idle sense message to the next, in an attempt to locate a next idle sense message. If the slave is again unsuccessful, it may stay active until it locates an idle sense message from the master, or, if power consumption is a concern, the slave may enter a power conserving mode at the end of the time period 3247 and activate at a later time to monitor for an idle sense message.
In the event the master device remains outside the range of the slave devices in the peripheral LAN for a period long enough such that communication is hindered, one of the slave devices may take over the functionality of the master device. Such a situation is useful when the slave devices need to communicate with each other in the absence of the master. Preferably, such a backup device has the ability to communicate with devices on the premises LAN. If the original master returns, it listens to the channel to determine idle sense messages from the backup, indicates to the backup that it has returned and then begins idle sense transmissions when it reestablishes dominance over the peripheral LAN.
The access point periodically broadcasts HELLO messages 3261 indicating that it is available for communication. The master device monitors the HELLO messages during a time period 3263, and, upon determining that the base does not need servicing, enters a power conserving mode during a time period 3265. The master then activates for a time period to monitor the next HELLO message from the base. If the master has data to send to the base, it transmits the data during a time period 3271. Likewise, if the base has data to send to the master, the base transmits the data during a time period 3269. Once the data is received or sent by the master, it may again enter a power conserving mode. While HELLO message protocol is discussed, a number of communication protocols may be used for communication between the base and the master device. As may be appreciated, the peripheral LAN master device acts as a slave to access points in the premises LAN.
Generally, the communication exchange between the master and the slave is similar to that described above in reference to
Upon receipt of the range value from the destination device at a block 3321, the source peripheral LAN device evaluates its battery parameters to identify a subsequent data rate for transmission at a block 3323. If range value indicates that the destination peripheral LAN device is very near, the source peripheral LAN device selects a faster data rate. When the range value indicates a distant master, the source device selects a slower rate. In this way, even without adjusting the power level, the total energy dissipated can be controlled to utilize only that necessary to carry out the transmission. However, if constraints are placed on the maximum or minimum data rates, the transmission power may also need to be modified. For example, to further minimize the complexity associated with a fully random range of data rate values, a standard range and set of several data rates may be used. Under such a scenario, a transmission power adjustment might also need to supplement the data rate adjustment. Similarly, any adjustment of power must take into consideration maximum and minimum operable levels. Data rate adjustment may supplement such limitations. Any attempted modification of the power and data rate might take into consideration any available battery parameters such as those that might indicate a normal or current battery capacity, the drain on the battery under normal conditions and during transmission, or the fact that the battery is currently being charged. The latter parameter proves to be very significant in that when the battery is being charged, the peripheral LAN slave device has access to a much greater power source for transmission, which may justify the highest power transmission and possibly the slowest data rate under certain circumstances.
Finally, at a block 3325, an indication of the identified data rate is transmitted back to the destination device so that future transmissions may take place at the newly selected rate. The indication of data rate may be explicit in that a message is transmitted designating the specific rate. Alternately, the data rate may be transferred implicitly in that the new rate is chose and used by the source, requiring the destination to adapt to the change. This might also be done using a predefined header for synchronization.
In addition, at the block 3325, in another embodiment, along with the indication of the identified data rate, priority indications are also be communicated. Whenever battery power is detected as being low, a radio transmits a higher priority indication, and each receiver thereafter treats the radio as having a higher protocol priority than other such radios that exhibit normal power supply energy. Thus, the remaining battery life is optimized. For example, in a non-polling network, the low power device might be directly polled periodically so to allow scheduled wake-ups and contention free access to a receiver. Similarly, in an alternate embodiment, priority indications not need to be sent. Instead, the low battery power device itself exercises protocol priority. For example, for channel access after detecting that the channel is clear at the end of an ongoing transmission, devices with normal energy levels are required to undergo a pseudo-randot back-off before attempting a transmission (to avoid collision). The low power device may either minimize the back-off period or ignore the back-off period completely. Thus, the low power device gains channel access easier than other normal power level devices. Other protocol priority schemes may also be assigned by the receivers to the low power device (via the indication), else may be taken directly by the low power device.
Similarly, to receive data, the RF signal received by the selected one of the plurality of antennas 3513 is communicated to a receiver RF processing circuit 3517. After performing a rather coarse frequency selection, the receiver RF processing circuit 3517 amplifies the RF signal received. The amplified received signal undergoes a frequency shift to an IF range via a frequency translation circuit 3519. The frequency translation circuit 3519 provides the center frequency for the frequency shift. Thereafter, a receiver signal processing circuit receives the IF signal, performs a more exact channel filtering and demodulation, and forwards the received data to the control processor 3503, ending the process. Together, the receiver signal processing 3521, translator 3517, receiver RF processing 3517 and associated support circuitry constitute the receiver circuitry.
The control processor 3503 operates pursuant to a set of software routines stored in memory 3522 which may also store incoming and outgoing data. Specifically, the memory 3522 contains routines which define a series of protocols for concurrent communication on a plurality of LANS. As part of such operation, the control processor 3503 provides for power savings via a power source control circuit 3523, i.e., whenever the participating protocols permit, the control processor 3503 causes selective power down of the radio transceiver circuitry via a control bus 3525. Also via the bus 3525, the control processor sets the frequency of the frequency generator 3509 so as to select the appropriate band and channel of operation required by a correspondingly selected protocol. Similarly, the control processor 3503 selects the appropriate antenna (via the antenna switching circuitry 3515) and channel filtering in preparation for operation on a selected LAN. Responding to the software routines stored in the memory 3522, the control processor 3503 selects the appropriate LANs to establish participation, detaches from those of the selected LANs in which participation is no longer needed, identifies from the selected LANs a current priority LAN in which to actively participate, maintains a time-shared servicing of the participating LANs. Further detail regarding this process follows below.
In one embodiment, the control processor 3503 constitutes a typical microprocessor on an independent integrated circuit. In another embodiment, the control processor 3503 comprises a combination of distributed processing circuitry which could be included in a single integrated circuit as is a typical microprocessor. Similarly, the memory 3522 could be any type of memory unit(s) or device(s) capable of software storage.
The radio circuitry illustrated is designed with the frequency nimble frequency generator 3509 so as to be capable of operation on a plurality of LANs/WANs. Because each of the plurality may be allocated different frequency bands, more than one antenna may be desirable (although a single antenna could be used, antenna bandwidth limitations might result in an unacceptable transmission-reception inefficiency). Thus, to select the appropriate configuration, the control processor 3503 first identifies the LAN/WAN on which to participate and selects the corresponding radio configuration parameters from the memory 3521. Thereafter, using the configuration parameters and pursuant to control routines stored in the memory 3522, the control processor 3503 sets the frequency of the generator 3509, selects the appropriate antenna via the antenna switching circuit 3515, and configures the receiver RF and signal processing circuits 3517 and 3521 for the desired LAN/WAN.
More particularly, the antenna switching circuit 3515 comprises a plurality of digitally controlled switches, each of which is associated with one of the plurality of antennas 3513 so as to permit selective connection by the control processor 3503 of any available antenna to the transceiver circuitry.
With the illustrated configuration, the center frequency of the VCO 3601 is a function of the reference frequency as follows:
Thus, to vary the center frequency of the VCO 3601 to correspond to a band of a selected LAN/WAN in which active participation is desired, the control processor 3503 (
More specifically, although any other scheme might be implemented, the value R in the divide-by-R circuit 3605 is chosen so as to generate an output equal to the channel spacing of a desired LAN/WAN, while the value N is selected as a multiplying factor for stepping up the center frequency of the VCO 3601 to the actual frequency of a given channel. Moreover, the frequency of the reference oscillator is chosen so as to be divisible by values of R to yield the channel spacing frequencies of all potential LANs and WANs. For example, to participate on both MTEL Corporation'"'"'s Two Way Paging WAN (operating at 900 MHz with 25 KHz and 50 KHz channel spacings) and ARDIS Corporation'"'"'s 800 MHz specialized mobile radio (SMR) WAN (operating at 25 KHz channel spacings centered at multiples of 12.5 KHz), a single reference frequency may chosen to be a whole multiple of 12.5 KHz. Alternately, multiple reference frequencies may be chosen. Moreover, the value N is chosen to effectively multiply the output of the divide-by-R circuit 3605 to the base frequency of a given channel in the selected WAN.
For frequency hopping protocols, the value of R is chosen so as to yield the spacing between frequency hops. Thus, as N is incremented, each hopping frequency can be selected. Randomizing the sequence of such values of N provides a hopping sequence for use by an access point as described above. Pluralities of hopping sequences (values of N) may be stored in the memory 3522 (
In addition to the single port phase locked loop configuration for the frequency generator 3509, other configurations might also be implemented. Exemplary circuitry for such configurations can be found in U.S. patent application Ser. No. 08/205,639 (Attorney Docket Nos. DN37139XXA; 10458US03), filed Mar. 4, 1994 by Mahany et al., entitled “Method of and Apparatus For Controlling Modulation of Digital Signals in Frequency-Modulated Transmissions”. This application is incorporated herein in its entirety.
After passing through the switching circuit 3703, the filtered IF data signal is then amplified by an IF amplifier 3707. The amplified IF signal is then communicated to a demodulator 3709 for demodulation. The control processor retrieves the incoming demodulated data signal for processing and potential storage in the memory 3522 (
Specifically, in the memory unit 3522, among other information and routines, software routines relating to the media access control (MAC) sublayer of the communication protocol layers can be found. In general, a MAC sublayer provides detail regarding how communication generally flows through a corresponding LAN or WAN. Specifically, the MAC sublayer handles functions such as media access control, acknowledge, error detection and retransmission. The MAC layer is fairly independent of the specific radio circuitry and channel characteristics of the LAN or WAN.
As illustrated, premises LAN, peripheral LAN, vehicular LAN and WAN MAC routines 3811, 3813, 3815 and 3817 provide definition as to how the control processor 3503 (
Below the MAC layer in the communication hierarchy, hardware and channel related software routines and parameters are necessary for radio control. For example, such routines govern the specific switching for channel filtering and antenna selection required by a given LAN or WAN. Similarly, these routines govern the control processor 3503'"'"'s selection of parameters such as for R and N for the frequency generator 3509 (
A set of MAC select/service routines 3823 govern the management of the overall operation of the radio in the network. For example, if participation on the premises LAN is desired, the MAC select/service routines 3823 direct the control processor 3503 (
Although not shown, additional protocol layers as well as incoming and outgoing data are also stored with the memory 3522, which, as previously articulated, may be a distributed plurality of storage devices.
If additional participation is not needed at block 3901, or if the additional LAN has not been located at block 3907, or once participation of the radio unit on the additional LAN has been established at block 3909, the control processor next determines at a block 3911 whether any of the participating LANs require servicing. If any given participating LAN requires servicing, at a block 3913, the radio unit may be required by the protocol of the given LAN to reestablish an active participation status on that LAN, i.e., indicate to the given LAN that the radio unit has ended the sleep mode. Next, at a block 3915, the radio unit services the given LAN as needed or until the servicing of another LAN takes priority over that of the given LAN. At a block 3917, the radio unit may then be required to register sleep mode operation with the given LAN if the LAN'"'"'s protocol so requires.
At that point, or if no participating LAN needs servicing at block 3911, the control processor determines at a block 3919 whether the radio needs to detach from any given participating LAN. If so, the radio unit may implicitly detach at a block 3923 if the protocol of the LAN from which the radio wishes to detach requires no action by the radio unit. However, at a block 3921, the radio unit may be required to establish active participation on the LAN in order to explicitly detach at block 3923. For example, such a situation may arise when a portable terminal desires to operate on a shorter range vehicular LAN and detaches from a premises LAN. The portable terminal may be required by the protocol of the premises LAN to establish active communication on the premises LAN to permit the radio unit to inform the premises LAN that it is detaching and can only be accessed through the vehicular LAN.
Once the radio unit is detached at block 3923, or if the radio unit does not need to detach from any participating LANs at block 3919, the control processor returns to block 3901 to again determine whether the radio unit needs to participate on an additional LAN, and repeats the process.
However, if the control processor determines at block 3965 that servicing has not been, or may not be, completed, the radio unit does not detach from the slave LAN. In that case, before returning to block 3957 to service the master LAN, the radio unit may be required by the protocol of the slave LAN to register sleep mode operation with the slave LAN at a block 3969.
In another embodiment, shown in
The inventory computer 4511, which can range from a personal to main frame computer, provides central control over the retail inventory by monitoring the inventory status. Thus, the inventory computer 4511 must monitor both sales and delivery information regarding inventoried goods. To monitor sales information, the cash registers 4503 and 4505 include code scanners, such as tethered code scanners 4507 and 4509, which read codes on product labels or tags as goods are purchased. After receiving the code information read from the scanners 4507 and 4509, the cash registers 4503 and 4505 communicate sales information to the inventory computer 4511 via the backbone LAN 4501. To monitor delivery information, when the truck 4513 makes a delivery, the information regarding the goods delivered is communicated to the inventory computer 4511 via the access point 4517. As illustrated, the access point 4517 acts as a direct access point to the backbone LAN 4501, even though a series of wireless hops might actually be required.
Upon receiving the sales information from the cash registers 4503 and 4505, the inventory computer 4511 automatically debits the inventory count of the goods sold. Similarly, upon receiving the delivery information, the inventory computer 4511 automatically credits the inventory count of the goods delivered. With both the sales and delivery information, the inventory computer 4511 accurately monitors the inventory of all goods stocked by the retail store. From the inventory information, the inventory computer 4511 generates purchase orders for subsequent delivery, automating the entire process.
In particular, the inventory computer 4511 receives sales information from the cash registers 4503 and 4505 as detailed above. Whenever the restocking process is initiated, the inventory computer 4511 checks the retail inventory for each item sold to determine if restocking is needed. If restocking proves necessary, the inventory computer 4511 evaluating recent sales history, determines the quantity of the goods needed. From this information, an “inventory request” is automatically generated by the inventory computer 4511. Once verified (as modified if needed), the inventory request is automatically forwarded by the inventory computer 4511 to the warehouse 4519. This forwarding occurs via either a telephone link using a modem 4521, or a WAN link using the backbone LAN 4501, access point 4517, and an antenna tower 4523.
At the remote warehouse 4519, the delivery truck 4513 is loaded pursuant to the inventory request received from the inventory computer 4511. After loading, the truck 4513 travels to the premises of the retail store. When within range of the access point 4517, the radio terminal 4515 in the truck 4513 automatically gains access to the retail premises LAN via the access point 4517 (as detailed above), and communicates an anticipated delivery list (a “preliminary invoice”), responsive to the inventory request, to the inventory computer 4511. In response, dock workers can be notified to prepare for the arrival of the delivery truck 4513. In addition, any rerouting information can be communicated to the terminal 4515 in the delivery truck 4513. If a complete rerouting is indicated, the truck 4513 may be redirected without ever having reached the dock.
While unloading the delivery truck 4513, codes are read from all goods as they are unloaded using portable code readers, which may be built into or otherwise communicatively attached to the radio terminal 4515. The codes read are compared with and debited against the preliminary invoice as the goods are unloaded. This comparing and debiting occurs either solely within the terminal 4515 or jointly within the terminal 4515 and the inventory computer 4511. If the codes read do not correspond to goods on the inventory request, or if the codes read do correspond but are in excess of what was required by the inventory request, the goods are rejected. Rejection, therefore, occurs prior to the actual unloading of the goods from the delivery truck 4513.
At the dock, the goods received from the delivery truck 4513 undergo a confirmation process by a dock worker who, using a radio terminal 4525 configured with a code reader, reads the codes from the goods on the dock to guarantee that the proper goods, i.e., those requested pursuant to the inventory request, were actually unloaded. This extra step of confirmation can be eliminated, however, where the dock worker directly participates in the code reading during the unloading process in the delivery truck 4513. Similarly, the code reading within the delivery truck 4513 could be eliminated in favor of the above described on-dock confirmation process, but, reloading of any wrongly unloaded goods would be required.
Upon confirmation of the delivery by the dock worker, a verified invoice is automatically generated by the radio terminal 4515 and routed to the inventory computer 4511 for inventory and billing purposes. In addition, the verified invoice is routed to the warehouse 4519. Such routing may occur as soon as the delivery truck returns to the warehouse 4519. However, to accommodate rerouting in situations where goods have been turned away at the retail store, the radio terminal 4515 communicates the final invoice immediately to the warehouse 4519. The warehouse 4519, upon receiving the final invoice, checks the final invoice with the list of goods loaded in the delivery truck 4513, and determines whether delivery of the remaining goods is possible. If so, the warehouse 4519 reroutes the truck 4513 to the next delivery site.
The communication of the final invoice and the rerouting information between the warehouse 4519 and the terminal 4515 may utilize a low cost communication pathway through the telephone link in the premises network of the retail store. In particular, the pathway for such communication utilizes the access point 4517, backbone LAN 4501, inventory computer 4511 and modem 4521. Alternately, the communication pathway might also utilize the WAN directly from the radio terminal 4515 to the warehouse 4519 via the antenna tower 4523. Moreover, the antenna tower 4523 is merely representative of a backbone network for the WAN. Depending on the specific WAN used, the tower 4523 may actually be comprised of a plurality of towers using microwave links to span the distance between the retail premises and the warehouse 4519. Similarly, satellite relaying of the communications might also be used.
For example, if any network device, e.g., an end-point device such as a wireless, hand-held computer terminal 4601, desires to communicate with another network device, e.g., a hard-wired computer 4603, a routing request is constructed which specifically identifies the destination device. After construction, the routing request is transmitted through a spanning tree pathway to the destination device.
In particular, the terminal 4601 formulates a routing request identifying the computer 4603. The routing request may also contain, for example, a message or data to be delivered or a request for data or program code. The terminal 4601 transmits the routing request downstream (toward the root of the spanning tree) to an access device 4605. The access device 4605 examines its spanning tree routing table entries, attempting to locate an upstream path to the destination device identified by the request. Because no entry exists, the access device 4605 transmits the routing request downstream to an access device 4607. After finding no routing table entry, the access device 46.07 routes the request to a root access device 4609. Finding no routing table entry for the computer 4603, the access device 4609 transmits the routing request onto a wired LAN 4610. Using its routing table which has an entry for the computer 4603, a root access device 4611 fields the routing request and transmits the request upstream to an access device 4613. Likewise, the access device 4613, having an entry, sends the routing request to an access device 4617. Upon receipt, the access device 4617 forwards the routing request to the computer 4603.
When a network device, an end-point device for example, has a need for remotely stored program code (i.e., program objects) or data (i.e., data objects) such as a schematic diagram, delivery address or repair manual, the end-point device formulates a code or data request and sends it in a downstream spanning tree pathway. Unlike a routing request, data and code requests do not have a specific destination designated. Instead, data/code requests (data requests and/or code request) only identify the specific data or code needed. This is because the requesting device need not know the destination of the data or code needed, promoting dynamic, spanning tree migration—as will become apparent below.
In addition, where possible, program code will be reduced to an interpretive form. Common libraries of program objects (in an object code form, i.e., executable form) are stored at each network terminal, computer or access server. Upon any request for an application program, for example, first, the sequence of calls to each program object is delivered along with a list of all program objects that are needed to fully execute the application program. Thereafter, if the specific underlying code for any of the delivered objects is not found locally, a renewed request for the executable code for those program objects is made. Upon delivery, the application program may be executed. Moreover, the movement of the program application and other specific program objects are tracked and migrated as described above in relation to generic data.
For example, the terminal 4667 typically operates using an application program directed to an exemplary installation and service industry. A driver of a vehicle 4666 enters the premises via a dock. Upon establishing a link with the network, the terminal 4667 reports its status. In response, the terminal 4667 receives from the computer 4652 a command via the premises network to load a docking application. After determining that it does not have the docking application stored locally, the terminal 4667 transmits a program code request specifying the application. Because of previous activity, for example, the access device 4659 (which receives the transmission) happens to have the program code stored locally. It fields the request, sending the list of program objects along with the “interpretive” program object sequence. Upon receipt, the terminal 4667 might identify that all program object executable code is stored locally, and, therefore, begins to execute the application program. Otherwise, if certain program object executable is not locally stored, the terminal 4667 transmits a subsequent request. This time, the access device 4659 might not currently store the executable program object code. Thus, the access server 4659 routes the request downstream toward a device which does store the code. Once located, the code is delivered upstream to the terminal 4667 for execution.
Requested data or program code may reside in one or more of those of the access devices 4605, 4607, 4609, 4611, 4613, 4615, 4617, 4619 and 4621 which happen to be configured as access servers. Otherwise, the data or code may be reside in one or more of the computers 4603, 4621, 4623 or 4625, if they are configured as servers.
For example, assuming that the access device 4619 has been configured as an access server and happens to store data needed by the terminal 4601, the terminal 4601 would begin the process of retrieving the data by formulating a data request. As previously mentioned, the data request does not identify the access device 4619, but only identifies the needed data. After formulation, the terminal 4601 routes the request downstream to the access device 4605. Upon receipt, the access device 4605 determines that it does not store the requested data, and fails to identify the requested data in a routing table entry. Thus, the access device 4605 forwards the data request to the access device 4607. As with device 4605, the access device 4607 cannot identify the requested data and routes the request to the access device 4609. Upon receipt, the access device 4609 consults its routing table and identifies an entry for the requested data. The entry lists the next device in an upstream path to the data, i.e., the access device 4619 is listed. Thus, the access device 4609 forwards the data request upstream to the access device 4619. The access device 4619 responds to the data request by: 1) locating the stored data; 2) formulating a routing request (containing the data) destined for the requesting device, the terminal 4601; and 3) sending the routing request downstream to the access device 4609. Using its routing table, the access device 4609 identifies the terminal 4601, and sends the routing request (with attached data) upstream to the access device 4607. Likewise, the access device 4607 sends the routing request upstream to the access device 4605. Finally, the access device 4607 sends the routing request to the destination, the terminal 4601, completing the process. Program code (e.g., program objects) may be similarly stored, requested and delivered.
Similarly, when remote processing is required, a network device formulates a processing request which identifies the specific remote processing needed, yet need not identify a processing destination. After formulation, the processing request is transmitted downstream toward an access server or computer server capable of performing the requested processing. For example, the access device 4617 fields processing requests from the computer 4603. After determining that it cannot perform the processing, the access device 4617 consults its spanning tree routing table, yet finds no upstream entry for any network device capable of performing the processing. Thus, the access device 4617 routes the processing request downstream to the access server 4613. Although the access device 4613 has not been configured for such processing, the access device 4613 does find an entry identifying a first network device, the access device 4615, in an upstream pathway to a location where such processing is handled. The access device 4613 forwards the processing request to the access device 4615 which is configured as an access server to handle the processing. Thereafter, the requested processing is carried out by the access device 4615, with any associated intercommunication with the computer 4603 needed via the same pathway using routing requests.
Thus, each spanning tree routing table not only includes entries for all upstream network devices, each also includes entries for all upstream data, program code and processing resources. Moreover, each such entry only identifies the next network device through which forwarded requests are to made in the pathway to the request destination. Each spanning tree table also contains an entry designating a downstream route for use when no upstream entry can be located.
In the communication network of the present invention, program code, data and local processing capabilities dynamically migrate through the network to optimize network performance. Specifically, each the access devices 4605, 4607, 4609, 4611, 4613, 4615, 4617, 4619 and 4621 are configured as access servers. However, a specific data object in high demand is not initially stored in any of the access devices. Instead, the data object in high demand is originally stored on the computer 4623, configured as a server.
Upon encountering a first data request by the terminal 4601 for the data object in high demand, each of the intermediate access servers, the access devices 4605, 4607 and 4609, fail to identify the data object which results in the sequential forwarding of the data request to the computer 4623. However, each of the intermediate access servers record entries for the data in their routing tables with a downstream destination. Thereafter, each time that a network device, such as the terminal 4601, requests the data object, the intermediate access servers which receive the request bump up a count stored in the routing table entry.
To make a determination of whether to migrate the data object or not, upon encountering a data request, each intermediate access server considers the: 1) associated count entry; 2) duration of time over which the count entry has accumulated; 3) cost of retrieving the data from the downstream source; 4) the size of the data object; and 5) its own resource availability (e.g., remaining storage space).
For example, after receiving a high number of recent requests for the data object and having a relatively high cost in extracting the downstream object, the access device 4605 determines that migration of a copy of the data object into its own available storage could improve network performance. Thus, instead of sending the data request downstream to the access device 4607, the access device 4605 substitutes and forwards a migration request instead of the data request.
Upon receiving the migration request, the remaining intermediate access servers, the access devices 4607 and 4609 merely forward the migration request to the computer 4623. In response, the computer 4623 records the migration event, i.e., the data object migrated and the migration destination (the access device 4605), for future updating control.
The computer 4623 also forwards a copy of the data object to the access device 4609 for relaying to the access device 4605 via the access device 4607. Upon receipt, the access device 4605 stores the data object locally, and forwards a further copy back to the requesting network device, the terminal 4601. Thereafter, instead of relaying each data request for that data object downstream, the access device 4605 responds by sending a copy of the locally stored data object toward the requesting device. In other words, the access device 4605 has effectively intercepted a copy of the data for local storage, and, thereafter, forwards a copy of the locally stored copy to service any incoming requests.
In addition, upon forwarding the data object from the source, the computer 4623, to the destination, the terminal 4601, the data object size and link cost associated with reaching a given intermediate access device is recorded. For example, if a wired communication link between the computer 4623 and the access device 4609 is assigned a cost of “1”, after fielding the data request, the computer 4623 constructs a data response which not only includes the requested data object, but also includes a link cost entry of “1” and an indication of the data object size. In turn, the access device 4609 identifies the cost to the access device 4607, for example a cost of “3”, the access device adds the “3” to the pending cost entry in the data response, and forwards the response to the access device 4607. Similarly, the access device 4607 assesses a cost of “3” for the communication link to the access device 4605, adds the “3” to the pending cost entry of 114, and forwards the data response to the access device 4605. After assessing a cost for the link to the terminal 4601, for example a cost of “4”, the data response is delivered to the terminal 4601. Thus, the terminal 4601 sees that to access the data again, it will most likely result in “11” units of communication cost. Moreover, for example, the terminal 4607 considers the cost of “3” when determining whether to migrate the data object or not.
Similarly, when a migration of a data object occurs, all intermediate access devices record the cost of the upstream link to the copy of the data object. Thereafter, upon receiving a data request for the data object, an intermediate access device can compare the cost of the upstream pathway to the copy with the downstream pathway to the original data object to choose the pathway with the lesser cost. A notification of deletion of a copy of a data object destined for a downstream source is also noted by each intermediate access devices, requiring deletions of the entries for the “copied then deleted” data object.
For example, if a locally stored copy of the data fails to be used for a period of time determined by the access device 4605 to be too long to justify local storage (in view of the communication link costs back to the original source, the size of the data object, and potentially dwindling local resources), the access device 4605 deletes the locally stored copy of the data, and routes to the computer 4623 an indication that the local copy of the data object has been deleted. Upon receiving the indication for relaying, the intermediate access devices 4607 and 4609, in turn, remove from their routing tables the entries to the recently deleted upstream copy. Upon receipt of the indication, the computer 4623 records the deletion, completing the purging process.
Although data objects were used above to describe the migration process, program code (or program objects) are similarly migrated to and deleted from local storage. In addition, to prevent instability, a certain amount of hysteresis must be built in to prevent vacillating migration and purging decisions.
In assigning cost units to the various communication links, comparisons between factors such as actual monetary costs, bandwidths, delays, loading and power consumption are taken into consideration. Moreover, such costs are stored as sub-entries in the spanning tree routing tables.
Although only migration of a copy from a source to a single destination was previously described, if a data or program object proves to be in high enough demand, several, or even all, access devices in the network might store a copy. All that is required is that each access device experience a significant and sustained quantity of requests for a common data object (or program code/object) to justify the storage of a local copy in view of communication link costs and available local resources.
Processing resources are similarly migrated and purged. To service a processing request, an access device must be configured not only with sufficient hardware resources but must also store the programming code and associated data necessary to perform the requested processing.
For example, if the terminal 4601 desires to search prior sales information but can neither store the information or the necessary search program routines because of limited local resources, the terminal 4601 formulates a processing request which it routes downstream to the access device 4605. In the illustrated embodiment, the access device 4609 is originally configured with the hardware and software necessary to perform the processing request. In particular, the access device 4609 uses bulk storage devices to store past sales data, and executes a search program in response to received processing requests.
Although the intermediate access server 4607 is configured with appropriate processing and storage resources, originally, it does not store the search program or the past sales data. Thus, while receiving repeated processing requests from the terminal 4601 via the intermediate access device 4605, the access device 4607 initially logs the request in its routing table and forwards the request downstream to the access device 4609 which fields, processes and responds to the requests.
Because the frequency of the requests, costs and available local resources, when not busy, the access device 4607 sends a migration inquiry downstream to the access device 4609. Upon receipt, the access device 4609 responds by sending an indication of the volume of the potential transfer upstream, to the access device 4607. Based on the indication along with the aforementioned other migration factors, the access device 4607 may or may not pursue the migration.
If migration is chosen, the access device 4607 assembles a migration request identifying the desired processing, and routes the request downstream to the access device 4609. In response, the access device 4609, records the migration (for future updating) and begins to transfer a copy of the program (or programming object(s)) and the past sales information to the access device 4607, preferably occurs during periods of low network traffic.
Although intermediate access devices between the source and destination of the processing migration are not shown in the exemplary illustration above, any intermediate access devices that do occur follow the same procedures previously set forth in reference to data object migration, recording and purging routing table entries to upstream and downstream processing devices.
As may be appreciated in view of the foregoing, in many instances, migration does not always flow immediately to the access device nearest a requesting network device. Instead, for example, an access device which receives the same data or program code requests from a plurality of different terminals will perform migration before any upstream access device unless upstream link costs are comparatively much higher.
As illustrated, each of the access devices 4655 and 4659 are configured for long distance, wireless communication with the access server 4665 via a second higher power radio and associated antenna, e.g., WAN, paging, cellular, etc. The corresponding first radio and associated antenna are used for relatively lower power premises network communication.
Because of the much higher cost associated with the communication link between the access server 4665 and the access device 4659, the access servers 4665 is much more likely to engage in the dynamic migration of data/code objects or processing resources than the other access servers located within the premises network. With a link cost assessed at “20” for example, the mobile access server 4665 rapidly decides to migrate, while slowly deciding to purge migrated data. The migration/purging process used is the same as that described above in reference to the premises network of
In addition, because of the high link cost, the mobile access server 4665 is also configured to provide anticipatory migration, and responds to direct migration commands from the terminal 4667 or other controlling network devices. Specifically, anticipatory migration may occur in two ways. First, if a driver is preparing to leave the premises to service a specific appliance, for example, the schematic diagram of the appliance may be migrated to the mobile access server 4665 in anticipation of future use. This form of anticipatory migration may be directed from a controlling device downstream in the premises network, e.g., the computer 4652 which also stores the schematic diagram, from the terminal 4667 upstream, or from the access server 4665 itself upon analysis of the work order.
A second form of anticipatory migration originates at the access server 4665 (although the resulting migration control could originate either up or downstream). The access server 4665 anticipates future migration needs through the storage and analysis of previous requests for data/code objects or processing resources. For example, if the access server 4665 determines that nearly every time the terminal 4667 request a given program code or program object, the terminal 4667 follows that request a short time thereafter with further requests for specific data objects. In such circumstances, instead of repeatedly initiating, requesting and delivering portions of data over the communication the higher cost link, the requested and anticipated requests are all handled in one communication session, saving money and time.
Similarly, the terminal 4667, through program design or through request monitoring, can also participate in anticipatory migration. For example, the terminal 4667 can be programmed to make all upcoming requests at one time, and often in advance of leaving the low power radio range of the premises network. The terminal 4667 can also be specifically programmed to issue direct migration and purging commands to the access server 4665, permitting further control of the migration process and system resources of the mobile access server 4665. Moreover, the terminal 4667 may be configured to historically monitor all requests so as to anticipate subsequent requests in the manner described above in reference to the access server 4665.
In addition, the terminals 4664 and 4667 are configured to receive keyed, voice and pen input. Other types of input such as video or thumbprint image capture might also be added. The terminals 4664 and 4667 can also be configured with code reading/image capturing devices, or be configured to receive input from external code reading/image capturing devices (via tethering or low power wireless links). Each terminal also provides voice and LCD (liquid crystal display) output for the user. Thus, it can be appreciated that there are many types of data to be delivered to and from the terminals 4664 and 4667. The data may take on the forms of keyed or penned in command information, penned images or signatures, captured images of 2-D codes, signatures, etc. and voice signals, for example.
Each type of data handled by the terminals 4664 and 4667 places specific requirements on the communication network. For example, when communicating voice signals, a communication channel or link providing real time voice delivery is often required. Dedicated bandwidth may be reserved for such communications through the spanning tree network illustrated, or can be established via a cellular link with the access device 4655. Cellular radios may be built into the terminals 4664 and 4667 (via PCMCIA slots, for example) or via tethered cellular phones.
If post-processed, signature images require at most a delayed delivery of a plurality of such images over inexpensive and possibly slower or less convenient communication links. Relatively small packages of one way communication to the terminal 4667 may travel through a lower cost paging network for delivery. They could also travel through the spanning tree network, cellular networks, or through other higher cost, two way WANs.
Because programs cannot always anticipate all of the available communication channels through which the different types of data may flow (availability which not only changes from one network installation to another, but also changes within a given installation due to terminal and device configurations and their locations within the network), the routing tables within each network device subdivide routing information based on the type of data to be forwarded.
For example, the access device 4665 begins receives a communication from the terminal 4667. The communication takes the form of a requested link for voice signal data destined for the computer 4651. In response, the access device 4665 consults its routing table, determines that voice data can take one of two pathways: through either a cellular radio or WAN route to the access device 4655. In response, the access device 4665 delivers the communication route options to the terminal 4667 for user and/or software consideration.
If the request is not aborted and the cellular route is selected, the access device 4665 establishes a cellular link with the access device 4655, and requests a voice link with the computer 4651. In response, the access point 4655 consults its routing table, and, for voice data to the computer 4651, it identifies the need for dedicated wired bandwidth on the wired LAN 4653 directly with the computer 4651. In response, the access device 4655 places the request on the wired LAN 4653. In response, the computer 4651 communicates an acknowledge message which is routed through the access device 4655 to the access device 4665. The access device 4665 delivers the acknowledge message to the terminal 4667. At that point, the terminal 4667 begins sending the voice data to the computer 4651 through the designated route.
If the cellular link to the access device 4655 is in use or the end-to-end link otherwise proves unavailable, the access device 4665 reports the status, again offering the remaining communication route via the WAN. If selected, the access device 4665 establishes the pathway to the access device 4659 via WAN communications. In turn, the pathway is established through the access device 4657, access device 4655 and the computer 4653. With a returned acknowledge from the computer 4653, the terminal 4667 begins voice communication.
Similarly, communication pathway between any other two network devices, such as from the computer 4651 to the terminal 4664, can be established. For example, if the computer 4651 desires the user of the terminal 4664 to obtain and compare a penned signature image for comparison with an authenticated signature stored at the computer 4651, the computer 4651 first attempts to communicate the request and image data to the terminal 4664 via the premises network. If the terminal 4664 happens to be out of range of the premises network, the computer 4651 attempts to page the terminal 4664 with the comparison request. In response, the terminal 4664 considers the data type via its routing table, identifies the route(s) available, and offers the route options to the user and/or program at the terminal 4664. If selected, the terminal 4664 establishes the selected communication link for the delivery of the associated comparison image.
Moreover, because of the high cost associated with the communication link from the access device 4665 to the premises network, the access device 4665 stores several types of lower priority data until such time or data storage size justifies delivery. Such deliver may not occur until the vehicle returns to the premises network, e.g., to a dock at the premises.
In addition, requests for communication may also include specific limitations. For example, the need for voice data only in real time can be specified, and will result in no consideration by any intermediate network device of other pseudo-random real time link options. Lowest cost delayed delivery can also be specified corresponding results. Requests with high priority specified, choose the fastest communication link regardless of cost.
Moreover, the terminals 4664 and 4667 can be configured to operate running application software under the DOS, Windows or OS/2 operating system environments.
Communication between the terminal 4667 and the access device 4665 occurs via an infrared link if the terminal 4667 is docked within the vehicle. Routing tables within the access device 4665 and terminal 4667 both contain dual entries for communication exchange pathways. First, the infrared link is attempted, if available. Otherwise a lower power RF communication transmission is used. Although a wired docking arrangement might be used instead of infrared, infrared is preferred inside the vehicle for ease of installation and to minimize wire clutter. Such infrared installations also provide support for communicating with printers, scanners and other peripheral devices within the vehicle, i.e., the vehicular LAN preferably operates via infrared except when communicating with a remotely located terminal 4667 or with other remotely located network devices.
In another embodiment illustrated by
Upon receiving a routing request as indicated at the event block 4703, the access server accesses its routing table, at a block 4705, in an attempt to identify the destination of the routing request in an upstream path. If the destination is identified, the access server forwards the routing request to the next network device in the upstream path toward the destination, at a block 4707. Otherwise, if the destination is not identified in the routing table at the block 4705, at the block 4707 the access server transmits the routing request to the next network device in the downstream path. Thereafter, the access server returns to the block 4701 to await another event.
At the block 4701, upon receiving and logging a migration request, the access server vectors from an associated event block 4709 to determine whether it stores the requested migration information (e.g., the requested code or data or the program code and/or data associated with a processing resource migration request) locally or not at a block 4711. If not, the access point branches to the block 4705 to identify the closest (or any) network device in the spanning tree pathway. For example, if the routing table carries no entries for the migration information, the access server routes the migration request to the next downstream network device. Otherwise, if the routing table carries only an upstream or a downstream entry, the access server routes the request as specified by the routing table. However, if more than one entry exists for the requested migration information, the access server routes the migration request along the lowest cost spanning tree pathway (as indicated in the routing table).
However, if, at the block 4711, the access server determines that it stores the migration information locally, the access server: 1) retrieves the migration information and records the migration event for update control, at a block 4713; 2) accesses its routing table to identify the forwarding pathway, at the block 4705; 3) forwards the retrieved migration information, at the block 4707; and 4) returns to the block 4701 to await another event.
After receiving and logging (counting the occurrence of) a processing request at the block 4701, the access server branches via an event block 4715 to determine whether the requested processing can be performed locally or not at a block 4717. If not, the access server forwards the processing request at the block 4707 per routing table instruction at the block 4705. Afterwards, the access server returns to the await another event at the block 4701.
However, if the access server determines that it can perform the requested processing at the block 4717, the access server performs the processing at a block 4719, generates a response at a block 4721, routes the response back to the requesting network device at the block 4707 per routing table instruction at the block 4705, and, finally, returns to the block 4701 to await another event.
Upon receiving and logging a data or code request at the block 4701, the access server vectors via an event block 4723 to determine whether the requested data or code is stored locally at a block 4725. If so, the access server branches to a block 4727 to retrieve the data or code from storage. Thereafter, the data or code is forwarded at the block 4707 per routing table instruction at the block 4705. Once forwarded, the access server branches to the block 4701 to await another event.
At the block 4725, if the access server determines that the requested data or code is not stored locally, the access server considers whether it should migrate the data at a block 4729. The access server analyzes the overall link cost, the size of the requested data or code, the frequency of such requests, available local storage resources (some of which it may determine to recapture by purging other locally stored data, code or processing resources) Specifically, if sufficient local resources are (or can be made) available, the access server determines the weighted average frequency of the requests for that data or code. The frequency is then multiplied by a predetermined fraction (50%) of the overall link cost for retrieving the data or object to the access server from the current source. The resulting number is then compared to a migration threshold number, for example “10”.
If, at the block 4729, the access server determines that the threshold number is greater than the resulting number, the access server, deciding not to migrate, branches to route the data/code request per routing table instruction at the blocks 4705 and 4707. Alternatively, if the access server determines that the threshold number is equal or less than the resulting number at the block 4729, the access server decides to migrate. Thus, at a block 4731, the access server creates and sends a migration request (instead of merely forwarding the data/code request) and awaits delivery of the requested code or data. Upon receipt, at a block 4733, the access server stores the data or code. Thereafter, the data/code is retrieved at the block 4727 for routing to the requesting network device via the blocks 4705 and 4707. Once routing is complete, the access server again returns to the block 4701 to await another event.
Finally, upon receiving a time out event signifying the periodic need to perform migration evaluation and processing, the access server branches to execute migration procedures at a block 4737, as described in more detail below.
Upon encountering a time out event (occurring every 15 minutes), an access server begins the illustrated procedure of
At a block 4755, fifty percent (50%) of the overall cost of the link, i.e., from the access server to another source of the locally stored data/code, is multiplied by the newly recorded weighted frequency. The access server compares the results of the multiplication with a hysteresis threshold at a block 4757. The hysteresis threshold is also referred to herein as a purging threshold. In premises network locations, for example, the hysteresis threshold is set at five (5) units below the migration threshold of the block 4729 in
If the hysteresis threshold is exceeded, the access server determines that it should continue to store the data/code, and branches to a block 4759 to determine whether there are any remaining entries for locally stored data/code which have not yet been considered for purging. Alternatively, if the hysteresis threshold is not exceeded, the access server determines that the data/code item should be purged, and does so at a block 4761. Thereafter, the access server branches to the block 4759.
If, at the block 4759, other data/code items which have not yet been considered for purging, the access server repeats the purging consideration of the blocks 4751 through 4759 until all locally stored data/code items have been considered. At that point, the access server branches to block 4763 to begin migration and purging consideration of processing resources.
First, the access server retrieves a routing table entry relating to processing resources, i.e., supporting program code and any associated data. At a block 4765, the access server ages the entry, i.e., performs the aforementioned weighted frequency averaging. Thereafter, fifty percent (50%) of the overall link cost is multiplied with the new weighted frequency at a block 4767. If the entry indicates local storage of the processing resources at a block 4769, the access server compares the results with the hysteresis threshold at a block 4771. If above the hysteresis threshold, the access server continues to store the processing resources, branching to consider any remaining processing resource entries at a block 4775. Otherwise, the access server purges the stored resources at a block 4773 before considering any remaining entries at the block 4775.
Alternately, if the routing table entry indicates that the processing resources are not stored locally, at a block 4777, the access server determines whether it has been configured with the hardware necessary to perform the processing. If not, the access server branches to the block 4775 to consider process other entries. Otherwise, at a block 4779, the access server compares the migration threshold with the result, i.e., 50% of the link cost multiplied by the new weighted frequency. If the result does not exceed the migration threshold, the access server branches to the block 4775 to consider other entries. If the result exceeds the migration threshold, the access server formulates and routes a migration request for the processing resources, awaits the responsive delivery and stores the resources locally at a block 4781, before branching to the block 4775.
At the block 4775, if the access server determines that other processing resource entries have not be considered for purging or migration, it repeatedly branches back to the block 4763 to carry out the consideration cycle until complete. Thereafter, the migration/purging procedure ends, and the access point returns to the block 4701 of
Processing circuitry 4811 provides at least three processing functions for the access server by managing or performing: 1) communication processing functionality; 2) migration and purging; and 3) local resource processing wherein incoming communications. Although in most embodiments, the processing circuitry 4811 comprises a single microprocessor, it may comprise several. Moreover, if the processing circuitry 4811 is not configured to perform migration and local resource processing, the illustrated access device operates as an access point.
The processing circuitry 4811 utilizes a memory 4813 for short term and long term bulk storage. The memory 4813 comprises hard drive storage, dynamic RAM (random access memory), flash memory, and ROM (read only memory). However, all other types of memory circuits or devices might alternately be used.
Specific hardware configurations needed to accommodate specialized processing requests are represented by a circuit/device block 4815. However, such hardware need not be present to service relatively basic processing requests. Additionally, access servers may either be battery powered although, if the network configuration permits, AC (alternating current) power is preferred.
To enable the CCD to operate properly, however, it may first be necessary for the reader to focus the image on the CCD. Such focusing can, for example, be performed by conventional techniques known in the camera art. As another example, one or more spotter beams are presently used to ensure that the user is holding the reader the proper distance from the code to enable the CCD to properly capture the image.
Once captured, the code image may then be digitized within the reader to create a digital signal representative of the code image, which is then transferred, via RF transmissions, to other network devices for further processing. Alternatively, the reader 4901 may transmit a modulated analog signal representative of the code image to other network devices for further processing.
In any event, the code reader 4901, an end-point device, forwards the code image signal downstream in the premises LAN to the first access server in the network that has the capability of decoding the signal into the usable information represented by the code 4903. As discussed above, any one or all of the access devices 4907-4913 may be an access server and contain the digital signal processing circuitry necessary to decode the code image signal. For example, the network may be designed such that the access device 4907 is an access server which performs decoding for all code readers, such as the code reader 4901, being used in a designated area. If, however, the access device 4907 is merely an access point, or is an access server but does not have decoding capability, then the access device 4907 relays the code image signal downstream.
More specifically, and as discussed more completely above, the code reader 4901 sends a processing request downstream to the access device 4907. If the access device 4907 is an access point, the processing request is simply relayed downstream to the access device 4909. If the access device 4907 is an access server, it looks up in its table to determine whether it has the capability to perform the type of processing requested, i.e., decoding. If it does, the access device 4907 sends an acknowledge and the code reader 4901 forwards the code image signal to the access device 4907 for decoding. Once decoded, the information may be re-transmitted to the code reader 4901 for display on a screen (not shown). In addition, or alternatively, the access device 4907 may send a good read signal to the code reader 4901 to indicate to the user that the reading operation has resulted in a valid reading. The decoded information may also be transmitted to a host computer 4915 or other network device for further processing.
If the access device 4907 does not find decode capability listed in its table, it forwards the processing request downstream to access device 4909. Likewise, if access device 4909 is an access point or an access server without decode capability, the processing request is forwarded downstream to the access device 4913. Once access device 4913 receives the processing request, it also examines its table to determine whether it, or any device upstream of it (such as, for example, access device 4911), has the capability to service the processing request. If it does locate such capability, it sends an acknowledge upstream to the code reader 4901 which forwards the code image signal to the access device 4913 for decoding thereby or for routing to the upstream access device having that capability.
If the access device 4913 does not locate decode capability in its table, it forwards the processing request to host computer 4915 for decoding thereby or so that the host computer 4915 can locate a device having the capability to service the processing request. Of course, as mentioned above, the network could be configured such that each one of the access devices 4907-4913 is an access server having the circuitry necessary for decoding.
While a CCD type code reader is preferred with respect to the embodiment of
In addition, the code reader 4929 is configured to collect signature, printed text and handwriting images for further processing. Although further processing can be performed on-board, within the reader 4929, in one embodiment it occurs within an access server.
Either way, such processing first involves the identification of the type of information contained within the image. If the user does not simplify the process by identifying the type of image captured, automatic identification is invoked. This occurs by first attempting to identify the image as a 2-D code. If this fails, the processing involves an attempt at character recognition to identify any printed text that might exist within the image. If no text is found, an analysis is performed to determine whether the image is a handwritten signature. Finally, if all else fails, the image is generically classified as a picture. Several examples of pictures include: images of bakery shelf space in a given store for subsequent collection and evaluation of ones competition; images of broken equipment for transmission to remote experts for service advice; and images of meter displays for billing verification.
After identification, each type of data receives yet further processing. Decoded 2-D code information is forwarded and acknowledged. Handwritten signatures are compared with known authentic counterparts. Other types of S images may be associatively forwarded, stored, displayed and/or acknowledged.
As above, if the access device 4925 is simply an access point, the processing request is simply relayed downstream, via either RF or infrared transmissions, to a further access device downstream. If the access device 4925 is an access server, it looks up in its table to determine whether it has the capability to perform the type of processing requested. If it does, the access device 4925 sends an acknowledge via infrared transmissions to the code reader 4917 and the code reader 4917 forwards the code image signal to the access device 4925 via infrared transmissions for decoding. The access device 4925 may then transmit the decoded information to the code reader 4917 for display on a screen and/or forward the decoded information to a host computer 4927 for further processing.
If the access device 4925 does not find decode capability listed in its table, the access device 4925 forwards the processing request to one of the access devices 4924, 4926, or 4928 to locate such decoding capability similarly as discussed above with respect to
In one embodiment, the holster access device 4931 may be configured to perform decoding so that when the code reader 4929 is placed inside the holster access device 4931, the code reader 4929 may transmit the code image data to the holster access device 4931 for immediate decoding thereby. Alternatively, if the holster access device 4931 does not house the necessary decoding circuitry, the holster access device 4931 transmits a processing request downstream to one of access devices 4937-4943 to locate such decoding capability similarly as discussed above with respect to
In a scenario where numerous codes 4945 are to be read successively by the code reader 4929, the code reader 4929 may store the read image data and perform a batch transmission to the holster access device 4931 for immediate decoding thereby if the holster access device 4931 is configured with decoding circuitry. In another embodiment where the holster access device 4931 is not so configured, the code reader 4929 transmits a processing request to the holster access device 4931 via infrared transmissions. The holster access device 4931 in turn forwards the processing request downstream via RF transmission to one of the access devices 4937-4943 to locate such decoding capability similarly as discussed above with respect to
In an alternate embodiment, batch transmission of stored image data may be performed via a docking access server 4949. When a user has completed his code reading tasks, he docks the code reader 4929 in a bay 4951 of the docking access server 4949. Other users, when their tasks are completed, may similarly dock their code readers in other bays of the docking access server 4949. In one embodiment, similarly as discussed above with respect to the holster access device 4931, once a code reader is docked in the docking access server 4949, the code reader performs a batch transmission of its stored code image data to the docking access server 4949 for immediate decoding thereby if the docking access server 4949 is configured with decoding circuitry. In another embodiment where the docking access server 4949 is not so configured, the code reader 4929 transmits a processing request to the docking access server 4949 via infrared transmissions. The docking access server 4949 in turn forwards the processing request downstream via RF transmission to one of the access devices 4937-4943 to locate such decoding capability similarly as discussed above with respect to
In the embodiments of
In a memory 5007, the access point 5001 also stores a database of known 2-D images in an image database 5009. To further support 2-D code processing, digital signal processing circuitry 5011 has been added.
As configured, the signal processing circuitry 5011 assists the exact decoding of 2-D images, and may also be used in the image comparison process of received 2-D images with the database 5009 of stored images.
After its analysis is complete, the access server next determines whether the exact identification was successful at a block 5103. Determining whether an identification was successful often depends on the type of code used. If enough redundancy is built into the code, then the loss of a number of bits of data resulting from, for example, a partially blurred image may not be fatal to a successful exact identification. If, on the other hand, the type of 2-D code being read is less “tolerant,” then even the loss of a single bit might result in a failed exact identification.
In any event, if the exact identification is successful, at a block 5105, the access server sends the identified code information to a predetermined destination for further processing, and acknowledges the successful identification. If the exact identification is not successful, however, the access point performs a further analysis of the image data to attempt to identify the corresponding code information.
At blocks 5107 and 5109, the access server compares the received image to stored images located in its image database and attempts to locate the closest or best match. Although grey scale considerations and image-shifting correlation techniques are contemplated, in a relatively simple embodiment, such a comparison involve a process of scaling the received image to correspond to the stored images, then performing an “exclusive OR” of the received image with the stored images. More exact matches will yield an overall sum value nearer to zero.
After the access point completes its comparison and has identified the closest or best match between the received image data and the stored images, the access point then determines at a block 5111 if the overall value resulting from the best match comparison is above a predetermined accuracy threshold. Such an accuracy threshold may vary depending on, again, the type of code that was read, and the level of importance associated with a good read. If the overall value is below the predetermined threshold, the access server, as above, sends the identified code information (corresponding to the best match stored image) at a block 5105 to a predetermined destination for further processing, and acknowledges the successful decode.
If the overall value of the best match comparison is above the predetermined threshold, then, at a block 5113, the access server forwards a bad read or retry message to the code reader to indicate to the user to re-read the code.
If the overall value is below the threshold, then the access server attempts the exact identification and determines success at blocks 5123 and 5125. If such exact identification is successful, then the access device forwards the code information at block 5121. If it is not successful, the access device forwards a retry message to the code reader at block 5127.
Using such a hierarchical categorization, the access server can more rapidly perform the process of image comparisons. For example, at a main category level in the hierarchy, a grocery image, an office supply image and general merchandize image might be the only three types of main category images known to the access point. If after comparing the received and the stored main categorization images, no acceptable match is found, the attempted comparison ends without ever having to compare the remainder of the potentially thousands of remaining images stored in the image database. Similarly, if a main level match is found with the stored office supply image, no comparison need be made with the plethora of remaining images under the grocery image main category.
Further detail of the efficiency of such a hierarchical organization can be found below in reference to
Otherwise, if the comparison is within the accuracy threshold at the block 5405, the comparison process continues with the access server checking to see if there are any further sub-categories at a block 5409. Because other sub-categories exist, the access point branches to repeat the process beginning at the block 5401. This time, the access server extracts from the received image the image portion relating to the first sub-category (beans) for comparison at the block 5403 with only those first known sub-category images having “grocery” as the main category.
Again if no match within the threshold is found, the access point vectors to indicate failure at the block 5407, and terminates the process. However, if a sub-category match is found, the access point branches to handle the sub-sub-category in a similar way. If, at the block 5409 after successfully repeating the comparison a number of times, the access point concludes that there are no further sub-categories to compare, the access point delivers the 2-D code information stored in the image database and associated with the matching stored image, and successfully ends the code identification process.
The known image database is supplemented by exact decoding as illustrated for example in
Moreover, it will be apparent to one skilled in the art having read the foregoing that various modifications and variations of this communication system according to the present invention are possible and is intended to include all those which are covered by the appended claims.