Tower discovery and failover
1. A method for a client device to communicate with at least one broadcast tower within a service region, the method comprising:
- during a service activation;
allocating a home frequency; and
allocating a home service region;
after the service activation;
identifying a valid broadcast channel for the client device, comprising;
initiating a frequency sweep;
selecting a station frequency during the frequency sweep;
tuning a receiver to the selected station frequency;
receiving frames over a sample-interval with the receiver;
storing the received frames over the sample-interval;
analyzing the stored frames to determine a validity status associated with the stored frames;
locking the selected station frequency when the stored frames identify a valid signal; and
selecting another station frequency when the stored frames indicate an invalid signal;
after a valid broadcast channel is identified;
extracting the assigned home frequency from the stored frames;
extracting the assigned home service region from the stored frames; and
assigning the home frequency and home service region to the client device.
Described is a communication system including wireless client devices. In the described system, the client devices may be wrist-worn watches such as are in common use today, except that the watches are specially configured to receive transmissions from broadcast towers. A client device is associated with one or more home service regions, and is configured to receive personal messages on a home channel when in the home service region. The client device employs a self-assignment method to identify and select a home channel without the need for interaction by a user. A tower discovery method is employed to identify broadcast towers and available channels within a service region. A failover method is employed to identify a change in the broadcast system, and take appropriate action such as, for example, changing to another broadcast tower, selecting another frequency, selecting a sleep mode, as well as others.
- 1. A method for a client device to communicate with at least one broadcast tower within a service region, the method comprising:
during a service activation; allocating a home frequency; and allocating a home service region; after the service activation; identifying a valid broadcast channel for the client device, comprising; initiating a frequency sweep; selecting a station frequency during the frequency sweep; tuning a receiver to the selected station frequency; receiving frames over a sample-interval with the receiver; storing the received frames over the sample-interval; analyzing the stored frames to determine a validity status associated with the stored frames; locking the selected station frequency when the stored frames identify a valid signal; and selecting another station frequency when the stored frames indicate an invalid signal; after a valid broadcast channel is identified; extracting the assigned home frequency from the stored frames; extracting the assigned home service region from the stored frames; and assigning the home frequency and home service region to the client device.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
- 15. A client device that is arranged in communication with at least one broadcast tower, the client device comprising:
a means for scheduling reception on the client device; a means for tuning a receiver in the client device to a selected station; a means for receiving a transmission frame with the client device when scheduled for reception, wherein the transmission frame includes a frame header and a message payload; a means for storing the received transmission frame; a means for analyzing that is arranged to determine a validity status associated with the stored transmission frame; a means for changing the selected station when the validity status is determined as invalid; a means for extracting a station list from the frame header when the validity status is determined as valid; a means for selecting a home station from the station list, wherein the home station is automatically assigned by the client device utilizing a unique code that is associated with the client device; and a means for changing the default for the selected station to the home station; and a means for decoding a personal message from the stored transmission frame, wherein the stored transmission frame is encoded with an encryption key that is determined from the unique code that is identified with the client device.
- View Dependent Claims (16)
This patent application is a continuation application of U.S. patent application Ser. No. 10/317,737, filed on Dec. 11, 2002 now U.S. Pat. No. 7,043,214, entitled “TOWER DISCOVERY AND FAILOVER”, which application is hereby incorporated by reference.
The present invention relates generally to broadcast systems. More particularly, the present invention relates to a system and method for discovering broadcast towers within a service region, and automatically selecting a tower within the service region.
As society becomes increasingly mobile, mobile computing devices are enjoying a tidal wave of popularity and growth. Cell phones, wireless PDAs, wireless laptops and other mobile communication devices are making impressive inroads with mainstream customers. Constraining this growth and limiting customer satisfaction, however, is the lack of a truly adequate high-coverage-area, inexpensive, small, battery-efficient wireless communication system. Cellular data-transmit telephony-based solutions are far from power-efficient, and impose (relative) cost and size burdens that make them unusable. Likewise, other attempts to solve these problems have proved equally unsuitable. For instance, a few entities have attempted to make use of mobile devices that receive information over Frequency Modulated (FM) subcarriers. FM subcarriers (also known as “SCA” for Subsidiary Communications Authorization) utilize the available frequencies above FM stereo within the available modulation bandwidth of an FM station. Subcarriers are typically leased by radio stations, subject to FCC or other national regulation.
Some examples of FM subcarrier systems include the QUOTREK system owned and maintained by the Data Broadcast Corporation (DBC) to deliver stock price quotes to a handheld mobile device. However, the QUOTREK system is a single purpose system limited to receiving stock quotes. The system has various other limitations that make it unusable as a mobile computing device. Likewise, the Seiko Corporation implemented an FM subcarrier system wherein short messages were transmitted to a wrist-worn device. However, the hardware and communications scheme used were relatively primitive, resulting in a need for excessive redundancy in message transmission. These and other shortcomings rendered the Seiko system less than acceptable. Similarly, certain paging systems are based on FM subcarrier use, such as the Radio Data System (RDS) or Mobile Broadcasting System (MBS) systems. However, those systems involve short messages transmitted in a broadcast fashion with limited data rates. Unfortunately, an acceptable mobile device solution has eluded those skilled in the art.
Cellular telephones technologies communicate with a wireless network that is arranged as cells in a grid. Communication with the wireless network and the cellular telephone are established when the power to the cellular telephone is initially applied. The cellular telephone will attempt to locate the closest communication tower using criteria such as signal strength and triangulation techniques. Cellular telephones initially operate at a fixed frequency while communications are established with the network. The cellular telephone will attempt to locate the closest communication tower using criteria such as signal strength and triangulation techniques.
The present invention is related to a communication system including wireless client devices. In the described system, the client devices may be wrist-worn watches such as are in common use today, except that the watches are specially configured to receive transmissions from broadcast towers. A client device is associated with one or more home service regions, and is configured to receive personal messages on a home channel when in the home service region. The client device employs a self-assignment method to identify and select a home channel without the need for interaction by a user. A tower discovery method is employed to identify broadcast towers and available channels within a service region. A failover method is employed to identify a change in the broadcast system, and take appropriate action such as, for example, changing to another broadcast tower, selecting another frequency, selecting a sleep mode, as well as others.
These and various other features and advantages, which characterize the present invention, will be apparent from a reading of the following detailed description in conjunction with the associated drawings.
The present invention is described in the context of a communication system that includes wireless client devices. In the described embodiments, the client devices may be watch type devices that are specially configured to receive communication signals, as is described in greater detail below. As will become apparent from a reading of the following detailed description, the client devices establish a communication link with a broadcast tower through a tower discovery process that includes a failover procedure. Minor deviations from the described embodiments will also become apparent without departing from the spirit of the invention.
Although described here in the context of a watch-based system, it will be apparent that the teachings of the application have equal applicability to any other mobile or non-mobile devices, such as portable and desktop computers, personal digital assistants (PDAs), cellular telephones, and the like. The use of a watch is for illustrative purposes only to simplify the following discussion, and may be used interchangeably with “mobile device.”
The overall operating environment for the tower discovery and failover system will be discussed as follows below with reference to
FM sub-carriers are often referred to as an SCA as identified by the Federal Communications Committee (FCC) term for the Subsidiary Communications Authorization. An FM sub-carrier utilizes bandwidth that is otherwise unused in the FM stereo-band about an FM station. In the United States of America the FCC requires the modulation bandwidth to be roughly from 53 KHz to 100 KHz within the modulation bandwidth of the FM station.
The electronic system (210) is arranged to operate as either a receiver or transceiver type of device. As illustrated in the figure, the electronic system includes a transceiver (220), a microcomputer unit (MCU 230), and an analog radio (240). The antenna connects to, and is controlled by, the transceiver (220). Transactions between the MCU (230) and the radio components are mediated over a MCU-digital transceiver interface. The components of the watch device (200) are housed in a watch-sized enclosure and rely on battery power for operation.
The transceiver (220) generally includes a digital signal processor (DSP 224), which performs control, scheduling, and post-processing tasks for the transceiver, and a real time device (RTD 226), which includes a digital radio, system timing, and real-time event dispatching. The DSP (224) is coupled to the MCU (230), and transceiver tasks are commanded by the MCU (230).
One of the DSP'"'"'s tasks may be to process received data for such purposes as subcarrier phase recovery, baud recovery and/or tracking, compensation for fading effects, demodulation, de-interleaving, channel state estimation and error-correction. The post-processing of packets may occur when an entire packet has been received, or another subsequent time. The DSP (224) analyzes the transmitted data packets to determine the station'"'"'s signal timing with respect to the local clock of the RTD (226). The local clock is synchronized with the transmitter'"'"'s clock signal to maintain signal sampling integrity. The receiver is periodically brought into symbol synchronization with the transmitter to minimize misreading of the received data.
The digital section of the RTD (226) may include system time-base generators, such as a crystal oscillator that provides the system clock for the MCU (230) and the DSP (224). The time-base also provides baud and sample timing for transmit and receive operations, start/stop control for radio operation, and controls the periods of clock suspension to the MCU (230) and the DSP (224). The RTD (226) also performs radio operations, and may perform additional operations as well. The radio (240) is arranged to receive segments of data that is arranged in packets.
The operating environment shown in
Wireless Service Regions
Each wireless client device is configured to operate in at least one service region. A service region is a geographic area that is serviced by one or more broadcast transmitter towers (see
Each service region includes at least one broadcast transmitter tower. Each broadcast station (broadcast frequency) is considered equally capable of servicing any particular service region such that the least powerful and least well located of all available broadcast frequencies will define the bounds of a service region. When a service region includes multiple broadcast towers, different towers within the service region may not have identical coverage. The service region for multiple broadcast towers is defined as the minimal area for which all towers have adequate coverage. Each wireless client device within a service region is viewed as a client type of device that is capable of receiving the broadcast transmissions from the broadcast towers.
A failover condition occurs when a signal on a particular frequency is no longer operating properly. The number of broadcast towers in a service region may be variable, and a particular broadcast tower may become unavailable. The failover condition may be the result of a broadcast tower going offline unexpectedly, or some other failure condition.
In accordance with the present invention, each broadcast transmitter tower is arranged to provide a communication signal that is configured for reception by wireless client devices within a service region. As shown in
The scheduling interface is configured as a means for selecting one or more services. In one example, a wireless client device user interacts with the scheduling interface to select services such as news, stock prices, weather, and other features such as a personal calendar, address book, and the like. Selected services are entered in a database for broadcast transmission at a later time. At the designated time (or time interval) the scheduling interface communicates with the broadcast server to begin a transmission sequence of data for the selected services. The broadcast server subsequently formats the data for reception by one or more wireless client device, queues the data for transmission, and communicates the queued data to the FM broadcast tower for transmission. In an alternative example, the scheduling interface communicates the selected services to the broadcast server. The broadcast server schedules the time interval for transmission of the selected service.
Each broadcast transmission corresponds to the transmission of one or more frames. Each frame is organized with at least one header and a message payload that includes the content for one or more selected services as previously described. The message payload may correspond to global messages or personal messages. Every client device that is located within the designated service region may receive global messages, while a single client device may decode a personal message.
The header includes a service region identifier and a list of available stations for the identified service region. Control information may also be included in one of the headers to indicate broadcast conditions such as a change in available channels, an assignment of a service region to a particular wireless client device, and an assignment of a particular channel (frequency). In one example, each frame includes a change counter in one of the headers to indicate a change has taken place in the system. Wireless client devices (clients) may use the change counter to determine when to initiate failover.
An exemplary scheduling interface may be implemented as a computing device. Also, the broadcast server may be implemented as a computing device. An exemplary computing device (500) is illustrated in
In a basic configuration, computing device 500 typically includes at least one processing unit 502 and system memory 504. Depending on the exact configuration and type of computing device, system memory 504 may be volatile (such as RAM), non-volatile (such as ROM, flash memory, etc.) or some combination of the two. System memory 504 typically includes operating system 505, one or more program modules 506, and may include program data 507. This basic configuration is illustrated in
Computing device 500 may also have additional features or functionality. For example, computing device 500 may also include additional data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape. Such additional storage is illustrated in
Computing device 500 also contains communications connection(s) 516 that allow the device to communicate with other computing devices 518, such as over a network. Communications connection(s) 516 is an example of communication media. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, microwave, satellite, infrared and other wireless media. The term computer readable media as used herein includes both storage media and communication media.
Broadcast Channel Self-Assignment
Wireless client devices may not have a transmitter that is capable of communicating with the broadcast system servers. For example, a watch device may have receiver capabilities without any transmitter capability. Clients (wireless devices) of the broadcast system are presumed to have no transmitter capability such that channel (broadcast frequency) selection for personal messages must be arrived at through another mechanism.
A home frequency corresponds to a particular broadcast channel for which the client device must be tuned in order to receive personal messages. The server device and the client device select the same broadcast channel without any direct communication. Homing is the process by which the client device and the server device arrive at a shared understanding of the selected broadcast channel for communicating personal messages. The selection criteria for a home station (home broadcast channel) is regionally based on criteria such as signal reliability, load balancing and scaling. A home service region is assigned to a client device during activation. The user selects the home service region based on a zip code, area code, or some other regional indicator through a scheduling interface (see
Once the server assigns a home service region to the client, the assigned home service region is communicated to the client device through a broadcast transmission. The broadcast transmission includes a header that indicates a list of available channels which each correspond to a particular frequency. The client device performs a sweep of the FM frequencies looking for valid frame data. When a valid frame is received the client reads the header to retrieve a list of towers assigned to the service region. The client device retrieves personal messages from the assigned channel slot numbers, and decrypts the personal messages using a unique code.
The client device computes a unique code (e.g., a 128-bit code) using an encryption string (e.g., “hello world”) and a unique control key. A unique identifier that is assigned to the client device (e.g., a serial number) determines the unique control key. In one example, the unique identifier is used as a seed for a code generator such as a seed for a random number generator. Client numbers are generated from the unique code such as tower assignment and private message channel numbers (home station). In one example, the unique identifier corresponds to a unique serial number that is associated with the client device. An exemplary unique code may be a 128-bit code, where 32-bits of the unique code are used as an offset amount to determine tower assignment from the list of available towers in the service region. For example, offset=N modulo n, where N corresponds to the 32-bits from the unique code, and where n is the number of stations that are available in the service region.
The broadcast server is arranged to encode personal messages for transmission to a particular client with a similar method as described above. The broadcast server is aware of the unique control keys for every client device. Each personal message is encoded according to the unique control keys and the unique identifier for the client device. In one example, the broadcast server computes a 128-bit code that is identical to the 128-bit code that is computed by the client device. Auto assignment of the broadcast tower and personal messages channels are determined using the above-described self-assignment procedure.
Homing and Roaming
As described previously, each client device (e.g., see
In one example, the homing procedure is initiated in a geographic area where separate service regions (see
In some instances, the client will attempt activation in a geographic location where more than one broadcast service region exists. For example, activation of the client device in an overlapping or contained service region may create an uncertainty about which service region the client will assign to the client device. Directed homing may be employed to override the automatic service region assignment such that the proper service region identifier will be assigned to the client device. Directed homing may be initiated by any appropriate method including: a user initiated key sequence, and broadcasting of control information from the servers on the appropriate transmission towers in the overlapping or contained service regions. Once the client device is assigned to the home service region, the client will ignore received frames from other service regions.
The client device may be configured to restart the homing process (re-homing) when the received signal fades on the home frequency for more than a set number of frames (e.g., 10 frames).
The client device performs a basic homing procedure by searching for a valid signal while sweeping through the available frequency range. During the frequency sweep, the client device receives one or more frames of data. The client device selects the first station in the home service region and retrieves the station list. When the station list is the same then the client device presumes there is a problem with the reception on the home station, temporarily tunes to any station, and checks for the home station in the service region'"'"'s station list at regular intervals (e.g., 10 minute intervals). The procedure for homing and re-homing will be described in more detail with reference to
When the home station is no longer found in the service region'"'"'s station list the client device selects a failover mode. In the failover mode, the client device reselects a home station from the station list employing the self-assignment procedure previously described above. The server device automatically re-routes personal data to the appropriate stations when the home station is removed from the service region station list.
The client device selects a roaming mode when the entire frequency band sweep fails to find a station in the home service region. In roaming mode, the client receives frames from any service region, and temporarily assigns the new service region to the device. The station list is accessed for the new service region and an appropriate station is selected using the self-assignment procedure previously described above.
Discovery and Failover
The number of broadcast towers in a service region may be variable. One or more towers may go off air, while other towers may be brought on air. For example, additional broadcast towers may be necessary to service a larger client base as the number of clients in a service region grows. The self-assignment procedure described above will ensure that clients are equally distributed between broadcast towers, and that the assignment of towers to clients automatically occurs whenever a change in the number of broadcast towers in the service region occurs.
As previously described, each frame may include a change counter (e.g., a 2-bit counter) in one of the headers to indicate a change has taken place in the system. Each client compares the change counter to a locally stored copy (a cached copy). Whenever a change occurs in the system (i.e., a broadcast tower is brought on-line), the change counter is modified. Each client recognizes the change in the change counter and initiates a homing procedure to acquire a new station list, and re-assign the client to the appropriate broadcast tower. The broadcast server (see previous discussion) modifies the change counter without any interaction from the client when a change occurs in the configuration of the broadcast towers. As described previously, the self-assignment procedures accomplish channel and tower assignment without requiring interaction with the client.
Home Service region Changes
As described previously, each client device (e.g., see
A commuting situation is exemplified in
During times t1 through t2, the client device has a home service region corresponding to the first service region. During times t3 through t4 the client device has a home service region corresponding to the second service region. Between times t2 and t3 the client device may be located within either or both service regions. This type of situation may occur when a particular person is a commuter that travels between particular service regions at regular time intervals. Broadcast towers are scheduled to provide selected services and related content over the traveling time intervals through appropriate towers within the service regions. During the time intervals where the client device may be in either service region, broadcast towers in both service regions will attempt to communicate with the client device. In this case, the client device is instructed to receive messages from each service region according to the commuting schedule.
In some instances a client may require multiple home service regions. For example, a client device may be located in a boundary area between two or more service regions, and thus require two or more home service regions to ensure that broadcast transmissions are received. In this case, the client device will select the first service region that it receives and self-assign an appropriate tower in that service region. The broadcast servers will transmit messages for the client device in each of the multiple home service regions.
An example procedural flow (700) for homing/re-homing is illustrated in
The current receiver frequency is selected (locked) at block 740. Processing continues from block 740 to block 745, where the station list is extracted from the received frame, and the client device selects the appropriate station based on the self-assignment algorithm previously described.
Processing flows from decision block 750 to block 720 when the last frequency in the frequency sweep has not been reached. At block 720 the next available frequency in the frequency sweep is selected. Alternatively, processing continues from decision block 750 to block 760 when the last frequency is reached and a valid signal has not been found. At block 760 it is determined that a valid receiver frequency was not found and a tune failure procedure may be initiated. Processing is concluded at block 790.
Another example procedural flow (800) for homing/re-homing is illustrated in
Another example procedural flow (900) for homing/re-homing is illustrated in
In one example of the present invention, the frequency sweep range is from 88-108 MHz (the FM broadcast spectrum). The receiver frequency may be increased in 100 kHz increments when the frequency is changed. The frequency sweep may be varied linearly, logarithmically, in predetermined steps, or according to a table of frequencies in the client device. The client device records received signals over the sample interval period. The received signals are analyzed to locate a data sync pattern. The data sync pattern is employed to determine when a valid signal is received. The data sync pattern may be distributed over several segments. When the correlation of the data sync pattern indicates that proper synchronization is achieved (e.g., finding a peak in the correlation of the data sync pattern), then a valid signal is identified. Once the valid signal is achieved the frequency sweep is terminated and the current sweep frequency is locked. After the station list is retrieved, the previously discussed self-assignment procedure is employed to select an appropriate station for receiving personal messages. The client device tunes to the self-assigned station and begins receiving messages.
Although the preceding description describes various embodiments of the system, the invention is not limited to such embodiment, but rather covers all modifications, alternatives, and equivalents that fall within the spirit and scope of the following claims.