Wireless clock synchronization

• US 7,030,812 B2
• Filed: 11/14/2001
• Issued: 04/18/2006
• Est. Priority Date: 11/14/2000
• Status: Expired due to Term

• Current Assignee: Extreme Networks, Inc.
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bridgelall, Raj, Goren, David, Bekritsky, Benjamin J., Sakoda, William
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/992,200
• Publication Number:
  US 20020059535A1
• Time in Patent Office: 1,616 Days
• Field of Search: 342/387, 342/465
• US Class Current: 342/387
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 1/1639 the display being based on projection
• CPC Class Codes: G06F 21/305 by remotely controlling device operation
• CPC Class Codes: G06F 21/6209 to a single file or object, e.g. in a secure envelope, encrypted and accessed using a key, or with access control rules appended to the object itself
• CPC Class Codes: G06F 21/74 operating in dual or compartmented mode, i.e. at least one secure mode
• CPC Class Codes: G06F 21/88 Detecting or preventing theft or loss
• CPC Class Codes: G06F 2221/2105 Dual mode as a secondary aspect
• CPC Class Codes: G06F 2221/2115 Third party
• CPC Class Codes: G06F 3/0481 based on specific properties of the displayed interaction object or a metaphor-based environment, e.g. interaction with desktop elements like windows or icons, or assisted by a cursor's changing behaviour or appearance
• CPC Class Codes: G11B 20/10009 Improvement or modification of read or write signals
• CPC Class Codes: G11B 20/10425 by counting out-of-lock events of a PLL
• CPC Class Codes: G11B 20/22 for reducing distortions
• CPC Class Codes: H03L 7/091 the phase or frequency detector using a sampling device H03L7/087 takes precedence
• CPC Class Codes: H04B 10/25754 Star network topology
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence
• CPC Class Codes: H04B 7/2687 Inter base stations synchronisation
• CPC Class Codes: H04J 13/0077 Multicode, e.g. multiple codes assigned to one user
• CPC Class Codes: H04J 13/16 : Code allocation
• CPC Class Codes: H04J 3/0658 : Clock or time synchronisation among packet nodes
• CPC Class Codes: H04L 1/0066 : Parallel concatenated codes
• CPC Class Codes: H04L 1/0068 : by puncturing
• CPC Class Codes: H04L 1/1685 : the supervisory signal being transmitted in response to a specific request, e.g. to a polling signal
• CPC Class Codes: H04L 1/1841 : Resequencing
• CPC Class Codes: H04L 12/4641 : Virtual LANs, VLANs, e.g. virtual private networks [VPN] LAN interconnection over a bridge based backbone H04L12/462; encapsulation techniques H04L12/4633; routing of packets H04L45/00; packet switches H04L49/00; virtual private networks for security H04L63/0272
• CPC Class Codes: H04L 25/03038 : with a non-recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/4902 : Pulse width modulation; Pulse position modulation
• CPC Class Codes: H04L 25/4904 : using self-synchronising codes, e.g. split-phase codes
• CPC Class Codes: H04L 25/497 : by correlative coding, e.g. partial response coding or echo modulation coding transmitters and receivers for partial response systems transversal equalizers at the transmitter end H04L25/03343
• CPC Class Codes: H04L 27/156 : with demodulation using temporal properties of the received signal, e.g. detecting pulse width
• CPC Class Codes: H04L 41/06 : Management of faults, events, alarms or notifications
• CPC Class Codes: H04L 41/5009 : Determining service level performance parameters or violations of service level contracts, e.g. violations of agreed response time or mean time between failures [MTBF]
• CPC Class Codes: H04L 43/0829 : Packet loss
• CPC Class Codes: H04L 47/15 : in relation to multipoint traffic arrangements for broadcast or multicast in data networks H04L12/18
• CPC Class Codes: H04L 47/70 : Admission control; Resource allocation
• CPC Class Codes: H04L 47/72 : using reservation actions during connection setup
• CPC Class Codes: H04L 47/745 : Reaction in network
• CPC Class Codes: H04L 47/765 : triggered by the end-points
• CPC Class Codes: H04L 47/822 : Collecting or measuring resource availability data
• CPC Class Codes: H04L 47/824 : Applicable to portable or mobile terminals
• CPC Class Codes: H04L 47/83 : based on usage prediction
• CPC Class Codes: H04L 51/04 : Real-time or near real-time messaging, e.g. instant messaging [IM]
• CPC Class Codes: H04L 51/48 : Message addressing, e.g. address format or anonymous messages, aliases
• CPC Class Codes: H04L 51/58 : Message adaptation for wireless communication
• CPC Class Codes: H04L 61/2553 : Binding renewal aspects, e.g. using keep-alive messages
• CPC Class Codes: H04L 63/126 : the source of the received data
• CPC Class Codes: H04L 65/1016 : IP multimedia subsystem [IMS]
• CPC Class Codes: H04L 65/1043 : Gateway controllers, e.g. media gateway control protocol [MGCP] controllers
• CPC Class Codes: H04L 65/1101 : Session protocols
• CPC Class Codes: H04L 65/1104 : Session initiation protocol [SIP]
• CPC Class Codes: H04L 65/4061 : Push-to services, e.g. push-to-talk or push-to-video
• CPC Class Codes: H04L 9/085 : Secret sharing or secret splitting, e.g. threshold schemes
• CPC Class Codes: H04L 9/304 : based on error correction codes, e.g. McEliece
• CPC Class Codes: H04M 1/724 : User interfaces specially adapted for cordless or mobile telephones
• CPC Class Codes: H04M 1/72415 : for remote control of appliances
• CPC Class Codes: H04M 3/42221 : Conversation recording systems at the subscriber's set H04M1/656
• CPC Class Codes: H04M 7/0057 : Services where the data services network provides a telephone service in addition or as an alternative, e.g. for backup purposes, to the telephone service provided by the telephone services network
• CPC Class Codes: H04M 7/1295 : Details of dual tone multiple frequency signalling
• CPC Class Codes: H04N 1/00957 : Compiling jobs, e.g. for batch processing H04N1/3208 takes precedence; program code compilation G06F8/41
• CPC Class Codes: H04N 1/32106 : separate from the image data, e.g. in a different computer file
• CPC Class Codes: H04N 1/40 : Picture signal circuits H04N1/387 takes precedence
• CPC Class Codes: H04N 19/109 : among a plurality of temporal predictive coding modes
• CPC Class Codes: H04N 19/139 : Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability
• CPC Class Codes: H04N 19/51 : Motion estimation or motion compensation
• CPC Class Codes: H04N 19/517 : by encoding
• CPC Class Codes: H04N 19/527 : Global motion vector estimation
• CPC Class Codes: H04N 19/625 : using discrete cosine transform [DCT]
• CPC Class Codes: H04N 19/70 : characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 19/91 : Entropy coding, e.g. variable length coding [VLC] or arithmetic coding
• CPC Class Codes: H04N 21/2543 : Billing , e.g. for subscription services payment schemes, architectures or protocols G06Q20/00; e-commerce G06Q30/00; arrangements for billing for the use of broadcast information or broadcast-related information H04H60/21
• CPC Class Codes: H04N 21/4181 : for conditional access
• CPC Class Codes: H04N 21/426 : Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/433 : Content storage operation, e.g. storage operation in response to a pause request, caching operations
• CPC Class Codes: H04N 21/4623 : Processing of entitlement messages, e.g. ECM [Entitlement Control Message] or EMM [Entitlement Management Message] arrangements for conditional access to broadcast information or to broadcast-related services H04H60/14
• CPC Class Codes: H04N 21/47211 : for requesting pay-per-view content payment schemes payment architectures or payment protocols G06Q20/00, G07F
• CPC Class Codes: H04N 21/6175 : involving transmission via Internet broadcast-related systems characterised by the transmission system being the Internet H04H60/82
• CPC Class Codes: H04N 21/6187 : involving transmission via a telephone network, e.g. POTS
• CPC Class Codes: H04N 21/6582 : Data stored in the client, e.g. viewing habits, hardware capabilities, credit card number arrangements where receivers interact with the broadcast H04H20/38
• CPC Class Codes: H04N 2201/0094 : Multifunctional device, i.e. a device capable of all of reading, reproducing, copying, facsimile transception, file transception
• CPC Class Codes: H04N 2201/3212 : of data relating to a job, e.g. communication, capture or filing of an image
• CPC Class Codes: H04N 2201/3222 : of processing required or performed, e.g. forwarding, urgent or confidential handling
• CPC Class Codes: H04N 2201/3274 : Storage or retrieval of prestored additional information
• CPC Class Codes: H04N 23/57 : Mechanical or electrical details of cameras or camera modules specially adapted for being embedded in other devices
• CPC Class Codes: H04N 5/38 : Transmitter circuitry for the transmission of television signals according to analogue transmission standards H04N5/14 takes precedence
• CPC Class Codes: H04N 5/4448 : for frame-grabbing
• CPC Class Codes: H04N 5/445 : for displaying additional information H04N5/50 takes precedence
• CPC Class Codes: H04N 5/45 : Picture in picture , e.g. displaying simultaneously another television channel in a region of the screen
• CPC Class Codes: H04N 5/46 : for receiving on more than one standard at will deflecting circuits of multi-standard receivers H04N3/27
• CPC Class Codes: H04N 5/64 : Constructional details of receivers, e.g. cabinets or dust covers furniture aspects of television cabinets A47B81/06
• CPC Class Codes: H04N 5/66 : Transforming electric information into light information scanning details H04N3/00
• CPC Class Codes: H04N 5/76 : Television signal recording
• CPC Class Codes: H04N 5/775 : between a recording apparatus and a television receiver
• CPC Class Codes: H04N 5/85 : on discs or drums
• CPC Class Codes: H04N 5/907 : using static stores, e.g. storage tubes or semiconductor memories H04N5/91 takes precedence
• CPC Class Codes: H04N 7/0112 : one of the standards corresponding to a cinematograph film standard
• CPC Class Codes: H04N 7/0122 : the input and the output signals having different aspect ratios
• CPC Class Codes: H04N 7/163 : by receiver means only
• CPC Class Codes: H04N 7/17327 : with deferred transmission or handling of upstream communications
• CPC Class Codes: H04N 9/3129 : scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161
• CPC Class Codes: H04N 9/642 : Multi-standard receivers
• CPC Class Codes: H04N 9/7925 : for more than one standard
• CPC Class Codes: H04N 9/8042 : involving data reduction
• CPC Class Codes: H04Q 3/0025 : Provisions for signalling
• CPC Class Codes: H04W 12/10 : Integrity
• CPC Class Codes: H04W 12/61 : Time-dependent
• CPC Class Codes: H04W 24/00 : Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/00 : Network traffic management; Network resource management
• CPC Class Codes: H04W 28/18 : Negotiating wireless communication parameters
• CPC Class Codes: H04W 28/26 : Resource reservation
• CPC Class Codes: H04W 36/02 : Buffering or recovering information during reselection ; Modification of the traffic flow during hand-off
• CPC Class Codes: H04W 4/10 : Push-to-Talk [PTT] or Push-On-Call services
• CPC Class Codes: H04W 4/12 : Messaging; Mailboxes; Announcements
• CPC Class Codes: H04W 4/14 : Short messaging services, e.g. short message services [SMS] or unstructured supplementary service data [USSD]
• CPC Class Codes: H04W 40/00 : Communication routing or communication path finding
• CPC Class Codes: H04W 48/08 : Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00
• CPC Class Codes: H04W 52/30 : using constraints in the total amount of available transmission power
• CPC Class Codes: H04W 56/00 : Synchronisation arrangements
• CPC Class Codes: H04W 64/00 : Locating users or terminals or network equipment for network management purposes, e.g. mobility management
• CPC Class Codes: H04W 72/23 : in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 74/002 : Transmission of channel access control information
• CPC Class Codes: H04W 74/0833 : Random access procedures, e.g. with 4-step access
• CPC Class Codes: H04W 76/10 : Connection setup
• CPC Class Codes: H04W 76/12 : Setup of transport tunnels
• CPC Class Codes: H04W 76/18 : Management of setup rejection or failure
• CPC Class Codes: H04W 76/30 : Connection release
• CPC Class Codes: H04W 76/34 : Selective release of ongoing connections
• CPC Class Codes: H04W 76/45 : for Push-to-Talk [PTT] or Push-to-Talk over cellular [PoC] services
• CPC Class Codes: H04W 8/245 : from a network towards a terminal
• CPC Class Codes: H04W 8/26 : Network addressing or numbering for mobility support
• CPC Class Codes: H04W 8/265 : for initial activation of new user
• CPC Class Codes: H04W 84/042 : Public Land Mobile systems, e.g. cellular systems
• CPC Class Codes: H04W 84/08 : Trunked mobile radio systems
• CPC Class Codes: H04W 84/12 : WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 88/06 : adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: H04W 88/085 : Access point devices with remote components
• CPC Class Codes: H04W 88/16 : Gateway arrangements
• CPC Class Codes: Y10S 370/906 : Fiber data distribution interface, FDDI
• CPC Class Codes: Y10S 370/907 : Synchronous optical network, SONET
• CPC Class Codes: Y10S 707/99943 : Generating database or data structure, e.g. via user interface

Abstract

A system and method for synchronizing internal clocks of receiving stations of a locating system are described. A beacon transmits reference data packets at a known position. A first arrival time is compared to a second arrival time to determine a correlated arrival time data. The first arrival time is a time of reception of the reference data packets by a first receiving station, and the second arrival time is a time of reception of the reference data packets by a second receiving station. A linear polynomial fit is computed as a function of the correlated arrival time data and the first and second arrival times. Times of arrival of data packets at the first and second receiving stations is synchronized as a function of the linear polynomial fit.

Claims

1. A method for synchronizing internal clocks of a first pair of first and second receiving stations A and B of a system, comprising the steps of:

transmitting a series of reference data packets from a beacon at a known position proximate to a geographical center point of a first pair of first and second receiving stations A and B;

assuming that the beacon is at the geographical center point;

correlating first arrival times t_A, and second arrival times t_A, by plotting times t_A and t_B against each other for the series of reference data packets, a first arrival time t_A being a time of reception of a particular reference data packet by receiving station A, a corresponding second arrival time t_B being a time of reception of the particular reference data packet by receiving station B;

computing a linear polynomial fit t_B=m t_A+b, where slope m is function of the difference in the frequencies of the internal clocks of the receiving stations A and B and y-intercept b is the offset due to different start times of the internal clocks of the receiving stations A and B;

determining a bias for the internal clocks using known difference in distance between the beacon and the receiving stations A and B,

synchronizing the internal clocks of the receiving stations A and B according to the slope m, the offset b and the bias.

2. The method according to claim 1, further comprising repeating the correlating and computing steps for third and fourth receiving stations to determine a further slope, a further y-intercept and a further bias for the third and fourth receiving stations.

3. The method according to claim 2, further comprising repeating the correlating and computing steps for a third receiving station in conjunction with the first receiving station A to determine a further slope, a further y-intercept and a further bias for the first and third receiving stations.

4. The method according to claim 3, further comprising the step of:

correcting an arrival time difference between the first and second receiving stations and the third and fourth receiving stations as a function of an arrival time of a first data packet sent by a mobile device and a slope, a y-intercept and a bias computed for first and second pairs of the receiving stations, each of the first and second pairs including any two stations of the first, second, third and fourth receiving stations, the first pair including at least one receiving station which is not included in the second pair.

5. The method according to claim 1, further comprising the step of:

repeating the transmitting, comparing and computing steps to update synchronization of the internal clocks of the receiving stations at a predetermined rate.

6. A method for determining a location of a mobile device, comprising the steps of:

synchronizing internal clocks of receiving stations according to the method of claim 1;

receiving a data packet from the mobile device by first and second receiving stations of the receiving stations;

determining a synchronized arrival time of the data packet at the first and second receiving stations;

calculating an arrival time difference between the first and second receiving stations; and

computing the location of the mobile device, using a hyperbolic trilateration, as a function of the synchronized arrival time.

7. The method according to claim 6, further comprising the step of:

determining a corresponding synchronized arrival time for at least first and second pairs of the receiving stations, each of the first and second pairs including any two of the first receiving station, the second receiving station, a third receiving station and a fourth receiving station, the first pair including at least one receiving station which is not included in the second pair.

8. The method according to claim 6, further comprising the step of:

determining a corresponding synchronized arrival time for at least first, second and third pairs of the receiving stations, the first, second and third pairs of the receiving stations including any two of the first receiving station, the second receiving station, the third receiving station, the fourth receiving station, a fifth receiving station and a sixth receiving station, the first pair including at least one receiving station which is not included in the second and third pairs, the second pair including at least one receiving station which is not included in the third pair.

9. The method according to claim 6, wherein the synchronizing step includes the sub steps:

transmitting a reference data packet from a beacon at a known position;

comparing a first arrival time and a second arrival time to determine a correlated arrival time data, the first arrival time being a time of reception of the reference data packet at the first receiving station, the second arrival time being a time of reception of the reference data packet by the second receiving station;

computing a linear polynomial fit as a function of the correlated arrival time data and the first and second arrival times; and

synchronizing arrival time of the reference data packet at the first and second receiving stations as a function of the linear polynomial fit.

10. A system for synchronizing internal clocks of a mobile device locating network, comprising:

receiving stations having the internal clocks;

a processor connected to the receiving stations;

and a beacon adapted for transmitting to the receiving stations a series of reference data packets, the beacon having a known location proximate to a geographical center point of the receiving stations,

wherein each of the receiving stations is adapted to forward arrival times of the series of reference data packets to the processor, wherein the processor is adapted to compute;

a linear polynomial fit t_B=m t_A+b for a pair of receiving stations A and B, where t_A and t_B are the reception times of the series of reference data packets at receiving stations A and B, respectively, where slope m is function of the difference in the frequencies of the internal clocks of the receiving stations A and B, and where y-intercept b is the offset due to different start times of the internal clocks of the receiving stations A and B; and

a bias for the internal clocks of receiving stations A and B using known difference in distance between the beacon and the receiving stations A and B; and

wherein the processor is further adapted to synchronize the internal clocks of the receiving stations A and B according to the slope m, the offset b and the bias.

11. The system according to claim 10, wherein the receiving stations includes are divided in pairs and wherein at least two pairs are used to locate the mobile device.

12. The system according to claim 10, wherein the processor receives first and second arrival times, the first arrival time being a time of reception of the reference data packet by a first receiving station of the receiving stations, the second arrival time being a time of reception of the reference data packet by a second receiving station of the receiving stations, wherein the processor comparing the first arrival time against the second arrival time to determine a correlated arrival time data, wherein the processor computes a slope and a intercept as a function of the correlated arrival time data and the first and second arrival times, assuming equal distances between the beacon and the first and second receiving stations, and wherein the processor computes a bias of the correlated arrival time data from known distance differences between the beacon and the first and second receiving stations.

13. A method of synchronizing internal clocks of receiving stations of a locating system, comprising the steps of:

for a first pair of receiving stations A and B in the location system,

transmitting a series of reference data packets from a beacon at a known position;

assuming that the beacon is at the geographical center point between receiving stations A and B;

correlating first arrival times t_A and second arrival times t_A by plotting times t_A and t_B against each other for the series of reference data packets, where a first arrival time t_A is a time of reception of the a particular reference data packet by the receiving station A, and corresponding second arrival time t_B is a time of reception of the particular reference data packet by the receiving station B, computing a linear polynomial fit t_B=m t_A+b, where slope m is function of the difference in the frequencies of the internal clocks of the first and second receiving stations and y-intercept b is the offset due to different start times of the internal clocks of the first and second receiving stations;

determining a bias for the internal clocks using known difference in distance between the beacon and the first and second receiving stations,

synchronizing the internal clocks for the first pair of receiving stations A and B according to the slope m, the offset b and the bias; and

repeating the preceding steps for a second pair of receiving stations in the locating system.

14. The method according to claim 13, wherein a first one of the receiving stations is included in both the first and second pairs of receiving stations.

15. The method according to claim 13, wherein the first pair of receiving stations includes first and second receiving stations and the second pair of receiving stations includes third and fourth receiving stations.