Methods and apparatus for identifying asset location in communication networks

• US 20020097182A1
• Filed: 11/14/2001
• Published: 07/25/2002
• Est. Priority Date: 11/14/2000
• Status: Active Grant

• Current Assignee: Extreme Networks, Inc.
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bridgelall, Raj, Goren, David P., Bekritsky, Benjamin J., Kawaguchi, Dean, Zegelin, Chris
• Granted Patent: US 7,030,811 B2
• Time in Patent Office: Days
• US Class Current: 342/357.4
• 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 74/008 : with additional processing of random access related information at receiving side
• 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

The location of unmodified wireless assets in a wireless communication network may be identified using time differences of arrivals of a communication sequence at different network receivers. Time-stamping devices may include correlator circuits in parallel with signal decoders to time-stamp communication sequences. Cellular wireless networks may be frequency-multiplexed to increase spatial time-stamping density. Tags may be attached to passive assets to provide location identification information to network devices. Locations of assets broadcasting standard 802.11 radio frequency structures may be identified. Noise inherent in correlating a communication sequence may be reduced by using a selected correlation function.

Claims

1. An apparatus for identifying a location of a wireless asset comprising:

a synchronization signal generator; and

at least one network resource in electrical communication with said generator, said resource configured to time-stamp an 802.11 communication sequence.

2. The system of claim 1 wherein said resource is configured to time-stamp an 802.11 data packet.

3. The system of claim 1 wherein said resource is configured to time-stamp an 802.11a data packet.

4. The system of claim 1 wherein said resource is configured to time-stamp an 802.11b data packet.

5. A system for providing a time-of-arrival estimate of a communication sequence at a location, said system comprising:

a device for receiving radio frequency signals; and

a first circuit in electronic communication with said device;

wherein said first circuit comprises at least one correlator selected from the group;

a. a two-symbol correlator;

b. a three-symbol correlator;

c. a four-symbol correlator;

d. a five-symbol correlator;

e. an N-symbol correlator, wherein N is an integer greater than five; and

f. a combination of at least two of a-e.

6. The system of claim 5 wherein said first circuit comprises a sliding correlator.

7. The system of claim 5 comprising at least two correlators arranged in parallel.

8. The system of claim 5 further comprising a second circuit in electronic communication with said device, said second circuit configured to decode said communication sequence.

9. The system of claim 5 further comprising a third circuit in electronic communication with said first circuit, said third circuit configured to separate a multipath peak from a line of sight peak in a correlation signal generated by said correlator.

10. The system of claim 5 further comprising a fourth circuit in electronic communication with said first circuit, said fourth circuit configured to output a signal indicative of said time-of-arrival.

11. The system of claim 5 further comprising a fifth circuit in electronic communication with said device, said fifth circuit configured to parse a mobile transmitter device identification code in said communication sequence.

12. The system of claim 5 wherein said device comprises an antenna in electronic communication with said device.

13. The system of claim 12 wherein said device comprises:

a central processing unit; and

a radio module, said unit controlling said module, said module in electronic communication with said antenna.

14. The system of claim 13 wherein said module is selected from the group:

a. a PCMCIA card;

b. a CompactFlash™

card; and

c. a mini PCI card.

16. The circuit of claim 15 wherein said time-stamping circuit comprises a multipath processor.

17. The circuit of claim 15 further comprising a descrambler circuit in serial electronic communication with said correlator and said interface, wherein said descrambler circuit is between said correlator and said interface.

18. The circuit of claim 15 further comprising a correlator bypass, said bypass connecting said tracking circuit to said time-stamping circuit.

20. The method of claim 19 wherein, when said network comprises at least one third receiver pair configured to receive at a third frequency, said method further comprises receiving a third communication sequence from said asset using said third receiver pair and said identifying further comprises using a third time-difference-of-arrivals corresponding to said third receiver pair.

21. The method of claim 20 wherein, when said network comprises at least one additional receiver pair configured to receive at an additional frequency, said method further comprises receiving an additional communication sequence from said asset at said additional frequency using said additional receiver pair and said identifying further comprises using an additional time-difference-of-arrivals corresponding to said additional receiver pair.

22. The method of claim 19 wherein each of said receivings comprises receiving at least one wireless IEEE 802.11 compatible communication sequence.

23. The method of claim 19 wherein, when said second receiver pair comprises auxiliary receivers, said receiving a second communication sequence comprises switching the operating frequency of said auxiliary receivers.

25. The method of claim 24 wherein, when said network comprises at least one third receiver pair configured to receive signals at a third frequency, said method further comprises transmitting a third communication sequence configured for estimation of said location at said third frequency.

26. The method of claim 25 wherein, when said network comprises at least one additional receiver pair configured to receive at an additional frequency, said method further comprises transmitting an additional communication sequence configured for estimation of said location at said additional frequency.

27. The method of claim 24 wherein each of said transmittings comprises transmitting at least one wireless IEEE 802.11 compatible communication sequence.

29. The method of claim 28 wherein said receiving comprises receiving a communication sequence having a unique asset identifier.

30. The method of claim 28 further comprising selecting at least one mobile asset identifier.

31. The method of claim 28 further comprising storing at least one mobile asset identifier

32. The method of claim 28 further comprising comparing said asset identifier to a selected identifier.

33. The method of claim 28 further comprising calculating at least one time-of-arrival of said communication sequence, said time-of-arrival corresponding to a time of arrival of said communication sequence at a receiver in said network.

34. The method of claim 33 wherein said estimating comprises quantifying a time-difference-of-arrivals using at least two times-of-arrival.

36. The method of claim 35 further comprising determining if said data signal is encoded for time stamping.

37. The method of claim 35 further comprising transmitting said data signal from a wireless asset.

38. The method of claim 37 wherein said transmitting comprises generating a communication sequence corresponding to a preselected reference signal selected for determining said time-of-arrival estimate.

39. The method of claim 38 wherein said generating comprises generating a sequence of at least two consecutive identical symbols.

40. The method of claim 39 wherein:

said generating a sequence of at least two consecutive identical symbols comprises generating a sequence of chipping codes.

41. The method of claim 36 wherein:

said optionally selecting a correlation function comprises selecting a reference sequence; and

said correlation function depends on said reference sequence.

42. The method of claim 41 wherein, when said decoded signal comprises a preselected time-of-arrival estimation sequence, said selecting a reference signal comprises identifying a preselected reference sequence.

43. The method of claim 42 further comprising:

storing a representation of said decoded signal in a buffer;

wherein said estimating comprises correlating said preselected reference sequence with said representation.

44. The method of claim 41 wherein said selecting a reference sequence comprises applying a rule to said decoded signal to select said sequence.

45. The method of claim 44 wherein said applying comprises identifying in said decoded signal a communication sequence corresponding to at least one of a plurality of stored reference sequences.

46. The method of claim 44 further comprising:

storing a representation of said decoded signal in a buffer;

wherein said estimating comprises correlating said reference sequence with said representation.

47. The method of claim 45 wherein said identifying comprises identifying in said decoded signal a communication sequence selected from the group:

a. a single Barker code sequence;

b. a series of Barker code sequences;

c. a series of identical Barker code sequences;

d. a single PN code;

e. a series of PN codes;

f. a series of identical PN codes; and

g. a combination of any of a-f.

48. The method of claim 41 wherein said optionally selecting a reference sequence comprises selecting a reference sequence selected from the group:

a. a single Barker code sequence;

b. a series of Barker code sequences;

c. a series of identical Barker code sequences;

d. a single PN code;

e. a series of PN codes;

f. a series of identical PN codes; and

g. a combination of any of a-f.

49. The method of claim 35 wherein said estimating comprises:

evaluating said function using said data signal and a reference sequence; and

determining at least one time-of-arrival estimator value using said function.

50. The method of claim 49 wherein said determining comprises calculating an average of said at least one time-of-arrival estimator value.

51. The method of claim 50 further comprising setting said time-of-arrival equal to said average.

52. The method of claim 49 wherein said determining comprises computing an extreme value.

53. The method of claim 52 wherein-said computing comprises computing a quantity selected from the group:

a. a substantially maximum value; and

b. a substantially minimum value.

54. The method of claim 49 further comprising determining a time value corresponding to said time-of-arrival estimator value.

55. The method of claim 49 further comprising calculating a time value corresponding to said time-of-arrival estimator value using a time selected from the group:

a. an access point clock time; and

b. a network clock time.

56. The method of claim 35 wherein said estimating comprises separating multipath components from line of sight signal components in a correlation signal corresponding to said correlation function.

57. The method of claim 56 wherein said separating comprises detecting a leading edge of a peak in said correlation signal.

58. The method of claim 56 wherein said separating comprises performing channel estimation.

59. The method of claim 35 further comprising optionally selecting a correlation function for said decoded signal if said data signal is encoded for time stamping.

60. The method of claim 59 further comprising identifying a communication sequence in said decoded signal, said communication sequence selected from the group:

a. a single Barker code sequence;

b. a series of Barker code sequences;

c. a series of identical Barker code sequences;

d. a single PN code;

e. a series of PN codes;

f. a series of identical PN codes;

g. a combination of any of a-f;

h. a single CCK symbol;

i. a series of CCK symbols;

j. a series of identical CCK symbols;

k. a single PBCC symbol;

l. a series of PBCC symbols;

m. a series of identical PBCC symbols;

n. a single OFDM symbol;

o. a series of OFDM symbols;

p. a series of identical OFDM symbols;

q. a combination of any of h-p.

61. The method of claim 59 wherein said estimating comprises selecting a reference signal selected from the group:

a. a single Barker code sequence;

b. a series of Barker code sequences;

c. a series of identical Barker code sequences;

d. a single PN code;

e. a series of PN codes;

f. a series of identical PN codes;

g. a combination of any of a-f;

h. a single CCK symbol;

i. a series of CCK symbols;

j. a series of identical CCK symbols;

k. a single PBCC symbol;

l. a series of PBCC symbols;

m. a series of identical PBCC symbols;

n. a single OFDM symbol;

o. a series of OFDM symbols;

p. a series of identical OFDM symbols;

q. a combination of any of h-p.

15. A signal processing circuit for processing radio signals comprising:

a carrier tracking circuit having a tracking circuit output;

a chipping code correlator circuit having a correlator circuit output;

a time-stamping circuit; and

a receiver interface;

wherein;

said correlator circuit is in serial electronic communication with said tracking circuit and said receiver interface; and

said time-stamping circuit is connected to said tracking circuit output, said correlator circuit output, and said receiver interface.

19. A method for identifying a location of an asset in a communication network, said network having at least one first receiver pair and at least one second receiver pair, said first receiver pair configured to receive signals at a first frequency, said second receiver pair configured to receive signals at a second frequency, said method comprising:

receiving a first communication sequence from said asset using said first receiver pair;

receiving a second communication sequence from said asset using said second receiver pair; and

identifying said location using a first time-difference-of-arrivals and a second time-difference-of-arrivals, said first time-difference-of-arrivals corresponding to said first receiver pair, said second time-difference-of-arrivals corresponding to said second receiver pair.

24. A method for providing location estimation information to a communication network, said information corresponding to an asset, said asset having a location, said network having at least one first receiver pair and at least one second receiver pair, said first receiver pair configured to receive signals at a first frequency, said second receiver pair configured to receive signals at a second frequency, said method comprising:

transmitting a first communication sequence configured for estimation of said location at said first frequency; and

transmitting a second communication sequence configured for estimation of said location at said second frequency.

28. A method for selectively identifying a location of a mobile asset in a communication network, said method comprising:

receiving a communication sequence from said asset, said communication sequence having an asset identifier, said asset identifier identifying said asset; and

optionally estimating said location when said asset identifier corresponds to a selected identifier.

35. A method for providing a time-of-arrival estimate of a data signal at a receiver, said method comprising:

receiving said data signal;

demodulating said signal;

decoding said signal to form a decoded signal;

optionally selecting a correlation function for said decoded signal if said data signal is not encoded for time stamping; and

estimating said time-of-arrival using said correlation function.

62. A method for identifying a location of an asset in a communication network, said network having at least a first receiver device and a second receiver device, each receiver device having a known position, said method comprising:

optionally selecting a correlation function for said decoded signal if said data signal is not encoded for time-stamping;

estimating a first time-of-arrival using said correlation function, said first time-of-arrival corresponding to arrival at said first receiver device of a communication sequence transmitted by said asset;

estimating a second time-of-arrival using said correlation function, said second time-of-arrival corresponding to arrival at said second receiver device of said communication sequence; and

calculating a first time-difference-of-arrivals using said first and second times-of-arrival.

63. The method of claim 62 further comprising optionally selecting a correlation function for said decoded signal if said data signal is not encoded for time-stamping.

64. The method of claim 62 further comprising receiving said communication sequence using said first receiver.

65. The method of claim 62 further comprising receiving said communication signal using said second receiver.

66. The method of claim 62 further comprising selecting said correlation function.

67. The method of claim 66 wherein said selecting comprises using information about said communication sequence to select said correlation function.

68. The method of claim 63 wherein said calculating comprises subtracting said first time-of-arrival from said second time-of-arrival.

69. The method of claim 63 further comprising estimating said location using said first time-difference-of-arrivals.

70. The method of claim 63 wherein said calculating comprises determining a first plurality of asset location solutions.

71. The method of claim 70 wherein, when said network comprises at least one additional receiver device, said estimating further comprises:

determining a second plurality of asset location solutions using said additional receiver device; and

identifying said location using said first and second pluralities of asset location solutions.

72. The method of claim 71 wherein said identifying comprises estimating an intersection of said first plurality and said second plurality.

73. The method of claim 71 wherein said identifying comprises using hyperbolic trilateration.

74. The method of claim 71 wherein said determining a second plurality comprises estimating a distance between said asset and said additional receiver device.

75. The method of claim 74 wherein said estimating comprises calculating a travel time for said communication signal.

76. The method of claim 74 wherein said estimating a distance comprises estimating a signal strength of said communication signal.

77. The method of claim 71 wherein said determining a second plurality comprises calculating a second time-difference-of-arrivals using a third time-of-arrival, said third time-of-arrival corresponding to arrival of said communication signal at said additional receiver, said second time-difference-of-arrivals substantially equal to a difference between said third time-of-arrival and one of said first and second times-of-arrival.

78. The method of claim 71 wherein, when said network comprises at least a third receiver and a fourth receiver, said determining a second plurality comprises calculating a second time-difference-of-arrivals using a third time-of-arrival and a fourth time-of-arrival, said third time-of-arrival corresponding to arrival of said communication signal at said third receiver, said fourth time-of-arrival corresponding to arrival of said communication signal at said fourth receiver, said second time-difference-of-arrivals substantially equal to a difference between said third and fourth times-of-arrival.

80. The method of claim 79 wherein said calculating comprises:

for each second time-of-arrival estimator value that corresponds to one first time-of-arrival estimator value, quantifying a difference between said second time-of-arrival estimator value and said first time-of-arrival estimator value; and

if at least two differences are quantified, averaging said differences.

81. The method of claim 79 wherein said averaging comprises setting said time-difference-of arrivals equal to an average of said first and second time-of-arrival estimator values.

82. The method of claim 79 further comprising:

receiving said communication signal using said first receiver; and

receiving said communication signal using said second receiver.

83. The method of claim 79 further comprising selecting said correlation function.

79. A method for identifying a location of an asset in a communication network, said network having a first receiver device and a second receiver device, each receiver device having a known position, said method comprising:

estimating more than one first time-of-arrival estimator value using a correlation function, said first time-of-arrival estimator value corresponding to arrival at said first station of a communication signal from said asset;

estimating more than one second time-of-arrival estimator value using said correlation function, said second time-of-arrival estimator value corresponding to arrival of said communication signal at said second station;

calculating a time-difference-of arrivals using said first and second time-of-arrival estimators.

84. A method for identifying a location of an asset in a communication network, said network having at least three receivers, said method comprising:

decoding a data signal from said asset to form a decoded signal;

determining if said decoded signal is encoded for time-stamping;

selecting a correlation function for estimating a time-of-arrival of a communication sequence at said receivers;

collecting at least one time-of-arrival estimate for each of said receivers, said estimate corresponding to a time-of-arrival of said communication sequence at a respective one of said receivers;

calculating a difference for each of at least two pairs of said estimates; and

estimating said location using said differences.

85. The method of claim 84 wherein said estimating comprises defining at least one asset location solution set for each difference.

86. The method of claim 84 wherein said estimating further comprises:

setting at least one solution set criterion; and

discarding a solution set that does not satisfy said criterion.

87. The method of claim 86 wherein said solution set criterion is based on a geometric feature of said network.

88. The method of claim 86 wherein said solution set criterion is based on an index of precision of a time-of-arrival estimate.

89. The method of claim 85 wherein said estimating further comprises finding the maximum likelihood estimator of said location using said solution sets.

90. The method of claim 89 further comprising weighting each time-of-arrival estimate in proportion to an index of precision of the estimate.

91. The method of claim 85 wherein said estimating further comprises finding the least squares estimate of said location using said solution sets.

92. A method for identifying a location of an asset in a communication network, said network having at least a first receiver device and a second receiver device, each receiver device having a known position, said method comprising:

estimating a first time-of-arrival of an 802.11 communication sequence transmitted by said asset, said first time-of-arrival corresponding to arrival of said sequence at said first receiver device;

estimating a second time-of-arrival of said sequence, said second time-of-arrival corresponding to arrival of said sequence at said second receiver device; and

calculating a first time-difference-of-arrivals using said first and second times-of-arrival.

93. The method of claim 92 further comprising receiving said communication sequence using said first receiver.

94. The method of claim 92 further comprising receiving said communication signal using said second receiver.

95. The method of claim 92 wherein said calculating comprises subtracting said first time-of-arrival from said second time-of-arrival.

96. The method of claim 92 further comprising estimating said location using said first time-difference-of-arrivals.

97. The method of claim 92 wherein said estimating comprises determining a first plurality of location solutions for said asset.

98. The method of claim 97 wherein, when said network comprises at least one additional receiver device, said estimating further comprises:

determining a second plurality of asset location solutions using said additional receiver device; and

identifying said location using said first and second pluralities of asset location solutions.

99. The method of claim 98 wherein said identifying comprises estimating an intersection of said first plurality and said second plurality.

100. The method of claim 98 wherein said identifying comprises using hyperbolic trilateration.

101. The method of claim 98 wherein said determining a second plurality comprises estimating a distance between said asset and said additional receiver device.

102. The method of claim 101 wherein said estimating comprises calculating a travel time for said communication signal.

103. The method of claim 101 wherein said estimating a distance comprises estimating a signal strength of said communication signal.

104. The method of claim 98 wherein said determining a second plurality comprises calculating a second time-difference-of-arrivals using a third time-of-arrival, said third time-of-arrival corresponding to arrival of said communication signal at said additional receiver, said second time-difference-of-arrivals substantially equal to a difference between said third time-of-arrival and one of said first and second times-of-arrival.

105. The method of claim 98 wherein, when said network comprises at least a third receiver and a fourth receiver, said determining a second plurality comprises calculating a second time-difference-of-arrivals using a third time-of-arrival and a fourth time-of-arrival, said third time-of-arrival corresponding to arrival of said communication signal at said third receiver, said fourth time-of-arrival corresponding to arrival of said communication signal at said fourth receiver, said second time-difference-of-arrivals substantially equal to a difference between said third and fourth times-of-arrival.

106. A method for identifying a location of an asset in a communication network, said network having a first receiver device and a second receiver device, each receiver device having a known position, said method comprising:

estimating more than one first time-of-arrival estimator value, said first time-of-arrival estimator value corresponding to arrival at said first station of an 802.11 communication signal from said asset;

estimating more than one second time-of-arrival estimator value, said second time-of-arrival estimator value corresponding to arrival of said communication signal at said second station;

calculating a time-difference-of arrivals using said first and second time-of-arrival estimators.

107. The method of claim 106 wherein said calculating comprises:

for each second time-of-arrival estimator value that corresponds to one first time-of-arrival estimator value, quantifying a difference between said second time-of-arrival estimator value and said first time-of-arrival estimator value; and

if at least two differences are quantified, averaging said differences.

108. The method of claim 106 wherein said averaging comprises setting said time-difference-of arrivals equal to an average of said first and second time-of-arrival estimator values.

109. The method of claim 106 further comprising:

receiving said communication signal using said first receiver; and

receiving said communication signal using said second receiver.

110. The method of claim 106 further comprising selecting a correlation function.

111. A method for identifying a location of an asset in a communication network, said network having at least three receivers, said method comprising:

estimating a time-of-arrival of an 802.11 communication sequence at said receivers;

collecting at least one time-of-arrival estimate for each of said receivers, said estimate corresponding to a time-of-arrival of said communication sequence at a respective one of said receivers;

calculating a difference for each of at least two pairs of said estimates; and

estimating said location using said differences.

112. The method of claim 111 wherein said estimating comprises defining at least one asset location solution set for each difference.

113. The method of claim 111 wherein said estimating further comprises:

setting at least one solution set criterion; and

discarding a solution set that does not satisfy said criterion.

114. The method of claim 113 wherein said solution set criterion is based on a geometric feature of said network.

115. The method of claim 113 wherein said solution set criterion is based on an index of precision of a time-of-arrival estimate.

116. The method of claim 112 wherein said estimating further comprises finding the maximum likelihood estimator of said location using said solution sets.

117. The method of claim 116 further comprising weighting each time-of-arrival estimate in proportion to an index of precision of the estimate.

118. The method of claim 112 wherein said estimating further comprises finding the least squares estimate of said location using said solution sets.