CODING IN A WIDE AREA POSITIONING SYSTEM (WAPS)

• US 20130057436A1
• Filed: 06/28/2012
• Published: 03/07/2013
• Est. Priority Date: 09/10/2009
• Status: Active Grant

• Current Assignee: NextNav, LLC
• Original Assignee: Arun Raghupathy, Norman Krasner
• Inventors: KRASNER, Norman, RAGHUPATHY, Arun
• Granted Patent: US 9,119,165 B2
• Time in Patent Office: Days
• US Class Current: 342/464
• CPC Class Codes: G01S 19/11 wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
• CPC Class Codes: G01S 19/45 by combining measurements of signals from the satellite radio beacon positioning system with a supplementary measurement
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Embodiments describe determining position by selecting a set of digital pseudorandom sequences. The magnitudes of the cross-correlation between any two sequences of the chosen set are below a specified threshold. A subset of digital pseudorandom sequences are selected from the set such that the magnitudes of the autocorrelation function of each member of the subset, within a specified region adjacent to the peak of the autocorrelation function, are equal to or less than a prescribed value. Each transmitter transmits a positioning signal, and at least a portion of the positioning signal is modulated with at least one member of the subset. At least two transmitters of the plurality of transmitters modulate respective positioning signals with different members of the subset of digital pseudorandom sequences.

Claims

1. A method for transmitting position location signals from a plurality of transmitters, comprising:

selecting a set of digital pseudorandom sequences, wherein magnitudes of a cross-correlation function between any two sequences of the set of digital pseudorandom sequences are below a specified threshold;

selecting from the set of digital pseudorandom sequences a subset of digital pseudorandom sequences, wherein the magnitudes of an autocorrelation function of each member of the subset of digital pseudorandom sequences, within a specified region adjacent to a peak of the autocorrelation function, are at least one of equal to and less than a prescribed value; and

transmitting from each transmitter of the plurality of transmitters a positioning signal, wherein at least a first portion of each positioning signal is modulated in accordance with at least one member of the subset of digital pseudorandom sequences, wherein at least two transmitters of the plurality of transmitters modulate the first portion of respective positioning signals in accordance with different members of the subset of digital pseudorandom sequences.

2. The method of claim 1, wherein the set of digital pseudorandom sequences comprises a set of binary pseudorandom sequences.

3. The method of claim 2, wherein the set of binary pseudorandom sequences is selected from a set of Gold codes.

4. The method of claim 3, wherein the prescribed value is the peak value of the autocorrelation function divided by a non-repeating length of the digital pseudorandom sequences.

5. The method of claim 2, wherein the set of binary pseudorandom sequences is one of Kasami codes, Bent codes, and Gold-like codes.

6. The method of claim 1, wherein at least one digital pseudorandom sequence of the set of digital pseudorandom sequences has a truncated sequence length, wherein the truncated sequence length is shorter than a standard sequence length.

7. The method of claim 1, wherein at least one digital pseudorandom sequence of the set of digital pseudorandom sequences has an extended sequence length, wherein the extended sequence length is longer than a standard sequence length.

8. The method of claim 1, comprising transmitting from at least one of the plurality of transmitters a positioning signal during a first period of time for which the first portion of the positioning signal is modulated with a first member of the subset of digital pseudorandom sequences, wherein the first member of the subset of digital pseudorandom sequences has a first length, and transmitting the positioning signal during a second period of time for which a second portion of the positioning signal is modulated with a second member of the subset of digital pseudorandom sequences, wherein the second member of the subset of digital pseudorandom sequences has a second length.

9. The method of claim 8, wherein the first length and the second length are different.

10. The method of claim 8, wherein the second portion of the positioning signal is further modulated in accordance with a data sequence.

11. The method of claim 1, wherein the set of digital pseudorandom sequences has an alphabet size greater than two (2).

12. The method of claim 11, wherein the set of digital pseudorandom sequences is a set of quaternary sequences.

13. The method of claim 11, wherein the alphabet size is a power of two (2).

14. The method of claim 1, wherein the specified region adjacent to the peak of the autocorrelation function comprises at least ten (10) consecutive symbols immediately adjacent to the peak of the autocorrelation function.

15. A transmitter in a positioning system comprising a plurality of transmitters, the transmitter comprising:

a processor coupled to a memory, wherein the processor is running at least one application, wherein the at least one application,

selects a set of digital pseudorandom sequences, wherein magnitudes of a cross-correlation function between any two sequences of the set of digital pseudorandom sequences are below a specified threshold;

selects from the set of digital pseudorandom sequences a subset of digital pseudorandom sequences, wherein the magnitudes of an autocorrelation function of each member of the subset of digital pseudorandom sequences, within a specified region adjacent to a peak of the autocorrelation function, are at least one of equal to and less than a prescribed value; and

transmits a positioning signal, wherein at least a first portion of the positioning signal is modulated in accordance with at least one member of the subset of digital pseudorandom sequences, wherein the transmitter modulates positioning signals in accordance with a member of the subset of digital pseudorandom sequences different than that used by at least one other transmitter in the plurality of transmitters.

16. The transmitter of claim 15, wherein the set of digital pseudorandom sequences comprises a set of binary pseudorandom sequences.

17. The transmitter of claim 16, wherein the set of binary pseudorandom sequences is selected from a set of Gold codes.

18. The transmitter of claim 17, wherein the prescribed value is the peak value of the autocorrelation function divided by a non-repeating length of the digital pseudorandom sequences.

19. The transmitter of claim 16, wherein the set of binary pseudorandom sequences is one of Kasami codes, Bent codes, and Gold-like codes.

20. The transmitter of claim 15, wherein at least one digital pseudorandom sequence of the set of digital pseudorandom sequences has a truncated sequence length, wherein the truncated sequence length is shorter than a standard sequence length.

21. The transmitter of claim 15, wherein at least one digital pseudorandom sequence of the set of digital pseudorandom sequences has an extended sequence length, wherein the extended sequence length is longer than a standard sequence length.

22. The transmitter of claim 15, comprising transmitting the positioning signal during a first period of time for which first portion of the positioning signal is modulated in accordance with a first member of the subset of digital pseudorandom sequences, wherein the first member of the subset of digital pseudorandom sequences has a first length, and transmitting the positioning signal during a second period of time for which a second portion of the positioning signal is modulated with a second member of the subset of digital pseudorandom sequences, wherein the second member of the subset of digital pseudorandom sequences has a second length.

23. The transmitter of claim 22, wherein the first length and the second length are different.

24. The transmitter of claim 15, wherein the set of digital pseudorandom sequences have an alphabet size greater than two (2).

25. The transmitter of claim 24, wherein the set of digital pseudorandom sequences is a set of quaternary sequences.

26. The transmitter of claim 24, wherein the alphabet size is a power of two (2).

27. The transmitter of claim 15, wherein the specified region adjacent to the peak of the autocorrelation function comprises at least ten (10) consecutive symbols immediately adjacent to the peak of the autocorrelation function.

28. The transmitter of claim 15, wherein the first portion of the positioning signal is modulated in accordance with a member of the subset of digital pseudorandom sequences, and a second portion of the positioning signal includes the positioning signal further modulated in accordance with a data sequence.

29. The transmitter of claim 15, wherein the plurality of transmitters are synchronized.

30. The transmitter of claim 29, wherein the plurality of transmitters transmit assistance data.

31. The transmitter of claim 30, wherein the plurality of transmitters form a CDMA network.

32. The transmitter of claim 30, wherein the plurality of transmitters form a TDMA network.

33. The transmitter of claim 30, wherein a carrier signal of at least one transmitter is offset in frequency from the carrier signal of at least one other transmitter of the plurality of transmitters.

34. The transmitter of claim 30, wherein the assistance data comprises at least one of system time at a rising edge of a pulse of a waveform, system time at a falling edge of a pulse of a waveform, geocode data of the plurality of transmitters, geocode data of transmitters adjacent to each of the plurality of transmitters, index of a sequence used by at least one transmitter in proximity of the plurality of transmitters, clock timing corrections for at least one transmitter, local atmospheric corrections, and indication of local environment.

35. A receiver in a positioning system, comprising:

a processor coupled to a memory, wherein the processor is running at least one application that acquires positioning signals from a plurality of transmitters and computes position information of the receiver using the positioning signals, wherein at least a first portion of a first positioning signal is modulated in accordance with a member of a subset of digital pseudorandom sequences, wherein at least a first portion of a second positioning signal is modulated in accordance with a different member of the subset of digital pseudorandom sequences;

wherein selection of the subset of digital pseudorandom sequences comprises selecting a set of digital pseudorandom sequences such that magnitudes of a cross-correlation function between any two sequences of the set of digital pseudorandom sequences are below a specified threshold, and selecting the subset of digital pseudorandom sequences from the set of digital pseudorandom sequences, wherein the magnitudes of an autocorrelation function of each member of the subset of digital pseudorandom sequences, within a specified region adjacent to the peak of the autocorrelation function, are at least one of equal to and less than a prescribed value.

36. The receiver of claim 35, wherein the set of digital pseudorandom sequences comprises a set of binary pseudorandom sequences.

37. The receiver of claim 36, wherein the set of binary pseudorandom sequences is selected from a set of Gold codes.

38. The receiver of claim 37, wherein the prescribed value is the peak value of the autocorrelation function divided by a non-repeating length of the digital pseudorandom sequences.

39. The receiver of claim 36, wherein the set of binary pseudorandom sequences is one of Kasami codes, Bent codes, and Gold-like codes.

40. The receiver of claim 35, wherein at least one digital pseudorandom sequence of the set of digital pseudorandom sequences has a truncated sequence length, wherein the truncated sequence length is shorter than a standard sequence length.

41. The receiver of claim 35, wherein at least one digital pseudorandom sequence of the set of digital pseudorandom sequences has an extended sequence length, wherein the extended sequence length is longer than a standard sequence length.

42. The receiver of claim 35, wherein a second portion of the first positioning signal is modulated in accordance with a member of the subset of digital pseudorandom sequences.

43. The receiver of claim 42, wherein the member of the subset of digital pseudorandom sequences used to modulate the first portion has a first sequence length, and the member of the subset of digital pseudorandom sequences used to modulate the second portion has a second sequence length, and the first sequence length is different from the second sequence length.

44. The receiver of claim 42, wherein the member of the subset of digital pseudorandom sequences used to modulate the first portion is different from the member of the subset of digital pseudorandom sequences used to modulate the second portion.

45. The receiver of claim 35, wherein the set of digital pseudorandom sequences have an alphabet size greater than two (2).

46. The receiver of claim 45, wherein the set of digital pseudorandom sequences is a set of quaternary sequences.

47. The receiver of claim 46, wherein the alphabet size is a power of two (2).

48. The receiver of claim 35, wherein the specified region adjacent to the peak of the autocorrelation function comprises at least ten (10) consecutive symbols immediately adjacent to the peak of the autocorrelation function.

49. The receiver of claim 35, wherein a first portion of the positioning signal is modulated with a member of the subset of digital pseudorandom sequences, and a second portion of the positioning signal includes the positioning signal further modulated in accordance with a data sequence.

50. The receiver of claim 35, wherein the positioning signal includes data describing timing differences between transmissions from different transmitters of the plurality of transmitters.

51. The receiver of claim 35, wherein each of the positioning signals is initially synchronized to a time reference, and timing corrections corresponding to the synchronization are provided to the receiver.

52. The receiver of claim 35, wherein the receiver identifies multipath components of the positioning signals using high resolution earliest time of arrival estimates that include an estimated reference correlation function.

53. The receiver of claim 52, wherein the receiver identifies multipath components of the positioning signals using high resolution earliest time of arrival estimates that include a partitioning of signal and noise subspaces.

54. The receiver of claim 35, wherein the receiver identifies multipath components of the positioning signals by generating a cross-correlation function by cross-correlating received samples with a sequence transmitted from a transmitter, and extracting from the cross-correlation function a peak vector that includes a first number of samples left of a peak of the cross-correlation function and a second number of samples right of the peak.

55. The receiver of claim 54, wherein the receiver identifies multipath components of the positioning signals by generating a reference peak vector from a correlation function measured in a channel environment that has low noise and at least one of easily separable multipath and no-multipath components, and improving a signal-to-noise ratio in the peak vector by coherently averaging across at least a plurality of pseudorandom code periods.

56. The receiver of claim 55, wherein the receiver identifies multipath components of the positioning signals by calculating a Fourier Transform of the peak vector, and generating a frequency domain estimate of a channel corresponding to the transmitted sequence using the Fourier Transform of a measured peak vector and the Fourier Transform of the reference peak vector.

57. The receiver of claim 56, wherein the receiver identifies multipath components of the positioning signals by generating a reduced channel estimate vector from the frequency domain estimate of the channel, defining an estimated covariance matrix of the reduced channel estimate vector, and performing singular value decomposition on the estimated covariance matrix.

58. The receiver of claim 57, wherein the receiver identifies multipath components of the positioning signals by generating a vector of sorted singular values, and using the vector of sorted singular values to separate signal and noise subspaces, generating a noise subspace matrix, and estimating time of arrival of a first path using the noise subspace matrix.

59. The receiver of claim 35, wherein the receiver receives assistance data, wherein the assistance data comprises at least one of system time at a rising edge of a pulse of a waveform, system time at a falling edge of a pulse of a waveform, geocode data of the plurality of transmitters, geocode data of transmitters adjacent to the plurality of transmitters, index of a sequence used by at least one transmitter in proximity of the plurality of transmitters, clock timing corrections for at least one transmitter, local atmospheric corrections, relationship of WAPS timing to GNSS time, indication of local environment to aid the receiver in pseudorange resolution, and at least one of an offset from base index of a set of pseudorandom sequences, a list of pseudorandom number sequences from a set of transmitters, and a list of transmitters that utilize a particular pseudorandom number sequence.