Position location signaling method apparatus and system utilizing orthogonal frequency division multiplexing

• US 20060050625A1
• Filed: 09/07/2004
• Published: 03/09/2006
• Est. Priority Date: 09/07/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Krasner, Norman F.
• Granted Patent: US 7,826,343 B2
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: G01S 1/04 Details
• CPC Class Codes: G01S 1/042 Transmitters
• CPC Class Codes: G01S 1/045 Receivers
• CPC Class Codes: G01S 1/20 using a comparison of transit time of synchronised signals transmitted from non-directional antennas or antenna systems spaced apart, i.e. path-difference systems
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

Position location signaling system, apparatus, and method are disclosed. Position location beacons can each be configured to transmit a frequency interlaced subset of orthogonal frequencies spanning substantially an entire channel bandwidth. The orthogonal frequencies can be pseudorandomly or uniformly spaced, and each beacon can be allocated an equal number of orthogonal frequencies. Each frequency of the interlaced subset of orthogonal frequencies can be modulated with an element of a predetermined data sequence. A mobile device can receive one or more of the beacon signals and determine a position using a position location algorithm that determines position in part on an arrival time of the beacon signal. Where the mobile device can receive three or more beacon signals, the mobile device can perform position location by trilateration to the beacon positions based, for example, on a time difference of arrival.

Claims

1. A method of transmitting position location signals, the method comprising:

defining a plurality (Q) of orthogonal frequencies, wherein each of the Q orthogonal frequencies are separated from one another by a multiple of a fixed frequency spacing (w);

selecting a first subset of orthogonal frequencies from the plurality of orthogonal frequencies;

generating a first Orthogonal Frequency Division Multiplex (OFDM) symbol based on the first subset of orthogonal frequencies and substantially orthogonal to a second OFDM symbol generated from a second subset of orthogonal frequencies from the plurality of orthogonal frequencies; and

transmitting a position location signal containing said first OFDM symbol from a first geographical location distinct from a second geographical location from which the second OFDM symbol is transmitted.

2. The method of claim 1, wherein defining the plurality of orthogonal frequencies comprises defining a plurality of uniformly spaced orthogonal frequencies.

3. The method of claim 1, wherein defining the plurality of orthogonal frequencies comprises defining the plurality of orthogonal frequencies spanning substantially an entire channel bandwidth.

4. The method of claim 1, wherein defining the plurality of orthogonal frequencies comprises defining the plurality of orthogonal frequencies spanning substantially 5.5 MHz.

5. The method of claim 1, wherein selecting the first subset of orthogonal frequencies comprises selecting a subset of uniformly spaced orthogonal frequencies from the plurality of orthogonal frequencies.

6. The method of claim 1, wherein selecting the first subset of orthogonal frequencies comprises selecting a subset of randomly spaced orthogonal frequencies from the plurality of orthogonal frequencies.

7. The method of claim 1, wherein selecting the first subset of orthogonal frequencies comprises selecting a subset of pseudorandomly spaced orthogonal frequencies from the plurality of orthogonal frequencies.

8. The method of claim 1, wherein selecting the first subset of orthogonal frequencies comprises:

defining a number (M) of distinct position location signals; and

selecting Q/M of orthogonal frequencies from the plurality of orthogonal frequencies.

9. The method of claim 1, further comprising modulating each frequency in the first subset of orthogonal frequencies.

10. The method of claim 1, further comprising:

generating a binary data sequence; and

modulating each frequency in the first subset of orthogonal frequencies based in part on the binary sequence.

11. The method of claim 10, wherein generating the binary sequence comprises generating a pseudorandom binary sequence.

12. The method of claim 10, wherein generating the binary sequence comprises generating a pseudo random binary sequence of a type selected from a group comprising a maximal length binary sequence, a Barker code, a Gold code, and a Walsh code.

13. The method of claim 10, wherein modulating each frequency in the subset of orthogonal frequencies comprises phase modulating each frequency in the subset of orthogonal frequencies.

14. The method of claim 1, further comprising:

generating a nonbinary signal; and

modulating each frequency in the first subset of orthogonal frequencies based in part on the nonbinary signal.

15. The method of claim 14, wherein modulating each frequency comprises modulating one of a phase, amplitude, or combination of phase and amplitude.

16. The method of claim 14, wherein the nonbinary signal comprises a constant signal over a period at least 1/w.

17. The method of claim 1 wherein transmitting the signal containing said first OFDM symbol comprises transmitting a first signal time synchronized to a first external event.

18. The method of claim 17, wherein transmitting the signal containing said second OFDM symbol comprises transmitting a second signal time synchronized to a second external event.

19. The method of claim 1, wherein generating the first OFDM symbol comprises transforming the first subset of orthogonal frequencies to a time domain signal using an Inverse Fourier Transform.

20. The method of claim 1, wherein generating the first OFDM symbol comprises transforming the first subset of orthogonal frequencies to a time domain signal using a Q-point Inverse FFT.

21. The method of claim 1, wherein transmitting the signal containing the first OFDM symbol comprises wirelessly transmitting an electromagnetic signal containing said first OFDM symbol.

22. The method of claim 1, wherein transmitting the signal containing the first OFDM symbol comprises periodically transmitting the OFDM symbol.

23. The method of claim 1, wherein transmitting the signal containing the first OFDM symbol comprises periodically transmitting the signal containing the first OFDM symbol using a television broadcast transmitter.

24. The method of claim 1, wherein a duration of said first OFDM symbol is substantially equal to 1/w.

25. The method of claim 1, wherein a duration of said first OFDM symbol is extended to be greater than 1/w.

26. A method of transmitting position location signals, the method comprising:

defining a plurality (Q) of orthogonal frequencies;

defining a number (M) of distinct position location signals;

generating M disjoint subsets of orthogonal frequencies from the plurality of orthogonal frequencies;

generating at least two Orthogonal Frequency Division Multiplex (OFDM) symbols corresponding to at least two of the M subsets; and

transmitting one of the at least two OFDM symbols periodically from a first geographical location over a wireless communication channel, the first geographical location distinct from a second geographical location from which the second of the at least two OFDM symbols is transmitted.

27. The method of claim 26, wherein generating M disjoint subsets of orthogonal frequencies comprises generating M subsets having Q/M mutually exclusive orthogonal frequencies from the plurality of orthogonal frequencies.

28. The method of claim 26, further comprising Phase Shift Key modulating at least one of the M disjoint subsets of orthogonal frequencies using a pseudorandom binary sequence.

29. A method of transmitting position location signals, the method comprising:

generating a first frequency interlaced Orthogonal Frequency Division Multiplex (OFDM) signal from a first subset of orthogonal frequencies;

synchronizing the first frequency interlaced OFDM signal to a time reference;

generating a second frequency interlaced OFDM signal from a subset of orthogonal frequencies disjoint from said first subset;

synchronizing the second frequency interlaced OFDM signal to the time reference; and

wirelessly transmitting the first and the second frequency interlaced OFDM signals from two different geographical locations.

30. A position location signal generating apparatus, the apparatus comprising:

means for generating at least two out of a total of M subsets of orthogonal frequencies from a plurality of Q orthogonal frequencies;

means for generating at least two Orthogonal Frequency Division Multiplex (OFDM) symbols, each of said symbols constructed from a different subset from the M subsets;

means for transmitting one of said OFDM symbols periodically over a first wireless communications link; and

means for transmitting a second of said OFDM symbols periodically over a second wireless communications link.

31. A position location signal generating apparatus, the apparatus comprising:

means for generating at least two frequency interlaced Orthogonal Frequency Division Multiplex (OFDM) signals from a subset of orthogonal frequencies;

means for synchronizing each of said frequency interlaced OFDM signals to a time reference; and

means for concurrently transmitting each of said frequency interlaced OFDM signals from each of two different geographical locations.

32. A position location signal generating apparatus, the apparatus comprising:

an orthogonal signal generator configured to generate at least a subset of orthogonal carriers out of a larger set of Q orthogonal frequency carriers;

a modulation data module configured to generate a pseudorandom data sequence;

a modulator coupled to the modulation data module and configured to modulate the subset of orthogonal carriers based in part on a pseudorandom data sequence;

an Orthogonal Frequency Division Multiplex (OFDM) modulator having an input coupled to the orthogonal signal generator, and configured to generate a first OFDM symbol based in part on the subset of orthogonal carriers; and

a transmitter coupled to the OFDM modulator and configured to wirelessly transmit the first OFDM symbol from a first geographical location distinct from a second geographical location from which a second OFDM symbol, orthogonal to the first OFDM symbol, is transmitted.

33. The apparatus of claim 32, wherein the pseudorandom data sequence comprises a code selected from the group comprising a Gold code, a Barker code, a maximal length code, and a Walsh code.

34. The apparatus of claim 32, wherein the pseudorandom data sequence comprises a sequence of a length equal to a number of carriers in the subset of orthogonal frequencies.

35. The apparatus of claim 32, wherein the modulator is configured to perform modulation on each of the carriers of the subset of orthogonal carriers based in part on the pseudorandom data sequence, wherein said modulation is by one of phase modulation, amplitude modulation, or combined phase and amplitude modulation.

36. The apparatus of claim 32, wherein the modulator is configured to Binary Phase Shift Key (BPSK) modulate each of the carriers of the subset of orthogonal carriers based on a value of a corresponding bit in the binary sequence.

37. The apparatus of claim 32, wherein the OFDM modulator comprises:

an Inverse Fast Fourier Transform (IFFT) module configured to perform an IFFT of the subset of orthogonal carriers of size at least Q; and

a parallel to serial converter coupled to the output of the IFFT module and configured to generate a serial output from an output of the IFFT module.

38. The apparatus of claim 32, wherein the orthogonal signal generator is configured to generate one of M subsets of orthogonal carriers by generating Q/M orthogonal carriers.

39. The apparatus of claim 38, wherein the Q/M orthogonal carriers comprise uniformly spaced orthogonal carriers.

40. The apparatus of claim 38, wherein the Q/M orthogonal carriers comprise pseudo randomly spaced orthogonal carriers.

41. A method of position location, the method comprising:

receiving an Orthogonal Frequency Division Multiplex (OFDM) signal;

performing a cross-correlation operation of said received OFDM signal against a reference signal;

determining a presence of a received OFDM symbol from said cross-correlation operation; and

determining a location based at least in part on the OFDM symbol.

42. The method of claim 41, further comprising determining a Doppler shift of the OFDM symbol.

43. The method of claim 42, wherein determining the Doppler shift comprises:

hypothesizing multiple Doppler shifts;

determining a corresponding strength of said received OFDM symbol in response to each of said hypothesized Doppler shifts; and

performing an interpolation operation upon said corresponding strengths.

44. The method of claim 41, further comprising:

rejecting spurious cross correlation products within the received OFDM signal by hypothesizing multiple Doppler shifts;

determining corresponding strengths of said cross-correlation in response to said hypothesized Doppler shifts; and

examining a variation in said strengths.

45. The method of claim 44, wherein rejecting cross correlation products comprises rejecting the OFDM symbol if the variation in said strengths differs by more than a predetermined threshold.

46. The method of claim 41, wherein receiving the OFDM signal comprises receiving a frequency interlaced OFDM symbol generated from a subset of orthogonal frequencies spanning substantially a channel bandwidth of a broadcast band.

47. The method of claim 41, wherein receiving the OFDM signal comprises receiving at least one of M frequency interlaced OFDM symbols, each of the M frequency interlaced OFDM symbols comprising a subset of Q/M frequencies from a set of Q orthogonal frequencies.

48. The method of claim 41, wherein receiving the OFDM signal comprises receiving a frequency interlaced OFDM symbol from a television broadcast transmitter.

49. The method of claim 41, wherein determining the location comprises:

determining a pseudorange based on said cross-correlation operation; and

determining the location based in part on the pseudorange.

50. The method of claim 49, wherein determining the location further comprises transmitting the pseudorange to an entity distinct from a system transmitting the OFDM signal.

51. The method of claim 41, wherein performing the cross-correlation comprises performing one of a matched filter operation or an FFT operation.

52. A mobile device configured for position location, the device comprising:

means for receiving an Orthogonal Frequency Division Multiplex (OFDM) signal;

means for cross-correlating at least a portion of the OFDM signal to one of a predetermined number of OFDM symbols; and

means for determining a location based at least in part on a result of said cross correlation operation.

53. A mobile device configured for position location, the device comprising:

a receiver configured to receive an Orthogonal Frequency Division Multiplex (OFDM) signal;

a correlator configured to correlate the received OFDM signal against a plurality of frequency interlaced OFDM symbols; and

a position location module configured to determine a location based in part on an output of the correlator if at least one frequency interlaced OFDM symbol correlates with the received OFDM signal by greater than a predetermined correlation threshold.

54. The device of claim 53, wherein the correlator comprises:

a matched filter module configured to provide matched filter response for each OFDM symbol; and

a peak detection module coupled to an output of the matched filter module.

55. The device of claim 53, wherein the correlator comprises:

a Fast Fourier Transform (FFT) module configured to transform the received OFDM signal to frequency domain signal;

a modulator configured to modulate the frequency domain signal;

an IFFT module configured to transform an output of the modulator to a time domain signal; and

a peak detection module coupled to the output of the IFFT producing an indication of said level of correlation.