Reduced computation communication techniques for location systems

• US 8,384,584 B2
• Filed: 12/10/2010
• Issued: 02/26/2013
• Est. Priority Date: 12/10/2010
• Status: Active Grant

• Current Assignee: Santa Mionica Semiconductor
• Original Assignee: RoundTrip, LLC
• Inventors: Karr, Lawrence J.
• Primary Examiner(s): Brainard, Timothy A
• Application Number:
  US12/964,832
• Publication Number:
  US 20120146834A1
• Time in Patent Office: 809 Days
• Field of Search: 342 42- 51
• US Class Current: 342/44
• CPC Class Codes: G01S 13/325 using transmission of coded signals, e.g. P.S.K. signals
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement
• CPC Class Codes: G01S 7/356 involving particularities of FFT processing
• CPC Class Codes: G01S 7/358 using I/Q processing

Abstract

Techniques are generally disclosed for communications between a locator device and a transponder device. The locator device may be located in a space based location such as on a surface of a remote celestial body, on a space craft or space station, on a satellite, or on a low earth orbit aircraft. The locator can encode an interrogation signal for receipt by one or more distant transponders. The transponder devices can receive the communications from the distant locator device and determine frequency, phase, cadence, and Doppler for encoding a reply transmission to the locator device. The encoding process estimates Doppler shift and adapts the reply transmission for a quantized reverse Doppler shifted frequency and cadence, which effectively pre-compensates for the Doppler shift that will be apparent to the locator due to the relative velocity. The locator can use the Doppler quantization scheme to reconstruct the actual relative velocity.

Claims

1. A method for locating a transponder (MT) with a remote locator (RL), the method comprising:

transmitting, by the RL, an interrogation signal including an interrogation sequence that is encoded with a specific identifier associated with the MT;

capturing, by the MT, samples associated with the interrogation signal with a receiver in the MT;

determining, by the MT, that the captured samples correspond to the interrogation signal encoded with the specific identifier associated with the MT, and if the interrogation signal is determined to be encoded with the specific identifier associated with the MT;

determining, by the MT, a quantized Doppler measurement associated with the interrogation signal,

adjusting, by the MT, transmission characteristics of a transmitter in the MT with the quantized Doppler measurement such that twice the quantized Doppler measurement is effectively subtracted from the carver frequency and cadence of the transmitter,

selecting, by the MT, a reply sequence for transmission,

encoding, by the MT, a Doppler compensation factor in a coded message for transmission in at least a portion of the reply sequence, and

transmitting, by the MT, the reply sequence with the coded message as a reply signal;

capturing, by the RL, samples associated with the reply signal with a receiver in the RL;

determining, by the RL, that the captured samples correspond to the reply signal from the MT; and

when the reply signal is determined to be from the MT;

extracting, by the RL, the Doppler compensation factor from the coded message associated with the reply signal,

determining, by the RL, a Doppler shift associated with the reply signal using the Doppler compensation factor extracted from the coded message, and

determining a direction from the RL to the MT based on the determined Doppler shift associated with the reply signal.

2. The method of claim 1, further comprising:

determining, by the RL, a distance between the RL and the MT based on the roundtrip time of flight between the transmission of the interrogation signal and the receipt of the reply signal.

3. The method of claim 2, further comprising:

determining a location associated with the MT based on a known location of the RL and the determined direction and distance from the RL to the MT.

4. The method of claim 1, wherein adjusting the transmission characteristics of the transmitter in the MT comprises adjusting one or more of a timing, phase, cadence, or frequency associated with the transmission by the transmitter in the MT.

5. The method of claim 1, wherein encoding the Doppler compensation factor in the coded message comprises encoding the reply signal with one or more of a transmission time modulation, a transmission phase angle modulation, transmission frequency modulation, and/or a sample rotation of the reply sequence.

6. The method of claim 1, wherein determining that the captured samples from the receiver in the MT correspond to the interrogation signal comprises identifying a correlation of the captured samples from the receiver in the MT with a reference pattern that is coded with an identifier associated with the MT.

7. The method of claim 1, wherein determining that the captured samples from the receiver in the RL correspond to the reply signal comprises identifying a correlation of the captured samples from the receiver in the RL with a reference pattern that is coded with an identifier associated with the MT.

8. The method of claim 1, wherein determining the quantized Doppler measurement associated with the interrogation signal comprises:

estimating a Doppler shift associated with the receipt of the interrogation signal using an internal oscillator associated with the MT, rounding the estimated Doppler shift to an integer value that corresponds to a fixed number of bits of resolution to generate the quantized Doppler measurement.

9. The method of claim 8, wherein the fixed number of bits is in a range of four bits to nine bits.

10. The method of claim 1, wherein adjusting the transmission characteristics of the transmitter in the MT with the quantized Doppler measurement comprises at least offsetting a carrier frequency associated with the carrier wave of the transmitter in the MT such that twice the quantized Doppler measurement is effectively subtracted from the carrier wave of the transmitter, and twice a proportional factor is effectively subtracted from the cadence associated with the transmitter.

11. A method for a transponder (MT) to communicate with a remote locator (RL), the method comprising:

capturing samples associated with an interrogation signal with a receiver in the MT;

determining that the captured samples correspond to the interrogation signal encoded with the specific identifier associated with the MT;

adjusting transmission characteristics of a transmitter in the MT for subsequent transmission from the MT to the RL; and

when the interrogation signal is determined to be encoded with the specific identifier associated with the MT;

determining a quantized Doppler measurement associated with the interrogation signal,

adjusting transmission characteristics of the transmitter in the MT with the quantized Doppler measurement such that twice the quantized Doppler measurement is effectively subtracted from the carrier frequency and cadence of the transmitter,

selecting a reply sequence for transmission,

encoding a Doppler compensation factor in a coded message for transmission in at least a portion of the reply sequence, and

transmitting the reply sequence with the coded message as a reply signal.

12. The method of claim 11, wherein adjusting the transmission characteristics of the transmitter in the MT comprises adjusting one or more of a timing, phase, cadence, or frequency associated with the transmission by the transmitter in the MT.

13. The method of claim 11, wherein encoding the Doppler compensation factor in the coded message comprises encoding the reply signal with one or more of a transmission time modulation, a transmission phase angle modulation, transmission frequency modulation, and/or a sample rotation of the reply sequence.

14. The method of claim 11, wherein determining that the captured samples from the receiver in the MT correspond to the interrogation signal comprises identifying a correlation of the captured samples from the receiver in the MT with a reference pattern that is coded with an identifier associated with the MT.

15. The method of claim 11, wherein determining the quantized Doppler measurement associated with the interrogation signal comprises:

estimating a Doppler shift associated with the receipt of the interrogation signal using an internal oscillator associated with the MT, rounding the estimated Doppler shift to an integer value that corresponds to a fixed number of bits of resolution to generate the quantized Doppler measurement.

16. The method of claim 11, wherein adjusting the transmission characteristics of the transmitter in the MT with the quantized Doppler measurement comprises at least offsetting a carrier frequency associated with the carrier wave of the transmitter in the MT such that twice the quantized Doppler measurement is effectively subtracted from the carrier wave of the transmitter, and twice a proportional factor is effectively subtracted from the cadence associated with the transmitter.

17. A method for a remote locator (RL) to locate a transponder (MT), the method for the RL comprising:

transmitting an interrogation signal with an interrogation sequence that is encoded with a specific identifier associated with the MT;

capturing samples associated with a reply signal from the MT with a receiver in the RL, wherein the reply signal is pre-compensated such that a quantized Doppler measurement is effectively subtracted from the carrier frequency and cadence of the MT prior to transmission of the reply signal;

determining that the captured samples correspond to the reply signal from the MT; and

when the reply signal is determined to be from the MT;

extracting a Doppler compensation factor from a coded message associated with the reply signal, wherein the Doppler compensation factor is associate with the quantized Doppler measurement, and

determining a Doppler shift associated with the reply signal using the Doppler compensation factor extracted from the coded message, and

determining a direction from the RL to the MT based on the determined Doppler shift associated with the reply signal.

18. The method of claim 17, further comprising:

determining a distance between the RL and the MT based on the roundtrip time of flight between the transmission of the interrogation signal and the receipt of the reply signal.

19. The method of claim 18, further comprising:

determining a location associated with the MT based on a known location of the RL and the determined direction and distance from the RL to the MT.

20. The method of claim 17, wherein extracting the Doppler compensation factor from the coded message comprises decoding one or more of decoding a transmission time modulation, decoding a transmission phase angle modulation, decoding a transmission frequency modulation, and/or decoding a sample rotation of the reply sequence.

21. The method of claim 17, wherein determining that the captured samples from the receiver in the RL correspond to the reply signal comprises identifying a correlation of the captured samples from the receiver in the RL with a reference pattern that is coded with an identifier associated with the MT.

22. A transponder (MT) adapted to communicate with a remote locator (RL), the MT comprising:

a memory configured to store a complex reference pattern associated with an interrogation signal encoded with a specific identifier of the MT;

a sequence generator configured to generate a reply transmission sequence;

a transmitter configured to selectively transmit the reply transmission sequence as a reply signal transmission using digitally synthesized transmitter timing signals when a transmit signal is asserted, wherein the transmitter block includes a high rate Doppler adjust block that is adapted such that twice a quantized Doppler measurement is effectively subtracted from a carrier frequency and cadence of the reply signal transmission;

a receiver configured to capture complex samples of a signal transmission spectrum using digitally synthesized receiver timing signals when a capture signal is asserted;

a signal processor configured to evaluate complex captured samples from the receiver block, correlate the complex captured samples with the complex reference pattern to detect the interrogation signal, and determine the quantized Doppler measurement associated with the interrogation signal when the interrogation signal is detected;

a time controller configured to digitally synthesize timing signals for the transmitter block, the receiver block, and the baseband and signal processing block based on the carrier phase, frequency, cadence and timing determined from the detected interrogation signal; and

a processor configured to;

assert a capture signal after a wake-up interval;

encode a Doppler compensation factor in a coded message for a reply signal, wherein the Doppler compensation factor is associated with the quantized Doppler shift determined for the interrogation signal; and

assert the transmit signal after the processor identities receipt of the interrogation signal to initiate transmission of the reply signal to an RL with the coded message.

23. The MT of claim 22, further comprising a sample sequence rotator that is coupled to the memory and the transmitter, and configured to encode the Doppler compensation factor in the reply signal transmission by rotating the order of transmission of samples in the complex reference pattern.

24. The MT of claim 22, further comprising an offset time modulator, wherein the offset time modulator is configured to the Doppler compensation factor in the reply signal transmission by adjusting a time offset to the transmission time of the reply signal transmission relative to an expected reply signal transmission time.

25. The MT of claim 22, further comprising an angle modulator in the transmitter block, wherein the angle modulator is configured to encode the Doppler compensation factor in the reply signal transmission by statically adjusting the rotational phase angle of the third transmission by a fixed amount relative to an expected transmission phase angle.

26. The MT of claim 22, further comprising a frequency modulator in the transmitter block, wherein the frequency modulator is configured to encode the Doppler compensation factor in the reply signal transmission by statically adjusting the carrier frequency of the reply signal transmission by a fixed amount relative to an expected reply signal transmission frequency.

27. The MT of claim 22, the baseband and signal processing block further comprising a correlator that is configured to correlate the complex reference pattern retrieved from the memory with the complex captured samples retrieved from the receiver.

28. The MT of claim 27, wherein the correlator includes a cyclic correlator and a frequency shifter, wherein the frequency shifter is configured to frequency shift one of the complex captured samples and the complex reference pattern prior to a trial correlation with the cyclic correlator.

29. The MT of claim 27, wherein the correlator includes a cyclic correlator and a frequency shift selector, wherein the cyclic correlator is configured in cooperation with the frequency shift selector such that previously frequency shifted versions of one of the complex captured samples and the complex reference pattern is retrieved from the memory block by the frequency shift selector prior to a trial correlation with the cyclic correlator.

30. The MT of claim 22, wherein the transmitter comprises a high rate Doppler adjust system that is configured to adjust a carrier frequency and cadence associated with the reply signal transmission.

31. A remote locator (RL) adapted to communicate with a transponder (MT), the RL comprising:

a memory configured to store a complex reference pattern that is associated with a reply signal for an MT;

a sequence generator configured to generate a transmission sequence that is encoded with a specific identifier associated with the MT;

a transmitter configured to selectively transmit the transmission sequence as an interrogation signal transmission using digitally synthesized transmitter timing signals when a transmit signal is asserted;

a receiver configured to selectively capture samples of a signal transmission spectrum using digitally synthesized receiver timing signals when the capture signal is asserted;

a signal processor configured to evaluate complex captured samples from the receiver block, correlate the complex captured samples with the complex reference pattern to identify a reply transmission from the MT, and when the reply transmission is identified, extract a Doppler compensation factor from a coded message in the reply transmission, and determine a Doppler shift associated with the receipt of the reply signal transmission using the Doppler compensation factor; and

a time controller configured to digitally synthesize timing signals for the transmitter, the receiver, and the signal processor; and

a processor configured to;

assert the transmit signal to initiate the interrogation signal transmission;

assert a capture signal after the interrogation signal transmission is complete; and

determining a direction from the RL to the MT based on the determined Doppler shift associated with the reply signal.

32. The RL of claim 31, wherein the processor is further configured to determine a distance between the RL and the MT based on the roundtrip time of flight between the transmission of the interrogation signal and the receipt of the reply signal.

33. The RL of claim 32, wherein the processor is further configured to determine a location associated with the MT based on a known location of the RL and the determined direction and distance from the RL to the MT.

34. The RL of claim 31, wherein the signal processor is further configured to extract the Doppler compensation factor from the coded message by one or more of:

decoding a transmission time modulation, decoding a transmission phase angle modulation, decoding a transmission frequency modulation, and/or decoding a sample rotation of the reply sequence.

35. The RL of claim 31, wherein the signal processor further comprises a correlator configured to correlate the complex captured samples with the complex reference pattern to identify a reply transmission from the MT.

36. The RL of claim 35, wherein the correlator includes a cyclic correlator and a frequency shifter, wherein the frequency shifter is configured to frequency shift one of the complex captured samples and the complex reference pattern prior to a trial correlation with the cyclic correlator.

37. The RL of claim 35, wherein the correlator includes a cyclic correlator and a frequency shift selector, wherein the cyclic correlator is configured in cooperation with the frequency shift selector such that previously frequency shifted versions of one of the complex captured samples and the complex reference pattern is retrieved from the memory block by the frequency shift selector prior to a trial correlation with the cyclic correlator.

38. A method for locating a transponder (MT) with a remote locator (RL), the method comprising:

transmitting, by the RL, an interrogation signal including an interrogation sequence that is encoded with a specific identifier associated with the MT;

capturing, by the MT, samples associated with the interrogation signal with a receiver in the MT;

determining, by the MT, that the captured samples correspond to the interrogation signal encoded with the specific identifier associated with the MT, and if the interrogation signal is determined to be encoded with the specific identifier associated with the MT;

determining, by the MT, a quantized Doppler measurement associated with the interrogation signal,

adjusting, by the MT, transmission characteristics of a transmitter in the MT with the quantized Doppler measurement such that twice the quantized Doppler measurement is effectively subtracted from the carrier frequency and cadence of the transmitter,

selecting, by the MT, a reply sequence for transmission, and

transmitting the reply sequence as a coded message in a reply signal;

capturing, by the RL, samples associated with the reply signal with a receiver in the RL;

determining, by the RL, that the captured samples correspond to the reply signal from the MT; and

when the reply signal is determined to be from the MT;

extracting the reply sequence as a coded message.

39. A method of communicating between locator and transponder devices that are far apart or moving at a high relative velocity, comprising the steps of:

receiving a signal at the transponder from the locator;

estimating the Doppler shift of the signal at the transponder; and

transmitting a return signal to the locator from the transponder with a reverse Doppler shifted transmission characteristic that pre-compensates for the Doppler shift.

40. The method of claim 39, wherein twice the estimated Doppler shift is subtracted from the carrier frequency and cadence of the return signal.