GLOBAL NAVIGATION RECEIVER

• US 20100238976A1
• Filed: 12/05/2008
• Published: 09/23/2010
• Est. Priority Date: 12/05/2007
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Young, Philip John
• Granted Patent: US 8,705,591 B2
• Time in Patent Office: Days
• US Class Current: 375/131
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain

Abstract

A signal processing system and method for a GNSS digital signal wherein a carrier-stripped GNSS signal, is sampled according to a variable rate, determined by the code NCO, and including a timing circuit arranged to generate a timestamp code determining the sampling time of at least one of the samples in the buffer memory. By taking code samples in this way it is possible to transfer the samples asynchronously to a separate processor for the search task to be performed, for example an asynchronous parallel correlator implemented in the same silicon in hardware, or a media processor such as a graphics accelerator implemented in the same device or a separate physical device.

Claims

1. A signal processing system for a GNSS digital signal comprising spread-spectrum radiolocalization signals received from radiolocalization satellites, each satellite transmitting a radiolocalization signal modulated by a known modulation code, having a Doppler shift and a code phase shift, the signal processing system comprising:

at least one sampling stage, reading a carrier-stripped GNSS signal, the at least one sampling stage comprising;

a programmable oscillator which is programmed to generate a reference timing signal in accord with one predetermined feature of the modulation code of a satellite whose acquisition is intended;

an accumulator driven by the programmable oscillator to generate a number of samples of programmable duration, determined by the reference timing signal; and

one sample buffer and buffer memory, arranged to store a succession of samples produced by the sampling stage; and

a timing circuit arranged to generate a timestamp code determining a sampling time of at least some of the samples in the buffer memory.

2. The system of claim 1, wherein the timing circuit is responsive to the programmable oscillator, and/or the programmable oscillator is operatively arranged to oscillate in accord with the chip rate or with some multiple of the chip rate of the modulation code.

3. The system of claim 2, wherein the timing circuit is operatively arranged to oscillate in accord with the chip rate or with some multiple of the chip rate of the modulation code compensated for Doppler shift and clock drift.

4. The system of claim 3, wherein timing circuit is arranged to create timestamp values in response to a reference event where the timestamp value is a measure of the code phase.

5. The system of claim 1, further comprising at least one carrier wipeoff unit, to remove a carrier component from said GNSS signal and provide a carrier-stripped GNSS signal.

6. The system of claim 1, further comprising at least one correlator, arranged to correlate the samples in the buffer memory with local replicas of the modulation codes to generate a plurality of correlation values.

7. The system of claim 6, wherein at least one of said correlators comprises a separate processor operating asynchronously from the sampling stage, arranged to locate the time position of the samples in the buffer memory based on the time information provided by the timing circuit.

8. The system of claim 7, wherein the separate processor is a vector processor or a graphic accelerator or a media processing engine or a sound processor or a physics processor.

9. The system of claim 7, further including a serial bus arranged to transfer the samples and/or the time information to the separate processor.

10. The system of claim 1, wherein the timing circuit comprises a counter arranged to count the reference signal of the programmable oscillator.

11. A processing method for a GNSS radiolocalization signal comprising:

generating or receiving a carrier-stripped GNSS signal comprising spread-spectrum radiolocalization signals, received from radiolocalization satellites, each satellite transmitting a radiolocalization signal modulated by a known code, having a Doppler shift and a code phase shift;

piloting a programmable oscillator to generate a reference timing signal in accord with one predetermined feature of the modulation code of a satellite whose acquisition is intended;

accumulating and sampling the carrier-stripped GNSS signal at sampling times determined by the reference timing signal and storing the samples so obtained in one memory;

generating one or several timestamp codes determining the sampling time of at least one of the samples in the buffer memory;

extrapolating the sampling times of the samples in the buffer memory based on the timestamp codes; and

correlating the samples in the buffer memory with local replicas of the modulation code to generate a plurality of correlation values.

12. The processing method of claim 11, wherein the programmable oscillator is piloted to generate a reference timing signal in accord with the Doppler-shifted modulation code.

13. The processing method of claim 11, further comprising:

transferring the samples across a serial bus to a separate processor operating asynchronously from the sampling stage, arranged to carry out said locating step and said correlating.

14. The processing method of claim 12, further comprising:

padding the samples to ensure a coherent correlation in the event of missed data samples.

15. The processing method of claim 11, wherein the timestamp codes are generated by sampling a counter counting the reference signal of the programmable oscillator.

16. The processing method of claim 11, wherein the timestamp codes are generated on the occurrences of an external event.

17. The processing method of claim 12 wherein the timestamp value is used to control the alignment of the samples in memory to improve the efficiency of the correlation process.

18. An apparatus for use in processing GNSS signals, the apparatus comprising:

a programmable oscillator to generate a reference timing signal in accord with one predetermined feature of a modulation code of a GNSS signal;

an accumulator responsive to said programmable oscillator, for generating a plurality of samples of a carrier-stripped GNSS signal based on a programmable duration determined by said reference timing signal;

a timing circuit to generate a timestamp code associating a sampling time of at least one of said plurality of samples;

memory arranged to store a succession of said plurality of samples and said timestamp code, and wherein at least one of said plurality of samples stored in said memory is not stored with a corresponding timestamp code; and

a processor to reconstruct a phase relationship for at least said plurality of samples stored in said memory based, at least in part, on at least one said timestamp code stored in said memory.

19. The apparatus as recited in claim 18, wherein at least a portion of said plurality of samples stored in said memory are obtained by said processor as non-contiguous data samples, and wherein said processor to further generate padding applicable to said non-contiguous data samples based, at least in part on said at least one said timestamp code stored in said memory.

20. The apparatus as recited in claim 18, further comprising:

one or more correlators to correlate said plurality of samples stored in said memory with local replicas of said modulation codes to generate a plurality of correlation values.

21. The apparatus as recited in claim 18, wherein:

said timing circuit is responsive to said programmable oscillator; and

said programmable oscillator to oscillate in accord with a chip rate of said modulation code or a multiple of said chip rate of said modulation code.

22. The apparatus as recited in claim 18, wherein:

said timing circuit to oscillate in accord with a chip rate of said modulation code compensated for a Doppler shift and/or a clock drift, or a multiple of said chip rate of said modulation code compensated for said Doppler shift and/or said clock drift.

23. The apparatus as recited in claim 18, wherein said timing circuit to generate said timestamp code in response to a reference event.

24. The apparatus as recited in claim 18, wherein said timestamp code comprises a measure of code phase.

25. The apparatus as recited in claim 18, further comprising:

at least one carrier wipeoff unit to remove a carrier component from said GNSS signal to obtain said carrier-stripped GNSS signal.

26. The apparatus as recited in claim 18, said timing circuit comprising a counter to count a reference signal of said programmable oscillator.

27. An apparatus for use in processing GNSS signals, the apparatus comprising:

means for generating a reference timing signal in accord with one predetermined feature of a modulation code of a GNSS signal;

means for generating a plurality of samples of a carrier-stripped GNSS signal based on a programmable duration determined by said reference timing signal;

means for generating a timestamp code associating a sampling time of at least one of said plurality of samples;

means for storing a succession of said plurality of samples and said timestamp code, and wherein at least one of said plurality of samples is not stored with a corresponding timestamp code; and

means for reconstructing a phase relationship for at least said plurality of samples based, at least in part, on at least one said timestamp code.

28. The apparatus as recited in claim 27, wherein at least a portion of said plurality of samples are obtained by said means for reconstructing said phase relationship as non-contiguous data samples, and wherein said means for reconstructing said phase relationship further comprises:

means for generating padding applicable to said non-contiguous data samples based, at least in part on said at least one said timestamp code.

29. The apparatus as recited in claim 27, further comprising:

means for correlating said plurality of samples with local replicas of said modulation codes to generate a plurality of correlation values.

30. The apparatus as recited in claim 27, wherein said means for generating said timestamp code is responsive to a reference event.

31. The apparatus as recited in claim 27, wherein said timestamp code comprises a measure of code phase.

32. The apparatus as recited in claim 27, further comprising:

means for removing a carrier component from said GNSS signal to obtain said carrier-stripped GNSS signal.

33. A method for use in processing GNSS signals, the method comprising:

generating a reference timing signal in accord with one predetermined feature of a modulation code of a GNSS signal;

generating a plurality of samples of a carrier-stripped GNSS signal based on a programmable duration determined by said reference timing signal;

generating a timestamp code associating a sampling time of at least one of said plurality of samples;

storing a succession of said plurality of samples and said timestamp code, and wherein at least one of said plurality of samples is not stored with a corresponding timestamp code; and

reconstructing a phase relationship for at least said plurality of samples based, at least in part, on at least one said timestamp code.

34. The method as recited in claim 33, further comprising:

accessing at least a portion of said stored plurality of samples as non-contiguous data samples; and

generating padding applicable to said non-contiguous data samples based, at least in part on said at least one said timestamp code.

35. The method as recited in claim 33, further comprising:

correlating said plurality of samples with local replicas of said modulation codes to generate a plurality of correlation values.

36. The method as recited in claim 33, wherein generating said timestamp code is responsive to a reference event.

37. The method as recited in claim 33, wherein said timestamp code comprises a measure of code phase.

38. The method as recited in claim 33, further comprising:

removing a carrier component from said GNSS signal to obtain said carrier-stripped GNSS signal.

39. An article comprising:

a data storage device having stored therein instructions executable by at least one processor in a GNSS receiver to;

obtaining from a memory;

a plurality of samples of a carrier-stripped GNSS signal based on a programmable duration determined by a reference timing signal in accord with one predetermined feature of a modulation code of a GNSS signal, and

a timestamp code associating a sampling time of at least one of said plurality of samples, and wherein at least one of said plurality of samples is not associated with a corresponding timestamp code; and

reconstructing a phase relationship for at least said plurality of samples based, at least in part, on at least one said timestamp code.

40. The article as recited in claim 39, said instructions being further executable by said at least one processor to

obtain at least a portion of said stored plurality of samples as non-contiguous data samples;

and

generate padding applicable to said non-contiguous data samples based, at least in part on said at least one said timestamp code.

41. The article as recited in claim 39, wherein said timestamp code is associated with a reference event.

42. The article as recited in claim 39, wherein said timestamp code comprises a measure of code phase.