Spread spectrum receiver architectures and methods therefor

• US 20030081660A1
• Filed: 08/16/2001
• Published: 05/01/2003
• Est. Priority Date: 08/16/2001
• Status: Active Grant

• Current Assignee: CSR plc (Qualcomm, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Harbour, Robert B., Riemer, Denise C., Hoover, Andrew P., King, Thomas Michael
• Granted Patent: US 6,775,319 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• 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
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/70753 Partial phase search
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

Methods and architectures for code phase searching spread spectrum signals having a repeating sequence of bits. The signals are searched virtually in parallel by segmenting with a divider (314) received signals by sequentially, partially correlating signal segments with a corresponding replica signal segments for a predetermined number of phase delays during a time interval not greater than that required to form the next signal segment. Multiplexors (322) and (330) provide Doppler and replica signal segments data from Doppler signal and replica signal generators (318) and (320) to corresponding multipliers (326) and (332), respectively, for multiplication with corresponding signal segments in a segment register (316). The partial correlation results for each phase delay and at each Doppler frequency are stored in corresponding memory locations in a coherent accumulation RAM (334). The signals may be searched over one or more phase delays and at one or more Doppler frequencies.

Claims

1. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a first spread spectrum signal;

forming a first signal segment by segmenting a first portion of the first spread spectrum signal;

forming a second signal segment by segmenting a second portion of the first spread spectrum signal after forming the first signal segment;

partially correlating the first signal segment with a corresponding first replica signal segment for all phase delays in a time interval not greater than that required to form the second signal segment;

storing first partial correlation results for all phase delays of the first signal segment in corresponding memory locations.

2. The method of claim 1,

forming a third signal segment by segmenting a third portion of the first spread spectrum signal;

partially correlating the second signal segment with a corresponding second replica signal segment for all phase delays while forming the third signal segment;

storing second partial correlation results for all phase delays of the second signal segment in corresponding memory locations.

3. The method of claim 2, forming summed partial correlation results for all phase delays by adding the first and second partial correlation results, storing the summed partial correlation results for all phase delays in corresponding memory locations.

4. The method of claim 1, separating a last signal sample of the first signal segment from a first signal sample of the second signal segment by a single sample.

5. The method of claim 1, partially correlating the first signal segment with the corresponding first replica signal segment for all phase delays in one chip or half-chip increments based on a processor controlled input..

6. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a first spread spectrum signal;

forming a plurality of signal segments having unequal numbers of samples by segmenting the first spread spectrum signal;

storing each signal segment;

partially correlating each signal segment with a corresponding first replica signal segment for a predetermined number of phase delays in a correlator.

7. The method of claim 6, communicating a segment length signal to the correlator for at least some of the signal segments partially correlated.

8. The method of claim 6, storing partial correlation results for each of the predetermined phase delays of each signal segment in corresponding memory locations.

9. The method of claim 6, forming summed correlation results for each of the predetermined phase delays by adding partial correlation results for each of the signal segments, storing the summed correlation results for each of the predetermined phase delays in corresponding memory locations.

10. The method of claim 6, storing each signal segment in a first register, partially correlating one signal segment while forming a subsequent signal segment, storing the subsequent signal segment in the first register after correlating the previous signal segment.

11. The method of claim 6, separating a last signal sample of one signal segment from a first signal sample of a subsequent signal segment by a single sample.

12. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a plurality of spread spectrum signals;

forming a plurality of signal segments having unequal numbers of samples by segmenting the plurality of spread spectrum signals;

storing each signal segment;

partially correlating each signal segment with corresponding segments of a plurality of replica signals for a predetermined number of phase delays,

each of the plurality of replica signals corresponding to one of the plurality of spread spectrum signals.

13. The method of claim 12, partially correlating each signal segment with corresponding segments of a plurality of replica signals for a predetermined number of phase delays virtually in parallel by sequentially correlating at a rate greater than a rate at which the plurality of spread spectrum signals are received.

14. The method of claim 12, partially correlating each signal segment with corresponding segments of the plurality of replica signals for the predetermined number of phase delays in one chip or half-chip increments based on a processor controlled input.

15. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a plurality of spread spectrum signals;

forming a plurality of signal segments by segmenting the plurality of spread spectrum signals;

storing each signal segment;

partially correlating each signal segment with corresponding segments of a plurality of replica signals for all phase delays over the repeating sequence of bits,

each of the plurality of replica signals corresponding to one of the plurality of spread spectrum signals.

16. The method of claim 15, forming summed partial correlation results for all phase delays of the plurality of spread spectrum signals by adding the partial correlation results for each of the plurality of signal segments correlated with corresponding segments of a particular replica signal, the partial correlation results for each segment added to the partial correlation results for a previous signal segment upon completion of partially correlating each signal segment.

17. The method of claim 15, separating a last signal sample of one signal segment from a first signal sample of a subsequent signal segment by a single sample.

18. A method for code phase searching a plurality of spread spectrum signals, having repeating sequences of bits, from corresponding signal sources, comprising:

identifying attributes for a plurality of spread spectrum signals received;

determining a code phase search range for each of the spread spectrum signals based upon attributes identified for the corresponding spread spectrum signals;

forming a plurality of signal segments by segmenting the plurality of spread spectrum signals;

partially correlating each signal segment with corresponding segments of a plurality of replica signals for the code phase search range determined,

each of the plurality of replica signals corresponding to one of the plurality of spread spectrum signals.

19. The method of claim 18,

forming summed partial correlation results for the determined code phase search range by adding the partial correlation results for each of the plurality of signal segments correlated with a particular replica signal, the partial correlation results for each segment added to the partial correlation results for a previous signal segment upon completion of partially correlating each signal segment.

20. The method of claim 18, determining a different code phase search range for at least some of the spread spectrum signals based upon attributes identified for the corresponding spread spectrum signals.

21. The method of claim 18, partially correlating each signal segment with corresponding segments of the plurality of replica signals for the code phase search range determined in one chip or half-chip increments based on a processor controlled input.

22. A method for code phase searching a plurality of spread spectrum signals having repeating sequences of bits from corresponding signal sources, comprising:

determining a Doppler search range having at least one Doppler Bin with a corresponding Doppler frequency for each of a plurality of spread spectrum signals received;

segmenting each Doppler bin into a plurality of Doppler segments;

forming a plurality of signal segments by segmenting the plurality of spread spectrum signals;

sequentially forming a plurality of product signal segments for each of the plurality of signal segments by multiplying each signal segment by corresponding Doppler segments for each of the plurality of Doppler bins for each of the spread spectrum signals;

partially correlating each of the product signal segments with corresponding segments of a plurality of replica signals for a predetermined number of phase delays, each of the plurality of replica signals corresponding to one of the plurality of spread spectrum signals.

23. The method of claim 22, sequential partially correlating each of the product signal segments by partially correlating one product signal segment before partially correlating a subsequently formed product signal segment.

24. A method for code phase searching a plurality of spread spectrum signals having repeating sequences of bits from corresponding signal sources, comprising:

forming a plurality of signal segments by segmenting a spread spectrum signals received;

forming a plurality of first Doppler signal segments;

forming a first product signal segment by multiplying a first signal segment by a first Doppler signal segment;

partially correlating the first product signal segment with a corresponding segment of a replica signal for a predetermined number of phase delays;

forming a second product signal segment by multiplying the first signal segment by a second Doppler signal segment;

partially correlating the second product signal segment with a corresponding segment of a replica signal for a predetermined number of phase delays after partially correlating the first product signal segment.

25. The method of claim 24, the spread spectrum signal having a repeating sequence of pseudorandom code bits modulated with data message bits having a data bit time that is an integer number of a repeat time of the pseudorandom code bits,

multiplying a result of partially correlating the first product signal segment with a replica data modulation signal segment corresponding in time to the partially correlated first product signal segment;

after multiplying, accumulating partial correlation results for a time period exceeding the data bit time.

26. The method of claim 25, preventing the partial correlation of unknown data message bits by partially correlating the unknown data message bits with corresponding zero magnitude portions of the replica data modulation signal.

27. The method of claim 24, separating a last signal sample of the first Doppler signal segment from a first signal sample of the second Doppler signal segment by a single sample.

28. A method for searching spread spectrum signals having a repeating sequence of bits, comprising:

receiving a plurality of spread spectrum signals;

determining a Doppler search range comprising at least one Doppler Search bin for at least one of the plurality of spread spectrum signals;

correlating virtually in parallel at least one of the plurality of spread spectrum signals over the corresponding Doppler search range for a predetermined number of phase delays by sequentially correlating at a rate greater than a rate at which the spread spectrum signal is received.

29. A method for searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a plurality of spread spectrum signals;

correlating virtually in parallel the plurality of spread spectrum signals over a predetermined number of phase delays by sequentially correlating the plurality of spread spectrum signals with corresponding replica signals at a rate greater than a rate at which the spread spectrum signals are received.

30. The method of claim 29, correlating virtually in parallel at least one of the plurality of spread spectrum signals over a corresponding Doppler search range by sequentially correlating with Doppler signals within the corresponding Doppler search ranges at a rate greater than a rate at which the spread spectrum signals are received.

31. A method for searching a plurality of spread spectrum signals having repeating sequences of bits from corresponding signal sources, comprising:

receiving a plurality of spread spectrum signals;

assigning a Doppler search range to each of the spread spectrum signals received;

generating at least one Doppler search signal for each of the assigned Doppler search ranges, the number of Doppler search signals generated for at least two of the Doppler search ranges being different.

32. The method of claim 31, generating the Doppler search signals totaling in number not more than a predetermined number of Doppler search signals.

33. The method of claim 31, applying a Doppler step size increment between each of the Doppler search signals within a particular Doppler search range.

34. The method of claim 33, applying different Doppler step size increments for different spread spectrum signals

35. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a plurality of spread spectrum signals at a sample rate;

forming a plurality of signal segments by segmenting the plurality of spread spectrum signals;

partially correlating the plurality of signal segments with corresponding segments of a first replica signal having a first time shift for a predetermined number of phase delays, the first replica signal corresponding to one of the plurality of spread spectrum signals;

partially correlating the plurality of signal segments with corresponding segments of the first replica signal having a second time shift for a predetermined number of phase delays.

36. The method of claim 35, selecting the first and second time shifts so that a difference between the first and second time shifts is a fractional multiple of a time interval of the sample rate.

37. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

accumulating a magnitude of results of partially correlating a plurality of signal segments with corresponding replica signal segments for a to predetermined number of phase delays;

determining which of the accumulated magnitudes is greatest;

determining whether a subsequent accumulation of the greatest accumulated magnitude will result in an accumulation overflow;

scaling all subsequent accumulated magnitudes for all of the predetermined phase delays with a common scaling factor if it is determined that the subsequent accumulation of the greatest accumulated magnitude will result in an accumulation overflow;

storing the common scaling factor.

38. The method of claim 37, partially correlating each of the plurality of signal segments with the corresponding replica signal segments for the predetermined number of phase delays for a coherent integration time period.

39. The method of claim 37, scaling all subsequent accumulated magnitudes for all of the predetermined phase delays with a common scaling factor in non-coherent memory.

40. A method for code phase searching a spread spectrum signal having a repeating sequence of bits, comprising:

receiving a plurality of spread spectrum signals;

correlating of the spread spectrum signals with a plurality of replica signals for a predetermined number of phase delays, each of the plurality of replica signals corresponding to one of the plurality of spread spectrum signals;

scaling at least some results of correlating each of the spread spectrum signals by different scale factors.

41. The method of claim 40, preventing accumulation overflow by adjusting the scale factor for each of the plurality of spread spectrum signals.

42. The method of claim 40, scaling at least some results of correlating each of the spread spectrum signals by different scale factors in coherent memory.

43. A method for code phase searching a spread spectrum signal, comprising:

determining a correlation magnitude for a predetermined number of phase delays;

determining which of the correlation magnitudes for the predetermined number of phase delay is greatest and second greatest;

determining a difference of phase delays of the first and second greatest correlation magnitudes;

confirming an approximate phase delay determination corresponding to a phase delay of the greatest magnitude by determining whether a magnitude of the phase delay difference is equal to one unit of phase delay.

44. A spread spectrum signal receiver comprising:

a signal segmentation circuit having an n-bit signal segment output coupled to an input of an n-bit signal segment register;

a first n-bit replica signal segment register;

a multiplier circuit having a signal segment input coupled to an output of the n-bit signal segment register, the multiplier circuit having a replica signal segment input coupled to an output of the n-bit replica signal segment register;

a correlator having an input coupled to an output of the multiplier circuit;

a coherent integrator having an input coupled to an output of the correlator.

45. The receiver of claim 44, a second n-bit replica signal segment register, a first multiplexor having an output coupled to the replica signal segment input of the multiplier circuit, the outputs of the first and second n-bit replica signal segment registers coupled to inputs of the first multiplexor.

46. The receiver of claim 45, first and second Doppler signal segment registers, a second multiplexor having first and second inputs coupled to corresponding outputs of the first and second Doppler signal segment registers, an output of the second multiplexor and an output of the signal segment register coupled to a first multiplier circuit, an output of the first multiplier circuit and the output of the first multiplexor coupled to inputs of a second multiplier circuit having an output coupled to the correlator.

47. The receiver of claim 44, receiver quality clock coupled to the signal segmentation circuit and the n-bit signal segment register, a second non-receiver quality clock coupled to the first n-bit replica signal segment register, the multiplier circuit, the correlator and the coherent integrator.

48. The receiver of claim 44, the receiver being driven by at least two clock sources, one of said clock sources being of receiver quality clock stability coupled to the signal segmentation circuit and the n-bit signal segment register, and another of said clock sources being of non-receiver quality clock stability, said first clock source coupled to the first n-bit replica signal segment register, the multiplier circuit, the flash correlator and the coherent integrator.

49. The receiver of claim 44, the signal segmentation circuit for forming a plurality of signal segments having unequal numbers of samples not greater than n-bits.

50. The receiver of claim 44, the correlator for correlating at a rate greater than a rate at which the spread spectrum signal is received.