Pseudo-noise correlator for a GPS spread spectrum receiver

• US 6,400,753 B1
• Filed: 09/05/2000
• Issued: 06/04/2002
• Est. Priority Date: 04/25/1996
• Status: Expired due to Term

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Kohli, Sanjai, Cahn, Charles R., Chansarkar, Mangesh, Chen, Steven, Turetsky, Greg
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Liu, Shuwang
• Application Number:
  US09/655,633
• Time in Patent Office: 637 Days
• Field of Search: 375/130, 375/147, 375/134, 375/140, 375/150, 375/137, 375/142, 702/343, 702/149, 342/352, 342/357.12, 701/201
• US Class Current: 375/134
• CPC Class Codes: G01C 21/26 specially adapted for navigation in a road network
• CPC Class Codes: G01C 22/00 Measuring distance traversed on the ground by vehicles, persons, animals or other moving solid bodies, e.g. using odometers, using pedometers
• CPC Class Codes: G01S 19/11 wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• 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 19/34 Power consumption
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled
• CPC Class Codes: G01S 19/50 whereby the position solution is constrained to lie upon a particular curve or surface, e.g. for locomotives on railway tracks
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7095 Sliding correlator type
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2001/70706 using a code tracking loop, e.g. a delay locked loop
• CPC Class Codes: H04B 2201/70715 with application-specific features
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]
• CPC Class Codes: H04L 27/30 : wherein each code element is represented by a combination of frequencies

Abstract

A terrestrial C/A code GPS receiver system digitally samples, filters and stores a segment of 11 half chips of the received composite as a binary number and multiplexes this number for parallel correlation with each of a series of multibit code replicas for the satellites to be tracked. Each of the time delay specific correlation products are accumulated in a cell of a memory matrix so that at least twenty two delays for each satellite may be evaluated each code period providing fast reacquisition, even within a city intersection, as well as correction of multipath tracking and multipath interference. All cells of the memory matrix may be used for a acquisition of a single satellite in about 4 ms. Two satellite tracking, in addition to altitude hold, uses cross track hold alternating with clock hold to update the cross track estimate. Single satellite tracking uses cross track and clock hold together. Navigation data is updated with detected changes in motion including turns.

Claims

1. A method of operating a GPS C/A code receiver, comprising the steps of:

forming x multibit digital segment values per C/A code period, each multibit digital segment value representing a sequential code segment of a received composite of satellite signals;

correlating each digital segment value with n satellite specific sets of m differently time delayed segments of C/A code modulation to form at least n times m time delay specific correlation values; and

determining navigation information from the correlation values.

2. The method of claim 1 wherein m is greater than the number of bits in each multibit digital segment value.

3. The method of claim 1 wherein each bit of the multibit digital segment value represents an integer fraction of a C/A code chip.

4. The method of claim 1 wherein the correlating step further comprises:

tracking different satellites by selecting the satellite specific sets to represent n different satellites.

5. The method of claim 1 wherein the correlating step further comprises:

tracking different satellites by selecting more than one of the satellite specific sets to represent the same satellite.

6. The method of claim 3 wherein the time delay segments of the satellite specific sets representing the same satellite are sequential.

7. The method of claim 5 wherein the time delay segments of the satellite specific sets representing the same satellite are interlaced.

8. The method of claim 5 wherein the differential time delay of the segments of the satellite specific sets representing the same satellite represent less than a maximum expected time delay error for a temporarily obscured satellite in an urban environment.

9. The method of claim 1 wherein the correlating step further comprises:

tracking different satellites by selecting the satellite specific sets to represent an integer fraction of n different satellites.

10. The method of claim 1 wherein the correlating step further comprises:

tracking n/2 satellites by selecting the satellite specific sets to represent n/2 different satellites.

11. The method of claim 1 wherein the correlating step further comprises:

acquiring a satellite by selecting the satellite specific sets to represent the same satellite; and

repeating the correlating step for the same satellite with a different set of time delayed segments.

12. The method of claim 1 wherein x, m and n are each prime factors of the number code chips per C/A code period.

13. The method of claim 1, further comprising the step of:

forming the series of m/2 differently time delayed segments by sequentially changing one bit of a previous segment to form the next segment.

14. The method of claim 13 wherein each bit represents one half of C/A code chip.

15. The method of claim 1, wherein the step of determining navigation information further comprises the steps of:

comparing the magnitudes of two equal correlation values to the magnitude of a correlation value therebetween to select a prompt delay.

16. The method of claim 15 wherein the comparing step further comprises:

selecting the prompt delay to be more than half way between the time delays represented by the equal correlation values when the magnitude of the equal correlation products is equal to less than half of a peak correlation value therebetween.

17. The method of claim 15 wherein the comparing step further comprises:

selecting the prompt delay to be less than half way between the time delays represented by the equal correlation values when the magnitude of the equal correlation products is equal to more than half of a peak correlation value therebetween.

18. The method of claim 1 wherein the step of forming digital segment values further comprises the steps of:

sampling the received composite at a first bit rate;

digitally filtering the first composite to form the digital segment values at a bit rate substantially lower than the first bit rate.

19. The method of claim 1 further comprising the step of:

interrupting the step of correlating for a series of code periods to reduce receiver energy consumption.

20. The method of claim 19 wherein the series of code periods of interruption are less than the time required for an internal receiver clock to drift the time delay represented by the series of time delay segments related to one particular satellite.

21. The method of claim 20, wherein the step of interrupting further comprises the step of:

periodically correlating with a replica of the particular satellite to update the internal clock.

22. The method of claim 21 wherein the step of periodically correlating further comprises the step of:

correlating with a plurality of satellite specific replicas to update the navigation information.

23. The method of claim 21 further comprising the step of:

correlating with a plurality of satellite specific replicas to update the navigation information in response to operator intervention.