Pseudo-noise correlator for GPS spread-spectrum receiver

• US 20040136446A1
• Filed: 11/24/2003
• Published: 07/15/2004
• Est. Priority Date: 04/25/1996
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Charles R. Cahn, Greg Turetsky, Mangesh Chansarkar, Sanjai Kohli, Steve Chen
• Inventors: Kohli, Sanjai, Cahn, Charles R., Chansarkar, Mangesh, Chen, Steven, Turetsky, Greg
• Granted Patent: US 7,406,114 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• 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 an 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 system for operating a GPS C/A code receiver comprising:

means for 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; and

means for 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.

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

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

4. The system of claim 1 wherein the correlating means comprises means for tracking different satellites by selecting the satellite specific sets to represent n different satellites.

5. The system of claim 1 wherein the correlating means comprises means for tracking different satellites by selecting more than one of the satellite specific sets to represent the same satellite.

6. The system of claim 5 wherein the time delay segments of the satellite specific sets representing the same satellite are sequential.

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

8. The system 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 system of claim 1 wherein the correlating means comprises means for tracking different satellites by selecting the satellite specific sets to represent an integer fraction of n different satellites.

10. The system of claim 1 wherein the correlating means comprises means for tracking n/2 satellites by selecting the satellite specific sets to represent n/2 different satellites.

11. The system of claim 1 wherein the correlating means is adapted to:

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

repeat the correlation for the same satellite with a different set of time delayed segments.

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

13. The system of claim 1 further comprising means for 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 system of claim 1 wherein the forming means comprises:

means for sampling the received composite at a first bit rate; and

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

15. The system of claim 1 further comprising means for interrupting the correlating means for a series of code periods to reduce receiver energy consumption.

16. A system for tracking the movement of an object, said system comprising:

a GPS C/A code receiver associated with the object and adapted to;

form 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; and

correlate 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

means for determining navigation information from the correlation values.

17. The system of claim 16 wherein the determining means comprises means for comparing the magnitudes of two equal correlation values to the magnitude of a correlation value therebetween to select a prompt delay.

18. The system of claim 17 wherein the comparing means comprises means for 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.

19. The system of claim 17 wherein the comparing means comprises means for 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.

20. A method of operating a GPS C/A code receiver comprising:

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

accumulating the correlation values in a n time m matrix.