Spread spectrum receiver with multi-bit correlator

• US 6,748,015 B2
• Filed: 03/18/2002
• Issued: 06/08/2004
• 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, Chen, Steven
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US10/101,138
• Publication Number:
  US 20020150150A1
• Time in Patent Office: 813 Days
• Field of Search: 375/130, 375/147, 375/150, 375/142, 375/343, 375/149, 375/145, 342/357-6-3, 701/213-216, 340/426.19, 340/539.13
• 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 method of processing signals received by a spread spectrum receiver from at least one of a plurality of transmitting sources each having an associated code, said method comprising:

correlating each sequential segment of a spread spectrum signal with at least one series of differentially time delayed code replicas to generate a plurality of correlation results using a single multi-bit digital correlator; and

accumulating the plurality of correlation results in a matrix of correlation magnitudes as a function of time delay.

2. The method of claim 1 wherein correlating each sequential segment comprises simultaneously correlating portions of each sequential segment with portions of a segment of a code replica.

3. The method of claim 1 wherein correlating each sequential segment comprises correlating a half code chip width portion of each sequential segment with a half code chip width portion of a segment of a code replica.

4. The method of claim 1 wherein the correlation results are related to the correlation of the spread spectrum signal with each of the time delayed code replicas.

5. The method of claim 1 wherein the correlation results are related to the correlation of the spread spectrum signal with each of a plurality of series of code source specific time delayed code replicas.

6. The method of claim 1 wherein each sequential segment of a spread spectrum signal is correlated with at least two series of differently time delayed code replicas.

7. The method of claim 1 further comprising:

forming a plurality of sets of differently time delayed correlation products for each segment for the same code; and

selecting a code specific delay for the associated code when at least one of the correlation products for that code achieves a predetermined threshold.

8. The method of claim 1 further comprising:

forming sets of differently time delayed correlation products for each sequential segment for each of a plurality of different codes; and

selecting a code specific delay for each code when at least one of the correlation products for that code achieves a predetermined threshold.

9. The method of claim 1 wherein accumulating the plurality of correlation results comprises accumulating the power or amplitude of each correlation.

10. The method of claim 1 further comprising:

sampling the spread spectrum signal to form partial chip width samples; and

collecting a sequential series of the partial chip samples to form each sequential segment.

11. The method of claim 1 further comprising providing a series of satellite specific, time delayed multi-chip segments of a replica of each code for correlation with each of the sequential segments.

12. The method of claim 1 wherein correlating each sequential segment comprises:

synchronizing a series of satellite specific, time delayed multi-chip replicas for correlation with each of the sequential segments;

synchronizing the local clock with a clock associated with a source of the code being received; and

synchronizing the local clock with a clock associated with a source of the code being received after being temporarily obscured.

13. The method of claim 1 further comprising:

tracking a prompt delay from a source of the code; and

monitoring correlation products representing lesser time delays than the prompt delay to detect the inaccurate tracking of a multipath signal from the course of the code.

14. The method of claim 1 further comprising selecting a time delay not equal to one of the time delays of the replicas as a prompt delay.

15. The method of claim 1 further comprising:

forming digitized samples of signals received from code sources at a first rate;

forming the sequential segments from the digitized samples at a second rate substantially slower than the first rate.

16. The method of claim 1 further comprising:

selectively configuring the matrix to form either

a) n different code specific sets of m different time delayed correlation products, or

b) n times m different time delayed correlation products for one code.

17. A spread spectrum receiver for processing signals from at least one of a plurality of transmitting sources each having an associated code, said receiver comprising:

a single multi-bit digital correlator for correlating each sequential segment of a spread spectrum signal with at least one series of differentially time delayed code replicas to generate a plurality of correlation results; and

matrix means responsive to the correlator for accumulating the plurality of correlation results in a matrix of correlation magnitudes as a function of time delay.

18. The receiver of claim 17 wherein the single multi-bit digital correlator comprises a set of correlators for simultaneously correlating portions of each sequential segment with portions of a segment of a code replica.

19. The receiver of claim 17 wherein the single multi-bit correlator comprises a series of single bit correlators, each for correlating a half code chip width portion of each sequential segment with a half code chip width portion of a segment of a code replica.

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

a spread spectrum receiver associated with the object and adapted to

correlate each sequential segment of a spread spectrum signal with at least one series of differentially time delayed code replicas to generate a plurality of correlation results using a single multi-bit digital correlator; and

accumulate the plurality of correlation results in a matrix of correlation magnitudes as a function of time delay; and

means for determining navigation information for the object from the correlation results.