Spread spectrum receiver with multi-path correction

• US 20010002203A1
• Filed: 12/11/2000
• Published: 05/31/2001
• Est. Priority Date: 04/25/1996
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Charles R. Cahn, Mangesh Chansarkar, Sanjai Kohli
• Inventors: Kohli, Sanjai, Cahn, Charles R., Chansarkar, Mangesh
• Granted Patent: US 6,917,644 B2
• Time in Patent Office: Days
• US Class Current: 375/142
• 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 19/29 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: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• 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 1/7115 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]

Abstract

A spread spectrum receiver uses a comparison of the magnitude of the code correlation amplitudes at equal power at a one chip spacing to the magnitude at a central position there between to determine if multipath interference is present. The lead or lag error from constructive or destructive multipath interference may also be determined. Inaccuracies due to such interference may then be corrected or minimized by, for example, determining the residual code phase error and/or the prompt or accurate code phase delay.

Claims

1. A spread spectrum receiver, comprising:

means for correlating a received, code modulated spread spectrum signal with a code modulated signal replica at a first selected code phase delay and at a second selected code phase delay; and

comparison means for comparing characteristics of said correlations to derive information related to any residual code phase error in said second code phase delay.

2. The invention of

claim 1

, wherein said first code phase delay is selected to have a characteristic having a first known relationship to a characteristic of said third code phase delay.

3. The invention of

claim 2

, wherein said first known relationship between characteristics of said first and third code phase delays includes a second known relationship between any correlation of said received signal with said replica at said first and third code phase delays.

4. The invention of

claim 3

, wherein said characteristics are correlation magnitudes.

5. The invention of

claim 4

, wherein said second known relationship is equality.

6. The invention of

claim 2

, wherein said first known relationship includes a third known relationship related to magnitudes of said first and third code phase delays.

7. The invention of

claim 6

, wherein said third known relationship is that the magnitudes of said first and third code phase delays differ by a predetermined magnitude proportional to a chip of said code modulation.

8. The invention of

claim 6

, wherein predetermined magnitude is the width of one chip of said code modulation.

9. The invention of

claim 8

, wherein said second code phase delay is midway between said first and third code phase delays.

10. The invention of

claim 1

, wherein said comparison means further comprises:

error means for determining the existence of residual code phase lead or lag error.

11. The invention of

claim 10

, wherein said error means further comprises:

means for determining the existence of multipath interference in said received, code modulated spread spectrum signal causing a residual code phase lag error if the magnitude of the correlation product at the second selected code phase delay is less than twice the magnitude of the correlation product at the first selected code phase delay.

12. The invention of

claim 10

, wherein said error means further comprises:

means for determining the existence of multipath interference in said received, code modulated spread spectrum signal causing a residual code phase lead error if the magnitude of the correlation product at the second selected code phase delay is more than twice the magnitude of the correlation product at the first selected code phase delay.

13. The invention of

claim 10

, wherein said error means further comprises:

means for determining that said received, code modulated spread spectrum signal is substantially free of multipath interference error if the magnitude of the correlation product at the second selected code phase delay is substantially equal to the magnitude of the correlation product at the first selected code phase delay.

14. The invention of

claim 1

, wherein said comparison means further comprises:

means for selecting a prompt phase delay between said first and second code phase delays if the magnitude of the correlation product at the second selected code phase delay is less than twice the magnitude of the correlation product at the first selected code phase delay.

15. The invention of

claim 1

, wherein said comparison means further comprises:

means for selecting a prompt phase delay at a correlation product peak between said first and second code phase delays if the magnitude of the correlation product at the second selected code phase delay is less than twice the magnitude of the correlation product at the first selected code phase delay.

16. The invention of

claim 1

, wherein said comparison means further comprises:

means for selecting a prompt phase delay between said second and third code phase delays if the magnitude of the correlation product at the second selected code phase delay is more than twice the magnitude of the correlation product at the first selected code phase delay.

17. The invention of

claim 1

, wherein said comparison means further comprises:

means for selecting a prompt phase delay at a peak between said second and third code phase delays if the magnitude of the correlation product at the second selected code phase delay is more than twice the magnitude of the correlation product at the first selected code phase delay.

18. The invention of

claim 1

, wherein said comparison means further comprises:

means for selecting a prompt phase delay at said second code phase delay if the magnitude of the correlation product at the second selected code phase delay is substantially equal to the magnitude of the correlation product at the first selected code phase delay.

19. The invention of

claim 1

, further comprising:

means responsive to the comparison means for adjusting the code phase delay of a prompt correlation.

20. A method of processing coded, spread spectrum signals with potential multipath interference comprising the steps of:

generating a local replica of the code;

correlating the local replica with coded, spread spectrum signals as received at a plurality of code phase delays; and

determining prompt code phase delay from differences in magnitude between at least two of said correlations.

21. The method of

claim 20

, wherein the correlating step further comprises the step of:

correlating the local replica with the received signals at a first pair of code phase delays separated by a predetermined phase delay difference.

22. The method of

claim 21

, wherein the step of correlating at a pair of code delays further comprises the step of:

determining a second pair of code delays, separated by a predetermined phase delay difference, the magnitudes of the correlations at said second pair of code delays having a predetermined relationship.

23. The method of

claim 22

, wherein said first and second pair of code delays include a common code delay.

24. The method of

claim 23

, wherein said first pair of code phase delays are separated by a code chip width and said second pair of code phase delays are separated by one half of a code chip width.

25. The method of

claim 21

further comprising the step of:

selecting one of the first pair of code phase delays by determining a second pair of code phase delays, separated by a single code chip width, producing equal correlation magnitudes above a threshold value.

26. The method of

claim 25

, further comprising the step of:

selecting the other of the first pair of code phase delays to be equidistant between said second pair of code phase delays.

27. The method of

claim 26

, wherein the comparison step further comprises the step of:

determining the presence of multipath interference from the ratio of correlation product magnitudes at said first pair of code phase delays.

28. The method of

claim 27

, wherein the step of determining the presence of multipath interference further comprises the step of:

determining the presence of multipath interference if the ratio of correlation product magnitudes at said first pair of code phase delays is substantially different than two.

29. The method of

claim 27

, further comprising the step of:

adjusting one of the first pair of phase delays to be the prompt code phase delay in response to the difference between the ratio of the correlation products and two.