Method and apparatus for performing signal correlation at multiple resolutions to mitigate multipath interference

• US 20100098136A1
• Filed: 12/28/2009
• Published: 04/22/2010
• Est. Priority Date: 05/18/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Global Locate Incorporated (Broadcom, Inc.)
• Inventors: Abraham, Charles, Fuchs, Donald L.
• Granted Patent: US 8,411,726 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: G01S 1/045 Receivers
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/254 relating to Doppler shift of satellite signals
• CPC Class Codes: G01S 19/256 relating to timing, e.g. time of week, code phase, timing offset
• 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: G06F 17/15 Correlation function computation including computation of convolution operations arithmetic circuits for sum of products per se, e.g. multiply-accumulators G06F7/5443; digital filters, e.g. FIR, IIR, adaptive filters H03H17/00
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/70757 with increased resolution, i.e. higher than half a chip H04B1/70758 takes precedence
• CPC Class Codes: H04B 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/7095 Sliding correlator type
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A method and apparatus for selecting a signal processing resolution. A received signal is processed using a first resolution. When a multipath condition is detected, the signal is processed using a second resolution.

Claims

1. A method for selecting a signal-processing resolution in a satellite-signal receiver, the method comprising:

receiving a signal at the satellite-signal receiver;

producing a plurality of samples of the signal;

processing a first set of the plurality of samples of the signal; and

processing a second set of the plurality of samples of the signal responsive to a multipath condition being detected from processing the first set, wherein the second set comprises more of the plurality of samples than the first set.

2. The method of claim 1, wherein the signal is a satellite signal transmitted by at least one satellite in a satellite positioning system.

3. The method of claim 2, wherein the satellite positioning system comprises at least one of a Global Positioning System (GPS), Galileo, or GLONASS.

4. The method of claim 1, wherein processing a first set of the plurality of comprises performing signal correlation to generate a correlation result.

5. The method of claim 1 wherein measuring a width of a correlation result comprises:

measuring a slope of an ascending edge of the correlation result;

measuring a slope of a descending edge of the correlation result;

measuring a mean noise level;

computing a first intersection of the ascending edge and the mean noise level;

computing a second intersection of the descending edge and the mean noise level; and

computing, as a distance between the first and second intersections, the width of the correlation result.

6. The method of claim 5, wherein the predetermined value is two chips of the signal.

7. The method of claim 1, wherein detecting a multipath condition comprises:

measuring a slope of an ascending edge of the correlation result;

measuring a slope of a descending edge of the correlation result;

comparing the ascending slope to the descending slope; and

indicating a multipath condition when the ascending slope differs from the descending slope.

8. The method of claim 1, wherein the first resolution is a one-half chip interval and the second resolution is a one-fifth chip interval.

9. The method of claim 1, wherein processing a second set of the plurality of samples comprises:

performing signal correlations to generate a signal correlation; and

selecting an earliest peak in the signal correlations.

10. An apparatus for processing a satellite signal comprising:

a satellite signal receiver for receiving a signal;

a sampler for producing a plurality of samples of the signal;

a correlator for processing (i) a first set of the plurality of samples of the signal, and (ii) a second set of the plurality of samples responsive to a multipath condition being detected from processing the first set, wherein the second set comprises more samples of the plurality of samples than the first set; and

a detector, coupled to the correlator for detecting a multipath condition from processing of the first set of the plurality of samples of the signal, and for causing the correlator to process the second set of the plurality of samples after detecting the multipath condition.

11. The apparatus of claim 10, wherein the satellite positioning system comprises at least one of a Global Positioning System (GPS), Galileo, or GLONASS.

12. The apparatus of claim 11, wherein the correlator performs signal correlation to generate a correlation result.

13. The apparatus of claim 10, wherein the processor measures the width of the correlation result by measuring a slope of a ascending edge of the correlation result;

measuring a slope of a descending edge of the correlation result;

measuring a mean noise level;

computing a first intersection of the ascending edge and the mean noise level;

computing a second intersection of the descending edge and the mean noise level; and

computing the width of the correlation result as a distance between the first and second intersections.

14. The apparatus of claim 10, wherein the predetermined value is two chips of the signal.

15. The apparatus of claim 10, wherein the detector measures a slope of a ascending edge of the correlation result;

measures a slope of a descending edge of the correlation result;

compares the ascending slope to the descending slope; and

if the ascending slope differs from the descending slope, indicating a multipath condition.

16. The apparatus of claim 10, wherein the first resolution is a one-half chip interval and the second resolution is a one-fifth chip interval.

17. The apparatus of claim 10, wherein the correlator performs signal correlations to generate a signal correlation;

and selects an earliest peak in the signal correlations.