Multipath processing for GPS receivers

• US 20040184516A1
• Filed: 03/30/2004
• Published: 09/23/2004
• Est. Priority Date: 03/28/1997
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Charles R. Cahn, Sanjai Kohli
• Inventors: Kohli, Sanjai, Cahn, Charles R.
• Granted Patent: US 7,301,992 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 19/29 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: 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 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]

Abstract

A GPS receiver system determines the presence of trackable signals at code delays less than the prompt delay being tracked for a particular, signal and changes the prompt delay to correspond to the smallest code delay having a trackable signal. Trackable signals at large code delays are multipath signals and may be separately tracked to aid in dead reckoning. The trackable signals at code delays not adjacent to the current tracked prompt delay may be tracked in the same channel as the prompt delay so that all satellite channels are continuously evaluated for multipath signals being tracked or a non-satellite specific channel may be used to sequentially step through the satellite signals to evaluate multipath on a satellite by satellite basis.

Claims

1. A method of operating a spread spectrum receiver comprising:

tracking a first signal as a direct signal;

tracking a second signal as a multipath signal;

monitoring the delay between the direct signal and the multipath signal;

when the delay is within 1.5 chips, modeling the correlation products for the multipath signal; and

compensating for the modeled correlation product.

2. The method of claim 1 wherein compensating for the modeled correlation product comprises subtracting the modeled correlation from the direct signal correlation.

3. The method of claim 1 wherein tracking a second signal comprises:

detecting a plurality of second signals;

comparing the magnitudes of the second signals; and

tracking the second signal having the greatest magnitude.

4. The method of claim 1 further comprising:

when the direct signal is obscured, tracking the multipath signal as the direct path signal.

5. The method of claim 1 further comprising:

tracking changes in the progression of the delay; and

maintaining a model of the direct signal based on the progression of the delay.

6. The method of claim 5 further comprising:

when the direct signal is obscured, using the modeled direct path signal as the direct path signal.

7. A spread spectrum receiver comprising:

means for tracking a first signal as a direct signal;

means for tracking a second signal as a multipath signal;

means for monitoring the delay between the direct signal and the multipath signal;

means for modeling the correlation products for the multipath signal when the delay is within 1.5 chips; and

means for compensating for the modeled correlation product.

8. The receiver of claim 7 wherein the compensating means comprises means for subtracting the modeled correlation from the direct signal correlation.

9. The receiver of claim 7 wherein means for tracking a second signal comprises:

means for detecting a plurality of second signals;

means for comparing the magnitudes of the second signals; and

means for tracking the second signal having the greatest magnitude.

10. The receiver of claim 7 further comprising:

means for tracking the multipath signal as the direct path signal when the direct signal is obscured.

11. The receiver of claim 10 further comprising:

means for tracking changes in the progression of the delay; and

means for maintaining a model of the direct signal based on the progression of the delay.

12. The receiver of claim 11 further comprising:

means for using the modeled direct path signal as the direct path signal, when the direct signal is obscured.