Method for reducing auto-correlation or cross-correlation in weak signals

• US 20020064209A1
• Filed: 07/20/2001
• Published: 05/30/2002
• Est. Priority Date: 08/24/2000
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Falk, Henry D., Norman, Charles P., Turetzky, Gregory Bret
• Granted Patent: US 7,106,786 B2
• Time in Patent Office: Days
• US Class Current: 375/142
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• 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 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/708 Parallel implementation
• 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 1/7097 Interference-related aspects
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

The present invention discloses methods, apparatuses, and systems for eliminating auto- and cross-correlation in weak signal CDMA systems, such as GPS systems. The invention uses parallel data paths that allow standard correlation of signals in parallel with verification of the lock signal to determine whether the system has locked onto the proper signal within the scanned signal window. The invention can be made with multiple CPUs, a single CPU with dual input modes, on multiple IC chips, or as a single IC chip solution for small, low cost reception, downconversion, correlation, and verification systems.

Claims

1. A method for reducing auto-correlation and cross-correlation in a CDMA receiver, comprising:

correlating an incoming CDMA signal, located within a scanned signal window, with a locally generated signal on a first data path;

verifying the incoming CDMA signal, located within the scanned signal window, against a lock signal on a second data path;

determining, using the second data path, whether the incoming CDMA signal has at least one characteristic which differentiates the incoming CDMA signal from an auto-correlated or cross-correlated signal; and

continuing to search the scanned signal window for a second incoming CDMA signal if the incoming CDMA signal lacks the at least one characteristic.

2. The method of claim 1, wherein the first data path, the second data path, and the means for continuing to search are located on a single integrated circuit.

3. The method of claim 2, wherein the CDMA receiver is a Global Positioning System (GPS) receiver.

4. The method of claim 3, further comprising receiving, substantially in parallel with the incoming CDMA signal, a wireless signal for transmitting and receiving data.

5. The method of claim 4, wherein the at least one characteristic is a predetermined signal strength of the incoming CDMA signal.

6. The method of claim 4, wherein the at least one characteristic is a predetermined Signal-to-Noise Ratio (SNR) of the incoming CDMA signal.

7. The method of claim 4, wherein the at least one characteristic is selected from a group comprising a correlation to a different satellite code being stronger than the correlation to a desired satellite code, and a correlation to a different delay of the incoming CDMA signal being stronger than the correlation to the first data path'"'"'s locally generated code delay.

8. The method of claim 4, wherein the at least one characteristic is at least two characteristics selected from a group comprising:

a predetermined signal strength of the incoming CDMA signal, a predetermined Signal-to-Noise Ratio (SNR) of the incoming CDMA signal, and a predetermined amount of data present on the incoming CDMA signal.

9. The method of claim 8, wherein the first data path is controlled by a first central processing unit (CPU), and the second data path is controlled by a second CPU.

10. A method for reducing auto-correlation and cross-correlation in a GPS receiver co-located with a cellular telephone, comprising:

transmitting and receiving cellular telephone signals using a cellular telephone transceiver;

correlating an incoming GPS signal, located within a scanned signal window, with a locally generated signal, using a first data path;

verifying the incoming GPS signal, located within the scanned signal window, against a lock signal using a second data path, the second data path determining whether the incoming GPS signal has at least one characteristic which differentiates the incoming GPS signal from an auto-correlated signal and a cross-correlated signal;

monitoring the first data path; and

continuing to search the scanned signal window for a second incoming GPS signal when the incoming GPS signal does not contain the at least one characteristic.

11. The method of claim 10, wherein the at least one characteristic is a predetermined signal strength of the incoming GPS signal.

12. The method of claim 10, wherein the at least one characteristic is a predetermined Signal-to-Noise Ratio (SNR) of the incoming GPS signal.

13. The method of claim 10, wherein the at least one characteristic is selected from a group comprising a correlation to a different satellite code being stronger than the correlation to a desired satellite code, and a correlation to a different delay of the incoming CDMA signal being stronger than the correlation to the first data path'"'"'s locally generated code delay.

14. The method of claim 10, wherein the at least one characteristic is at least two characteristics selected from a group comprising:

a predetermined signal strength of the incoming CDMA signal, a predetermined Signal-to-Noise Ratio (SNR) of the incoming GPS signal, and a predetermined amount of data present on the incoming GPS signal.

15. The method of claim 10, wherein the cellular transceiver and the GPS receiver are located on a single integrated circuit.

16. The method of claim 15, wherein the at least one characteristic is a predetermined signal strength of the incoming GPS signal.

17. The method of claim 15, wherein the at least one characteristic is a predetermined Signal-to-Noise Ratio (SNR) of the incoming GPS signal.

18. The method of claim 15, wherein the at least one characteristic is selected from a group comprising a correlation to a different satellite code being stronger than the correlation to a desired satellite code, and a correlation to a different delay of the incoming CDMA signal being stronger than the correlation to the first data path'"'"'s locally generated code delay.

19. The method of claim 15, wherein the at least one characteristic is at least two characteristics selected from a group comprising:

a predetermined signal strength of the incoming CDMA signal, a predetermined Signal-to-Noise Ratio (SNR) of the incoming GPS signal, a correlation to a different satellite code being stronger than the correlation to a desired satellite code, and a correlation to a different delay of the incoming CDMA signal being stronger than the correlation to the first data path'"'"'s locally generated code delay.

20. The method of claim 19, wherein the cellular telephone transceiver and the GPS receiver share a central processing unit.