Method and apparatus for performing frequency synchronization

• US 8,989,236 B2
• Filed: 06/24/2013
• Issued: 03/24/2015
• Est. Priority Date: 10/22/2003
• Status: Expired due to Fees

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Global Locate Incorporated (Broadcom, Inc.)
• Inventors: Goldberg, Jason, Abraham, Charles, Tapucu, Emre
• Primary Examiner(s): Kim, Kevin
• Application Number:
  US13/925,538
• Publication Number:
  US 20130279541A1
• Time in Patent Office: 638 Days
• Field of Search: 375/142, 375/150
• US Class Current: 375/150
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/70752 Partial correlation

Abstract

A method and apparatus for performing frequency analysis of sub-epoch correlations to estimate an unknown frequency of a received signal is provided. The method includes forming a sequence of correlation values from a plurality of correlations performed over a period less than a repeating period of a code, and analyzing the sequence of correlation values to estimate the frequency that is used to receive a signal comprising the code.

Claims

1. A method for frequency estimation of a correlation signal comprising a sequence of correlation values formed from a plurality of correlations performed over a period less than a repeating period of a code, the method comprising:

generating, using a processing device and based on the correlation signal, a first estimate of a frequency error;

generating, using the processing device and based on the correlation signal, a second estimate of the frequency error based on the first estimate;

determining, using the processing device and based on the second estimate, a frequency for receiving a signal comprising the code, wherein the determined frequency corresponds to a signal magnitude of the correlation signal or a signal power of the correlation signal; and

computing an expected bit timing and Doppler shift of a satellite based on the determined frequency and a satellite range model or a satellite rate model.

2. The method of claim 1, further comprising:

generating subsequent estimates of the frequency error until a residual frequency error associated with the correlation signal is smaller than a predetermined amount.

3. The method of claim 1, wherein the determined frequency is determined without providing feedback to a numerically controlled oscillator (NCO) and without performing an additional correlation after the sequence of correlation values has been formed.

4. The method of claim 1, wherein the first estimate of the frequency error and the second estimate of the frequency error are generated using a frequency discriminator.

5. The method of claim 4, wherein generating the second estimate of the frequency error comprises:

generating the second estimate of the frequency error by applying the first estimate of the frequency error to the frequency discriminator.

6. The method of claim 1, wherein the repeating period of the code is about 1 millisecond.

7. The method of claim 1, wherein a plurality of possible frequencies for the determined frequency are spaced by approximately 100 Hz.

8. The method of claim 1, further comprising:

determining information used to update a receiver model of oscillator frequency and clock timing based on the determined frequency and the satellite range model or the satellite rate model.

9. The method of claim 1, further comprising:

performing a standard correlation on a Global Positioning System (GPS) signal using the determined frequency.

10. A receiver, comprising:

a signal convolution processor configured to produce a sequence of correlation values produced over a period less than a repeating period of a code;

a correlation history memory, coupled to the signal convolution processor, configured to store the sequence of correlation values; and

a processor, coupled to the correlation history memory, configured to;

generate, based on the sequence of correlation values, a first estimate of a frequency error,

generate, based on the sequence of correlation values, a second estimate of the frequency error based on the first estimate of the frequency error,

determine, based on the second estimate of the frequency error, a frequency for receiving a signal comprising the code, wherein the determined frequency corresponds to a signal magnitude of the correlation values or a signal power of the sequence of correlation values, and

compute an expected bit timing and Doppler shift of a satellite based on the determined frequency and a satellite range model or a satellite rate model.

11. The receiver of claim 10, wherein the processor is further configured to:

generate subsequent estimates of the frequency error until a residual frequency error is smaller than a predetermined amount.

12. The receiver of claim 10, further comprising:

a tuner comprising a numerically controlled oscillator (NCO), wherein the processor is configured to determine the frequency without providing feedback to the NCO and without requiring an additional correlation to be performed by the signal convolution processor.

13. The receiver of claim 10, wherein the processor is configured to generate the first estimate and the second estimate using a frequency discriminator.

14. The receiver of claim 13, wherein the processor is configured to apply the first estimate to the frequency discriminator to generate the second estimate.

15. The receiver of claim 10, wherein the repeating period of the code is about 1 millisecond.

16. The receiver of claim 10, wherein a plurality of possible frequencies for the determined frequency are spaced by approximately 100 Hz.

17. The receiver of claim 10, wherein the processor is further configured to:

determine information used to update a receiver model of oscillator frequency and clock timing based on the determined frequency and the satellite range model or the satellite rate model.

18. The receiver of claim 10, wherein the processor is further configured to:

perform a standard correlation on a Global Positioning System (GPS) signal using the determined frequency.

19. A receiver, comprising:

a signal convolution processor configured to produce a sequence of correlation values over a period less than a repeating period of a code;

a correlation history memory, coupled to the signal convolution processor, configured to store the sequence of correlation values; and

a processor, coupled to the correlation history memory, configured to;

generate, based on the sequence of correlation values, a first estimate of a frequency error,

generate, based on the sequence of correlation values, a second estimate of the frequency error based on the first estimate of the frequency error,

determine, based on the second estimate of the frequency error, a frequency for receiving a signal comprising the code, wherein the determined frequency corresponds to a signal magnitude of the sequence of correlation values or a signal power of the sequence of correlation values, and

determine information used to update a receiver model of oscillator frequency and clock timing based on the determined frequency and a satellite range model or a satellite rate model.

20. The receiver of claim 19, wherein the processor is further configured to:

compute an expected bit timing and Doppler shift of a satellite based on the determined frequency and the satellite range model or the satellite rate model.