METHOD AND APPARATUS FOR PERFORMING FREQUENCY SYNCHRONIZATION

• US 20100272161A1
• Filed: 07/02/2010
• Published: 10/28/2010
• Est. Priority Date: 10/22/2003
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Global Locate Incorporated (Broadcom, Inc.)
• Inventors: Abraham, Charles, Goldberg, Jason, Tapucu, Emre
• Granted Patent: US 8,472,503 B2
• Time in Patent Office: Days
• 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 comprising:

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 a frequency that is used to receive a signal comprising the code.

2. The method of claim 1, wherein analyzing the sequence of correlation values comprises:

hypothesizing a plurality of possible frequencies;

determining a quantity indicative of a power in the sequence of correlation values at each of the plurality of possible frequencies; and

estimating the frequency as a function of the quantity.

3. The method of claim 2, further comprising:

compensating the sequence of correlation values with each of the plurality of possible frequencies to form frequency-compensated correlation values;

accumulating the frequency-compensated correlation values to form an accumulation; and

determining a quantity indicative of the power in the sequence of correlation values as a function of the accumulation.

4. The method of claim 1, further comprising:

compensating the sequence of correlation values based on the frequency to form a frequency-compensated sequence of correlation values; and

accumulating the frequency-compensated sequence of correlation values to form a second sequence of correlation values that form a correlation vector.

5. The method of claim 4, further comprising:

accumulating values indicative of a power of each of the second sequence of correlation values.

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

7. The method of claim 2 wherein the plurality of possible frequencies are spaced by approximately 100 Hz.

8. The method of claim 2 wherein the estimating step further comprises interpolating the function.

12. The apparatus of claim 6, further comprising:

a second mixer for compensating the sequence of correlation values based on the frequency to form a frequency-compensated sequence of correlation values; and

an accumulator for accumulating the frequency-compensated sequence of correlation values to form a second sequence of correlation values.

9. An apparatus comprising:

a memory for storing a sequence of correlation values produced over a period less than a repeating period of a code;

a processor for accessing the sequence of correlation values from the memory and processing the values to produce a frequency estimate that is used to receive a signal comprising the code.

10. The apparatus of claim 9, wherein the processor hypothesizes a plurality of possible frequencies, determines a quantity indicative of a power in the sequence of correlation values at each of the plurality of possible frequencies and estimates the frequency as a function of the quantity.

11. The apparatus of claim 10, further comprising:

a mixer for compensating the sequence of correlation values with each of the plurality of possible frequencies to form frequency-compensated correlation values;

an accumulator for accumulating the frequency-compensated correlation values to form an accumulation; and

an absolute value circuit for determining a quantity indicative of a power as a function of the accumulation.

13. The apparatus of claim 9, further comprising:

an absolute value circuit for determining power of each of the second sequence of correlation values.

14. The apparatus of claim 9 wherein the period of the code is about 1 millisecond.

15. The apparatus of claim 10 wherein the plurality of possible frequencies are space by approximately 100 Hz.

16. The apparatus of claim 10 wherein the coprocessor interpolates the function to estimate the frequency.

17. A GNSS receiver comprising:

a tuner comprising a numerically controlled oscillator for adjusting an intermediate frequency;

a GNSS signal convolution processor, coupled to the tuner, for producing a sequence of correlation values, where the sequence of correlation values are produced over a period less than a repeating period of a code;

a correlation history memory, coupled to the convolution processor, for storing the sequence of correlation values;

a processor, coupled to the correlation history memory, for analyzing a power of the correlation values and controlling a frequency of the numerically controlled oscillator.

18. The GNSS receiver of claim 17 wherein the period of the code is about 1 MS.