Method and apparatus for performing signal correlation

• US 20030219066A1
• Filed: 03/21/2003
• Published: 11/27/2003
• Est. Priority Date: 05/18/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Serge De La Porte Charles Abraham, Sergei Podshivalov To Global Locate Incorporated
• Inventors: Porte, Serge de la, Podshivalov, Sergei, Abraham, Charles
• Granted Patent: US 7,190,712 B2
• Time in Patent Office: Days
• US Class Current: 375/150
• 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 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 5/0205 Details
• 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 1/7077 Multi-step acquisition, e.g. multi-dwell, coarse-fine or validation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A method and apparatus for performing signal correlation is described. In one example, portions of a pseudorandom reference code are multiplied with portions of a repeating code of the digital signal to produce a plurality of inner products. The plurality of inner products are then integrated over a period less than a period of the repeating code to produce a correlation result with a broadened frequency response. In another example, the digital signal is correlated with a pseudorandom reference code to produce a first correlation. The digital signal is then correlated with the pseudorandom code reference code to produce a second correlation. The first and second correlations are then used to determine first and second signal delays. The frequency shift of the digital signal is computed using a difference between the first and second signal delays over time.

Claims

1. A method of computing a correlation between a pseudorandom reference code and a satellite signal, the method comprising:

(a) receiving a satellite signal having a repeating code modulated thereon;

(b) correlating the pseudorandom reference code with a portion of the satellite signal to produce a correlation over a period less than a period of the repeating code.

2. The method of claim 1, further comprising:

(c) forming values representative of a magnitude or a power of the correlation to produce an energy signal;

(d) repeating steps (b) and (c) to produce a plurality of energy signals; and

(e) summing the plurality of energy signals as each energy signal is produced.

3. The method of claim 1, wherein step (b) comprises:

(b1) dividing the pseudorandom reference code into a plurality of code segments;

(b2) selecting a code segment;

(b3) forming an inner product between the selected code segment and a portion of the repeating code of the satellite signal; and

(b4) repeating steps (b2) and (b3) to produce a plurality of inner products.

4. The method of claim 3, further comprising:

generating the code segments from a lookup table by selecting one of a fixed number of non-overlapping segments of the pseudorandom code.

5. The method of claim 3, wherein the repeating code is a C/A code of a global positioning system.

6. The method of claim 5, wherein step (a3) comprises:

multiplying each sample in the portion of the C/A code with a respective chip of the selected code segment; and

summing each multiplication result with other multiplication results to produce the inner product.

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

8. The method of claim 1, further comprising:

dividing the satellite signal into in-phase and quadrature components; and

separately performing step (b) on the in-phase and quadrature components.

9. A receiver of global positioning system (GPS) signals, comprising:

an RF/IF converter for filtering and frequency translating received GPS signals having a repeating code to form an IF signal;

a tuner for producing an in-phase (I) signal and a quadrature (Q) signal;

a convolution processor for multiplying portions of a C/A reference code with portions of the repeating code of the I and Q signals to produce a plurality of I and Q inner products; and

a first accumulator for accumulating the I inner products over a period less than a period of the repeating code to-produce an I correlation over a period less than a period of the repeating code; and

a second accumulator for accumulating the Q inner products over a period less than a period of the repeating code to produce a Q correlation over a period less than a period of the repeating code.

10. The receiver of claim 9, further comprising:

a signal normalizer for generating normalizer values representative of the magnitude or power of the I and Q correlations; and

a magnitude accumulator for summing the normalizer values.

11. The receiver of claim 10, further comprising:

a plurality of processing channels, where each channel produces an I correlation and a Q correlation for a different GPS signal.

12. The receiver of claim 10, further comprising:

a computer for computing a position location using the sum of the normalizer values.

13. A method of estimating a frequency shift in a digital signal having a repeating code, comprising:

correlating the digital signal with a pseudorandom reference code to produce a first correlation;

correlating the digital signal with a pseudorandom reference code to produce a second correlation;

determining a first signal delay from the first correlation;

determining a second signal delay from the second correlation; and

computing the frequency shift using a difference between the first and second signal delays over time.

14. The method of claim 13, wherein the steps of correlating the digital signal to produce the first correlation and correlating the digital signal to produce the second correlation comprise:

multiplying portions of the pseudorandom reference code with portions of the digital signal to produce a correlation over a first period.

15. The method of claim 14, further comprising:

forming values representative of a magnitude or a power of the correlation to produce an energy signal;

repeating the steps of multiplying and forming to produce a plurality of energy signals; and

summing the plurality of energy signals as each energy signal is produced.

16. The method of claim 14, wherein the step of multiplying comprises:

(a) dividing the pseudorandom reference code into a plurality of code segments;

(b) selecting a code segment;

(c) forming an inner product between the selected code segment and a portion of the repeating code of the digital signal; and

(d) repeating steps (b) and (c) to produce the correlation.

17. The method of claim 14, further comprising:

correlating the digital signal with a pseudorandom reference code to produce at least one additional correlation by multiplying portions of the pseudorandom reference code with portions of the digital signal over a second period.

18. The method of claim 17, wherein the second period is longer than the first period.

19. The method of claim 18, wherein the first period is less than a period of the repeating code.

20. The method of claim 19, wherein the period of the repeating code is 1 millisecond.

21. The method of claim 20, wherein the repeating code comprises a C/A code of a global positioning system.