Method and apparatus for computing signal correlation at multiple resolutions

• US 20020172267A1
• Filed: 07/06/2001
• Published: 11/21/2002
• Est. Priority Date: 05/18/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Global Locate Incorporated (Broadcom, Inc.)
• Inventors: Abraham, Charles, Fuchs, Donald L.
• Granted Patent: US 6,704,348 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 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• 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: 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 computing a convolution between an input GPS signal and a C/A code reference by generating the convolution result in real time without storing unprocessed signal samples. The method and apparatus is capable of operating in multiple modes of resolution so as to enhance the sensitivity of the convolution processing.

Claims

1. A method for computing correlations of a digital signal with a pseudorandom reference code comprising:

a) selecting a sample spacing from a plurality of sample spacings;

b) sampling the digital signal to produce a first set of digital signal samples having a first sample spacing;

c) dividing a pseudorandom reference code into a plurality of code segments;

d) selecting a code segment;

e) forming an inner product between said selected code segment and the first set of digital signal samples to produce a partial correlation;

f) repeating steps d) and e) to produce a plurality of partial correlations;

g) summing the plurality of partial correlations as each partial correlation is produced to form a plurality of first correlations.

2. The method of claim 1 further comprising:

h) selecting a region of interest using said first correlations;

i) sampling the digital signal to produce a second set of digital signal samples having a second sample spacing; and

j) performing one or more second correlations between said pseudorandom reference code and said second set of digital signal samples within said region of interest to produce one or more second correlations.

3. The method of claim 2 wherein step j) further comprises:

j1) dividing the pseudorandom reference code into a plurality of code segments;

j2) selecting a code segment;

j3) forming an inner product between said selected code segment and the second set of digital signal samples to produce a partial correlation;

j4) repeating steps j2) and j3) to produce a plurality of second partial correlations; and

j5) summing the plurality of second partial correlations as each second partial correlation is produced to form a plurality of second correlations.

4. The method of claim 1 further comprising:

dividing the pseudorandom reference code into a fixed number of non-overlapping code blocks;

dividing each of said code blocks into a fixed number of non-overlapping code segments; and

storing each said code blocks in a lookup table.

5. The method of claim 4 wherein said step d) comprise:

selecting a code block as said code segment from said lookup table.

6. The method of claim 2 wherein the pseudorandom reference code is a C/A code of the global positioning system.

7. The method of claim 6 wherein said first sample spacing is ½

of a C/A code chip.

8. The method of claim 6 wherein said second sample spacing is ⅕

of a C/A code chip.

9. The method of claim 1 further comprising:

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

separately performing steps a) through g) on said in-phase and said quadrature components.

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

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

an analog to digital converter for digitizing said IF signal;

a tuner for removing Doppler shift from said digitized signal and producing an in-phase (I) and a quadrature (Q) signal;

a decimation circuit for subsampling said I and Q signals, said subsampled I and Q signals having either a first sample spacing or a second sample spacing;

a mode selection processor for selecting either said first sample spacing or said second sample spacing; and

a convolution processor for performing convolution operations between a C/A reference code and said subsampled I and Q signals.

11. The receiver of claim 10 wherein said convolution processor comprises:

a code generator for producing a C/A reference code comprising a code lookup table and a first and a second code extender.

12. The receiver of claim 10 wherein said convolution processor comprises:

a first shift register for storing a segment of said subsampled I signal; and

a second shift register for storing a segment of said subsampled Q signal.

13. The receiver of claim 10 further comprising:

a plurality of processing channels, where each channel produces a convolution for a different GPS signal.

14. The receiver of claim 13 further comprising:

a computer for computing a position location using a plurality of convolutions.

16. The apparatus of claim 15 further comprising:

g) means for selecting a region of interest using said first correlations;

h) means for sampling the digital signal to produce a second set of digital signal samples having a second sample spacing; and

i) means for performing one or more second correlations between said pseudorandom reference code and said second set of digital signal samples within said region of interest to produce one or more second correlations.

17. The apparatus of claim 16 wherein means for performing one or more correlations further comprises:

j1) means for dividing the pseudorandom reference code into a plurality of code segments;

j2) means for selecting code segments;

j3) means for forming inner products between each of said selected code segments and the second set of digital signal samples to produce a plurality of second partial correlations; and

j4) summing the plurality of second partial correlations as each second partial correlation is produced to form a plurality of second correlations.

18. The apparatus of claim 15 further comprising:

means for dividing the pseudorandom reference code into a fixed number of non-overlapping code blocks;

means for dividing each of said code blocks into a fixed number of non-overlapping code segments; and

means for storing each said code blocks in a lookup table.

19. The apparatus of claim 18 wherein said means for selecting said code segments comprises:

means for selecting a code block as said code segment from said lookup table.

20. The apparatus of claim 16 wherein the pseudorandom reference code is a C/A code of the global positioning system.

21. The apparatus of claim 20 wherein said first sample spacing is ½

of a C/A code chip.

22. The apparatus of claim 20 wherein said second sample spacing is ⅕

of a C/A code chip.

15. Apparatus for computing correlations of a digital signal with a pseudorandom reference code comprising:

a) means for selecting a sample spacing from a plurality of sample spacings;

b) means for sampling the digital signal to produce a first set of digital signal samples having a first sample spacing;

c) means for dividing a pseudorandom reference code into a plurality of code segments;

d) means for selecting code segments;

e) means for forming inner products between each of said selected code segments and the first set of digital signal samples to produce plurality of partial correlations;

f) means for summing the plurality of partial correlations as each partial correlation is produced to form a plurality of first correlations.