Method and apparatus for performing signal correlation

• US 20020175857A1
• Filed: 02/22/2002
• Published: 11/28/2002
• 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
• Granted Patent: US 6,891,880 B2
• Time in Patent Office: Days
• US Class Current: 342/357.12
• 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 1/7075 with code phase acquisition
• 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 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 apparatus comprises a vector multiplier running at high speed to achieve the same result as a vector multiplier sized to process an entire epoch. Additionally, the input samples to, and the output samples of, the vector multiplier can be quantized to reduced circuit complexity.

Claims

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

a decimation circuit for producing a subsampled in-phase (I) signal and a subsampled quadrature (Q) signal from received GPS signals;

a quantizer for producing quantized I and Q samples from the subsampled I and Q signals;

a convolution processor for producing I and Q correlations.

3. The receiver of claim 1 wherein the quantizer produces the quantized I and Q samples by assigning each sample of the subsampled I and Q signals to one of a plurality of bins in accordance with one or more magnitude thresholds.

4. The receiver of claim 3 wherein samples of the subsampled I and Q signals having a zero value are assigned to one of the plurality of bins in a substantially random manner.

5. The receiver of claim 3 wherein samples of the subsampled I and Q signals having a zero value are assigned to one of the plurality of bins according to a repeating pattern.

6. The receiver of claim 1 further comprising a second quantizer for quantizing the I and Q correlations.

2. The receiver of claim 2 wherein the quantized I and Q samples are represented using two bits.

7. A method of receiving global positioning system (GPS) signals comprising:

decimating received GPS signals to produce a subsampled in-phase (I) signal and a subsampled quadrature (Q) signal;

quantizing the subsampled I and Q signals to produce quantized I and Q samples;

multiplying a C/A reference code with the quantized I and Q samples to produce I and Q correlations.

8. The method of claim 7 wherein the step of quantizing the subsampled I and Q signals further comprises representing the I and Q samples with two bits.

9. The method of claim 7 wherein the quantized I and Q samples are produced by assigning each sample of the subsampled I and Q signals to one of a plurality of bins in accordance with one or more magnitude thresholds.

10. The method of claim 9 wherein samples of the subsampled I and Q signals having a zero value are assigned to one of the plurality of bins in a substantially random manner.

11. The method of claim 9 wherein samples of the subsampled I and Q signals having a zero value are assigned to one of the plurality of bins according to a repeating pattern.

12. The method of claim 7 further comprising quantizing the I and Q correlations.

15. The receiver of claim 14 wherein the magnitude approximation circuit produces the complex magnitude values by individually computing the absolute value of the I and Q values and outputting

17. The receiver of claim 16 further comprising an offset value register for accumulating offsets stored in the minimum value register.

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

a decimation circuit for producing a subsampled in-phase (I) signal and a subsampled quadrature (Q) signal from received GPS signals;

a convolution processor for producing I and Q correlations;

a divider for reducing the number of bits of precision of the I and Q correlations to produce quantized I and Q correlations;

a signal normalizer for normalizing the quantized I and Q correlations to produce complex magnitude values; and

a magnitude accumulator for summing the complex magnitude values.

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

a decimation circuit for producing a subsampled in-phase (I) signal and a subsampled quadrature (Q) signal from received GPS signals;

a convolution processor for producing I and Q correlations;

a magnitude approximation circuit for normalizing the I and Q correlations to produce complex magnitude values; and

a magnitude accumulator for summing the complex magnitude values.

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

a decimation circuit for producing a subsampled in-phase (I) signal and a subsampled quadrature (Q) signal from received GPS signals;

a convolution processor for producing I and Q correlations;

a signal normalizer for normalizing the quantized I and Q correlations to produce complex magnitude values;

a magnitude accumulator for summing subsets of the complex magnitude values; and

a minimum value register for storing a minimum magnitude value for each of the subsets of complex magnitude values to produce an offset, and for subtracting the offset from the complex magnitude values.