Apparatus and method for acquiring spread-spectrum signals

• US 7,471,717 B2
• Filed: 05/17/2004
• Issued: 12/30/2008
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: Prolific Technology Inc.
• Inventors: Huang, Yi Ping
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): LAM, KENNETH T
• Application Number:
  US10/847,244
• Publication Number:
  US 20050254560A1
• Time in Patent Office: 1,688 Days
• Field of Search: 375/150, 375/130, 375/140, 375/147
• US Class Current: 375/150
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

An apparatus for acquiring spread-spectrum signals includes a mixer for generating an in-phase signal and a quadrature signal from the spread-spectrum signal, a decimator for subsampling the in-phase signal and the quadrature signal, a correlation engine for producing an in-phase correlation between the subsampled in-phase signal and a PN code and producing a quadrature correlation between the subsampled quadrature signal and the PN code, a first coherent integrator for accumulating a plurality of in-phase correlations to produce an in-phase coherent integration, a second coherent integrator for accumulating a plurality of quadrature correlations to produce a quadrature coherent integration, an incoherent integrator for accumulating the in-phase coherent integrations and the quadrature coherent integrations to produce an incoherent integration, and a signal detector for checking the presence of the spread-spectrum signal based on the incoherent integration.

Claims

1. An apparatus for acquiring spread-spectrum signals comprising:

a decimator means for generating a plurality of samples based on the spread-spectrum signal;

a serial-to-parallel converter means connected to the decimator means for grouping a plurality of samples into a word;

a first memory means with a data width for storing the word;

a correlation engine means having a plurality of partial correlation modules connected to the first memory, said correlation engine means for calculating a partial correlation between the word and a PN code segment, wherein the partial correlation module comprises;

a plurality of multipliers and an adder for calculating an inner product of the word and the PN code segment to produce the partial correlation; and

an accumulator means for accumulating a plurality of partial correlations to produce a complete correlation;

a coherent integrator means connected to the correlation engine means for accumulating a plurality of complete correlations to generate a coherent integration;

an incoherent integrator means connected to the coherent integrator means for accumulating a plurality of coherent integrations to generate an incoherent integration; and

a signal detector means connected to the incoherent integrator means for checking the presence of the spread-spectrum signal based on the incoherent integration, said incoherent integrator means comprises;

an incoherent memory means for storing the incoherent integration;

a first squaring means for squaring an in-phase component of the coherent integration;

a second squaring means for squaring a quadrature component of the coherent integration;

a third squaring means for squaring a previous incoherent integration;

an adding means for summing outputs of the first, second and third squaring means for generating a squared value; and

a square-root means for taking a square-root of the squared value to generate the incoherent integration and for halving a number of bits required for storing the output from the adding means.

2. The apparatus for acquiring spread-spectrum signals of claim 1, wherein the signal detector means comprises:

a first registering means for storing a largest peak value of the incoherent integration and its corresponding offset within the incoherent integration, said first registering means having a first set of registers;

a second registering means for storing a second largest peak value of the incoherent integration and its corresponding offset within the incoherent integration, said second registering means having a second set of registers; and

a comparing means for comparing the difference between the largest peak value and the second largest peak value with a programmed threshold to check the presence of the spread-spectrum signal.

3. The apparatus for acquiring spread-spectrum signals of claim 1, wherein the incoherent integrator means further comprises a DC-bias removal device, said DC-bias removal device comprising:

a second memory means for storing a minimal DC-bias of a previous incoherent integration;

a subtracting means subtracting an output of the adding means by the minimal DC-bias stored in the second memory means; and

a DC-bias detecting means for detecting the minimal DC-bias of a current incoherent integration from the subtracting means.

4. The apparatus for acquiring spread-spectrum signals of claim 1, wherein the decimator means generates the samples at a rate of K samples-per-chip, the word consists of M samples, and the correlation engine means includes M partial correlation modules for calculating the partial correlation.

5. The apparatus for acquiring spread-spectrum signals of claim 4, wherein the K is 2^N, M is multiple of K, and N and M are positive integer numbers.

6. An apparatus for acquiring spread-spectrum signals comprising:

a mixing means for generating an in-phase signal and a quadrature signal from the spread-spectrum signal;

a decimating means connected to the mixing means for subsampling the in-phase signal and the quadrature signal;

a correlation engine means connected to the decimating means for producing an in-phase correlation between the subsampled in-phase signal and a PN code, and a quadrature correlation between the subsampled quadrature signal and the PN code;

a first coherent integrating means connected to the correlation engine means for accumulating a plurality of in-phase correlations to produce an in-phase coherent integration;

a second coherent integrating means connected to the correlation engine means for accumulating a plurality of quadrature correlations to produce a quadrature coherent integration;

an incoherent integrating means connected to the first coherent integrating means and the second coherent integrating means for accumulating a plurality of in-phase coherent integrations and the quadrature coherent integrations to produce an incoherent integration; and

a signal detecting means connected to the incoherent integrating means for checking the presence of the spread-spectrum signal based on the incoherent integration, said incoherent integrating means comprises;

an incoherent memory means for storing the incoherent integration;

a first squaring means for squaring the in-phase coherent integration;

a second squaring means for squaring the quadrature coherent integration;

a third squaring means for squaring a previous incoherent integration;

an adding means for summing outputs of the first, second and third squaring means to generate a squared value; and

a square-root means for taking a square-root of the squared value to generate the incoherent integration and for halving a number of bits required for storage.

7. The apparatus for acquiring spread-spectrum signals of claim 6, wherein the signal detecting means comprises:

a first registering means for storing a largest peak value of the incoherent integration and its corresponding offset within the incoherent integration, said first registering means having a first set of registers;

a second registering means for storing a second largest peak value of the incoherent integration and its corresponding offset within the incoherent integration, said second registering means having a second set of registers; and

a comparating means for comparing the difference between the largest peak value and the second largest peak value with a programmed threshold to check the presence of the spread-spectrum signal.

8. The apparatus for acquiring spread-spectrum signals of claim 6, wherein the incoherent integrating means further comprises a DC-bias removal device, said DC-bias removal device comprising:

a memory means for storing a minimal DC-bias of a previous incoherent integration;

a subtracting means for subtracting the output of the adding means by the minimal DC-bias stored in the memory means; and

a DC-bias detecting means for detecting the minimal DC-bias of a current incoherent integration from the subtracting means.

9. The apparatus for acquiring spread-spectrum signals of claim 6, wherein the decimating means subsamples the in-phase signal and the quadrature signal at a rate of K samples-per-chip, the correlation engine means includes 2M partial correlation modules for calculating the partial correlation, and M is multiple of K.

10. The apparatus for acquiring spread-spectrum signals of claim 9, wherein the K is 2^N, and N is a positive integer.

11. A method for acquiring spread-spectrum signals comprising the steps of:

generating an in-phase signal and a quadrature signal from the spread-spectrum signal;

multiplying the in-phase signal with a PN code to produce an in-phase correlation, and multiplying the quadrature signal with the PN code so as to produce a quadrature correlation;

accumulating a plurality of in-phase correlations to produce an in-phase coherent integration and a plurality of quadrature correlations to produce a quadrature coherent integration;

accumulating a plurality of in-phase coherent integrations and quadrature coherent integrations so as to produce an incoherent integration; and

checking the presence of the spread-spectrum signal based on the incoherent integration, the incoherent integration is produced by the steps of;

squaring the in-phase coherent integration to produce a first value;

squaring the quadrature coherent integration to produce a second value;

squaring a previous incoherent integration to produce a third value;

summing the first, the second and third values to produce a fourth value; and

taking square root of the fourth value to generate the incoherent integration.

12. The method for acquiring spread-spectrum signals of claim 11, further comprising the steps of:

detecting a minimal DC-bias of a current incoherent integration; and

subtracting the incoherent integration by the minimal DC-bias.

13. The method for acquiring spread-spectrum signals of claim 11, wherein the presence of the spread-spectrum signal is checked by the steps of:

detecting a largest peak value of the incoherent integration;

detecting a second largest peak value of the incoherent integration; and

comparing the difference between the largest peak value and the second largest peak value with a programmed threshold to check the presence of the spread-spectrum signal.

14. The method for acquiring spread-spectrum signals of claim 11, wherein the in-phase correlation is produced by the steps of:

subsampling the in-phase signal to generate a plurality of samples at a rate of K samples-per-chip;

grouping M samples to form a word, wherein M is multiple of K and a positive integer number;

calculating an inner product between the word and a selected PN code segment to produce a partial correlation; and

summing a plurality of partial correlations to produce the in-phase correlation.

15. The method for acquiring spread-spectrum signals of claim 14, wherein K is 2^N, and N is a positive integer.

16. The method for acquiring spread-spectrum signals of claim 14, wherein the inner product is calculated by the steps of:

calculating a product between each sample of the word and a corresponding chip of the selected PN code segment; and

summing up the M products of the word and the selected PN code segment to generate the inner product.