Apparatus and method for acquiring spread-spectrum signals

• US 20050254560A1
• Filed: 05/17/2004
• Published: 11/17/2005
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: Prolific Technology Inc.
• Inventors: Huang, Yi Ping
• Granted Patent: US 7,471,717 B2
• Time in Patent Office: Days
• 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 generating a plurality of samples based on the spread-spectrum signal;

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

a first memory with a data width capable of storing the word; and

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

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

an accumulator for a plurality of partial correlations to produce a complete correlation.

2. The apparatus for acquiring spread-spectrum signals of claim 1, further comprising:

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

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

a signal detector connected to the incoherent integrator checking the presence of the spread-spectrum signal based on the incoherent integration.

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

a first set of registers storing a largest peak value of the incoherent integration and a corresponding offset thereof within the incoherent integration;

a second set of registers storing a second largest peak value of the incoherent integration and a corresponding offset thereof within the incoherent integration; and

a comparator for a 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.

4. The apparatus for acquiring spread-spectrum signals of claim 2, wherein the incoherent integrator comprises:

an incoherent memory storing the incoherent integration;

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

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

a third squaring device for a previous incoherent integration;

an adder for outputs of the first, second and third squaring devices so as to generate a squared value; and

a square-root device for the squared value to generate the incoherent integration and halves the number of bits required for storing the output from the adder.

5. The apparatus for acquiring spread-spectrum signals of claim 4, wherein the incoherent integrator further comprises a DC-bias removal devices, said removal device comprising:

a second memoryr storing a minimal DC-bias of a previous incoherent integration;

a subtracter for the output of the adder by the minimal DC-bias stored in the second memory; and

a DC-bias detector for the minimal DC-bias of a current incoherent integration from the subtracter.

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

7. The apparatus for acquiring spread-spectrum signals of claim 6, wherein the K is 2^N, M is multiple of K, and N and M are positive integer numbers.

8. An apparatus for acquiring spread-spectrum signals, comprising:

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

a decimator connected to the mixer for subsampling the in-phase signal and the quadrature signal;

a correlation engine connected to the decimator 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 integrator connected to the correlation engine accumulating a plurality of in-phase correlations to produce an in-phase coherent integration;

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

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

a signal detector connected to the incoherent integrator checking the presence of the spread-spectrum signal based on the incoherent integration.

9. The apparatus for acquiring spread-spectrum signals of claim 8, wherein the signal detector comprises:

a first set of registers storing a largest peak value of the incoherent integration and a corresponding offset thereof within the incoherent integration;

a second set of registers storing a second largest peak value of the incoherent integration and a corresponding offset thereof within the incoherent integration; and

a comparator for 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.

10. The apparatus for acquiring spread-spectrum signals of claim 8, wherein the incoherent integrator comprises:

an incoherent memory storing the incoherent integration;

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

a second squaring device for the quadrature coherent integration;

a third squaring device for a previous incoherent integration;

an adder for outputs of the first, second and third squaring devices to generate a squared value; and

a square-root device for the squared value to generate the incoherent integration and halves the number of bits required for storage.

11. The apparatus for acquiring spread-spectrum signals of claim 10, wherein the incoherent integrator further comprises a DC-bias removal device, said removal device comprising:

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

a subtracter for the output of the adder by the minimal DC-bias stored in the memory; and

a DC-bias detector for the minimal DC-bias of a current incoherent integration from the subtracter.

12. The apparatus for acquiring spread-spectrum signals of claim 8, wherein the decimator subsamples the in-phase signal and the quadrature signal at a rate of K samples-per-chip, the correlation engine comprises 2M partial correlation modules for calculating the partial correlation, M being a multiple of K.

13. The apparatus for acquiring spread-spectrum signals of claim 12, wherein the K is 2^N, and N is a positive integer.

14. 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.

15. The method for acquiring spread-spectrum signals of claim 14, wherein producing the incoherent integration is comprised of 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.

16. The method for acquiring spread-spectrum signals of claim 15, 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.

17. The method for acquiring spread-spectrum signals of claim 14, wherein checking the presence of the spread-spectrum signal is comprised of the steps of:

detecting the largest peak value of the incoherent integration;

detecting the 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.

18. The method for acquiring spread-spectrum signals of claim 14, wherein producing the in-phase correlation is comprised of 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.

19. The method for acquiring spread-spectrum signals of claim 18, wherein K is 2^N, and N is a positive integer.

20. The method for acquiring spread-spectrum signals of claim 18, wherein calculating the inner product is comprised of 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.