Determining the correlation between received samples and available replica samples

• US 7,272,168 B2
• Filed: 04/01/2003
• Issued: 09/18/2007
• Est. Priority Date: 04/01/2003
• Status: Expired due to Fees

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Inventors: Akopian, David
• Primary Examiner(s): BURD, KEVIN MICHAEL
• Application Number:
  US10/404,931
• Publication Number:
  US 20040196894A1
• Time in Patent Office: 1,631 Days
• Field of Search: 375/150, 375/152, 375/142, 375/343, 375/130, 375/140, 375/147, 375/316, 375/340
• US Class Current: 375/150
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• 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

Abstract

The invention relates to a method, a processing unit and a system for determining the correlation between consecutive sets of samples of a received, code modulated signal and replica samples. In order to reduce the computational load, the positions of samples in said replica code sequence are grouped, each of these positions and a predetermined number of respective subsequent positions forming a subgroup and each group comprising the respective first position of all subgroups with positions associated with a similar composition of consecutive replica samples. The method combines those values of samples of the first set of samples, which are associated by their position to a respective group, separately for each group to obtain a respective preliminary result. Determining a correlation value for each of the sets of samples then comprises combining the obtained preliminary results for all groups separately for each of the sets of samples.

Claims

1. A method for determining the correlation between consecutive sets of samples of a code modulated signal received at a receiver on the one hand and samples of an available replica code sequence on the other hand, a respective next set of samples being formed by adding at least one new sample of said received signal to a current set of samples and by removing at least the oldest sample from said current set of samples, the samples of a respective set of samples and of said replica code sequence being aligned to each other, wherein positions of samples in said replica code sequence are grouped, each of said grouped positions and a predetermined number of respective subsequent positions forming a subgroup and each group comprising the respective first position of all subgroups with positions associated with a similar composition of consecutive samples of said replica code sequence, said method comprising:

combining the values of those samples of a first set of samples, which are associated by their position to a respective group, separately for each group to obtain a respective preliminary result;

determining a correlation value for each of said sets of samples by combining the obtained preliminary results for all groups separately for each of said sets of samples taking into account for each group the respective composition of consecutive samples of said replica code sequence associated with those subgroups which are associated by their first positions to the respective group, and by adding the products between samples of the respective set of samples and of said replica code sequence at the same position for those positions at which said samples are not comprised in said preliminary results; and

using said correlation value for each of said sets of samples to determine the correlation between each of said sets of samples and said replica code sequence.

2. The method according to claim 1, wherein each group comprises the respective first position of all subgroups including consecutive positions associated with an identical composition of sample values of said replica code sequence.

3. The method according to claim 1, wherein each group comprises the respective first position of all subgroups including consecutive positions for which the composition of the differences between the values of the replica samples at all included positions except for the respective first position and the value of the replica sample associated with the respective first position is identical.

4. The method according to claim 3,

wherein the number of samples in each of said sets of samples and the number of samples of said replica code sequence is N, and wherein the number of said sets of samples is K+1,

wherein the employed code is a binary code using sample values of +1 and −

1, the samples of the k^th set of samples proceeding from an i^th iteration stage being denoted as;

x<sub>N−

1+k+i</sub>, x<sub>N+k−

1+i</sub>, x<sub>N+k−

2+i</sub>, . . . , x_k+2+i, x_k+1+i, x_k+1, with k=0 to K, and the samples of said replica code sequence being denoted as;

r<sub>N−

1</sub>,r<sub>N−

2</sub>, . . . ,r₃,r₂,r₁,r₀;

wherein 2^K groups J_{b1 . . . bk} are defined, b₁. . . b_K being a notation of sign changes with b_p=(r_j·

r<sub>j−

p</sub>), p=1 . . . K, and wherein a position j is defined to belong to a specific one of said groups J_{b1. . . bk}, if (r_jr<sub>j−

1</sub>. . . r<sub>j−

k</sub>)=±

(1,b₁, . . . , b_k) with j=k, . . . , N−

1;

wherein said preliminary result for each group is determined to be

5. The method according to claim 1, wherein it is determined whether a sample at a particular position in said received signal is associated by its position to a particular group by evaluating the composition of the values of the samples of said replica code sequence at said particular position and the following K−

1 positions.

6. The method according to claim 5, wherein the employed code is a binary code, and wherein said composition of the values of the samples of said replica code sequence at said particular position is evaluated by means of an XOR logic.

7. The method according to claim 1, wherein said signal received at a receiver is a signal transmitted by a satellite of a satellite positioning system.

8. A processing unit for determining the correlation between consecutive sets of samples of a code modulated signal received at a receiver on the one hand and samples of an available replica code sequence on the other hand, a respective next set of samples being formed by adding at least one new sample of said received signal to a current set of samples and by removing at least the oldest sample from said current set of samples, the samples of a respective set of samples and of said replica code sequence being aligned to each other, wherein positions of samples in said replica code sequence are grouped, each of said grouped positions and a predetermined number of respective subsequent positions forming a subgroup and each group comprising the respective first position of all subgroups with positions associated with a similar composition of consecutive samples of said replica code sequence, said processing unit cormprising:

a combining portion for combining those values of the samples of a first set of samples of a received signal, which are associated by their positions to a respective group, separately for each group to obtain a respective preliminary result;

a combining portion for determining a correlation value for each of said sets of samples by combining the obtained preliminary results for all groups separately for each of said sets of samples taking into account for each group the respective composition of consecutive samples of said replica code sequence associated with the subgroups which are associated by their first positions to the respective group, and by adding the products between samples of the respective set of samples and of said replica code sequence at the same position for those positions at which said samples are not comprised in said preliminary results; and

a determining portion for determining the correlation between each of said sets of samples and said replica code sequence using said correlation value for each of said sets of samples.

9. The processing unit according to claim 8, wherein said processing unit is a correlator.

10. The processing unit according to claim 9, wherein said processing unit is a matched filter.

11. The processing unit according to claim 8, wherein said processing unit is said receiver receiving said code modulated signal.

12. The processing unit according to claim 8, wherein said processing unit comprises a receiving component for receiving said samples of a signal received at said receiver from said receiver.

13. A system for determining the correlation between consecutive sets of samples of a code modulated signal received at a receiver on the one hand and samples of an available replica code sequence on the other hand, a respective next set of samples being formed by adding at least one new sample of said received signal to a current set of samples and by removing at least the oldest sample from said current set of samples, the samples of a respective set of samples and of said replica code sequence being aligned to each other, wherein positions of samples in said replica code sequence are grouped, each of said grouped positions and a predetermined number of respective subsequent positions forming a subgroup and each group comprising the respective first position of all subgroups with positions associated with a similar composition of consecutive samples of said replica code sequence, said system comprising:

a combining portion for combining those values of the samples of a first set of samples of a received signal, which are associated by their positions to a respective group, separately for each group to obtain a respective preliminary result;

a combining portion for determining a correlation value for each of said sets of samples by combining the obtained preliminary results for all groups separately for each of said sets of samples taking into account for each group the respective composition of consecutive samples of said replica code sequence associated with the subgroups which are associated by their first positions to the respective group, and by adding the products between samples of the respective set of samples and of said replica code sequence at the same position for those positions at which said samples are not comprised in said preliminary results; and

a determining portion for determining the correlation between each of said sets of samples and said replica code sequence using said correlation value for each of said sets of samples.

14. A computer program product for determining the correlation between consecutive sets of samples of a code modulated signal received at a receiver on the one hand and samples of an available replica code sequence on the other hand, a respective next set of samples being formed by adding at least one new sample of said received signal to a current set of samples and by removing at least the oldest sample from said current set of samples, the samples of a respective set of samples and of said replica code sequence being aligned to each other, wherein positions of samples in said replica code sequence are grouped, each of said grouped positions and a predetermined number of respective subsequent positions forming a subgroup and each group comprising the respective first position of all subgroups with positions associated with a similar composition of consecutive samples of said replica code sequence, said computer program product comprising computer readable software code stored on a computer readable medium, said computer readable software code realizing the following when executed by a computer:

combining the values of those samples of a first set of samples, which are associated by their position to a respective group, separately for each group to obtain a respective preliminary result;

determining a correlation value for each of said sets of samples by combining the obtained preliminary results for all groups separately for each of said sets of samples taking into account for each group the respective composition of consecutive samples of said replica code sequence associated with those subgroups which are associated by their first positions to the respective group, and by adding the products between samples of the respective set of samples and of said replica code sequence at the same position for those positions at which said samples are not comprised in said preliminary results; and

using said correlation value for each of said sets of samples to determine the correlation between each of said sets of samples and said replica code sequence.