Flexible sliding correlator for direct sequence spread spectrum systems

• US 6,363,105 B1
• Filed: 02/17/1998
• Issued: 03/26/2002
• Est. Priority Date: 02/17/1998
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Barrow, David, Ramesh, Rajaram, Roberts, Clarence V., Sourour, Essam, Bottomley, Greg
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Tran, Khai
• Application Number:
  US09/024,120
• Time in Patent Office: 1,498 Days
• Field of Search: 375/208, 375/343, 375/200, 375/207, 375/209, 375/349, 375/350, 375/229, 708/422, 708/425, 329/358, 329/351, 329/323
• US Class Current: 375/150
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70752 Partial correlation
• CPC Class Codes: H04B 1/70758 Multimode search, i.e. using multiple search strategies
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 1/7095 Sliding correlator type
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2201/70711 with modular structure

Abstract

A flexible sliding correlator for use in a spread spectrum receiver divides baseband signal samples into different groups, associates each group with a different section of a spreading code, and combines ones of the signal samples with corresponding values in the spreading code section. The groupings and spreading code sections can be changed during operation of the receiver to maximize performance of the receiver under different or changing conditions. In addition, the sample and spreading code value combinations can be further combined in different ways, and the further combinations can be changed during operation of the receiver. According to another aspect of the invention, the baseband signal can be sampled either uniformly or non-uniformly. The phase and frequency of the baseband sampling can be adjusted during operation of the receiver so that samples are taken very close to the optimum sampling position, at the peak of a chip waveform in the baseband signal.

Claims

1. A spread spectrum receiver, comprising:

an antenna for receiving a composite signal;

processing circuitry for converting the composite signal into a baseband signal;

a sampler for sampling the baseband signal non-uniformly; and

a sliding correlator for correlating the non-uniformly sampled baseband signal with at least one section of at least one spreading code, the sliding correlator including a delay line, a plurality of delay taps from the delay line, a plurality of multiplying taps, each multiplying tap connecting to a different one of the plurality of delay taps for multiplying a value carried by the corresponding delay tap to generate an output, and a plurality of summers, each summer summing outputs of the multiplying taps.

2. The spread spectrum receiver of claim 1 wherein the plurality of multiplying taps comprise a plurality of groups of multiplying taps and each summer sums outputs of the multiplying taps of one of the groups of multiplying taps.

3. The spread spectrum receiver of claim 1 further comprising a plurality of delay lines and a plurality of delay taps from each delay line and wherein each summer sums outputs of the multiplying taps corresponding to the same delay line.

4. The spread spectrum receiver of claim 1 wherein each multiplying tap multiplies the value carried by the corresponding delay tap with a plurality of code values corresponding to code sections and each summer sums outputs of the multiplying taps corresponding to the same delay line and same code section.

5. A sliding correlator comprising:

a delay line;

a plurality of series delay taps from the delay line;

a plurality of groups of multiplying taps, each multiplying tap connecting to a different one of the plurality of series delay taps from the delay line for multiplying a value carried by the corresponding delay tap to generate an output;

a plurality of summers, each summer summing outputs of the multiplying taps of one of the groups of multiplying taps to provide a respective sum for each group of multiplying taps such that each respective sum is a sum of less than all of the multiplying taps from the series delay line; and

a processor that generates a squared magnitude of one of the sums for a respective group of multiplying taps such that the squared magnitude is a squared magnitude of a sum of less than all of the multiplying taps from the delay line.

6. The sliding correlator of claim 5, wherein each of the groups of multiplying taps contains values corresponding to a different spreading code.

7. The sliding correlator of claim 5, wherein each of the groups of multiplying taps contains values corresponding to a different section of a spreading code.

8. The sliding correlator of claim 7, wherein the different sections of the spreading code are non-contiguous.

9. The sliding correlator of claim 7, wherein the different sections of the spreading code are contiguous.

10. The sliding correlator of claim 7, wherein an output of at least one of the summers is non-coherently added.

11. The sliding correlator of claim 7, wherein an output of at least one of the summers is coherently added.

12. A sliding correlator comprising:

a delay line;

a plurality of delay taps from the delay line;

a plurality of groups of multiplying taps, each multiplying tap connecting to a different one of the plurality of series delay taps for multiplying a value carried by the corresponding delay tap to generate an output; and

a plurality of summers, each summer summing outputs of the multiplying taps of one of the groups of multiplying taps;

wherein a first one of the groups of multiplying taps has a first number of multiplying taps, a second one of the groups of multiplying taps has a second number of multiplying taps, and the second number is different from the first number.

13. A sliding correlator comprising:

a delay line;

a plurality of delay taps from the delay line;

a plurality of groups of multiplying taps, each multiplying tap connecting to a different one of the plurality of delay taps for multiplying a value carried by the corresponding delay tap to generate an output; and

a plurality of summers, each summer summing outputs of the multiplying taps of one of the groups of multiplying taps;

wherein at least one of the groups of multiplying taps is turned off during operation of the sliding correlator.

14. A sliding correlator, comprising:

a delay line;

a plurality of delay taps from the delay line;

a plurality of multiplying taps, each multiplying tap connecting to a different one of the plurality of delay taps for multiplying a value carried by the corresponding delay tap with a plurality of code values corresponding to code sections to produce a plurality of outputs; and

a plurality of summers, each summer summing outputs of the multiplying taps corresponding to the same code section.

15. The sliding correlator of claim 14, wherein the different code sections correspond to contiguous sections of a spreading code.

16. The sliding correlator of claim 14, wherein outputs corresponding to different code sections are produced in parallel.

17. The sliding correlator of claim 14, wherein outputs corresponding to different code sections are produced sequentially.

18. The sliding correlator of claim 14, wherein only a subset of multiplying taps outputs are produced, corresponding to a subset of code sections.

19. The sliding correlator of claim 14, wherein an output of at least one of the summers is coherently added.

20. The sliding correlator of claim 14, wherein an output of at least one of the summers is non-coherently added.

21. A sliding correlator, comprising:

a plurality of delay lines;

a plurality of delay taps from each delay line;

a plurality of multiplying taps, each multiplying tap connecting to a different one of the plurality of delay taps for multiplying a value carried by the corresponding delay tap with a code value;

a plurality of summers, each summer summing outputs of the multiplying taps corresponding to the same delay line; and

a switch coupled between an output of of a first delay line and an input of a second delay line wherein the switch selectively couples the input of the second delay line to the output of the first delay line.

22. A sliding correlator, comprising:

a plurality of delay lines;

a plurality of delay taps from each delay line;

a plurality of multiplying taps, each multiplying tap connecting to a different one of the plurality of delay taps for multiplying a value carried by the corresponding delay tap with a plurality of code values corresponding to code sections to produce a plurality of outputs; and

a plurality of summers, each summer summing outputs of the multiplying taps corresponding to the same delay line and same code section.

23. A sliding correlator, comprising:

a memory for storing received samples;

a plurality of groups of combiners for combining different stored received samples with a code sequence to produce combined values;

a plurality of summers for adding combined values from each group of combiners to produce correlations such that each summer provides a respective sum for each group of combiners such that each respective sum is a sum of less than all of the combiners; and

a processor that generates a squared magnitude of one of the sums for a respective group of combiners such that the squared magnitude is a squared magnitude of a sum of less than all of the combiners.

24. A spread spectrum receiver comprising:

an antenna for receiving a composite signal;

processing circuitry for converting the composite signal into a baseband signal;

a sampler for sampling the baseband signal non-uniformly; and

a sliding correlator for correlating the non-uniformly sampled baseband signal with at least one section of at least one spreading code, the sliding correlator including a memory for storing received samples, a plurality of groups of combiners for combining different stored received samples with a code sequence to produce combined values, and a plurality of summers for adding combined values from each group of combiners to produce correlations.