Parallel correlator for a spread spectrum receiver

• US 6,009,118 A
• Filed: 06/26/1997
• Issued: 12/28/1999
• Est. Priority Date: 07/12/1996
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Harrison, Daniel David, Tiemann, Jerome Johnson
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/883,163
• Time in Patent Office: 915 Days
• Field of Search: 375/200, 375/202, 375/203, 375/206-208, 375/343
• US Class Current: 375/150
• CPC Class Codes: G01S 19/09 providing processing capability normally carried out by the receiver
• 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 19/34 Power consumption
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/0054 of actual mobile position, i.e. position calculation on base station
• 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 1/708 Parallel implementation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 2201/70709 with discontinuous detection
• CPC Class Codes: H04W 52/0283 with sequential power up or power down of successive circuit blocks, e.g. switching on the local oscillator before RF or mixer stages
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A direct sequence spread spectrum receiver samples an incoming signal and stores the sample in memory. The signal sample is read from memory as necessary to process the signal without further signal acquisition. The correlator calculates an inner product by simultaneously correlating each bit of the sample with a corresponding bit of a replica signal. If the inner product does not exceed a threshold value the correlator calculates another inner product between the same signal sample and another replica signal. This occurs until all available signals are identified. In one embodiment, memory is segmented and each segment is read by a separate correlator allowing faster identification of one signal or multiple signals to be acquired simultaneously. Such a receiver is useful in global positioning satellite (GPS) signal processing where the incoming signal contains several satellite transmissions encoded with CDMA encoding.

Claims

1. In a direct sequence spread spectrum receiver capable of receiving a plurality of signals from respective transmitters, apparatus comprising:

a tuner for receiving at least one of said signals;

a converter coupled to said tuner for producing a digital sample segment of said one signal;

a memory coupled to said converter for storing said digital sample segment;

a replica signal generator for producing replica representations;

a correlator coupled to said memory and said replica signal generator for correlating said digital sample segment and one of said replica representations to produce a correlation result, whereby said correlator simultaneously correlates corresponding samples of said digital sample segment and said one of said replica representations, said correlator comprising an array of multipliers for multiplying N corresponding bits of said digital sample segment and said replica representations, and a summer, whereby said array of multipliers simultaneously produces N multiplier results and said summer simultaneously adds said N multiplier results; and

means for identifying a predetermined transmitter from said result whereby, if said transmitter is not identified, said correlator correlates said digital sample segment with others of said replica representations until said identifying means identifies said transmitter.

2. The receiver of claim 1, wherein:

said replica signal generator is adapted to produce replica representations corresponding to another of said transmitters; and

said correlator is adapted to correlate said digital sample segment with said representations until said other transmitter is identified;

whereby said digital sample segment stored in said memory is accessed by said correlator as necessary until all possible transmitters are identified.

3. The receiver of claim 1, wherein said memory has N segments, N being an integer number;

and

said receiver has an additional N-1 correlators;

whereby each of said N memory segments provides a digital sample segment to corresponding ones of the N correlators.

4. The receiver of claim 1, wherein:

one of a group consisting of said memory and said replica signal generator has an output shift register; and

after a correlation the contents of said shift register are shifted for another correlation with the other one of said group.

5. The receiver of claim 1, wherein:

said replica signal generator includes a satellite code generator for providing satellite code and a Doppler offset generator for providing frequency offset, said replica signal generator being s adapted to provide combinations of said satellite code and said frequency offset.

6. The receiver of claim 1, wherein:

each multiplier of said array of multipliers is adapted to accept one-bit data.

7. The receiver of claim 1, wherein:

each multiplier of said array of multipliers is adapted to accept two-bit data.

8. The receiver of claim 1, wherein:

said correlator further comprises a converter for receiving said multiplier results and providing an analog representation of said multiplier results to said summer.

9. The receiver of claim 8, wherein:

said converter comprises an array of converters, one for each multiplier in said array of multipliers.

10. The receiver of claim 1, wherein:

said replica signal generator is adapted to provide separate parallel outputs for code replica and Doppler replica signals, wherein said code replica includes the combination of a code offset and a satellite code; and

said array of multipliers is adapted to accept said digital sample segment, said Doppler replica signals and said combination to produce correlation results.

11. The receiver of claim 10, including a converter for accepting said correlation results to produce differential analog results, said summer comprising a differential summer for accepting said differential analog results and producing an analog summation.

12. The receiver of claim 11, wherein said differential analog results are squared before said summer produces said analog summation.

18. The receiver of claim 1, wherein:

each of said correlators further comprises a converter for receiving results from said array of multipliers and providing an analog representation of said array of multipliers results to said summer.

13. In a direct sequence spread spectrum receiver capable of receiving a plurality of signals from respective transmitters, apparatus comprising:

a tuner for receiving at least one of said signals;

a converter coupled to said tuner for producing a digital sample segment of said one signal;

a memory coupled to said converter for storing said digital sample segment;

a plurality N of replica signal generators for producing replica representations;

N correlators coupled to said memory and to corresponding ones of said N replica signal generators for correlating said digital sample segment and one of said replica representations from each of said N replica signal generators to produce N correlation results, said correlators being adapted to simultaneously correlate corresponding samples of said digital sample segment and said one of said replica representations, each of said correlator comprising an array of multipliers for multiplying N corresponding bits of said digital sample segment and said replica representations, and a summer said multipliers being adapted to simultaneously produce N multiplier results and said summer being adapted to simultaneously add said N multiplier results; and

means for identifying a number of transmitters from said N correlation results, whereby if a number of N correlators do not identify said transmitters, said number of said N correlators correlate said digital sample segment with others of said replica representations from each of said corresponding N replica signal generators until said identifying means identifies said number of transmitters.

14. The receiver of claim 13, wherein:

one of a group consisting of said memory and said replica signal generators includes an output shift register; and

after a correlation of a corresponding sample of said digital sample segment and said one of said replica representations the contents of said shift register is shifted for another correlation of said digital sample segment with another of said replica representations.

15. The receiver of claim 13, wherein:

each of said replica signal generator includes a satellite code generator for providing satellite code and a Doppler offset generator for providing frequency offset, said each replica signal generator being adapted to provide combinations of said satellite code and said frequency offset.

16. The receiver of claim 13, wherein:

each multiplier of said array of multipliers is adapted to accept one-bit data.

17. The receiver of claim 13, wherein:

each multiplier of said array of multipliers is adapted to accept two-bit data.

19. The receiver of claim 13, wherein:

each of said correlators further comprises an array of converters, one for each multiplier in said array of multipliers, for receiving results from said multiplier array and providing an analog representation of said multiplier array results to said summer.

20. The receiver of claim 13, wherein:

each of said replica signal generator includes means for generating a separate Doppler frequency and a combination of a code offset and a satellite code, said array of multipliers being adapted to accept said one of said replica representations, said frequency offset and said combination to produce correlation results.

21. The receiver of claim 20, including a converter for accepting said correlation results to produce differential analog results, and wherein said summer comprises a differential summer for accepting said differential analog results and producing an analog summation.

22. The receiver of claim 20, including:

a converter for accepting said correlation results to produce differential analog results; and

squaring means coupling said converter to said summer, said summer comprising a differential summer for accepting said differential analog results and producing an analog summation.