Digital parallel correlator

• US 5,239,496 A
• Filed: 12/27/1989
• Issued: 08/24/1993
• Est. Priority Date: 12/27/1989
• Status: Expired due to Term

• Current Assignee: Verizon Patent and Licensing Incorporated (Verizon Communications Inc.)
• Original Assignee: NYNEX Science & Technology, Inc. (Verizon Communications Inc.)
• Inventors: Vancraeynest, Jan P.
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): NGO, CHUONG D
• Application Number:
  US07/457,363
• Time in Patent Office: 1,336 Days
• Field of Search: 364/728.03, 364/175.09, 375/1, 375/96, 371/40.1, 340/146.2, 380/34, 380/42, 380/46, 380/47
• US Class Current: 708/422
• 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

Abstract

An improved digital parallel correlator is disclosed. Illustratively, the inventive correlator utilizes a shift register which receives a signal comprising data bits encoded as chips. At each cycle of the signal, the chips in the shift register are compared to a reference sequence and the number of matches is obtained. Whenever the number of matches exceeds a fixed high threshold or falls below a fixed low threshold, indicating the presence of a binary 1 or binary 0 data bit, the chips in the shift register are set to a predetermined sequence such as the reference sequence or its complement. This amounts to correcting any chips of a bit that are received in error as soon as it is determined that the bit is a binary 1 or binary 0. This enables the high and low thresholds to be located as far as possible from the peak correlation values thereby increasing the number of chips that can be received in error.

Claims

1. A correlation device for determining a number of matches between binary elements comprised in a periodic signal and binary elements of a reference sequence comprising

a shift register for receiving a periodic signal comprising binary elements,

first circuit means operable during each cycle of said periodic signal for determining a number of matches between said binary elements in said shift register and a reference binary sequence and for outputting an indication signal when said number of matches exceeds a fixed high threshold or falls below a fixed low threshold to indicate the detection of a data bit, and

second circuit means for setting at least part of said shift register to a predetermined sequence of binary elements each time said indication signal indicates a data bit is detected thereby increasing the distance from said high and low thresholds to peak correlation values of said periodic signal and said reference sequence.

2. The correlation device of claim 1 wherein said predetermined sequence is equal to said reference sequence when said number of matches exceeds said high threshold, and wherein said predetermined sequence is equal to the complement of said reference sequence when said number of matches falls below said low threshold.

3. The correlation device of claim 1 wherein said binary elements comprising said signal received at said shift register are chips used to encode a data bit stream in a spread spectrum format.

4. The correlation device of claim 3 wherein said indication signal is used to form a reconstruction of said data bit stream.

5. The correlation device of claim 1 wherein said shift register comprises a plurality of storage elements, wherein a processing delay of said first and second circuit means is K cycles of said periodic signal, and wherein the first K storage elements of said shift register are not set to predetermined values in response to said indication signal.

6. The correlation device of claim 1 wherein said predetermined sequence is equal to the complement of said reference sequence when said number of matches exceeds said high threshold, and wherein said predetermined sequence is equal to said reference sequence when said number of matches falls below said low threshold.

7. A correlation device for determining a number of matches between binary elements comprised in a periodic signal and binary elements of a reference sequence comprising

a shift register for receiving a periodic signal comprising binary elements,

first circuit means operable during each cycle of said periodic signal for determining a number of matches between said binary elements in said shift register and a reference binary sequence and for outputting an indication signal when said number of matches exceeds a fixed high threshold or falls below a fixed low threshold, and

second circuit means for setting at least part of said shift register to a predetermined sequence of binary elements in response to said indication signal,

wherein said reference sequence comprises approximately an equal number of binary 1'"'"'s and binary 0'"'"'s and said predetermined sequence comprises only binary elements of the same binary value.

9. The correlation device of claim 7 wherein said shift register comprises a plurality of storage elements, wherein a processing delay of said first and second circuit means is K periods of said periodic signal, and wherein the first K storage elements of the shift register are not set to predetermined values.

8. A correlation device for reconstruction coded data bits in a spread spectrum communication system comprising

a shift register for receiving a periodic signal in a spread spectrum format and comprising data bits encoded by sequences of chips,

first circuit means operable during each period of said received periodic signal for determining a number of matches between the chips in the shift register and a reference sequence and for reconstructing said data bits by providing a data bit indicating signal when said number of matches exceeds a fixed high threshold or falls below a fixed low threshold, to indicate the detection of a data bit in said periodic signal, and

second circuit means responsive to said indicating signal of said first circuit means for setting the chips in at least a part of the shift register to predetermined values to maintain the number of matches between the high and low thresholds during transitions between said data bit indicating signals.

10. A method for correlating an encoded signal comprising chips to reconstruct a data bit stream represented by said chips, by determining the number of matches between binary values of said chips and the binary elements of a reference sequence, said method comprising

at each cycle of said encoded signal, comparing a group of said chips present in a shift register to a reference sequence and outputting a data bit indication signal if a number of matches between the group of chips and the reference sequence exceeds a fixed upper threshold or falls below a fixed lower threshold to indicate the detection of a data bit in said encoded signal,

and in response to the outputting of a data bit indication signal, setting at least a part of the group of chips in the shift register which resulted in the outputting of the data bit indication signal to a predetermined binary sequence thereby increasing the distance from said high and low thresholds to peak correlation values of said encoded signal and said reference sequence.

11. The method of claim 10 wherein said predetermined binary sequence comprises said reference sequence when said number of matches exceeds said high threshold and wherein said binary sequence comprises the complement of said reference sequence when said number of matches falls below said low threshold.

12. The method of claim 10 wherein said predetermined binary sequence comprises the complement of said reference sequence when said number of matches exceeds said high threshold and wherein said binary sequence comprises said reference sequence when said number of matches falls below said low threshold.

13. A method for correlating an encoded signal comprising chips to reconstruct a data bit stream represented by said chips, by determining the number of matches between binary values of said chips and the binary elements of a reference sequence, said method comprising

at each cycle of said encoded signal, comparing a group of said chips present in a shift register to a reference sequence and outputting a data bit indication signal if a number of matches between the group of chips and the reference sequence exceeds a fixed upper threshold or falls below a fixed lower threshold,

and in response to the outputting of a data bit indication signal, setting at least a part of the group of chips in the shift register which resulted in the outputting of the data bit indication signal to a predetermined binary sequence,

wherein said predetermined binary sequence comprises only binary elements of the same binary value.

14. A correlation device for determining a number of matches between binary elements comprised in a periodic signal and binary elements of a reference sequence comprising:

a shift register for receiving a periodic signal comprising binary elements,

a first circuit operable during each cycle of said periodic signal for determining a number of matches between said binary elements in said shift register and a reference binary sequence and for outputting an indication signal when said number of matches exceeds a fixed high threshold or falls below a fixed low threshold to indicate the detection of a data bit, and

a second circuit for increasing the distance from said high and low thresholds to peak correlation values of said periodic signal and said reference sequence comprising a circuit for setting at least part of aid shift register to a predetermined sequence of binary elements each time said indication signal indicates a data bit is detected.

15. A correlation device for determining a number of matches between binary elements of a periodic signal and binary elements of a reference sequence comprising:

a shift register for receiving the binary elements of said periodic signal,

a first circuit operable during each cycle of said periodic signal for determining a number of matches between said binary elements in said shift register and a reference binary sequence and for outputting an indication signal with a high signal component when said number of matches exceeds a fixed high threshold and a low signal component when said number of matches falls below a fixed low threshold, to indicate the detection of a data bit, and

a second circuit for increasing the distance from said high and low thresholds to peak correlation values of said periodic signal and said reference sequence comprising at least one OR gate, responsive to aid high and low indication signal components, for outputting a signal to said shift register for setting at least part of said shift register to a predetermined sequence of binary elements each time said high or low indication signal components indicate a data bit is detected.

16. A correlation device for determining a number of matches between binary elements of a periodic signal and binary elements of a reference sequence comprising:

a shift register comprising a plurality of storage locations for receiving the binary elements of said periodic signal,

a first circuit operable during each cycle of said periodic signal for determining a number of matches between said binary elements in said shift register and a reference binary sequence and for outputting a high indication signal when said number of matches exceeds a high threshold and a low indication signal when the number of matches falls below a low threshold to indicate the detection of a data bit in said periodic signal, and

a second circuit comprising on logic circuit for each storage location of said shift register, each logic circuit including input means for receiving said high and low indication signals from said first circuit and output means connected to a corresponding storage location of said shift register for writing into the storage location a particular bit value in response to said high and low indication signals, thereby enabling the distance from said high and low thresholds to peak correlation values of said periodic signal and reference sequence to be increased.