Pseudo-random-number code detection and tracking system

• US 4,203,070 A
• Filed: 08/08/1978
• Issued: 05/13/1980
• Est. Priority Date: 08/08/1978
• Status: Expired due to Term

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Cox, Duncan B. Jr., Bowles, William M.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US05/931,420
• Time in Patent Office: 644 Days
• Field of Search: 364/516, 364/572, 364/724, 364/728, 364/825, 179/15 AP, 179/15 BS, 178/69.1, 325/321, 325/323, 325/325, 340/146.1 D, 340/167 R, 328/133, 328/142, 328/155, 329/104, 329/178
• US Class Current: 375/317
• CPC Class Codes: H04B 1/69 Spread spectrum techniques

Abstract

A pseudo-random-number code detection and tracking system using a closed loop system wherein a detector having a non-linear response characteristic is responsive to a coded received signal and to a locally generated coded signal to produce an error signal. The error is used to control the characteristics of the local signal so as to cause the signals to become aligned. Means are further provided to dynamically control the non-linear response characteristics of the detector so that the coded received signal and coded local signal remain aligned over a controllable range of error signal levels. Thus, a relatively large range can be used during an acquisition operation and a relatively narrower range during the tracking operation.

Claims

1. A pseudo-random-number code detection and tracking system comprising

means for receiving a transmitted coded signal;

means for generating a local coded feedback signal;

detector means having non-linear response characteristics responsive to said coded received signal and to said local coded signal and including means for comparing said received and local signals to produce an error signal when said received and local signals are not aligned;

means responsive to said error signal for controlling the operation of said local coded feedback signal generating means to vary the characteristics of said local coded feedback signal so as to cause said signals to become aligned and, thereby, to minimize said error signal;

control means, responsive to the statistical characteristics of said error signal, capable of dynamically changing the non-linear response characteristics of said detector means to said local coded signal and to said received coded signal so that said signals remain substantially aligned over a controllable range of error signal levels.

2. A system in accordance with claim 1 wherein said detector means includes arranging means for the non-linear characteristics thereof so that said response is substantially linear over a first selected range of the error signal levels and is substantially constant over a second selected range of error signal levels.

3. A system in accordance with claim 2 wherein said control means includes means for dynamically varying said second selected range.

4. A system in accordance with claims 1 or 3 where said detector means includes

shift register means for time shifting said coded feedback signal to provide a first plurality of time-shifted coded feedback signal components advanced in time and a second plurality of time-shifted coded feedback signal components delayed in time;

and

means for combining said first and second plurality of coded feedback signal components to produce a time-shifted coded feedback signal for comparison with said received signal to produce said error signal.

5. A system in accordance with claim 4 wherein said control means includes

means for controllably selecting the numbers of said first and second plurality of time-shifted signal components, said selected numbers thereby providing a selected range of error signal levels over which said received coded signal and said local coded signal can be aligned.

6. A system in accordance with claim 5 wherein said controllable selecting means includes means for selecting a controlled number of said first plurality of time-shifted signal components and a controlled number of said second plurality of time-shifted signal components in accordance with the statistics of said error signal.

7. A system in accordance with claim 6 wherein said number selecting means selects said numbers in accordance with the mean-squared error determined by said noise/signal statistical charcteristics.

8. A system in accordance with claim 1 wherein said detector means includes

matched filter means for comparing in parallel a plurality of time-shifted components of said received signal with a plurality of time-shifted components of said coded feedback signal to produce a plurality of time-shifted parallel comparison signal components;

means for combining said parallel time-shifted comparison signals to produce a combined serial comparison signal component;

digital recirculating filter means responsive to said combined serial comparison signal components to produce filtered combined serial comparison signal components;

means for multiplying each of said serial comparison signal components by weighting factor, selected in accordance with a selected non-linear response characteristic of said detector means to produce weighted serial comparison signal components;

means for integrating said weighted serial comparison signal components to produce said error signal.

9. A system in accordance with claim 8 wherein said matched filter means includes

a pair of delay lines, said received signal being supplied to a first one of said delay lines to provide said plurality of time shifted components of said received signal and said coded feedback signal being supplied to the other of said delay lines to provide said time-shifted components of said coded feedback signals;

and

correlator means for comparing in parallel said time-shifted received signal components and said time-shifted coded feedback signal components.

10. A system in accordance with claim 1 wherein said detector means includes

shift register means for time shifting said coded feedback signal to provide a first plurality of time-shifted coded feedback signal components advanced in time and for time shifting such coded feedback signal to provide a second plurality of time-shifted coded feedback signal components delayed in time;

means for sequentially comparing said advanced and delayed time-shifted feedback signal components with said received signal to produce a comparison signal;

means for multiplying the advanced components of said comparison signal by a first polarity and the delayed components of said comparison signal by a second polarity to produce said error signal.

11. A system in accordance with claim 10 wherein said detector means further includes

means for supplying a controllably selected number of said first plurality of advanced feedback signal components and a controllably selected number of said second plurality of delayed feedback signal components to said sequential comparing means, said controllably selected numbers thereby providing a selected range of error signal levels over which said received coded signal and said locally generated coded signal can be aligned.

12. A system in accordance with claim 11 wherein said supplying means comprises means for supplying each of said controllably selected plurality of advanced and delayed feedback signal components for predetermined time periods to provide a weighted response characteristic for said detector means.

13. A system in accordance with claim 12 wherein said supplying means comprises switch means.