Spread spectrum CDMA subtractive interference canceler and method

• US 5,363,403 A
• Filed: 04/22/1993
• Issued: 11/08/1994
• Est. Priority Date: 04/22/1993
• Status: Expired due to Term

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Schilling, Donald L., Kowalski, John
• Primary Examiner(s): Swann, Tod R.
• Application Number:
  US08/051,017
• Time in Patent Office: 565 Days
• Field of Search: 375/1, 380/34
• US Class Current: 370/441
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation

Abstract

A spread-spectrum code division multiple access interference canceler for reducing interference in a direct sequence CDMA receiver having N chip-code channels. The interference canceler includes a plurality of correlators or matched filters, a plurality of spread-spectrum-processing circuits, subtracting circuits, and channel correlators or channel-matched filters. Using a plurality of chip-code signals, the plurality of correlators despreads the spread-spectrum CDMA signal as a plurality of despread signals, respectively. The plurality of spread-spectrum-processing circuits uses a timed version of the plurality of chip-code signals, for spread-spectrum processing the plurality of despread signals, respectively, with a chip-code-signal corresponding to a respective despread signal. For recovering a code channel using an i^th chip-code-signal, the subtracting circuits subtracts from the spread-spectrum CDMA signal, each of the N-1 spread-spectrum-processed-despread signals thereby generating a subtracted signal. The N-1 spread-spectrum-processed-despread signals do not include the spread-spectrum-processed-despread signal of the i^th channel of the spread-spectrum CDMA signal. The channel correlator or channel-matched filter despreads the subtracted signal.

Claims

1. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of means for generating a plurality of chip-code signals;

a plurality of despreading means, with each of said despreading means responsive to the respective distinct chip-code signal identifying a corresponding one of the N channels, for simultaneously despreading a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of means for timing the plurality of chip-code signals thereby generating a timed version of the plurality of chip-code signals, respectively;

a plurality of means, responsive to the timed version of the plurality of chip-code-signals, for simultaneously spread-spectrum processing the plurality of despread signals, respectively, with a chip-code-signal corresponding to a respective despread signal;

means, for an i^th chip-code signal, for subtracting from the spread-spectrum CDMA signal, simultaneously, each of the N-1 spread-spectrum-processed-despread signals, with the N-1 spread-spectrum-processed-despread signals not including a spread-spectrum processed-despread signal of the i^th despread signal, thereby generating a subtracted signal; and

channel means for despreading the subtracted signal with the i^th chip-code signal as an i^th channel.

2. The spread-spectrum CDMA interference canceler as set forth in claim 1 wherein each of said plurality of despreading means includes:

a filter;

a chip-code generator for generating a chip-code signal from a respective chip codeword; and

a mixer coupled between said filter and said chip-code generator.

3. The spread-spectrum CDMA interference canceler as set forth in claim 1 wherein each of said plurality of despreading means includes a matched filter having an impulse response matched to a respective chip codeword.

4. The spread-spectrum CDMA interference canceler as set forth in claim 1 wherein said channel-despreading means includes:

a filter;

a chip-code generator for generating a chip-code signal from a chip codeword corresponding to the i^th channel; and

a mixer coupled between said filter and said chip-code generator.

5. The spread-spectrum CDMA interference canceler as set forth in claim 2 wherein said channel-despreading means includes:

a filter;

a chip-code generator for generating a chip-code signal from a chip codeword corresponding to the i^th channel; and

a mixer coupled between said filter and said chip-code generator.

6. The spread-spectrum CDMA interference canceler as set forth in claim 3 wherein said channel-despreading means includes:

a filter;

a chip-code generator for generating a chip-code signal from a chip codeword corresponding to the i^th channel; and

a mixer coupled between said filter and said chip-code generator.

7. The spread-spectrum CDMA interference canceler as set forth in claim 3 wherein said channel-despreading means includes a matched filter having an impulse response matched to a chip codeword corresponding to the i^th channel.

8. The spread-spectrum CDMA interference canceler as set forth in claim 1 wherein each of said despreading means includes a digital signal processor with digital matched filter having an impulse response matched to a respective chip codeword.

9. The spread-spectrum CDMA interference canceler as set forth in claim 8 wherein said channel-despreading means includes a matched filter having an impulse response matched to a chip codeword corresponding to the i^th channel.

10. The spread-spectrum CDMA interference canceler as set forth in claim 1 wherein said channel-despreading means includes a digital signal processor with digital matched filter having an impulse response matched to a chip codeword corresponding to the i^th channel.

11. The spread-spectrum CDMA interference canceler as set forth in claim 8 wherein said channel-despreading means includes a surface acoustic wave (SAW) device having an impulse response matched to a chip codeword corresponding to the i^th channel.

12. The spread-spectrum CDMA interference canceler as set forth in claim 1 wherein each of said plurality of despreading means includes a surface acoustic wave (SAW) device having an impulse response matched to a chip codeword corresponding to the i^th channel.

13. The spread-spectrum CDMA interference canceler as set forth in claim 12 wherein said channel-despreading means includes a matched filter having an impulse response matched to a chip codeword corresponding to the i^th channel.

14. The spread-spectrum CDMA interference canceler as set forth in claim 12 wherein said channel-despreading means includes a chip-code generator for generating a chip-code signal from a digital matched filter having an impulse response matched to a chip codeword corresponding to the i^th channel.

15. The spread-spectrum CDMA interference canceler as set forth in claim 12 wherein said channel-despreading means includes a surface acoustic wave (SAW) device having an impulse response matched to a chip codeword corresponding to the i^th channel.

16. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of chip-code-signal generators for generating, simultaneously, a plurality of chip-code signals;

a plurality of correlators, responsive to a plurality of distinct chip-code-signals, for simultaneously despreading a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of delay devices coupled to said plurality of chip-code-signal generators for delaying the plurality of chip-code signals as a timed plurality of chip-code signals, respectively;

a plurality of mixers, responsive to the timed plurality of chip-code signals, for spread-spectrum processing, simultaneously, the plurality of despread signals, respectively, with a chip-code-signal corresponding to a respective despread signal;

a subtractor, for an i^th chip-code signal, for subtracting from the spread-spectrum CDMA signal, simultaneously, each of the N-1 spread-spectrum-processed-despread signals, with the N-1 spread-spectrum-processed-despread signals not including a spread-spectrum processed despread signal of the i^th despread signal, thereby generating a subtracted signal; and

a channel correlator for despreading the subtracted signal with the i^th chip-code signal as an i^th channel.

17. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N chip-code channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of matched filters, responsive to a plurality of distinct chip-code signals, for simultaneously despreading a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of chip-code-signal generators, responsive to a plurality of despread signals from the plurality of matched filters, for generating a timed plurality of chip-code signals, respectively;

a plurality of mixers, responsive to the plurality of despread signals from the plurality of matched filters and the timed plurality of chip-code signals from the plurality of chip-code-signal generators, respectively, for spread-spectrum processing, simultaneously, the plurality of despread signals, respectively, with a timed chip-code signal corresponding to a respective despread signal;

a subtractor, for an i^th chip-code signal, for subtracting from the spread-spectrum CDMA signal, simultaneously, each of the N-1 spread-spectrum-processed-despread signals, with the N-1 spread-spectrum-processed-despread signals not including a spread-spectrum processed despread signal of the i^th despread signal, thereby generating a subtracted signal; and

a channel matched filter for despreading the subtracted signal with the i^th chip-code-signal as an i^th channel.

18. A method for reducing interference in a spread-spectrum code division multiple access (CDMA) receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising the steps of:

despreading a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

spread-spectrum processing, simultaneously, using a timed version of the plurality of chip-code-signals, the plurality of despread signals, respectively, with a chip-code signal corresponding to a respective despread signal;

subtracting from the spread-spectrum CDMA signal, simultaneously, each of the N-1 spread-spectrum-processed-despread signals, with the N-1 spread-spectrum-processed-despread signals not including a spread-spectrum processed despread signal of the i^th despread signal, thereby generating a subtracted signal; and

despreading the subtracted signal with the i^th chip-code signal as an i^th channel.

19. The method as set forth in claim 18 wherein the first step of despreading includes the step of correlating the spread-spectrum CDMA signal as a plurality of despread signals.

20. The method as set forth in claim 18 wherein the first step of despreading includes the step of matched filtering the spread-spectrum CDMA signal as a plurality of despread signals.

21. A method for reducing interference in a spread-spectrum code division multiple access (CDMA) receiver having N channels, with each of the N channels identified by a distinct chip-code signal, using a first plurality of interference cancelers, comprising the steps, within each of said plurality of interference cancelers, of:

a. despreading, simultaneously, a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

b. spread-spectrum processing, simultaneously, using a timed version of the plurality of chip-code-signals, the plurality of despread signals, respectively, with a chip-code signal corresponding to a respective despread signal;

c. subtracting from the spread-spectrum CDMA signal, each of the N-1 spread-spectrum-processed-despread signals, with the N-1 spread-spectrum-processed-despread signals not including a spread-spectrum processed despread signal of the i^th despread signal, thereby generating a subtracted signal;

d. despreading the subtracted signal with the i^th chip-code signal as an i^th channel, producing a first set of estimates of the N channels;

e. repeating steps a through d, using a second plurality of interference cancelers, producing a second set of estimates of the N channels; and

f. repeating steps a through d, using an M^th plurality of interference cancelers, producing an M^th set of estimates of the N channels.

22. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of chip-code-signal generators for generating, simultaneously, a plurality of chip-code signals;

a plurality of correlators, responsive to a plurality of distinct chip-code-signals, for simultaneously despreading a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of delay devices coupled to said plurality of chip-code-signal generators for delaying the plurality of chip-code signals as a timed plurality of chip-code signals, respectively;

a plurality of mixers, responsive to the timed plurality of chip-code signals, for spread-spectrum processing, simultaneously, the plurality of despread signals, respectively, with a chip-code-signal corresponding to a respective despread signal, producing N spread-spectrum-processed-despread signals;

a plurality of subtractors, each of said plurality of subtractors for subtracting from the spread-spectrum CDMA signal all but a particular one of the N spread-spectrum-processed-despread signals, with the particular one of the N spread-spectrum-processed-despread signals being different for each of said plurality of subtractors, thereby generating a plurality of subtracted signals; and

a plurality of channel correlators for despreading the plurality of subtracted signals with a particular one of the plurality of chip-code signals, respectively, as a plurality of channels.

23. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of chip-code-signal generators for generating, simultaneously, a plurality of chip-code signals;

a plurality of correlators, responsive to a plurality of distinct chip-code-signals, for simultaneously despreading a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of delay devices coupled to said plurality of chip-code-signal generators for delaying the plurality of chip-code signals as a timed plurality of chip-code signals, respectively;

a plurality of mixers, responsive to the timed plurality of chip-code signals, for spread-spectrum processing, simultaneously, the plurality of despread signals, respectively, with a chip-code-signal corresponding to a respective despread signal, producing N spread-spectrum-processed-despread signals;

a first subtractor, for subtracting from the spread-spectrum CDMA signal, all but a first one of the N spread-spectrum-processed-despread signals, thereby generating a first subtracted signal;

a second subtractor, for subtracting from the spread-spectrum CDMA signal, all but a second one of the N spread-spectrum-processed-despread signals, thereby generating a second subtracted signal; and

an n^th subtractor, for subtracting from the spread-spectrum CDMA signal, all but an n^th one of the N spread-spectrum-processed-despread signals, thereby generating an n^th subtracted signal;

a first channel correlator for despreading the first subtracted signal with a first chip-code signal as an estimate of a first channel;

a second channel correlator for despreading the second subtracted signal with a second chip-code signal as an estimate of a second channel; and

an n^th channel correlator for despreading the n^th subtracted signal with an n^th chip-code signal as an estimate of an n^th channel.

24. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of matched filters, responsive to a plurality of distinct chip-code-signals, for despreading, simultaneously, a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of chip-code-signal generators, responsive to a plurality of despread signals from the plurality of matched filters, for generating, simultaneously, a timed plurality of chip-code signals, respectively;

a plurality of mixers, responsive to the plurality of despread signals from the plurality of matched filters and the timed plurality of chip-code signals from the plurality of chip-code-signal generators, respectively, for spread-spectrum processing, simultaneously, the plurality of despread signals, respectively, with a timed chip-code signal corresponding to a respective despread signal, producing N spread-spectrum-processed-despread signals;

a plurality of subtractors, each of said plurality of subtractors for subtracting from the spread-spectrum CDMA signal all but a particular one of the N spread-spectrum-processed-despread signals, with the particular one of the N spread-spectrum-processed-despread signals being different for each of said plurality of subtractors, thereby generating a plurality of subtracted signals; and

a plurality of channel-matched filters for despreading the plurality of subtracted signals with a particular one of the plurality of distinct chip-code signals, respectively, as a plurality of channels.

25. A spread-spectrum code division multiple access (CDMA) interference canceler for reducing interference in a spread-spectrum CDMA receiver having N channels, with each of the N channels identified by a distinct chip-code signal, comprising:

a plurality of matched filters, responsive to a plurality of distinct chip-code-signals, for simultaneously despreading a plurality of spread-spectrum channels of a spread-spectrum CDMA signal as a plurality of despread signals, respectively;

a plurality of chip-code-signal generators, responsive to a plurality of despread signals from the plurality of matched filters, for generating, simultaneously, a timed plurality of chip-code signals, respectively;

a plurality of mixers, responsive to the plurality of despread signals from the plurality of matched filters and the timed plurality of chip-code signals from the plurality of chip-code-signal generators, respectively, for spread-spectrum processing, simultaneously, the plurality of despread signals, respectively, with a timed chip-code signal corresponding to a respective despread signal, producing N spread-spectrum-processed-despread signals;

a first subtractor, for subtracting from the spread-spectrum CDMA signal, all but a first one of the N spread-spectrum-processed-despread signals, thereby generating a first subtracted signal;

a second subtractor, for subtracting from the spread-spectrum CDMA signal, all but a second one of the N spread-spectrum-processed-despread signals, thereby generating a second subtracted signal; and

an n^th subtractor, for subtracting from the spread-spectrum CDMA signal, all but an n^th one of the N spread-spectrum-processed-despread signals, thereby generating an n^th subtracted signal;

a first channel-matched filter for despreading the first subtracted signal with a first chip-code signal as an estimate of a first channel;

a second channel-matched filter for despreading the second subtracted signal with a second chip-code signal as an estimate of a second channel; and

an n^th channel-matched filter for despreading the n^th subtracted signal with an n^th chip-code signal as an estimate of an n^th channel.