Spread spectrum CDMA subtractive interference canceler system

• US 5,719,852 A
• Filed: 05/29/1996
• Issued: 02/17/1998
• 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, Moshavi, Shimon
• Primary Examiner(s): Hsu, Alphus H.
• Assistant Examiner(s): RAO, SEEMA SRINIVAS
• Application Number:
  US08/654,994
• Time in Patent Office: 629 Days
• Field of Search: 370/464, 370/479, 370/310, 370/342, 370/201, 370/331, 370/332, 370/333, 370/335, 375/200, 375/205, 375/206, 375/207, 375/208, 375/209, 375/210, 375/343, 375/346, 380/34
• US Class Current: 370/201
• CPC Class Codes: H04B 1/709 Correlator structure
• 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 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 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 a plurality of chip-code-signals, the plurality of despread signals, respectively, with a timed chip-code signal corresponding to a respective despread signal;

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

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

e. inputting the first set of estimates to a second plurality of interference cancelers;

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

g. inputting the second set of estimates to an M^th plurality of interference cancelers;

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

i. combining each estimate of the M^th set of estimates to produce an average.

2. A spread-spectrum code division multiple access (CDMA) interference-canceler system 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 interference cancelers, each of said interference cancelers including,

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

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

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

a first combiner for combining a first plurality of estimates of the first channel from said plurality of interference cancelers;

a second combiner for combining a second plurality of estimates of the second channel from said plurality of interference cancelers; and

an n^th combiner for combining an n^th plurality of estimates of the n^th channel from said plurality of interference cancelers.

3. A spread-spectrum code division multiple access (CDMA) interference-canceler system 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 interference cancelers, each of said interference cancelers including,

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 the 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 with a respective timed chip-code 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 timed chip-code signal as an estimate of a first channel;

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

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

a first combiner for combining a first plurality of estimates of the first channel from said plurality of interference cancelers;

a second combiner for combining a second plurality of estimates of the second channel from said plurality of interference cancelers; and

an n^th combiner for combining an n^th plurality of estimates of the n^th channel from said plurality of interference cancelers.

4. 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 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, the plurality of despread signals with a respective plurality of timed-chip-code signals, each of said plurality of timed-chip-code signals corresponding to a respective one of the plurality of despread signals, producing N spread-spectrum-processed-despread signals;

c. 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;

d. 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;

e. 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;

f. despreading the first subtracted signal with a first timed-chip-code signal as an estimate of a first channel;

g. despreading the second subtracted signal with a second timed-chip-code signal as an estimate of a second channel;

h. despreading the n^th subtracted signal with an n^th timed-chip-code signal as an estimate of an n^th channel;

i. combining a first plurality of estimates of the first channel;

j. combining a second plurality of estimates of the second channel; and

k. combining an n^th plurality of estimates of the n^th channel.

5. The method as set forth in claim 4, further comprising the steps of:

l. processing the first plurality of estimates, the second plurality of estimates, and the n^th plurality of estimates as a plurality of processed estimates;

m. inputting the plurality of processed estimates to a second plurality of interference cancelers; and

n. repeating steps a through k, using the second plurality of interference cancelers.

6. A spread-spectrum code division multiple access (CDMA) interference-canceler system having a plurality of interference cancelers 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;

despreading means, 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 plurality of timed-chip-code signals, respectively;

a first spreading mixer for spread-spectrum processing a first despread signal, of the plurality of despread signals, with a first timed-chip-code signal, of the plurality of timed-chip-code signals, to produce a first spread-spectrum-processed-despread signal;

a second spreading mixer for spread-spectrum processing a second despread signal, of the plurality of despread signals, with a second timed-chip-code signal, of the plurality of time-chip-code signals, to produce a second spread-spectrum-processed despread signal;

an n^th spreading mixer for spread-spectrum processing an n^th despread signal, of the plurality of despread signals, with an n^th timed-chip-code signal, of the plurality of timed-chip-code signals, to produce an n^th spread-spectrum-processed-despread signal;

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

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

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

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

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

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

a first combiner for combining a first plurality of estimates of the first channel from said plurality of interference cancelers as a first plurality of averaged estimates;

a second combiner for combining a second plurality of estimates of the second channel from said plurality of interference cancelers as a second plurality of averaged estimates;

an n^th combiner for combining an n^th plurality of estimates of the n^th channel from said plurality of interference cancelers as an n^th plurality of averaged estimates; and

decision means for processing the first plurality of averaged estimates, the second plurality of averaged estimates, and the n^th plurality of averaged estimates.

7. The spread-spectrum CDMA interference-canceler system as set forth in claim 6, said plurality of delay devices comprising;

a first delay device for delaying a first chip-code signal by a first time delay to generate a first timed-chip-code signal;

a second delay device for delaying a second chip-code signal by a second time delay to generate a second timed-chip-code signal; and

an n^th delay device for delaying an n^th chip-code signal by an n^th time delay to generate an n^th timed-chip-code signal.

8. The spread-spectrum CDMA interference-canceler system as set forth in claim 6, said despreading means comprising:

a plurality of correlators.

9. The spread-spectrum CDMA interference-canceler system as set forth in claim 6, said despreading means comprising:

a plurality of matched filters.

10. The spread-spectrum CDMA interference-canceler system as set forth in claim 9, said plurality of delay devices comprising;

a first adjustment device for aligning a first chip-code signal with the first despread signal;

a second adjustment device for aligning a second chip-code signal with the second despread signal; and

an n^th adjustment device for aligning an n^th chip-code signal with the n^th despread signal.

11. A spread-spectrum code division multiple access (CDMA) interference-canceler system having a plurality of interference cancelers 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 the plurality of despread signals from the plurality of matched filters, for generating, simultaneously, a plurality of timed-chip-code signals, respectively;

a first spreading mixer for spread-spectrum processing a first despread signal, of the plurality of despread signals, with a first timed-chip-code signal, of the plurality of timed-chip-code signals, to produce a first spread-spectrum-processed-despread signal;

a second spreading mixer for spread-spectrum processing a second despread signal, of the plurality of despread signals, with a second timed-chip-code signal, of the plurality of timed-chip-code signals, to produce a second spread-spectrum-processed-despread signal;

an n^th spreading mixer for spread-spectrum processing an n^th despread signal, of the plurality of despread signals, with an n^th timed-chip-code signal, of the plurality of timed-chip-code signals, to produce an n^th spread-spectrum-processed-despread signal;

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

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

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

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

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

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

a first combiner for combining a first plurality of estimates of the first channel from said plurality of interference cancelers;

a second combiner for combining a second plurality of estimates of the second channel from said plurality of interference cancelers;

an n^th combiner for combining an n^th plurality of estimates of the n^th channel from said plurality of interference cancelers; and

decision means for processing the combined estimates.

12. The spread-spectrum CDMA interference-canceler system as set forth in claim 11, said decision means comprising:

a first decision device for processing the first combined plurality of estimates;

a second decision device for processing the second combined plurality of estimates; and

a third decision device for processing the third combined plurality of estimates.