Method employed by a base station for spread spectrum CDMA subtractive interference cancellation

• US 7,230,938 B2
• Filed: 07/24/2002
• Issued: 06/12/2007
• Est. Priority Date: 04/22/1993
• Status: Expired due to Fees

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Schilling, Donald L., Kowalski, John
• Primary Examiner(s): Pham; Chi
• Assistant Examiner(s): Boakye; Alexander O.
• Application Number:
  US10/202,226
• Publication Number:
  US 20020196757A1
• Time in Patent Office: 1,784 Days
• Field of Search: 370/342, 370/441, 370/335, 370/310, 370/479, 370/331, 370/332, 375/343, 375/347, 375/346, 375/206, 375/207
• US Class Current: 370/335
• 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 cancellation method for a base station reduces interference in a direct sequence CDMA receiver having N chip-code channels. The interference canceller despreads the spread-spectrum CDMA signal as a plurality of despread signals. A timed version of a plurality of chip-code signals, spread-spectrum processes 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, subtracting circuits subtract 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 employed by a base station for reducing interference in a spread spectrum code division multiple access (CDMA) receiver having N channels wherein each of the N channels is identified by a distinct chip-code signal, comprising:

a) generating a plurality of chip-code signals;

b) simultaneously despreading a plurality of spread spectrum channels of a spread spectrum CDMA signal;

c) generating a timed version of the plurality of chip-code signals;

d) spread spectrum processing the plurality of despread signals with a chip-code signal corresponding to a respective despread signal;

e) subtracting from the spread spectrum CDMA signal N−

1 spread spectrum process despread signals with N−

1 spread spectrum process despread signals with the exception of a spread spectrum process despread of an i^th despread signal to general a subtractive signal; and

f) despreading a subtractive signal employ the i^th chip-code signal as an i^th channel.

2. The method of claim 1 wherein step (d) includes mixing each of the chip-code signals with a received spread spectrum CDMA signal and filtering each mixed signal.

3. The method of claim 2 wherein the filtering step includes filtering each channel each which filters each having an impulse response which is matched to an associated chip-code word.

4. A method employed by a base station for reducing interference in a received spread spectrum code division multiple access (CDMA) N channel signal, with each of the N channels identified by a distinct chip-code signal, comprising:

a) despreading a spread spectrum CDMA received signal as a plurality of despread signals;

b) simultaneously spread spectrum processing the plurality of despread signals employing a timed version of the plurality of chip-code signals with a chip-code signal corresponding to a respective despread signal;

c) simultaneously subtracting from the spread spectrum CDMA signal each of N−

1 spread spectrum process that despread signals employing N−

1 spread spectrum processed despread signals, except for a spread spectrum processed despread signal, of an i^th despread signal, to generate a subtractive signal; and

d) despreading the subtractive signal employing the i^th chip-code signal as an i^th channel.

5. The method of claim 4 wherein step (a) includes correlating the spread spectrum CDMA signal into a plurality of despread signals.

6. The method of claim 4 wherein step (a) includes matched filtering the spread spectrum CDMA signal as a plurality of despread signals.

7. A method employed by a base station for reducing interference in a received spread spectrum code division multiple access (CDMA) signal having N channels, with each of the N channels identified by a distinct chip-code signal through the use N groups of interference cancellers, comprising:

for each group of interference cancellers;

simultaneously despreading a plurality of spread spectrum channels of a spread spectrum CDMA signal as a plurality of despread signals;

simultaneously spread spectrum processing, using a time diversion of the plurality of chip-code signals, the plurality of despread signals each with a chip-code signal corresponding to a respective despread signal;

subtracting from the spread spectrum CDMA signal N−

1 spread spectrum processed signals in each interference canceller group the spread spectrum processed-despread signals omitting a different spread spectrum process despread signal of a first through an i^th of the despread signal, each generating a subtractive signal; and

despreading the subtracted signal of each group of interference cancellers with the chip-code signal of the omitted chip-code for that group of interference cancellers, thereby providing N sets of estimates of the N channels.

8. A method employed by a base station for reducing interference in a spread spectrum code division multiple access (CDMA) receiver having N channels wherein each of the N channels is identified by a distinct chip-code signal, comprising:

a) generating a plurality of chip-code signals;

b) simultaneously despreading a plurality of spread spectrum channels of a spread spectrum CDMA signal;

c) generating a timed version of the plurality of chip-code signals,

wherein step (c) further includes;

c1) mixing the output obtained at step (b) with a time delayed chip-code signal from a chip-code word corresponding to the i^th channel; and

c2) integrating the output obtained from step (c1);

d) spread spectrum processing the plurality of despread signals with a chip-code signal corresponding to a respective despread signal;

e) subtracting from the spread spectrum CDMA signal N−

1 spread spectrum process despread signals with N−

1 spread spectrum process despread signals with the exception of a spread spectrum process despread of an i^th despread signal to general a subtractive signal; and

f) despreading a subtractive signal employ the i^th chip-code signal as an i^th channel.