Apparatus and method of adaptive weighted parallel interference cancellation system for CDMA

• US 6,741,634 B1
• Filed: 01/21/2000
• Issued: 05/25/2004
• Est. Priority Date: 06/28/1999
• Status: Expired due to Term

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kang, Sugbong, Lee, Jeong Goo, Kim, Seong Rag, Choi, In Kyeong
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Ha, Dac V.
• Application Number:
  US09/491,079
• Time in Patent Office: 1,586 Days
• Field of Search: 375/130, 375/141, 375/142, 375/144, 375/148, 375/150, 375/343, 375/349, 370/335, 370/342, 455/63, 455/67.1, 455/67.3, 455/226.2, 455/226.3
• US Class Current: 375/144
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 2025/03611 Iterative algorithms
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence

Abstract

An adaptive weighted parallel interference cancellation system for CDMA that decreases MAI (multiple access interference) and thereby increases general performance, including K stages for iterative cancellation of MAI in a received signal of a user. Each stage includes a detector, a regenerator, and a subtractor. The detector is configured to determine a tentative bit decision from a despread signal. The regenerator that is connected with the detector in parallel is configured to spread an unmodulated signal, multiply a channel phase, and multiply by the output of the detector. The subtractor uses weighted signals that are adjusted user by user and according to changing environments.

Claims

1. An apparatus for an adaptive weighted parallel interference cancellation system for a CDMA receiver, comprising:

k stages for iterative cancellation of MAI (multiple access interference) in a received signal of a user, wherein each stage comprises;

a detector for determining tentative bit decision from despread signals of an arbitrary user m, wherein 1<

m<

M and m, M are natural number;

a regenerator connected with said detector in parallel for spreading unmodulated signal, for multiplying a channel phase, and for multiplying by an output of said detector; and

a subtractor for obtaining an MAI-cancelled signal on the basis of the weight and input signals of said detector wherein said detector includes;

a matched filter for obtaining maximum SNR from the despread signal of the user m;

a real-part selector for extracting a real-part from the despread signal of the user m with the maximum SNR;

a gain controller for adjusting gain as a function of a fidelity of an output signal of said real-part selector; and

a finite-bit quantizer for receiving gain-adjusted signals from said gain controller and quantizing the tentatively decided bit.

2. The apparatus of claim 1, wherein said finite-bit quantizer performs a hard decision or a soft decision.

3. The apparatus of claim 1, wherein said regenerator includes:

a spreading code multiplier for multiplying the unmodulated signal by a spreading code of the user m;

a pulse-shaping filter for shaping an output signal of said spreading code multiplier;

a channel phase multiplier for multiplying the channel phase of the user m by an output signal of said pulse shaping filter; and

a multiplier for multiplying an output signal of said channel phase multiplier by an output signal of said detector.

4. The apparatus of claim 3 wherein said subtractor includes:

a weight multiplier for multiplying an output signal of said multiplier by weight of present stage;

a first adder for summing weight multiplied signals of all users;

a subtractor for subtracting an output signal of the first adder from the received signal; and

a second adder for adding an output signal of said weight multiplier to an output signal of said subtractor and thereby obtaining the MAI-cancelled signal of the user m.

5. The apparatus of claim 4, wherein said subtractor further comprises:

a first multiplier for multiplying an output signal of said second adder by a spreading code of the user m; and

a second multiplier for multiplying an output signal of said first multiplier by the channel phase and thereby compensating a phase difference.

6. The apparatus of claim 4, wherein the weight of the present stage changes adaptively to minimize the following equation:

$E<br><br>\left[{<br><br>r<br><br>\left(t\right)-\underset{j=1}{\overset{M}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j^{\left(k\right)}<br><br>{\hat{I}}_j^{\left(k\right)}<br><br>}^2\right]$

Î

_j^(k);

estimated value of I_j^(k) (or regenerated signal) for user j^th stage k^th,

r(t);

received signal,

w_j^(k);

weight at stage k^th of user j^th, and

M;

total number of users in the system,

t;

time

K;

total stage number

wherein 0≦

k≦

K and j, K, m and M are a natural number.

7. A method of an adaptive weighted parallel interference cancellation system for a CDMA receiver comprising the steps of:

a) making a tentative bit decision on the basis of a despread signal of an arbitrary user m, wherein 1<

m<

M to obtain a tentatively decided bit, and m, M are natural number;

b) spreading an unmodulated signal and multiplying by a channel phase to obtain a spread and compensated signal;

c) multiplying the tentatively decided bit by a spread and compensated signal and generating, a received signal of the user m;

d) multiplying the received signal by a weight and generating an MAI-cancelled signal of the user m; and

e) Iterating steps a), b), c), and d) and canceling MAI and canceling MAI in received signals of each of users 1 to M wherein the step a) comprises;

obtaining maximum SNR from the despread signal of the user m;

extracting a real part from the despread signal having the maximum SNR;

controlling gain of an extracted real part from the despread signal; and

making a tentative bit decision of the gain-controlled signal.

8. The method of the adaptive weighted parallel interference cancellation system for CDMA according to claim 7, wherein b) and c) comprise:

multiplying the unmodulated signal by a spreading code of the user m to obtain a multiplied signal;

shaping the multiplied signal to obtain a shaped signal;

multiplying the shaped signal by the channel phase of the user m; and

multiplying the shaped signal by the tentatively decided bit.

9. The method of claim 8, wherein d) comprises:

multiplying the received signal of the user m by the weight of the present stage to obtain a weight-multiplied signal;

summing weight-multiplied signals of all users to obtain a summed signal;

subtracting the summed signal from a received baseband signal of the user to obtain a remainder signal; and

adding the weight-multiplied signal to the remainder signal and thereby obtain the MAI-cancelled signal.

10. The method of claim 9, wherein subtracting the summed signal comprises:

multiplying an MAI-cancelled signal of the user m by a spreading code of the user m to obtain a first multiplied signal; and

multiplying the first multiplied signal by the channel phase and thereby compensating for phase difference.

11. The method of claim 9, wherein the weight of the present stage changes adaptively to minimize the following equation:

$E<br><br>\left[{<br><br>r<br><br>\left(t\right)-\underset{j=1}{\overset{M}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>w_j^{\left(k\right)}<br><br>{\hat{I}}_j^{\left(k\right)}<br><br>}^2\right]$

Î

_j^(k);

estimated value of I_j^(k) for user j^th stage k^th,

r(t);

received signal,

w_j^(k);

weight at stage k^th of user j^th, and

M;

total number of users in the system,

t;

time

K;

total stage number

wherein 0≦

k≦

K and j, K, m and M are a natural number.