Decoding method and system for real-time wireless channel estimation

• US 7,974,368 B2
• Filed: 09/24/2007
• Issued: 07/05/2011
• Est. Priority Date: 09/25/2006
• Status: Active Grant

• Current Assignee: Sunplus Technology Co., Ltd
• Original Assignee: Sunplus Technology Co., Ltd
• Inventors: Han, Yung-Hsiang, Chen, Po-Ning, Shieh, Shin-Lin
• Primary Examiner(s): Payne, David C.
• Assistant Examiner(s): Stevens, Brian J
• Application Number:
  US11/902,549
• Publication Number:
  US 20080075204A1
• Time in Patent Office: 1,380 Days
• Field of Search: 375/341, 375/340, 375/316
• US Class Current: 375/341
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3905 Maximum a posteriori probability [MAP] decoding or approximations thereof based on trellis or lattice decoding, e.g. forward-backward algorithm, log-MAP decoding, max-log-MAP decoding
• CPC Class Codes: H03M 13/6337 Error control coding in combination with channel estimation
• CPC Class Codes: H03M 13/658 Scaling by multiplication or division
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0055 MAP-decoding
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 1/208 involving signal re-encoding
• CPC Class Codes: H04L 25/03171 Arrangements involving maximum a posteriori probability [MAP] detection

Abstract

A decoding method and system for real-time wireless channel estimation, which decodes a received signal with a noise. The received signal is coded by a concatenation code. At first, the received signal is performed a certain amount of decoding by a Max-Log-MAP decoding procedure. Next, an estimated amplitude of the received signal and an estimated variance of a noise are computed. Then, the received signal is adjusted in accordance with the estimated amplitude and the estimated variance to thereby produce an adjusted received signal. Finally, the adjusted received signal is decoded by a Log-Map decoding procedure.

Claims

1. A decoding method for real-time wireless channel estimation, which decodes a received signal with a noise, the received signal being coded by a turbo code, the method comprising the steps:

(A) receiving the received signal with K message bits transmitted between a base station and corresponding stations;

(B) applying a Max-Log-MAP decoding procedure to perform a predetermined amount of decoding on the received signal, wherein the predetermined amount is obtained by looking up a table in accordance with a code rate of concatenation code and a value of K;

(C) using temporary log-likelihood ratios (LLRs) to compute hard decisions of the K message bits of the received signal, wherein the hard decision of i-th message bit in step (C) is computed by;

û

_i^(s)=0, if Λ

_i^(s)≧

0; and

û

_i^(s)=1, if Λ

_i^(s)=0, where Λ

_i^(s) denotes the temporary LLR of the i-th message bit;

(D) computing an ensemble average of the K message bits based on the hard decisions and the K message bits, and accordingly assigning the ensemble average to an estimated amplitude of the received signal;

(E) computing an ensemble average of a first momentum based on absolute values of the K message bits; and

(F) computing a ratio based on the ensemble average of the first momentum and the estimated amplitude of the received signal, and computing an estimated variance of the noise based on the ratio; and

(G) adjusting the received signal in accordance with the estimated amplitude of the received signal and the estimated variance of the noise to thereby produce an adjusted received signal, and decoding the adjusted received signal by a Log-Map decoding procedure.

2. The method as claimed in claim 1, wherein the estimated amplitude Â

^ in step (D) is expressed by;

3. The method as claimed in claim 2, wherein the ensemble average W of the first momentum step (E) is expressed by:

4. The method as claimed in claim 1, wherein the estimated amplitude Â

in step (D) is expressed by

5. The method as claimed in claim 4, wherein the ensemble average W of the first momentum in step (E) is expressed by:

6. The method as claimed in claim 5, wherein the ratio a in step (F) is expressed by

7. The method as claimed in claim 6, wherein the estimated variance σ

² in step (F) is determined based on a polynomial of the ratio a.

8. The method as claimed in claim 7, wherein the estimated variance σ

² in step (F) is computed as follows;

σ

²=−

1.8833×

a²+8.6671×

a−

6.5398.

9. The method as claimed in claim 8, wherein the adjusted received signal in step (G) is obtained by dividing the received signal by

10. A decoding system for real-time wireless channel estimation, which decodes a received signal with a noise, the received signal being coded by a concatenation code and containing K message bits, the K message bits being grouped into systematic bits, first parity bits and second parity bits, the system comprising:

a first decoder, which receives a systematic bit log-likelihood ratio (LLR), a first parity bit LLR and a first prior information and accordingly produces a first extrinsic information and a first output LLR by selectively performing a Max-Log-MAP decoding or a Log-MAP decoding;

an interleaver, which is connected to the first decoder, in order to receive the systematic bit LLR and the first extrinsic information for re-arrangement to thereby produce a second prior information and an interleaved systematic bit LLR;

a second decoder, which is connected to the interleaver, in order to receive the interleaved systematic bit LLR, a second parity bit LLR and the second prior information and selectively performs the Max-Log-MAP decoding or the Log-MAP decoding for producing a second extrinsic information and a second output LLR;

a deinterleaver, which is connected to the second decoder, in order to receive the second extrinsic information for re-arrangement to thereby produce the first prior information;

a channel estimator, which is connected to the first decoder and the second decoder, in order to perform a channel estimation in accordance with the received signal, the first output LLR and the second output LLR to thereby produce an estimated amplitude of the received signal and an estimated variance to the first decoder and the second decoder; and

a controller, which is connected to the channel estimator, the first decoder and the second decoder in order to control the first decoder and the second decoder to first perform a predetermined amount of decoding on the received signal by a Max-Log-MAP decoding procedure, and then control the first decoder and the second decoder to perform a decoding on the received signal by a Log-MAP decoding procedure;

wherein the first decoder and the second decoder adjust the received signal in accordance with the estimated amplitude and the estimated variance when the Log-MAP decoding procedure is performed, and therefore produce an adjusted received signal.

11. The system as claimed in claim 10, further comprising a memory, which is connected to the controller, in order to store a specific table such that the controller depends on a code rate of the concatenation code and a value of K to look up the specific table and thereby obtain the predetermined amount.

12. The system as claimed in claim 10, wherein the adjusted received signal is obtained by dividing the received signal by

13. The system as claimed in claim 10, wherein the first decoder and the second decoder adjust the first extrinsic information and the second extrinsic information in accordance with the estimated amplitude and the estimated variance when the Log-MAP decoding procedure is performed, and therefore produce a scaled first extrinsic information and a scaled second extrinsic information respectively.

14. The system as claimed in claim 13, wherein the scaled first extrinsic information is obtained by dividing the first extrinsic information by

15. The system as claimed in claim 13, wherein the scaled second extrinsic information is obtained by dividing the second extrinsic information by

16. The system as claimed in claim 10, wherein the first decoder is a soft-input-soft-out (SISO) decoder and the second decoder is a soft-input-soft-out decoder.

17. The system as claimed in claim 10, wherein the concatenation code is a turbo code.