Efficient Channel Estimation Method against Channel Mismatch in Turbo Decoding

• Main Authors: Wei-Ting Chen, 陳威廷
• Other Authors: Yunghsiang S. Han
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/07807438214460391471

碩士 === 國立臺北大學 === 通訊工程研究所 === 94 === Turbo code was emphasized on its performance that achieves very close to {it Shannon-Limit}. Recently, turbo-coding was extensively used in many communication systems such as WCDMA system and 3GPP system, etc. The turbo decoding consists of {it a posteriori probability (APP) }algorithm and iterative decoding algorithm that utilize channel information in decoding process. Hence, an efficient method to estimate the signal-to-noise ratio (SNR) of the channel is very important and necessary. If the online estimation for SNR of the channel is mismatched badly, the performance degradation will be very serious in turbo decoding. Several online channel estimation methods, whose estimation complexities are too high for practical decoder design, were proposed before. In this thesis we propose a new on-line method to estimate the SNR of the additive while Gaussian noise (AWGN) channel on-line. Our goal is to get an acceptable performance and reduce the complexity of the estimation. The proposed decoding algorithm first runs Max-Log-MAP algorithm for a certain amount of iterations, utilizes the log-likelihood ratios as well as the absolute first order statistics to estimate the channel characteristics, and then switches to Log-MAP algorithm after the channel estimation are done. According to simulation results over the AWGN channel, our method has similar performance to the previous method but with much lower complexity.