SNR mismatch and online estimation in turbo decoding

Iterative decoding of turbo codes, as well as other concatenated coding schemes of similar nature, requires accurate knowledge of the signal-to-noise ratio of the channel so that proper blending of the a posteriori information of the separate decoders is achieved. In this paper, we study the sensitivity of decoder performance to mis-estimation of the SNR, and propose a simple on-line scheme that estimates the unknown SNR from each code block, prior to decoding. We show this scheme is suuciently adequate in accuracy to not appreciably degrade performance.