On the optimization of channel side information for turbo decoding

Since 1993, turbo code has shown its powerful capability for forward error correcting. In order to achieve a good bit error rate (BER) performance, turbo decoding needs to work on a soft metric that is based on the maximum likelihood function of a received bit. This soft metric requires knowledge of the signal-to-noise ratio (SNR) of the received signal, called channel side information (CSI). In an ordinary noisy channel, performance is optimized when the estimated CSI perfectly matches the actual channel SNR. But in some scenario such as fading and using a partially processed satellite, it is impossible to realistically utilize a perfectly matched CSI for turbo decoding. In this paper, the optimizations of CSI are illustrated for these scenarios in order to achieve the best performances.