SNR MISMATCH AND ONLINE ESTIMATION IN TURBO DECODING

Iterative decoding of turbo codes, as well as other concatenated codin g schemes of similar nature, requires knowledge of the signal-to-noise ratio (SNR) of the channel so that proper blending of the a posterior i information of the separate decoders is achieved. In this paper we s tudy the sensitivity of decoder performance to misestimation of the SN R, and propose a simple online scheme that estimates the unknown SNR f rom each code block, prior to decoding, We show that this scheme is su fficiently adequate in accuracy to not appreciably degrade performance .