SNR mismatch and online estimation in turbo decoding

Abstract

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 su ciently adequate in accuracy to not appreciably degrade performance.

Towards the capacity of noncoherent orthogonal modulation: BICM-ID for turbo coded NFSK

“…In our work, we assumed that the average E b /N o is known at the receiver, as our prior experience and reports in the literature indicate that estimating E b /N o over a large block of data is not difficult and turbo decoding is robust against slight SNR estimation errors [20]. Nevertheless, the problem of SNR estimation should be considered more thoroughly before the proposed technique can be fielded.…”

Error Rate Estimation Based on Soft Output Decoding and its Application to Turbo Coding

“…However, in it is shown that MAP and log-MAP decoders can tolerate a significant SNR estimation error without error rate degradation [20], [21]. Nevertheless, the expectation of LLR strongly depends on the SNR estimation error also if error rate is not.…”

Low-complexity time-domain SNR estimation for OFDM systems

“…The parameters are adapted according to channel conditions indicated by a knowledge of the signal-to-noise ratio (SNR). SNR estimation is also used in soft decoding algorithms and other applications [1].…”