On-line extraction of soft decoding information and applications in VLSI turbo decoding

In this paper, a set of variables which can be easily computed in the course of iterative decoding of turbo decoders named turbo decoding metrics (TDMs) are introduced. TDMs are measured twice per iteration. According to the measured values, a lot of information other than the signal-to-noise ratio (SNR) in the received data, such as how good (or bad) the current decoding block is and how close to the convergence the current decoding is, can be obtained. Detailed discussions are provided regarding why these variables are considered. Based on the measured TDMs after the first iteration, an approximate channel reliability value (denoted as L_c) can be obtained for MAP-based turbo decoders. Simulation results show that there is no performance degradation if approximated L_c values are used instead of using exact values. It is also shown that the adaptive decoding approach employing TDMs is more efficient than all existing methods in terms of hardware and latency. Other applications of TDMs are also pointed out.