Efficient approaches to improving performance of VLSI SOVA-based turbo decoders

In this paper, we propose two VLSI applicable approaches to improving performance of soft-output Viterbi algorithm (SOVA)-based turbo decoders. In the first approach, a pseudo-median filter is employed to modify the soft outputs of each SOVA-based constituent decoder. Compared with conventional SOVA-based turbo decoders, an extra coding gain of 0.2 dB can be achieved for a wide range of target bit-error-rate (BER). In the second approach, an easily obtainable variable and a simple mapping function are used to avoid the complex computation of the scaling factor for extrinsic information in SOVA-based turbo decoders. An extra coding gain of 0.3 to 0.5 dB can be obtained in general. This approach does not require signal-to-noise ratio (SNR) related information while the original method does. The hardware overhead and the extra latency for both approaches are negligible.