A New Scheme to Reduce Complexity of APP decoders working on the Dual Code

An a posteriori probability (APP) decoder working on the trellis of the dual code is preferred if the code rate is high. However, a hardware realisation of this decoder is quite complex due to very fine quantisation requirements. This paper explains the nature of the metrics in this dual-APP decoder and points out the underlying reason behind the unsuitability of a traditional log domain approach. We propose a new metric representation scheme and discuss the arithmetic operations involved for a trellis based implementation. Simulation results are given, showing a better performance tradeoff of the proposed scheme against quantisation