Arc Hyperbolic Tangent representation scheme for APP decoders working on the dual code

Inhalt:
An a posteriori probability (APP) decoder working on the trellis of the dual code is preferred if the code rate is high. However, the nature of the metrics in a dual-APP decoder makes a hardware realisation quite complex, due to very fine quantisation requirements. This paper points out the problem associated with a traditional log domain approach and proposes a new metric representation scheme. The arithmetic operations involved in a trellis based implementation are discussed and simulation results for a turbo code are given.