Bit-by-bit soft-decision decoding of trellis-coded M-DPSK modulation

We present a simple soft-decision decoding method for use with trellis-coded M-ary differential phase-shift keying (M-DPSK). The demodulator assigns a separate confidence level to each bit associated with an M-ary symbol, and these confidence levels are based only on the phase of the received symbol. Decoding is performed by the standard soft-decision Viterbi decoder that is normally used for binary modulation. Our soft-decision decoder is much simpler to implement than the typical trellis decoder, but we show that the performance is approximately the same.