Speed-optimized soft-decision demodulation of multilevel DAPSK

We propose a speed-optimized noncoherent soft-decision demodulation of multilevel differential amplitude and phase shift keying (DAPSK) signals as part of a generic transmission system for multimedia indoor communications. The computation of soft-decision bit metric increments as input to a Viterbi decoder is quite time-consuming for higher DAPSK levels, as the total number of constellation points increases exponentially. To effectively reduce this computational cost at the receiver, we quantize the received signals at an early stage of the demodulation process. From this point on, the remaining soft-decision DAPSK demodulation can be reduced to a single table look-up per symbol. We show that the proposed preprocessing allows for fast soft-decision demodulation and that for all investigated DAPSK levels the signal-to-noise ratio (SNR) penalty is less than 0.25 dB compared to the unquantized case