Reduced-Complexity Noncoherent Soft-Decision-Aided DAPSK Dispensing With Channel Estimation

Differential amplitude phase-shift keying (DAPSK), which is also known as star-shaped quadrature-amplitude modulation, has implementational advantages not only due to dispensing with channel estimation but as a benefit of its low signal detection complexity as well. It is widely recognized that separately detecting the amplitude and the phase of a received DAPSK symbol exhibits lower complexity than jointly detecting the two terms. However, since the amplitude and the phase of a DAPSK symbol are affected by correlated magnitude fading and phase rotations, detecting the two terms completely independently results in a performance loss, which is particularly significant for soft-decision-aided DAPSK detectors relying on multiple receive antennas. Therefore, in this contribution, we propose a new soft-decision-aided DAPSK detection method, which achieves optimum DAPSK detection capability at substantially reduced detection complexity. More specifically, we link each a priori soft-input bit to a specific part of the channel's output, so that only a reduced subset of the DAPSK constellation points has to be evaluated by the soft DAPSK detector. Our simulation results demonstrate that the proposed soft DAPSK detector exhibits lower detection complexity than that of independently detecting the amplitude and the phase, whereas the optimal performance of DAPSK detection is retained.