Near-Capacity Turbo Coded Soft-Decision Aided DAPSK/Star-QAM for Amplify-and-Forward Based Cooperative Communications

Abstract

Abstract-Multilevel Differential Amplitude and Phase-Shift Keying (DAPSK) schemes do not require any channel estimation, which results in low complexity. In this treatise we derive the soft-output probability formulas required for a soft-decision based demodulation of high-order DAPSK, in order to facilitate iterative detection by exchanging extrinsic information with an outer Turbo Code (TC). Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. Compared to the identical-throughput TC assisted 64-ary Differential Phase-Shift Keying (64-DPSK) scheme, the 4-ring based TC assisted 64-ary DAPSK arrangement has a powerefficiency improvement of 2.3 dB at a bit error rate (BER) of 10 −5 . Furthermore, when the TC block size is increased, the system operates closer to the channel capacity. More specifically, when using a TC block length of 400 modulated symbols, the 64 DAPSK (4, 16) scheme is 7.56 dB away from its capacity curve, while it had a reduced gap as low as 2.25 dB, when using a longer TC block length of 40 000 modulated symbols. Finally, as a novel application example, the soft-decision M-DAPSK scheme was incorporated into an Amplify-and-Forward (AF) based cooperative communication system, which attains another 4.5 dB SNR improvement for a TC block length of 40 000 modulated symbols.

Soft-Decision for Differential Amplify-and-Forward over Time-Varying Relaying Channel

“…This combiner can be seen as a counterpart of selection combining of DPSK in point-to-point communications with receive diversity studied in [12]- [15]. The soft-output probability formulas based high-order Differential Amplitude and Phase-Shift Keying (DAPSK) have been derived to approach the achievable channel capacity by iterative detection in [16]. On the other hand, if the normalized Doppler spread of the channel is large due to high mobility and/or low data rate, the channel is called fast or time-selective fading [17].…”