A peak power efficient cooperative diversity using star-QAM with coherent/noncoherent detection

In this paper, we propose a new simple relaying strategy based on bit-interleaved convolutionally coded star-quadrature amplitude modulation (QAM) along with coherent/noncoherent detection. Star-QAM is composed of multiple concentric circles of phase-shift keying (PSK). Exploiting this property, a hard limiter is used to enhance power amplifier (PA) efficiency at the relay. Moreover, we show that the proposed approach retains differential detectability, which results in a significant reduction of receiver complexity with robustness against phase ambiguity. By analyzing our proposed cooperation with coherent/noncoherent detection in terms of asymptotic pairwise error probability (PEP), we show that the full diversity order can be achieved on the condition that the minimum free distance of the convolutional codes is larger than the predetermined value specified by the number of available relays. Furthermore, the effectiveness of the proposed scheme in terms of PA efficiency is confirmed by comparing the statistical distributions of the corresponding instantaneous signal powers. All the theoretical results agree with those obtained by computer simulations.