Packet Retransmission Diversity Schemes for Higher Order Modulation with High Power and Bandwidth Efficiency

Abstract

Summary form only given. In this presentation, we present a bandwidth-efficient and power-efficient packet retransmission diversity scheme suitable for improving the performance of linear multi-level modulation schemes, such as pulse amplitude modulation (PAM), phase-shift keying modulation (PSK) and quadrature amplitude modulation (QAM), in wireless systems employing (H)ARQ protocols. Our proposed retransmission diversity scheme considers the interaction between (i) the number of retransmission diversity branches and (ii) the signal space of the modulation scheme, to improve the performance. The concept is to suitably rearrange the symbols (change the bit-to-symbol mapping) between retransmissions, while employing the modulation order M as an extra dimension. In this way the modulation order and the number of retransmission diversity branches together are viewed as creating an augmented signal space of higher dimension than the modulation signal space alone, and this is in turn exploited to improve the transmission quality. Both the robustness and the throughput performance are improved, and the number of retransmissions per packet is reduced compared to conventional packet retransmission schemes. As an extension, we apply the proposed method in conjunction with both space-time block coding and trellis coded modulation. While keeping the same rate and complexity, both analytical and simulation results show a significant improvement of the system performance. Our performance results show that the proposed concept improves the system performance over conventional packet retransmission schemes in both additive white Gaussian noise and flat-fading channels, in particular at low to medium E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . This proposed scheme is suitable for wireless LANs and future cellular applications due to its low complexity, bandwidth-and power efficiency.