An improved ARQ scheme with application to multi-level modulation techniques

We present a simple, but effective, packet combined ARQ scheme for multi-level modulation schemes such as MPAM, MPSK and MQAM. We propose an ARQ scheme that rearranges the symbols between different transmissions and also uses the modulation level, M, as an extra dimension to improve the quality of the signal and reduce the number of retransmissions per packet. The idea is to see the modulation level and number of retransmissions as an augmented signal space and use packet combining to improve the robustness and performance. Our results show that the proposed ARQ scheme obtains a 4 dB gain compared to a packet combined ARQ scheme employing Chase combining.