Optimal symbol mapping diversity for multiple packet transmissions

In this paper we present a simple, but effective method of creating and exploiting diversity from packet retransmissions in systems that employ nonbinary modulations such as PSK and QAM. This diversity results from differing the symbol mapping for each packet retransmission. By developing a general framework for evaluating the bit error rate (BER) upper hound with multiple transmissions, a criterion to obtain optimal symbol (re)mappings is attained for memoryless AWGN channels. The optimal adaptation scheme reduces to solutions of the Quadratic Assignment Problem (QAP). Symbol mapping adaptation only requires a small increase in receiver complexity hut provides very substantial BER gains.