Opportunistic Multi-Layer Transmission over Unknown Channels

We use the received bit information rate (RBIR) to analyze the performance of multi-layer transmission when combined with hybrid automatic repeat request (HARQ). The different layers are obtained from ordinary Gray-coded M-QAM and used for transmitting log2(M) codewords in parallel, exploiting that the different bits in Gray-coded M-QAM have very different reliability. The performance is analyzed when different layers are decoded in parallel (independently) as well as when successive decoding is used. In addition, we study how the RBIR can be used to select a suitable layer for a retransmission to further improve the performance. Simulation results based on a Wi-Fi like physical layer show that a significant gain compared to the standard approach can be achieved by using basic multilayer transmission, and also that using successive decoding and carefully selecting what layer to use for retransmission can give further gains.