Optimizing HARQ feedback and incremental redundancy in wireless communications

Wireless networks have been adjusting their transmit power, modulation order, and coding rate based on the channel conditions for a long time. Such adaptive protocols aim to maximize the overall throughput by striking a trade-off between transmitting as much information as possible and minimizing the probability of loosing such information. However, there is little literature on adaptive retransmissions when failures occur. This paper studies the trade-offs that hybrid automatic repeat request (HARQ) protocols face when choosing the type and amount of incremental redundancy (IR) that should be sent when the decoding of a data block fails at the receiver. It proposes a method to optimize such choice for a system with non-ideal error correcting codes (ECC) and limited feedback capabilities. Additionally, it is shown through simulations that the overall data rate can be significantly increased by bundling the acknowledgements.