Increasing the throughput of HARQ via multi-packet transmission

In this work we consider incremental redundancy hybrid ARQ (HARQ) transmission of data packets over independent block-fading channels. In HARQ, the transmitter, upon request (NACK), resends the "NACKed" packet in the next available block. Conventionally, the original and retransmitted packets occupy one block, each. In our approach, we allow the transmitter to share the resources between the new and the retransmitted packets. To implement such a multi-packet transmission we consider the superposition coding and the timesharing modulation as possible encoding schemes for simultaneous transmission of both packets. Targeting the maximization of the throughput, we cast the problem into the framework of Markov decision process (MDP), where the decisions about the optimal transmission strategy are taken using information about the state of the receiver in the previous transmissions. Numerical examples obtained in a Rayleigh block-fading channel show that proposed transmission strategy provides notable gains over a conventional HARQ.