Energy Optimization For Hybrid ARQ With Turbo Coding: Rate Adaptation and Allocation

We consider incremental redundancy (IR) hybrid automatic repeat request (HARQ) over independent block-fading channels with turbo coding. We consider different cases of channel state information (CSI) at the transmitter: the transmitter has no knowledge of any CSI, or knows the CSI in previous transmission rounds through a perfect feedback channel, or knows both current and previous CSI. The transmitter decides the forward error correction code rate based on the CSI it has. We minimize the energy consumption of turbo-coded HARQ, subject to a packet loss rate constraint. Numerical results show that the energy consumption of HARQ decreases when more CSI information is available at the transmitter. We also compare IR combining with Chase combining and the system without combining, and IR combining yields the least energy consumption.