An optimal power allocation scheme for the STC hybrid-ARQ over energy limited networks

In this paper, we show that for STC (Space-Time Coded) Hybrid-ARQ (Automatic Repeat reQuest) schemes with (re)transmission power control over independent Rayleigh block fading channels, the problem of optimizing energy efficiency with a PER (Packet Error Rate) constraint can be solved as a geometric programming problem. The optimum transmit power increases super-linearly with each requested retransmission and the fraction of the average power optimally allocated to each ARQ round only depends on the incremental diversity gain. The energy savings increases with a decrease in the PER targets and decreases with an increase in the diversity gain.