Energy optimization for hybrid-ARQ and AMC

We consider the energy optimization of a cross-layer design which combines hybrid automatic repeat request (HARQ) and adaptive modulation and coding. We consider two cases: variable alphabet size with constant transmit power, and variable alphabet size with variable transmit power. We optimize the alphabet size selection algorithm and/or the transmit power for each transmission round to minimize energy consumption, subject to an overall packet error probability constraint. Numerical results show that the variable alphabet size and variable power case significantly reduces energy consumption compared to conventional HARQ schemes. For example, at a packet error probability of 5 × 10~
²
, energy consumption of the proposed scheme is reduced by 40% relative to a comparison scheme.