A Necessary and Sufficient Condition for Optimal Transmission Power in Wireless Packet Networks with ARQ Capability

In this paper, we investigate the energy minimization problem for wireless packet networks with automatic repeat request (ARQ) capability. We formulate the problem under constrained packet delay and reliability, and derive a necessary and sufficient condition for optimal transmission power that achieves optimality regardless of the delay and reliability constraints. Numerical examples reveal that a significant amount of energy is saved by adopting the optimal transmission power and the performance gain is strongly correlated with the decreasing property of the frame error rate.