Energy-constrained modulation optimization for coded systems

We consider radio applications where the nodes operate on batteries so that energy consumption must be minimized while satisfying given throughput and delay requirements. In this context, we analyze the best modulation strategy to minimize the total energy consumption required to send a given number of bits when error-control codes are used. The total energy consumption includes both the transmission energy and the circuit energy consumption. We show that for both MQAM and MFSK the total energy consumption may be reduced significantly if the transmission time T_on is optimized to reduce the sum of transmission energy and circuit energy consumption. Our optimization considers both delay and peak-power constraints. Numerical examples are given, where we exhibit up to 90% energy savings over modulation strategies that minimize the transmission energy alone. We also show that the benefit of coding varies with the transmission distance and the underlying modulation schemes.