Optimal transmission policy for collaborative beamforming with finite energy storage capacity

This paper considers a communication scenario where multiple energy harvesting sensors equipped with finite-capacity energy storage devices cooperate to transmit a previously shared common message to a distant base station. The goal is to identify the jointly optimal transmission (power allocation) policy which maximizes the total data throughput until a given deadline. To that aim, we propose a semi-analytical procedure on which basis the optimal policy for each sensor can be computed as a concatenation of a number of battery operated like transmission policies. The computational complexity of such semi-analytical methods turns out to be much lower than that of other numerical optimization tools (e.g., interior point algorithm). The performance is extensively assessed by means of computer simulations, with a specific emphasis on inter-senor distance, total amount of harvested energy and other system parameters. As a benchmark, we consider a strategy where the transmission policy is separately optimized for each sensor.