Low-complexity policies for Wireless Sensor Networks with two energy harvesting devices

Recently, Wireless Sensor Networks (WSNs) with energy harvesting capabilities are experiencing increasing interest with respect to traditional ones, due to their promise of extended lifetime. We consider the case of a pair of Energy Harvesting Devices (EHDs), with the main goal of maximizing the long-term aggregate average importance associated with the transmitted data. The devices, at each time instant, have data of different importance levels to be transmitted, as well as different battery energy levels. In order to avoid collisions, a Central Controller (CC) allows at most the transmission of a single EHD per time slot. Assuming a negligible processing cost in terms of energy, our objective is to identify low-complexity transmission policies, that achieve good performance with respect to the optimal one. We numerically show that two policies, namely the Balanced Policy (BP) and the Heuristic Constrained Energy Independent Policy (HCEIP), despite being independent of the battery energy levels, achieve near optimal performance in most cases of interest, and can be easily found with an adaptation to the ambient energy supply. Moreover, we derive analytically an approximation of the BP and show that this policy can be considered a good lower bound for the performance of the Optimal Policy.