Link Scheduling in Rechargeable Wireless Sensor Networks with Harvesting Time and Battery Capacity Constraints

A link scheduler ensures the transmissions in rechargeable Wireless Sensor Networks (rWSNs) are collision-free. Hence, it plays a critical role in ensuring high network capacity and the energy used for transmission/reception is not wasted due to collisions. This paper proposes a scheduler that generates a Time Division Multiple Access link schedule for use in a rWSN. Different from most prior works, our scheduler considers the time required by each node to harvest sufficient energy to transmit/receive a packet. Further, it utilizes the more efficient Harvest-Use-Store (HUS) model and considers sensor nodes with finite battery capacity. We present a greedy heuristic that activates links according to the earliest time in which their end nodes have sufficient energy to transmit/receive a packet. Our simulation results show that the time to recharge a sensor node significantly increases the link schedule or superframe lengths; i.e., by up to 563.9% as compared to the case where sensor nodes have no energy constraint. Further, in comparison to the Harvest-Store-Use (HSU) model, using HUS can reduce superframe lengths by up to 45.3%. Our experiments also show that increasing battery capacity does not effect the superframe length significantly; i.e., it reduces the length only by up to 2.5%. Finally, our proposed heuristic can generate superframe lengths that are on average 23% longer as compared to the lower bound on the superframe length when nodes have energy constraint.