Optimal performance trade-offs in MAC for wireless sensor networks powered by heterogeneous ambient energy harvesting

In wireless sensor networks powered by ambient energy harvesting (WSNs-HEAP), sensor nodes´ energy harvesting rates are spatially heterogeneous and temporally variant, which impose difficulties for medium access control (MAC). In this paper, we first derive the necessary conditions under which channel utilization and fairness are optimal in a WSN-HEAP, respectively. Based on the analysis, we propose an earliest deadline first (EDF) polling MAC protocol, which regulates transmission sequence of the sensor nodes based on the spatially heterogeneous energy harvesting rates. It also mitigates temporal variations in energy harvesting rates by a prediction and update mechanism. Simulation results verify the performance tradeoff predicted by our analysis for the proposed HEAP-EDF protocol. In the presence of spatial heterogeneity and temporal variations in energy harvesting rates, our proposed protocol exhibits significant performance advantages compared to the existing MAC protocols for WSNs-HEAP in the literature.