Energy optimal channel attempt rate and packet size for ALOHA based underwater acoustic sensor networks

In this paper, we investigate the energy efficiency and throughput of ALOHA based underwater acoustic sensor networks (UASNs). We derive closed form expressions for the channel attempt rate and packet length at which energy efficiency and throughput are maximized separately. Based on our results, we observe that the packet length that maximizes energy efficiency leads to deterioration of throughput and vice versa. Motivated by these observations, we consider a cross layer optimization problem with the objective of maximizing the energy efficiency of the network, while meeting throughput criteria at the MAC layer and an SNR criteria at the PHY layer. With the aid of Karush–Kuhn–Tucker conditions, we derive closed form solutions for the optimal channel attempt rate and packet length that satisfy the desired objectives. For the analysis, we consider underwater acoustic channel specific parameters such as spreading losses and distance dependent bandwidth. Extensive performance evaluation study of our approach proves that, judicious selection of the packet lengths as well as channel attempt rates by the sensor nodes can ameliorate the energy efficiency of UASN remarkably, while satisfying the throughput criterion.