QoS and security in energy-harvesting wireless sensor networks

Wireless sensor networks are composed of small nodes that might be used for a variety of purposes. Nodes communicate together through a wireless connection that might be subject to different attacks when the network is placed in hostile environments. Furthermore, the nodes are usually equipped with very small batteries providing limited battery life, therefore limited power consumption is of utmost importance for nodes. This is in clear opposition with the requirement of providing security to communications as security might be very expensive from the power consumption stand point. Energy harvesting methods can be used to recharge batteries, but, in most of the cases the recharge profile cannot be known in advance. Therefore, nodes might face periods of time in which no recharge is available and the battery level is low. In this paper we introduce an optimization mechanism that allows the system to change the communication security settings at runtime with the goal of improving node lifetime, yet providing a suitable security level. The optimization mechanism further improves energy consumption by putting in place a quality of service mechanism: when energy is scarce, the system tends to send only essential packets. As shown by the simulations presented in this paper, this mechanism optimizes the energy consumption among different recharges.