Role Based Medium Access Control in Wireless Sensor Networks

Medium Access Control is a key component of the Wireless Sensor Network (WSN) protocol stack for conserving energy, as it is responsible for radio management of a sensor node. Traditional synchronous protocols for WSNs carry out periodic duty cycles consisting of awake and sleep periods in order to conserve energy. All nodes behave similarly, in that they follow the same actions defined by the medium access layer in unison. While this is a fundamentally acceptable practice for protocol design, the reality is that not all nodes may not be required to be turned on to actively take part in the collaborative sensing and relaying required in a WSN. In this paper, we classify nodes into two roles - either a relay node or a leaf node - depending on the type of actions performed in terms of forwarding packets. Leaf nodes can safely turn their radios off during the active period of a duty cycle, which leads to energy savings in the network, and increases network lifetime. We outline how to incorporate roles into synchronous MAC protocols like TMAC, and modify the protocol behavior based on the roles defined. While our approach is not a new MAC protocol by itself, this idea can be incorporated as an optimizing heuristic in existing protocols to gain additional energy savings. Simulation studies using the Castalia WSN simulator show that our approach outperforms both SMAC and TMAC protocols in terms of packet overhead and energy conservation.