Energy-Efficient Medium Access Control

Managing wireless communication will be the key to effective deployment of large scale sensor networks that need to operate for years. On the one hand, wireless communication is essential (i) to foster collaboration between neighboring sensor nodes to help overcome the inherent limitations of their cheap, and hence inaccurate sensors observing physical events, and (ii) to report those events back to a sink node connected to the wired world. On the other hand, wireless communication consumes a lot of energy, is error prone, and has limited range, forcing many nodes to participate in relaying information, all of which severely limit the lifetime of the (unattended) sensor network. In typical sensor nodes like the Mica2 mote, communicating one bit of information consumes as much energy as executing several hundred instructions. Therefore, one should “think” twice before actually transmitting a message. Nevertheless, whenever a message should be sent, the protocol stack must operate as efficiently as possible. In this report we will study the medium access layer, which is part of the Data Link layer (layer 2 of the OSI model) and sits directly on top of the Physical layer (layer 1) (see Figure .1). Since the medium access layer controls the radio, it has a large impact on the overall energy consumption, and hence, the lifetime of a node.