Cooperation helps power saving

In wireless sensor networks (WSN), energy efficiency is crucial to achieving satisfactory network lifetime. The most commonly used and may be the only efficient method to reduce the energy consumption significantly is to turn off the radios most of the time, except when it has to participate in data communication. The key challenge is to operate the radio at a low duty cycle but still ensure the delay is relatively low. Various power-saving medium-access control (MAC) protocols have been proposed along this thread. However, most of such protocols focus on a point-to-point communication setting, in which a node will drop an overheard packet if it is not the destination. On the other hand, cooperative wireless communication has been drawing extensive attention in the past few years. Node cooperation has been exploited to reduce end-to-end delay, improve transmission reliability, etc. However, not much has been done in utilizing node cooperation to save energy. This idea may sound absurd since cooperation requires more nodes involved in a communication and would result in more energy being consumed. But is this true? In this paper, we will exploit the possibility of cooperative power saving in wireless ad-hoc networks. The trade-off between energy consumption and delay will be studied. Interestingly, our analytical and simulation results show that cooperation can indeed help achieve a better delay-power consumption trade-off. Our results also show that cooperation together with asymmetric power allocation can achieve the optimal delay-power trade-off.