Improving Power Save Protocols Using Carrier Sensing and Busy-Tones for Dynamic Advertisement Windows

Energy efficient protocols are important in ad hoc networks since battery life for wireless devices is limited. The IEEE 802.11 protocol specifies a simple power save mechanism (PSM) to conserve energy. However, the protocol needlessly wastes energy when traffic is light in a network, and significantly increases packet latency. In this paper, we consider three techniques to improve the 802.11 PSM protocol. The first technique, Carrier Sense ATIM, uses carrier sensing to drastically reduce the energy wasted listening to the channel in 802.11 PSM. The second technique, Dynamic ATIM, dynamically extends the listening period in 802.11 PSM based on packet advertisements that are overheard. In this manner, we are able to advertise data packets just as effectively as 802.11 PSM while significantly reducing wasteful listening. The final technique, PerLink Beacon Intervals, allows sender and receiver pairs to schedule their wake-up times independent from all the other nodes in the network based on past packet arrival times. Our results show that this technique is able to significantly reduce the average packet latency causing no or relatively little increase in energy. All of the protocols are extensively tested using the ns-2 simulator.