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. Packets are advertised for a fixed length of time, known as an advertisement window, at epochs known as beacon intervals. However, the protocol needlessly wastes energy when traffic is relatively light in a network. In this paper, we address this problem by proposing the use of carrier sensing to dynamically adjust the size of the advertisement windows. The adjustment is based on the amount of traffic that needs to be advertised in the current window as opposed to the static window size used by 802.11 PSM. Carrier sensing is used for two different aspects of our protocol. First, carrier sensing is used as an energy efficient method to provide a binary signal which lets neighbors know if a node intends to advertise any packets in the upcoming window. Second, carrier sensing is used as a mechanism for nodes to keep track of whether their neighbors have already stopped listening for advertisements and possibly returned to sleep. Using the ns-2 simulator we show that our techniques can significantly reduce the energy consumption of 802.11 PSM while only slightly increasing latency
['Matthew J. Miller', 'Nitin H. Vaidya']
Improving power save protocols using carrier sensing for dynamic advertisement windows