A Power Saving MAC Protocol for Wireless Networks

This paper presents a protocol which improves on the power saving mechanism in the IEEE 802.11 Distributed Coordination Function (DCF). In the power saving mechanism (PSM) for DCF, all nodes are synchronized by beacons. In each beacon interval, there is a fixed time interval called the ATIM window where every node has to be awake. During the ATIM window, a source node informs a destination node about a pending packet by transmitting an ATIM frame. When the destination node receives an ATIM frame, it replies with an ATIM-ACK. Both the source and destination nodes stay awake for the remaining beacon interval. The source can transmit data after the ATIM window finishes. A node that does not have traffic to send or receive can enter the doze state after its ATIM window finishes. During the ATIM window in PSM, no data transmission is allowed. Thus, the available bandwidth in PSM is reduced according to the ATIM window size. Also, energy is consumed in transmitting and receiving ATIM and ATIM-ACK frames. This paper proposes a protocol that removes the overhead of the ATIM window and uses the bandwidth for data transmission. Simulation results show that removing the ATIM window gives better aggregate throughput and energy saving. This research is supported in part by National Science Foundation grants 99-76626 and 01-96410.