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Clustering in wireless ad hoc networks has shown to be a promising technique to ensure the scalability and efficiency of various communication protocols. Since stations in these networks are usually equipped with batteries as the power source, it is critical to ensure the energy efficiency of a clustering scheme. The Quorum-based Power Saving (QPS) protocols are widely studied over the past years, as they render extensive energy conservation comparing to the IEEE 802.11 Power Saving (PS) mode. However, most existing QPS protocols adopt a symmetric design where each pair of stations in a network are guaranteed to discover each other. Observing that in clustered environments there is no need to insist on all-pair neighbor discovery, we propose an Asymmetric Cyclic Quorum (ACQ) system. The ACQ system guarantees the neighbor discovery between each member node and the clusterhead in a cluster, and between clusterheads in the network. We show that by taxing slightly more energy consumption on the clusterhead, the average energy consumption of stations in a cluster can reduce substantially than can be achieved by traditional QPS protocols. A novel construction scheme is proposed in this work, which assembles the ACQ system in O(1) time. The constructing scheme is adaptive. Stations in a cluster can adjust their awake/sleep ratio collaboratively to strike the balance between energy efficiency and delay under various cluster conditions. Simulation results show that the ACQ system outperforms the previous studies up to 52% in energy efficiency, while introducing no extra worst-case latency.
Date of Publication: September 2011