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In this paper, we study two-layered heterogeneous sensor networks where two types of nodes are deployed: the basic sensor nodes and the cluster head nodes. The basic sensor nodes are simple and have limited power supplies, whereas the cluster head nodes are much more powerful and have many more power supplies, which organize sensors around them into clusters. Such two-layered heterogeneous sensor networks have better scalability and lower overall cost than homogeneous sensor networks. We propose using polling to collect data from sensors to the cluster head since polling can prolong network life by avoiding collisions and reducing the idle listening time of sensors. We focus on finding energy-efficient and collision-free polling schedules in a multihop cluster. To reduce energy consumption in idle listening, a schedule is optimal if it uses the minimum time. We show that the problem of finding an optimal schedule is NP-hard and then give a fast online algorithm to solve it approximately. We also consider dividing a cluster into sectors and using multiple nonoverlapping frequency channels to further reduce the idle listening time of sensors. We conducted simulations on the NS-2 simulator and the results show that our polling scheme can reduce the active time of sensors by a significant amount while sustaining 100 percent throughput.
Date of Publication: Feb. 2008