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Unformatted text preview: On Distributed TimeDependent Shortest Paths over DutyCycled Wireless Sensor Networks Shouwen Lai, Binoy Ravindran Department of Electrical and Computer Engineering Virginia Tech,Blacksburg, VA 24061 Email: { swlai,binoy } @vt.edu Abstract —We revisit the shortest path problem in asyn chronous dutycycled wireless sensor networks, which exhibit timedependent features. We model the timevarying link cost and distance from each node to the sink as periodic functions. We show that the timecost function satisfies the FIFO property, which makes the timedependent shortest path problem solvable in polynomialtime. Using the βsynchronizer, we propose a fast distributed algorithm to build alltoone shortest paths with polynomial message complexity and time complexity. The algorithm determines the shortest paths for all discrete times with a single execution, in contrast with multiple executions needed by previous solutions. We further propose an efficient distributed algorithm for timedependent shortest path maintenance. The proposed algorithm is loopfree with low message complexity and low space complexity of O ( maxdeg ) , where maxdeg is the maximum degree for all nodes. The performance of our solution is evaluated under diverse network configurations. The results suggest that our algorithm is more efficient than previous solutions in terms of message complexity and space complexity. I. INTRODUCTION The problem of routing over wireless sensor networks (WSNs) has attracted extensive attention in the recent years. Some WSN routing protocols [1], [2] presented in the litera ture are extended from routing protocols over wired/wireless adhoc networks. They find a path with the minimum hop count to the destination, which is based on the assumption that the link cost (or onehop transmission delay) is relatively static for all links. However, for asynchronous dutycycled WSNs, that assumption may not be valid. In asynchronous dutycycled WSNs, i.e., WSNs operating with MAClayer protocols such as BMAC [3] or XMAC [4], sensor nodes operate in low power listening (LPL) mode. In the LPL mode, a node periodically switches between active and sleep state. The period for one active/sleep switching is called the LPL checking interval, which can be identical, or can be adaptively varied for different nodes, refereed to as ALPL [5]. The asynchronous dutycycled mechanism have been shown to achieve excellent idle energy savings, scalability, and easiness in implementation. However, they suffer from timevarying neighbor discovery latencies which is also pointed out by Ye et.al. [6]. As shown in Figure 1, the neighbor discovery latency between two neighbors is varied with different departure times....
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This note was uploaded on 10/29/2010 for the course KFC 1234 taught by Professor Know during the Spring '10 term at Uni Wien.
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