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Unformatted text preview: ation of maintaining the capacity or connectivity of the network It is distributed and randomized algorithm in which the nodes make local decisions on whether to sleep or join to the backbone Each node decides based on an estimate of how many neighbors will benefit from it being awake and the energy available to it Improvement in the system lifetime increases along with the ratio of idle-to-sleep energy consumptions Non-coordinators remain in power saving mode and periodically check to see if they should wake up and become coordinators SPAN A good power saving technique for ad hoc networks should have the following: 1. 2. 3. 4. 5. 6. Allow as many as nodes to turn their radios off most of the time Forward packets between any source and destination with the minimum possible delay than if all nodes were awake Distributed algorithm where having each node making local decisions Backbone formed by the awake nodes should provide close to total capacity as the original networks such that congestion can be avoided Do not make many assumptions about the link layer's facilities for sleeping and work with any link layer that provides sleeping and periodic polling Inter-operate correctly with any routing algorithm being used SPAN fulfills all the above requirements Each node makes periodic local decisions to sleep or stay awake as a coordinator and participate in the forwarding backbone topology SPAN In order to keep the same level of capacity of the original network, a node may volunteer to become a coordinator if it figures out from the local information gathering that two of its neighbors cannot communicate directly or through one or two existing coordinators In order to keep the number of coordinators low and rotate this role amongst all nodes, each node delays sending message about its desire to become a coordinator by a random time interval The decision is based on two factors: 1. 2. the remaining battery energy the number of pairs of neighbors it can connect together This allows SPAN to maintain capacity-preserving backbone at any time with the nodes consuming about the same level of energy SPAN also scales well with the number of nodes SPAN SPAN Design The goals of SPAN includes: 1. 2. 3. 4. Ensures enough coordinators to be elected such that each node is in radio range of at least one coordinator Rotates coordinators to ensure that all nodes provides equal support to achieve global connectivity Increases the network lifetime, preserves the capacity with minimum latency by minimizing the number of elected coordinators Coordinators are elected based on local available information SPAN is proactive such that each node periodically broadcasts HELLO messages which contains the node's status (coordinator or not), its current coordinators, and its current neighbors From these HELLO messages, each node keeps tracks of a list of the node's neighbors and coordinators, and for each neighbor, a list of its neighbors and coordinators SPAN Coordinator Announcement Each non-coordinator node periodically determines whether it should become a coordinator or not The coordinator eligibility rules ensures that the network is covered with sufficient number of coordinators Coordinator Eligibility Rule A non-coordinator node should become a coordinator if it figures out from the local information gathering that two of its neighbors cannot communicate directly or through one or two existing coordinators If many nodes are willing to become coordinators, SPAN sol...
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This note was uploaded on 08/25/2011 for the course EEL 5937 taught by Professor Staff during the Spring '08 term at University of Central Florida.

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