Unformatted text preview: local processing to reduce communication and energy costs Challenges arises from the increased level of dynamics (systems and environmental) One of the most important challenge arises from energy constraints imposed by unattended systems These systems must be long-lived and operate without manual intervention They need to self-configure and adapt to environmental dynamics and some terrain conditions may result regions with non-uniform communication density These issues can be addressed by deploying redundant nodes and designing algorithms to use redundancy to extend the system lifetime Scaling challenges are associated with spatial coverage and robustness Central vs. Distributed When energy is constraint and environment is dynamic, distributed approaches are preferable and practical ASCENT Scalable wireless sensor networks require to avoid large amounts of data being transmitted over long distances ASCENT applies well-known techniques from MAC layer protocols to the problem of distributed topology formation Imagine a habitat monitoring sensor network that is deployed in remote forest The deployed systems must confer with the following conditions Ad-hoc deployment Energy constraints Unattended operation under dynamics If we use too few nodes initially: the distance between neighboring nodes will be too far packet loss rate may increase energy required to transmit over larger distances may be prohibitive ASCENT If we use all deployed nodes simultaneously: system will expand unnecessary energy nodes interfere with each other by congesting the channel ASCENT does not use localized distributed algorithm to find a single solution Adaptive self-configuration using localized is suited to problem spaces which have a vast number of possible solutions (in this case, large solution spaces means dense node deployment) ASCENT has the following two assumptions: Carrier Sense Multiple Access (CSMA) MAC protocol Possibilities for resource contention when too many neighboring nodes participate in the multi-hop network Does not detect or repair network partitions and assumes that there is enough node density to connect the entire region Reacts when links have high packet loss ASCENT Two essential contributions of ASCENT design are:
1. Adaptive techniques that allow applications to configure the topology based on the needs while saving energy to extend network lifetime. The techniques do not assume a specific model or fairness, degree of connectivity, or capacity required Self-configuring techniques that react to operating conditions are measured locally. It does not assume any specific radio propagation model, geographical distribution of nodes, or routing mechanisms used 2. ASCENT Design Adaptively elects active nodes from all the nodes Active nodes stay awake always and participate in routing while the other nodes remain passive and periodically checks if they should become active Initially, only some nodes are active while other are passively listening to packets but not transmitting ASCENT
ASCENT Design When source starts transmitting data packets towards the sink, the sink gets high message loss from the source due to limited radio range, called communication hole The receiver gets high packet loss due to poor connectivity with the sender Sink start sending help messages to neighbors that are in listen-only mode, called passive neighbors, to join the network
Help Messages Data Message Source Sink Passive Neighbor Active Neighbor (a) Communication H...
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- Spring '08
- Computer network, Sensor node, Wireless sensor network, Coordinator, Ad Hoc Networks, large ad hoc