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Introduction to Wireless Sensor Networks

Introduction to Wireless Sensor Networks. Peyman Teymoori. Definition. Wireless Sensor Networks (WSNs): Highly distributed networks of small, lightweight wireless nodes, Deployed in large numbers ,

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Introduction to Wireless Sensor Networks

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  1. Introduction to Wireless Sensor Networks Peyman Teymoori

  2. Definition • Wireless Sensor Networks (WSNs): • Highly distributed networks of small, lightweight wireless nodes, • Deployed in large numbers, • Monitors the environment or system by measuring physical parameters such as temperature, pressure, humidity. • Node: • sensing + processing + communication

  3. Applications of WSNs • Constant monitoring & detection of specific events • Military, battlefield surveillance • Forest fire & flood detection • Habitat exploration of animals • Patient monitoring • Home appliances

  4. Comparison with Ad Hoc Wireless Networks • Both consist of wireless nodes but they are different. • The number of nodes is very large • Being more prone to failure, energy drain • Not having unique global IDs • Data-centric, query-based addressing vs. address-centric • Resource limitations: memory, power, processing

  5. Design Issues & Challenges • Random deployment  autonomous setup & maintenance • Infrastructure-less networks  distributed routing • Energy, the major constraint  trading off network lifetime for fault tolerance or accuracy of results • Hardware energy efficiency • Distributed synchronization • Adapting to changes in connectivity • Real-time communication, QoS • Security

  6. Design Factors • Scalability • Fault tolerance • Power consumption • Sensor network architectures: • Layered • Clustered

  7. Layered Architecture • A single powerful base station (BS) • Layers of sensor nodes around BS • Layer i: All nodes i-hop away from BS • Applications: • In-building: BS is an access point • Military • Short-distance, low power tx

  8. Unified Network Protocol Framework (UNPF) • A layered architecture • A set of protocols • Integrates three operations: • Network Initialization & Maintenance Protocol • MAC Protocol • Routing Protocol

  9. Unified Network Protocol Framework (UNPF) • Network Initialization & Maintenance Protocol: • BS broadcasts its ID using CDMA common control channel (BS reaches all nodes in one hop) • Nodes record BS ID & send beacon signal with their own IDs at their low default power levels • All nodes the BS can hear are at 1-hop distance • The BS broadcasts a control packet with all layer one node IDs • All nodes send a beacon signal again • The layer one nodes record the IDs they hear-layer 2 • The layer one nodes inform the BS of the layer 2 • The BS broadcasts the layer2 nodes IDs,… • To maintain: periodic beaconing updates are required

  10. Unified Network Protocol Framework (UNPF) • Routing Protocol: • Downlink from the BS is by direct broadcast on the control channel • Enables multi-hop data forwarding to the BS • The remaining energy is considered when forwarding to the next hop (layer) • Only the nodes of the next layer need to be maintained in the routing table

  11. Clustered Architecture • Organizes the sensor nodes into clusters • Each cluster is governed by a cluster-head • Only heads send messages to a BS • Suitable for data fusion • Self-organizing

  12. Low-Energy Adaptive Clustering Hierarchy (LEACH) • Self-organizing and adaptive clustering protocol • Evenly distributes the energy expenditure among the sensors • Performs data aggregation where cluster heads act as aggregation points • Two main phases: • Setup phase: organizing the clusters • Steady-state phase: deals with the actual data transfers to the BS

  13. Low-Energy Adaptive Clustering Hierarchy (LEACH) • Setup phase: • Each sensor chooses a random number m between 0 and 1 • If m < T(n) for node n, the node becomes a cluster-head where • P : the desired percentage of cluster heads • r : the round number • G : the set of nodes that have not been cluster heads during the last 1 / P rounds • A cluster head advertises its neighbors using a CSMA MAC. • Surrounding nodes decide which cluster to join based on the signal strength of these messages • Cluster heads assign a TDMA schedule for their members

  14. Low-Energy Adaptive Clustering Hierarchy (LEACH) • Steady-state phase: • All source nodes send their data to their cluster heads • Cluster heads perform data aggregation/fusion through local transmission • Cluster heads send them back to the BS using a single direct transmission • After a certain period of time, cluster heads are selected again through the set-up phase

  15. Low-Energy Adaptive Clustering Hierarchy (LEACH) • Merits: • Accounting for adaptive clusters and rotating cluster heads • Opportunity to implement any aggregation function at the cluster heads • Demerits: • Highly dynamic environments • Continuous updates • Mobility

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