Protocols for Wireless Sensor Networks

1. Protocols for Wireless Sensor Networks

2. Outline • Introduction • Flat Routing Protocols • Directed Diffusion • SPIN • Hierarchical Routing Protocols • LEACH • PEGASIS • TEEN • Topic for Discussion • References

3. Introduction to WSNs • A sensor network is a computer network of many, spacially distributed devices using sensors to monitor conditions at different locations. • Involve three areas: sensing, communications, and computation.

4. Introduction to WSNs • Sensor nodes scattered in a sensor field • Each nodes has the capabilities to collect data and route data back to the sink (Base Station). • Protocols and algorithms with self-organization capabilities.

5. Introduction - WSNs Topology • Issues related to topology maintenance and change in three phases: • Pre-deployment and deployment phase: • Sensor nodes can be either thrown in mass or placed one by one in the sensor field. • Post-deployment phase: • Topology changes are due to change nodes' position, reachability, available energy, malfunctioning, and task details. • Re-deployment of additional nodes phase: • Additional sensor nodes can be redeployed at any time to replace malfunctioning nodes or due to changes in task dynamics.

6. Types of Routing Protocol for WSN • Single-hop Networks • The network consists of n nodes, and packets are transmitted from sources to destinations directly. • Multi-hop Networks • The final destination of a packet might not be reached directly and the other nodes can be used to route the packet to the final destination.

7. Flat Routing Protocols • Flat Networks • Every incoming packet is sent out on every outgoing line except the one it arrived on. • Vast numbers of duplicate packets are generated. • Routing Protocols: Directed Diffusion, SPIN.

8. The Directed Diffusion Protocol • Directed Diffusion consists of several elements: • Interests • Datamessages • Gradients • Reinforcements

9. Directed Diffusion - Interest & Data • Interest • type = wheeled vehicle • interval = 1 s • rect = [-100, 200, 200, 400] • timestamp = 01:20:40 // hh:mm:ss • expiresAt = 01:30:40 • Data • type = wheeled vehicle // type of vehicle seen • instance = trunk // instance of this type • location = [125, 220] // node location • intensity = 0.6 // signal amplitude measure • confidence = 0.85 // confidence in the match • timestamp = 01:20:40 // local event generation time

10. Directed Diffusion - Interest Propagation • The sink periodically broadcasts an interest message to each of its neighbors. • Every node maintains an interest cache.

11. Directed Diffusion - Gradient Establishment • That every pair of neighboring nodes establishes a gradient toward each other. • This technique can enable fast recovery from failed paths or reinforcement of empirically better paths.

12. Directed Diffusion - Data Propagation • A sensor node that detects a target, it computes the highest requested event rate among all its outgoing gradients. • To resend a received data message, a node needs to examine the matching interest entry's gradient list.

13. Directed Diffusion - Reinforcement • The node might choose that neighbor from whom it first received the latest event matching the interest to reinforce. • It is very reactive to changes in path quality.

14. The SPIN Protocol • Sensor Protocols for Information via Negotiation. • Start with a source node sending its data to all of its neighbors.

15. r q s A B (q, r) C (r, s) A (a) (a) B C (a) (a) D SPIN - Flooding deficiencies • Implosion & Overlap Implosion Problem Overlap Problem

16. SPIN-1 - three types of messages • ADV • When a SPIN node has data to share, it can advertise an ADV message containing meta-data. • REQ • A SPIN node sends an REQ message when it wishes to receive some actual data. • DATA • DATA messages contain actual sensor data with a meta-data header.

17. DATA REQ ADV DATA ADV REQ ADV ADV REQ ADV DATA The SPIN-1 Protocol • Steps C D B A E F

18. The SPIN-2 Protocol • When energy is plentiful, SPIN-2 nodes communicate using the same 3-stage protocol as SPIN-1 nodes. • When a SPIN-2 node observes that its energy is approaching a low-energy threshold, it adapts by reducing its participation in the protocol.

19. Hierarchical Routing Protocols • Hierarchical Networks • The main aim of hierarchical routing is to efficiently maintain the energy consumption of sensor nodes. • Performing data aggregation and fusion in order to decrease the number of transmitted messages to the sink. • Routing Protocols: LEACH, PEGASIS, TEEN.

20. The LEACH Protocol • Low-Energy Adaptive Clustering Hierarchy. • Distributed cluster formation technique that enables self-organization of large numbers of nodes.

21. LEACH - Cluster • Algorithms for adapting clusters and rotating cluster head positions to evenly distribute the energy load among all the nodes. • The nodes organize themselves into local clusters, with one node acting as the cluster head. • The cluster headperforms signal processing functions on the data, and transmits data to the remote BS.

22. LEACH - Set-up phase • Cluster Head • Each cluster head node broadcasts an advertisement message(ADV) let all the other nodes that they have chosen this role for the current round. • Non-Cluster Head • They transmits a join-request message(Join-REQ) back to the chosen cluster head.

23. LEACH - Set-up phase • The cluster head node sets up a TDMA schedule and transmits this schedule to the nodes in the cluster. • Ensures that there are no collisions among data messages. • Allows the radio components to be turned off at all times except during their transmit time.

24. LEACH - Steady-state phase • Broken into frames, where nodes send their data to the cluster head at most once per frame during their allocated transmission slot. • Once the cluster head receives all the data, it performs data aggregation.

25. ADV Join-REQ SCH Slot for NCH2 Set-up phase NCH1 NCH2 … … … NCHm-1 NCHm Frame LEACH - Time line • Time line showing LEACH operation

26. The PEGASIS Protocol • Power-Efficient GAthering in Sensor Information Systems. • The key idea in PEGASIS is to form a chain among the sensor nodes so that each node will receive from and transmit to a close neighbor.

27. PEGASIS - Chain • The nodes will be organized to form a chain, which can either be accomplished by the sensor nodes themselves using a greedy algorithm starting from some node. • When a node dies, the chain is reconstructed in the same manner to bypass the dead node.

28. PEGASIS - Leader • The main idea in PEGASIS is for each node to receive from and transmit to close neighbors and take turns being the leader for transmission to the BS. • Nodes take turns transmitting to the BS, and we will use node number i mod N (N represents the number of nodes) to transmit to the BS in round i.

29. PEGASIS - Token • Token passing approach N0 N1 N2 N3 N4 BS Token Data

30. The TEEN Protocol • Threshold sensitive Energy Efficient sensor Network protocol. • Proactive Protocols (LEACH) • The nodes in this network periodically switch on their sensors and transmitters, sense the environment and transmit the data of interest. • Reactive Protocols (TEEN) • The nodes react immediately to sudden and drastic changes in the value of a sensed attribute.

31. TEEN - Functioning • At every cluster change time, the cluster-head broadcasts to its members • Hard Threshold (HT) • This is a threshold value for the sensed attribute. • It is the absolute value of the attribute beyond which, the node sensing this value must switch on its transmitter and report to its cluster head. • Soft Threshold (ST) • This is a small change in the value of the sensed attribute which triggers the node to switch on its transmitter and transmit.

32. TEEN - Hard Threshold • The first time a parameter from the attribute set reaches its hard threshold value, the node switches on its transmitter and sends the sensed data. • The sensed value is stored in an internal variable in the node, called the sensed value (SV).

33. TEEN - Soft Threshold • The nodes will next transmit data in the current cluster period, only when both the following conditions are true: • The current value of the sensed attribute is greater than the hard threshold. • The current value of the sensed attribute differs from SV by an amount equal to or greater than the soft threshold.

34. TEEN - Drawback • If the thresholds are not reached, the user will not get any data from the network at all and will not come to know even if all the nodes die. • This scheme practical implementation would have to ensure that there are no collisions in the cluster.

35. References • I.F. Akyildiz, W. Su*, Y. Sankarasubramaniam, and E. Cayirci, • "Wireless sensor networks: a survey". • K. Akkaya, M. Younis, • "A Survey on Routing Protocols for Wireless Sensor Networks". • J.N. Al-Karaki, A.E. Kamal, • "Routing Techniques in Wireless Sensor Networks". • C. Intanagonwiwat, R. Govindan, and D. Estrin, • "Directed Diffusion: A Scalable and Robust Communication Paradigm for Sensor Networks". • W. Heinzelman, J. Kulik, and H. Balakrishnan, • "Adaptive Protocols for Information Dissemination in Wireless Sensor Networks". • W. Heinzelman, A. Chandrakasan, and H. Balakrishnan, • "An Application-Specific Protocol Architecture for Wireless Microsensor Networks". • S. Lindsey and C. Raghavendra, • "PEGASIS: Power-Efficient Gathering in Sensor Information Systems". • A. Manjeshwar and D. Agrawal, • "TEEN: A Routing Protocol for Enhanced Efficiency in Wireless Sensor Networks".