1. Energy-Efficient Communication Protocol for Wireless Microsensor Networks by Wendi Rabiner Heinzelman, Anantha Chandrakasan, and Hari Balakrishnan Presented by Sukun Kim Based on presentation of Neha Jain

2. Overview Introduction Key Features of Microsensors Sensor Network Model Direct Communication Protocol Minimum Transmission Energy Routing Protocol Clusters LEACH (Low-Energy Adaptive Clustering Hierarchy) Results Conclusion

3. INTRODUCTION Nodes maybe mobile(though very low mobility) Sensor networks are “data-centric” networks. They are application specific Adjacent nodes may have similar data. No need of Unique ID as routing to & from specific nodes is not required. Presence of large number of nodes implies large id thus, data sent may be less than the address.

4. Typical applications of Sensor Networks Reliable environment monitoring for commercial and military applications –For a security system, acoustic, seismic and video sensors can be used to form an adhoc network to detect intrusion. Monitor machines for fault detection and diagnosis

5. The Microsensor Networks Consists of tens of thousands of extremely small, low power and low cost devices which share wireless channel bandwidth in order to achieve high quality, fault tolerant sensing networks Equipped with programmable computing, multiple sensing and communication capability. Routing protocols exercise local collaboration to reduce bandwidth requirement have too much data to process hence automated data aggregation into small set of meaningful information is required Data fusion produces more accurate signal from unreliable data measurement. Operate and respond in a very dynamic environment

6. Assumptions for experiments the radio channel is symmetric, energy required to transmit a message from node A to B is same as energy required to transmit message from node B to A (symmetry among nodes) All the nodes in the network are homogeneous and energy constrained All sensors are sensing data at a fixed rate and always have data to send to the end –user.

7. Sensor Network Model BS

8. Direct Communication Protocol BS

9. Direct Communication Protocol Requires large amount of transmit power from each node if the BS is far away from the nodes. This will quickly drain the battery of the nodes and reduce system lifetime. The nodes furthest from the BS are the ones to die out first as they have the highest transmit energy.

10. Minimum Transmission Energy Routing Protocol BS Routing

11. Minimum Transmission Energy Routing Protocol In these protocols nodes route data destined ultimately for the base station through intermediate nodes. Thus nodes act as routers for other nodes’ data in addition to sensing the environment. First node dies out quicker using MTE than DC (if epsilon amp is large, these two will swap) Nodes closest to the BS are the first to die out in MTE routing, as they are the ones most used as “routers” for other sensors’ data

13. Which is more Energy Efficient ? When network diameter is small / the radio electronics energy is high, direct transmission is more energy efficient than MTE. The most energy efficient protocol to use depends on the network diameter and radio parameters of the system.

14. Clustering BS

15. Clustering Here nodes are organized into clusters that communicate with a local BS and these local Base Stations transmit the data to the global BS, where it is accessed by the end user. Reduced distance of data transmission as the local BS is typically close to all nodes in the Cluster but BS becomes energy constrained As soon as cluster -head node dies, all nodes from that cluster effectively die since there is no way to get their data to the base station. In Adaptive clustering, cluster heads change as nodes move in order to keep the network fully connected.

16. Optimal percentage of nodes, N that should be cluster heads If it is less than optimal N, some nodes have to transmit very far to reach the cluster head, large global energy. If more than optimal N, more cluster heads have to transmit the long haul distances to the base station, hence compression is less. N= 5%, reduces energy consumption by a factor of 7.

17. Hierarchical Clustering Each cluster head aggregates data & sends to the BS or higher level cluster head

18. Key Features of LEACH (Low-Energy Adaptive Clustering Hierarchy) Localized coordination and control for cluster set up and operation. Local compression to reduce global communication Randomized rotation of the cluster heads and the corresponding clusters. Random Death of nodes : there is no one section of the environment that is not being “sensed” as nodes die, as occurs in the other protocols.

19. Randomised Rotation The high energy cluster head position rotates among the various sensors in order to not to drain the battery of a single sensor. (currently just random) Sensors elect themselves to be the local cluster heads at any given time with a certain probability, and broadcast their status to other sensors each sensor node choosing the cluster-head with strongest signal (can minimize transmission power) Each node takes the decision independent of the other nodes to become cluster head. It is based on the suggested percentage determined a priori and round number

20. LEACH - Algorithm Details The operation is broken up into rounds –Advertisement phase use CSMA MAC protocol, and all cluster heads transmit with same energy –Set up phase : Cluster is organized each node transmits to which cluster head it wants to belong to using a CSMA MAC –Steady State Phase: Data Transfers to Base Station occur

21. LEACH Uses TDMA with CDMA TDMA CDMA code1 code2 code3

22. LEACH uses TDMA with CDMA Then cluster head creates a TDMA schedule for all nodes within its cluster telling each node when it can transmit. Allows radio component of each non cluster head to be turned off at all times except during its transmit time, thus minimizing the energy dissipated in the individual sensors. They must keep their receivers on during set up phase to hear the advertisements of all cluster heads. Transmission in one cluster will affect communication in a nearby cluster, hence each cluster communicates using different CDMA codes.

23. How is LEACH Energy Efficient ? Energy requirement is distributed among all the sensors by randomized rotation Local fusion of data in cluster head reduces amount of data to be transmitted to the base station (computation for fusion is cheaper than communication). Main energy saving is due to combining lossy compression with the data routing. tradeoff between quality of output and amount of compression resulting in substantial reduction of overall energy dissipation.

24. Total system energy dissipated using direct communication, MTE routing and LEACH for the 100-node random network. Eelec = 50 nJ/bit, messages are 2000 bits

25. System lifetime using direct transmission, MTE routing, static clustering, and LEACH with 0.5 J/node

26. Results LEACH reduces communication energy by as much as 8 times compared to direct transmission and MTE routing The first node death in LEACH occurs over 8 times later, and last node death occurs over 3 times later than any other protocol.

27. Conclusion LEACH outperforms conventional routing protocols like direct transmission, minimum-transmission-energy, static clustering algorithms LEACH is distributed. Nodes do not require control information from the base station nor knowledge of the global network

28. Possible Questions How much data fusion is possible in cluster head? (with randomized rotation of cluster head, it can be worse) What if BS has big antenna? What is the effect of contention and bandwidth limit? With parameters of mica or mica2?

30. Big antenna at base station BS Cost 5 Cost 20