An Application-Specific Protocol Architecture for Wireless Microsensor Networks

1. An Application-Specific Protocol Architecture for Wireless Microsensor Networks 컴퓨터 공학과 1132036002 오영준

2. Contents • Introduction • Backgrounds • LEACH Protocol Architecture • Analysis and Simulation • Conclusion

3. Introduction • Sensor network Challenge • Limited communication bandwidth • Limited energy • Problem Definition in WSN • Ease of Deployment • Sensor Network may contain hundreds until thousands node • System Life Time • Long life time as possible. • Latency • Data distribution is time sensitive • Quality • Reduce same redundant data between nodes • Neighboring nodes may same data • End user cares about a higher-level description of event

4. LEACH(Low-Energy Adaptive Clustering Hierarchy) • Randomized, adaptive, self-configuring cluster formation • Localized control of data transfers • Low energy media access control(MAC) • Application specific data processing, such as data aggregation and compression

5. Back ground • Network Scenario – Simple • All nodes communicate directly with the base station – always on • Problems: • Out of power fast! • Especially distant nodes • Signal strength is inversely proportional to the square of the distance Base Station

6. Back ground • Network Scenario – MTE(Minimum Transmission-Energy) • Each node discovers the best hop-by-hop path to the base station during an initialization phase • Problems: • close-in nodes overused • multiple hops -> latency Base Station

7. Back ground • Network Scenario – Clustering • Organize nodes into clusters • Nodes send data to Cluster Head • Cluster head aggregates the data and sends results to base station • Problem: • When cluster head’s energy depleted, no further data is sent from this cluster Base Station

8. LEACH Protocol Architecture • LEACH • Randomized rotation of cluster heads among the sensor • ALL non-cluster head nodes transmit data to their cluster heads • CH receives this data and performs signal processing functions on the data and transmits data to the BS

9. LEACH(Low-Energy Adaptive Clustering Hierarchy)

10. LEACH Protocol Architecture • Cluster Behavior During a Round • Organize new cluster • Each member node (in turn) transmits their data to the cluster head during the assigned time slot • Cluster head transmits to base station

11. Cluster Heads LEACH Protocol Architecture • Cluster Behavior During a Round • Each round consists of a set up period and some number of frames • Each round establishes a new structure of clusters • Each cluster has a new cluster head • Repeated rounds until the network fails (due to energy depletion) Round 1 Round 2 11

12. LEACH Protocol Architecture • Cluster Head Selection Algorithms • Pi(t) is the probability with which node i elect it self to be cluster Head at the beginning of the round r+1 (which starts at time t) such that expected number of cluster-head nodes for this round is k. k= # of cluster during each round N= # of nodes in the network • Each node will be cluster Head once in N/k rounds. • Probability for each node i to be a cluster-head at time t • Ci(t) = it determines whether node i has been a cluster • Head in most recent (r mod(N/k)) rounds.

13. LEACH Protocol Architecture • Cluster Head Selection Algorithms • = total no. of nodes eligible to be a cluster-head at time t. • This ensures energy at each node to be approx. equal after every N/k rounds. • Using (2) and (3), expected # of cluster Head per round is,

14. LEACH Protocol Architecture • Cluster Head Selection Algorithms • Nodes with more energy should have a higher probability of being chosen than nodes with less energy • Thus, the probability that a given node will be chosen is determined by that node’s share of the total remaining energy • Where Ei(t) is the energy of the ith node and

15. LEACH Protocol Architecture • Cluster Head Selection Algorithms • Notice that this algorithm requires each node to know (or have an estimate for) the value of Etotal(t) • To know the exact value would take time and consume energy • As an estimate we could compute the average energy of each node in a given cluster and multiply by N • Nodes report current energy to cluster head • Cluster head computes estimated Etotal(t) and returns the value to all nodes in the cluster

16. LEACH Protocol Architecture • Cluster Formation Algorithm • Cluster heads broadcasts “advertisement” message (ADV) using CSMA MAC protocol • ADV= node`s ID + distinguishable header • Non-cluster head nodes measure received strength of ADV and select strongest sender as their cluster head • Nodes notify cluster head of their selection with a “Join-REQ” message • Join-REQ = node`s ID + cluster head ID + header • Cluster head creates TDMA schedule for nodes in its cluster • Prevents collision among data messages. • Energy conserving in non-cluster head nodes.

17. LEACH Protocol Architecture • Steady State Phase • TDMA schedule is used to send data from node to cluster head. • Cluster head aggregates the data received from nodes in the cluster. • Communication is via direct-sequence spread spectrum(DSSS) and each cluster uses a unique spreading code to reduce inter-cluster interference. • Data is sent from the cluster head nodes to the BS using a fixed spreading code and CSMA.

18. LEACH Protocol Architecture • Steady State Phase • Assumption • Nodes are all time synchronized and start the set-up phase at same time. • BS sends out synchronized pulses to the nodes. • Cluster Head must be awake all the time. • To reduce inter-cluster interference, each cluster in LEACH communicates using direct-sequence spread spectrum(DSSS) • Data is sent from the cluster head nodes to the BS using a fixed spreading code and CSMA

19. LEACH Protocol Architecture • LEACH-C: BS Cluster Formation • Using a central control algorithm may produce better clustering • Each node sends location information and energy level to the base station • Base station: • Eliminates low energy nodes from consideration • Finds k optimal clusters (since this is NP-hard, uses the “Simulated annealing algorithm” ) • Goal is to minimize the total sum of squared distances between non-cluster heads and the nearest cluster head

20. ANALYSIS AND SIMULATION OF LEACH • Simulate the performance of four protocols (Static Clustering, MTE, LEACH, & LEACH-C) • Set up the simulation • Find the optimal number of clusters • Compare the protocols’ energy consumption performance

21. ANALYSIS AND SIMULATION OF LEACH d>d0 • Experiment setup • 100 nodes randomly distributed over a 100 X 100 grid: (0, 0) to (100, 100) • Base station placed outside the grid: (50, 175) • Channel bandwidth = 1 Mb/s • Packets have 25 byte header and 500 byte data size • Power loss determined by distance d • If d < do, loss µd 2(Free space model) • If d >= do, loss µd 4 (Multi-path model) Base Station d0 d d d0 d<d0

22. ANALYSIS AND SIMULATION OF LEACH • Experiment Setup • Eelec: energy consumed by the electronics to process l bits • efs: energy consumed by the amplifier to transmit l bits over distance d where d < do • emp: energy consumed by the amplifier to transmit l bits over distance d where d >= do

23. ANALYSIS AND SIMULATION OF LEACH • Experiment Setup • Then total energy consumed by the transmitter: • Total energy consumed by the receiver: • Eelec = 50 nJ/bit • efs = 10 pJ/bit/m2 • emp = 0.0013pJ/bit/m4 • Energy for Data Aggregation: EDA = 5 nJ/bit/signal

24. ANALYSIS AND SIMULATION OF LEACH • Optimum Number of Cluster • With a given spatial distribution of nodes and known energy consumption parameters, we can compute an optimal number of cluster heads (k) • Develop expressions for node energy use • Cluster heads (assumes dtoBS > do) • Non-cluster heads(assumes dtoCH < do) Listening Aggregating Transmitting

25. ANALYSIS AND SIMULATION OF LEACH • Optimum Number of Cluster • Develop an expression for the expected squared distance from the node in a cluster to the cluster head • In an M x M grid, each cluster occupies an area of M2/k • Clusters have a node distribution of p(x, y) • The cluster head is at the center of mass of the cluster • Then the expected d2 from the nodes to the cluster head is • Further assume the area is a circle -> radius R = (M/(pk)1/2) • And p(r, q) constant for r and q, then

26. ANALYSIS AND SIMULATION OF LEACH • Optimum Number of Cluster • Node density is uniform across all cluster -> p = (1/( M2/k)) • Combine energy and distance expression for non-cluster heads: • The for the entire cluster: • The total energy for the frame is

27. ANALYSIS AND SIMULATION OF LEACH • Optimum Number of Cluster • Set derivative of Etotal with respect to k to zero • Results for this case (100 nodes, etc.): Analytical method predicts 1 < kopt < 6

28. ANALYSIS AND SIMULATION OF LEACH • Energy Gains • Each node begins with only 2 J of energy and an unlimited amount of data to send to the BS. • Parameters tracked during simulations • Rate at which data packets were transferred to the BS • Energy required to get the data to the BS

29. ANALYSIS AND SIMULATION OF LEACH • Energy Gains • LEACH-C and LEACH deliver far more data than MTE and Static Clustering (SC) and they are far more energy efficient (as measured by signals per Joule) • SC fails when all cluster heads die, even with most energy still unused • MTE slow to deliver data due to multi-hops • LEACH-C is the best performer due to optimal cluster design

30. ANALYSIS AND SIMULATION OF LEACH • Energy Gains • LEACH-C and LEACH maintain full network availability far longer than MTE and SC • MTE lasts the longest, but at the price of very limited effective data delivery due to • Lack of data aggregation • Energy wasted in CSMA collisions • LEACH-C is again the best performer

31. Conclusion • Microsensor network protocol must be designed for • Bandwidth efficiency • Energy efficiency • High quality • LEACH • Better energy utilization and system lifetime • Load balancing is achieved • All node die at a time