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

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. 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) 11 Round 1 Round 2 Cluster Heads

12. LEACH Protocol Architecture Cluster Head Selection Algorithms –P i (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. 13 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, LEACH Protocol Architecture

14. 14 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 E i (t) is the energy of the i th node and LEACH Protocol Architecture

15. 15 Cluster Head Selection Algorithms –Notice that this algorithm requires each node to know (or have an estimate for) the value of E total (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 E total (t) and returns the value to all nodes in the cluster LEACH Protocol Architecture

16. 16 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. LEACH Protocol Architecture

17. 17 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. LEACH Protocol Architecture

18. 18 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 LEACH Protocol Architecture

19. 19 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 LEACH Protocol Architecture

20. 20 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 ANALYSIS AND SIMULATION OF LEACH

21. 21 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 < d o, loss µ d 2 (Free space model) If d >= d o, loss µ d 4 (Multi-path model) ANALYSIS AND SIMULATION OF LEACH Base Station d d0d0 d>d 0 d d0d0 d<d 0

22. 22 Experiment Setup –E elec : energy consumed by the electronics to process l bits –e fs : energy consumed by the amplifier to transmit l bits over distance d where d < d o –e mp : energy consumed by the amplifier to transmit l bits over distance d where d >= d o ANALYSIS AND SIMULATION OF LEACH

23. 23 Experiment Setup –Then total energy consumed by the transmitter: –Total energy consumed by the receiver: ANALYSIS AND SIMULATION OF LEACH E elec = 50 nJ/bit e fs = 10 pJ/bit/m 2 e mp = 0.0013pJ/bit/m 4 Energy for Data Aggregation: E DA = 5 nJ/bit/signal

24. 24 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 d toBS > d o ) Non-cluster heads (assumes d toCH < d o ) ANALYSIS AND SIMULATION OF LEACH Listening Aggregating Transmitting

25. 25 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 M 2 /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/(  k) 1/2 ) –And p(r, q) constant for r and q, then ANALYSIS AND SIMULATION OF LEACH

26. 26 Optimum Number of Cluster –Node density is uniform across all cluster -> p = (1/( M 2 /k)) –Combine energy and distance expression for non-cluster heads: –The for the entire cluster: –The total energy for the frame is ANALYSIS AND SIMULATION OF LEACH

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

28. 28 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 ANALYSIS AND SIMULATION OF LEACH

29. 29 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 ANALYSIS AND SIMULATION OF LEACH

30. 30 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 ANALYSIS AND SIMULATION OF LEACH

31. 31 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 Conclusion