Energy-Driven Adaptive Clustering Hierarchy (EDACH) for Wireless Sensor Networks Kyung Tae Kim, Hee Yong Youn (Sungkyunkwan University) Research supported by the “uAuto” Project uAuto: Ubiquitous Autonomic Computing and Network Project

Outline Introduction System Model Proposed Protocol - EDACH Performance Evaluation

WSN Wireless sensor network enables the collection of useful information in real life. It is composed of hundreds or thousands of sensor nodes. Since sensor nodes carry constrained power source, power conservation is a critical design issue for routing protocol.

Clustering-based Routing Selects a set of cluster-heads among the nodes in the network, and clusters the rest of nodes (member nodes) with the cluster-heads 2 clustering-based routing protocol referred to: LEACH EDACH

LEACH Low-Energy Adaptive Clustering Hierarchy, a protocol proposed to solve the energy consumption problem Employs randomized rotation of the cluster-heads to evenly distribute the energy load among the sensor nodes in the network

EDACH Energy-Driven Adaptive Clustering Hierarchy, an enhanced version of LEACH Increases the lifetime and reliability of sensor network in the presence of faults at the cluster-head

Outline Introduction System Model Proposed Protocol - EDACH Performance Evaluation

Single-Hop Clustered Network Nodes and cluster-heads are homogenous Communication over wireless link Objective of a sensor node: capture information sent directly to the local cluster-head in one hop Roles of a cluster-head: 1)aggregation of data flows coming from the local cluster of sensor nodes, and 2) forwarding the aggregated data streams to the base-station.

Energy Model of a Sensor 1st order radio model A radio dissipates Eelec (e.g. 50nJ/bit) to run the transmitter or receiver circuitry and εamp (e.g. 100pJ/bit) for the transmitter amplifier d: distance d2 energy loss due to channel attenuation εamp amplifier coefficient

Fault Model Consider only data transmission faults of cluster-head Data transmission faults in a cluster-head can be caused by hardware failure or energy depletion in it.

Outline Introduction System Model Proposed Protocol - EDACH Performance Evaluation

LEACH Overview The operation is divided into rounds. Each of these rounds consists of 2 phases: a set-up phase and a steady-state phase. During the set-up phase cluster-heads are determined and the clusters are organized. During the steady-state phase data trans-ference to the base station occurs.

EDACH Overview Periodic operation of the following 2 phases: a set-up phase and a self-organized data collection and transmission phase. The set-up phase is identical to LEACH. The 2nd phase is modified to deal with the possible problem that cluster-heads in the LEACH have no sufficient energy to carry out the duty of cluster-head. EDACH - Advanced version of LEACH.

Enhancement If a cluster encounters a problematic cluster-head, then a proxy is selected to operate in replace of the original cluster-head. By doing this, energy dissipation of the nodes is decreased and lifetime of the nodes and reliability of the wireless sensor networks are increased.

Set-up Phase In order to select cluster-heads, each node chooses a random number between 0 and 1. If the number is smaller than a threshold, the node becomes a cluster-head for the current round.

Set-up Phase The threshold is set as: where P is the desired percentage of cluster-heads, r is the current round, and G is the set of nodes that have not been cluster-heads in the last 1/P rounds. Every node becomes a cluster-head exactly once within 1/P rounds. Using this threshold, each node will be a cluster-head at some point within 1/P rounds. During round 0, each node has a probability P of becoming a cluster-head. The nodes that are cluster-heads in round 0 cannot be cluster-heads for the next 1/P rounds. Thus the probability that the remaining nodes are cluster-heads must be increased, since there are fewer nodes that are eligible to become cluster-heads. After 1/P-1 rounds, T=1 for any nodes that have not yet been cluster-heads, and after 1/P rounds, all nodes are once again eligible to become cluster-heads.

Set-up Phase After selection, every selected cluster-head advertises its token by CSMA/CA MAC protocol to all its neighbors. Comparing the signal strength of the token, non cluster-head nodes choose among the strongest and broadcasts an answer packet including node’s position and remaining energy also by CSMA/CA. (Carrier Sense Multiple Access/Collision Avoidance) A transmission technology that attempts to avoid collisions rather than detect them as in CSMA/CD. Used in wireless Ethernet (802.11) and Apple's LocalTalk, when a device needs to transmit, it listens to the network (senses the carrier) and waits for it to be free. In 802.11, it then waits a random period of time and transmits. If the receiver gets the frame intact, it sends back an ACK to the sender. In a LocalTalk network, when the network is free, the sending device broadcasts a tiny control packet indicating that it wants to transmit. All other stations wait until the data packet is transmitted.

Set-up State At last, the cluster-head node creates a TDMA schedule telling each node when it can transmit.

Self-organized Data Collection and Transmission Phase Starts after the set-up phase. Every nodes collected local data, and sends the packet to the cluster-head in its allocated transmission time. No doubt that cluster-heads consumes much more power and more likely to suffer from depletion.

Ways to Save the Energy For member nodes, by using the minimal amount of energy to transmit according to the signal strength of the token received For member nodes, by turning off until its allocated transmission time A Cluster-head aggregates the data gathered before sending it to the base station.

Difference A threshold value ETH is used as a measure for deciding if the current cluster-head has become obsolete. where kj is the length of the aggregated message in the j-th cluster-head, dCH is the distance between cluster-head and the base station

Difference Once the energy of a cluster-head drops below the threshold, the proxy node selection process begins. A cluster-head of EDACH maintains a table of remaining energy and nodes’ position of its members so it can select a member node to be a proxy node by comparing the 2 factors. Once the proxy is selected, it only temporarily take the authority of cluster-head. It can still be selected as a cluster-head in the next round.

Proxy Node Determination

Indicator Control Message Advertisement Process CHID: Cluster-Head ID, RNID: Receiving Node ID, PNID: Proxy Node ID, TDMS: new TDMA schedule

Outline Introduction System Model Proposed Protocol - EDACH Performance Evaluation

Network Lifetime Energy (J/node) Protocol The round a node begins to die The round the last node dies 0.25 Direct 41 97 LEACH 191 317 EDACH 276 411 0.5 91 184 453 623 786 1015

Number of Alive Sensors as the round proceeds with 0.25J/node

Location of Alive (Circle) and Dead (Dot) Sensor Nodes

Conclusion EDACH outperforms the LEACH more significantly when the initial energy is relatively high. The residual energy is well balanced among all the sensors because the protocol select the most capable node to be a proxy when facing problematic cluster-head. The dead nodes of EDACH well dispersed.