ACADEMIE ROYALE DES SCIENCES D OUTRE-MER BULLETIN DES SEANCES Vol. 4 No. 3 June 2015 pp. 41-48 ISSN: 0001-4176 A learning automata leach-based wireless sensor network clustering algorithm LALEACH Mina Shatzad, Mohammad Masdari Department of Computer Engineering, Urmia Branch, Islamic Azad University, Urmia, Iran Abstract: An important problem of sensor network clustering is provide optimal cluster size, coverage of all sensors in distributed network, energy consumption, connectivity in network, increase the network life time. In this paper we proposed learning automata leach based sensor network clustering algorithm that are provide an optimal cluster that in this paper, we propose a self-regulated deployment strategy based on learning automata called LALEACH. Sensor network energy consumption clustering is a fundamental issue that in this paper we have consider this parameter and maximized the coverage and several parameter are consider for optimal cluster degree. Increased network life time with control intra-cluster and inter-cluster communication and local cluster selection. Key words: Sensor network LALEACH Energy consumption optimizing the cluster head degree, optimizing cluster number [6, 7]. Each of the proposed algorithms tried to produce better results. The proposed automata-based clustering algorithm is independently run at each host in a fully distributed fashion [8]. In the proposed schemes, each host is equipped with a learning automaton [9]. The action-set of each host contains an action for each of its neighboring hosts as well as an action for itself [10]. In this the node are fixe and the network don’t clustered again, but in several of proposed algorithm the reclustering phases are consider for allows the cluster maintenance [11]. INTRODUCTION Wireless sensor network is an infrastructure-less self-organizing, self-configuring and multi-hop communication network that can be effectively used in disaster recovery, military operations, and battle fields and so on, where no infrastructure is available or a fixed infrastructure is difficult to install [1]. A sensor network is composed of many sensor nodes which have been distributed randomly in the area in order to gather special information from the environment, process the gathered information and finally send it to main nodes of information collectors [2]. Each cluster is composed of a cluster-head and a number of cluster members. Cluster-head is responsible for managing the basic operations of the cluster members such as channel access scheduling, power measurements, and coordination of intra and intercluster communications [3]. One important problem which may arise in designing a deployment strategy for a wireless sensor network is how to deploy a specific number of sensor nodes so that the covered section of the area is maximized [4]. Energy Cost of transmitting one separate bit of information equals to processing of thousands of functions in a sensor node [5]. The automata have an important role in optimizing of sensor network clustering. So several studies are doing in different area for increase network life time like: localized learning automata-based clustering, Corresponding Author: Mohammad Masdari RELATED WORK In [12] Akbari et al. has proposed localized learning automata-based clustering algorithm LLACA that minimized the messaging overhead, and tried to reduce the cluster heads number with the automaton and so allows the cluster maintenance by a re-clustering stage. In this algorithm each sensors are equipment with liner automata and this scheme consists of three phases the host actions set, cluster heads determines, and updating the probability actions vector. Each host calculate its cluster-degree, and if the host cluster-degree is less than or equal to its dynamic threshold, the selected action is rewarded and so this host updates its dynamic threshold with current cluster-degree, otherwise the selected action is given the penalized. 41 Kumar et al. [13] have proposed a new clustering algorithm called ELACCA. This scheme is an optimization technique that uses the concept of learning based upon the input parameters and produces an output. The area are divided to cell that include several sensors, the automaton is assumed to be deployed at each of the CH for capturing the information from the environment and then adaptively selects the operation to be performed. In this way with consider distance between the two cluster heads, average number of cluster heads, position of each node in the cell, degree threshold of cluster heads can choose the optimal action. Jabari Lotf et al. [14] have proposed a learning automata-based clustering algorithm LACA. In this scheme initially each node sends a message for other node for known itself neighbors and the probability action set are detected. So each node send another message according to probability vector for declare cluster head. If the receiver of the message is not a member of any cluster and its remaining energy is bigger than or equal to threshold, then according to learning algorithm its selection probability will increase and if not it will be decreased. Naseri et al. in [15] have proposed clustering algorithm based on weakly connected dominating set and learning automata that each host in the network is equipped with a learning automatons. This algorithm consists of three phases and the first step in cluster formation is recognition of the neighbors, in the second phases after number of iterations the weakly dominator set is made by activating randomized number of automata and clusters are formed, and finally in third phases the reclustering. In this scheme each node sends a message to each other for known its neighbor’s node. So the node that resaved this message replied a message contains sending the node's ID fields and energy level field. Using this method the transmitter determines the number of neighbors and the energy level of the nodes. Also after compare energy level in each iteration, if the current node energy level is higher than the average energy of other nodes in the cluster then action is rewarded otherwise the action is penalized. Kumar et al., have proposed a learning automata based clustering algorithm [16] LA-EEHSC. This scheme is heterogeneous, consisted of two type node normal and advanced node that each node is equipped with LA. This algorithm minimizes the energy consumption and increase the network lifetime, so optimized the CH number and for calculate optimal cluster number consider tree minimum value of distance from midpoint of BS, SN and CH. If the normal nodes energy are equal zero and the random number is equal or less than threshold, then selected action is rewarded otherwise the action is penalized, and if the advanced nodes are equal one and the random number is equal or less than advanced node threshold then are rewarded otherwise be penalized. Akbari et al have proposed a distributed learning automata-based clustering algorithm DLA-CC [17] that obtains a near optimal solution to the minimum WCDS (the weakly connected dominating set) which network is divided into several regions. In this scheme the automata create the WCDS, and so tried to minimize the cluster head degree. If the set size of the cluster head is smaller than the minimum cluster head set discovered so far, it is rewarded and is declared as a minimum set; otherwise, it is penalized and the comparison process continues. LEARNING AUTOMATA Learning automata (LA) are adaptive decision-making devices that operate on unknown random environments. A learning automaton has a finite set of actions that are select from and at each stage, so it choice action depends upon its action probability vector [18]. The environment responds the taken action in turn with a reinforcement signal. The action probability vector is updated based on the reinforcement feedback from the environment. The goal of a learning automaton is find the optimal action from the action-set, so the selected action is received penalty or reward. The stochastic automata are represented with quintuple } is represents { , , , , ∅}, where = { , , . . . , } the action set of the automata, = { , ,..., represents the input set, and the F is the production function and automata new state, G is an output function that maps the current state and input into the current output, G is a set of automata internal state [19]. Fig. 1: Learning automata and its environment The environment can be descript by a = { , , } where = { , , … , } represents the finite set of the } denotes the set of the inputs, = { , ,..., values that can be taken by the reinforcement signal, and = { , , … , } denotes the set of the penalty probabilities, where the element is associated with the given action [20]. If the penalty probabilities are constant, the random environment is said to be a stationary random environment, and if they vary with time, the 42 environment is called a non-stationary environment [21]. ( + 1) = ( ) + [1 − ( )] ∀, ( + 1) = (1 − ) ( ) ≠ When the taken action is penalized by the environment (i.e. and β(n) = 1). ( + 1) = (1 − ) ( ) In distributed algorithms, several aspects must be considered that each is important in its category. One of the very important aspects in distributed network is process of selection the optimum cluster heads number, and the node that will be cluster head. Also should be noted that, due to the amount of energy nodes and the loss of a number of nodes in the network lifetime, network topology and cluster head node must be changed during the life of the network. Therefore, most of the proposed methods are not comprehensive due to the all measures are not together. The solutions to these problems are not fixed solution, so the application of intelligent methods will produce better results. Distributed intelligent way that is beneficial for this problem, is learning automata that a few algorithms have been using this method. According to the evaluation algorithm based on LEACH and automaton the main problem that occurs is this that not consideration all of needed factors and necessarily the absolute superiority of one factor over another area. The leach algorithm itself is a series of shortcomings and disadvantages. The algorithm LEACH cluster head node selection process is done randomly and nodes with high competence not take into consideration the probability of unforeseen nodes. Therefore, deserve factors such as the amount of energy or of neighboring nodes is not more attention and so the number of selected cluster head is not controlled. In the proposed method, we have tried, to eliminate the disadvantages of other algorithms and also to implement the intelligent making. In the result improved performance of node in the network and increasing the lifetimes. The proposed scheme has two-phase, cluster formation and stable phase. Initially each of the sensor nodes is equipped with learning automata. In the first phase after node distribution identification neighbor and clustering process is performed using learning automata. Clustering process consists of several stages and at each stage; the node competency is checked for bee cluster head. Initially, all actions have equal probability, first the selection probability distribution of Node in the network is 0.05. If an action is rewarded, then increases the probability, otherwise reduced this probability. The clustering algorithm formation is fully distributed, where each of node select its cluster head based on local information that is received from its neighboring hosts. In the second phase is done collection sensed data by common nodes in the network and send them to the cluster head according to the schedule specified. Finally data is sent to the cluster head also will be transmitted to the sink. (1) (2) (3) ( + 1) = 1 − ) ( ), ∀ (4) −1 ( ≠ Where is the reward parameter, b is the penalty parameter, and r is the number of actions [22]. When value is either 0 or 1, environment is called PModel (Probabilistic model). ( ) = 1 as penalty and ( ) = 0as reward [23]. In the case of environment of Q-Model, ( ) is output of set with more than two values between [0, 1]. In S-Model, ( ) is a continuous random variable within the range [0, 1]. LEACH The operation of Low-Energy Adaptive Clustering Hierarchy or LEACH is divided into rounds [24]. Each round begins with a set-up phase when the clusters are organized, followed by a steady-state phase when data are transferred from the nodes to the BS. Furthermore, the setup phase consists of the following sub phases: Advertisement Cluster setup Broadcast schedule During the set-up phase, each node n chooses a random number between 0 and 1, so if the number is less than a threshold ( ), the node becomes a cluster head for the current round [25]. Threshold value is set through this formula: T(n) = 1− 0 ∗ ∈ 1 (5) Where, G is set of nodes that have not been selected as CHs in previous 1/ rounds, P is suggested percentage of CH, r is current round. If nodes become CHs in current round, these nodes will be CHs after next 1/p rounds [26]. In LEACH, the Cluster Heads compress data arriving from member nodes and send an aggregated packet to the BS in order to reduce the amount of information that must be transmitted to the BS [27]. PROPOSED CLUSTERING ALGORITHM 43 • The node that in first clustering step is not in the range of cluster heads, according to specified probability and number of times that was cluster head, declares itself as a cluster head. • Each common node should have a cluster head neighbor that can send its data into it. • The aim of this approach is to increase the number of cluster heads. As a result, efforts have been made to reduce the degree of clustering and increase the number of cluster head. Clustering phases: In the clustering phase, select the cluster heads and cluster formation occurs. A node that has more energy than the average energy of its immediate neighbors, and also the degree of clustering is less than or equal to a predetermined value, the selected action will be rewarded, otherwise penal tied. After role of all nodes in the cluster is determined, that node are cluster head either common. The first phase consists of four stages, each of which is as follows: Step 1: One of the most important parameters for the clustering is number of cluster heads and we intend to raise the number of cluster head nodes in the network. If the cluster head nodes have a balanced neighboring degree, cluster heads energy consumption will be substantially reduced and early discharge energy of cluster head can be avoided. In the first phase offer nodes distribution in the operating environment each of them begin to identifying their neighbors. Each node identifies around neighborhood and the total number of neighbors is calculated. Also each node within a message will notice to neighbors its energy levels and the energy average of neighbors of each node is calculated. P 1 T ( n ) 1 P ( r mod ) P reward functions are selected by (1), (2) and (3), (4) formulas. Clustering parameters to be considered, as follows: • Node energy rate: because the cluster head node is responsible for collecting information that are sent from the cluster and send it to the sink, where he is expected to have more energy. In this method, the candidate cluster head node energy is compared with the average energy of neighboring nodes. • The capacity of cluster heads: one of the criteria for the maximum size of the cluster is connected. If the number of members of a cluster head node cluster is too much more energy to receive and send data to the sink will lose and its energy is discharge faster, therefore by increasing the number of nodes in the cluster member the probability sending data by all the nodes in the cluster head is reduced. • Number of cluster head: an important purpose of this procedure is to establish the network connection. In this way with increasing number of cluster head, all nodes are covered and also with increasing number of cluster head the member nodes can easily transfer its data. Step 3: until the probability value of node is less than ε, the node process and rewards and penalties will continue and also if the probability of node is more than ε, the node is selected as cluster head. The condition of the cluster head possibility is compared dynamically with a random number in the interval [0, 1]. If the node probability is greater than the random number, declares itself as a cluster head. That this value is different for each individual node. Step 4: the node that their state is not specified in previous step entered this stage. In this stage initially the node which was not any role, decides the current round is to be cluster head based on the cluster heading percentage that is previously identified the number of times has been cluster head. This decision of node is done based on selecting a random number between zero and one, if the number is less than the threshold value T (n), the node will be cluster head in the current round. The threshold value is calculated based the following formula: With the addition this step the number of cluster head node increases and as a result, the network connection is maintained. Each node that in two final stages chose itself as a cluster head, notice to other node sends a message. Non-cluster head node, maintains received notice message from cluster head node for use in the set up phase. After the clustering phase is complete, the non-cluster head node selects a cluster head for these stages. The decision will be taken based on the signals received from the cluster head. Construction scheduling: cluster head node receive the messages cluster members and according to the number of nodes in the cluster create a schedule which (6) Step 2: In this step, using automaton node for the cluster head is selected. To use this technique, consider learning automata for each node and also each node can have one of two states cluster heads or normal, corresponding automaton can select one of two states according to probability vector. The nodes that is grated probability to be as CH and the node that have less probability will be chosen as the CN. First, the selection probability of each sensor node is equal to 0.05. The node that have more energy than the neighbors energy average and also number of nodes in the cluster is less than or equal to the specified capacity as the cluster head node probability is increased by the automaton (rewarded). Otherwise, the probability of selecting a cluster head node is reduced (penalized). With the selection of cluster head node may decrease or increase based on various parameters. Penalty and 44 Stability phase: Once the clusters been established, data transfer can be started, assuming that the nodes determines that when each node can send its data the scheduling is sent for all nodes in the cluster. Algorithm LALEACH ( ) Input host Begin algorithm Let T(n) the denote the be Cluster head in the previous step Let R denote the stage number which is initially set to 1 Let E denote the host energy Host detects its neighbors Host compute its Neighboring degree and denote its HOST_DEGREE Host compute its neighbor _ energy average and denote its ENG_AVG Host forms its action set Host randomly choose one of its actions according to its action probability Repeat IF E >= ENG_AVG AND HOST_DEGREE <= Threshold Reward choose action Else Penalty choose action ← +1 Until the probability with which host chooses its CH is greater than IF Host HOST_DEGREE = zero IF rand <= T (n) host chooses itself as a CH END algorithm Fig. 2: Pseudo-code of learning automata-based leach clustering algorithm Always have data to send during the time that is allocated to them sends their data to the cluster head. This sending is used of the minimum amount of energy. When all the data was received cluster head node performs signal processing operations until data is compressed into a units signal. This state is stability in the sensor network. The proposed clustering algorithm based on learning automata pseudo-code is presented below in this method we have optimized LEACH algorithm and by learning automata clustering process and selection of appropriately cluster head is done at the network level. The sink establishment position in (50, 50), respectively. A test for the number of sensor nodes is equal to 100 and the number of the program running in each round is 1000. The EXT, ERX, EDA Data aggregation and the amount of energy used for membership in the cluster and the reinforcement signal (the response to actions taken by the automaton is issued by the environment) is equal to 0.000000005. Different criteria have been considered to compare the performance of proposed algorithm which is divided into two categories the first group to study the life of nodes and the second is the quality of the proposed algorithm Criteria are as follows: 1) Energy 2) number of dead nodes 3) number of alive nodes 4) send packets in to BS 5) send packet in to CH SIMULATION The efficiency of the proposed algorithm is evaluated using different tests. Matlab software is used to perform tests. The proposed method by various aspects is compared with leach algorithm each on a separate chart provided. The sensor simulation environment is 100*100 m and the assumption is that n sensors (n number of distributed sensor nodes) randomly distributed in the environment also sensor radio range is 30 m , primary energy in each of the sensor nodes is 0.5 joules. Fig. 3: LEACH –based sensor networks clustering 45 First test: The lifetime of the sensor network is one of the basic criteria in sensor networks that in this scheme tied by selecting the optimal cluster head and network connecting have finally the productivity of all the nodes in our environment. This increases the lifetime of network due to a more balanced clusters of appropriate size and determine the cluster head with higher energy so by reducing the amount of energy transferred to another node of the cluster head responsibility. In the following charts the energy used by LEACH clustering algorithm and the proposed algorithm is compared. Where proposed method uses less energy and consequently will be increase the lifetime of network. Fig. 6: Comparing the number of dead nodes in the LALEACH and LEACH method Fig. 4: LALEACH-based sensor networks clustering Fig. 7: Comparing the number of dead nodes in the LALEACH and LEACH method Third Test: The overall objective of setting up a sensor network to collect information about the operating environment. That by the way we have tried with data aggregation by CH data will be sent to BS. According to the figs in the algorithm LALEACH (3-4) and (3-5), the number of packets sent by CH to BS compared with LEACH algorithm has been enhanced. The amount of information transmitted from the CH to CN has increased due to increased network life time. Fig. 5: Comparison of remaining energy by nodes in LEACH and LALEACH Second test: In this test, the number of live nodes and the number of dead nodes during the life of the network can be compared that LALEACH nodes due to the increase the lifetime the number of dead nodes is less than LEACH algorithm and therefore the number of alive nodes in the proposed algorithm is also more. 46 Fig. 8: Comparing the number of packets sent to the BS in the LEACH and LALEACH method REFERENCES 1. J.W. Branch, Ch. Giannella, B. Szymanski, R. Wolff, H. Kargupta”, In-network outlier detection in wireless sensor networks”, Knowledge and Information Systems 2013, Volume 34, pp. 23-54. 2. A. A. Abbasi, “A survey on clustering algorithms for wireless sensor networks”, Computer Communications 30 (2007), pp. 2826–2841. 3. B.C.P. Laua, E.W.M. Maa, T.W.S. 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Raghunandan, “A Comparative Analysis of Energy-Efficient Routing Protocols in Wireless Sensor Networks, Emerging Research in Electronics”, Computer Science and Fig. 9: Comparing the number of packets sent to the CH in the LEACH and LALEACH method In this way LEACH algorithm has been improved and equipped with recruiting automata. Service quality parameters such as energy consumption in sensor networks, Lifetime network and cluster degree, the number of cluster head node have been considered and improved. Our experiments show that the proposed method is optimum performance. Clustering algorithm based automaton that we have given in this way, we consider various metrics to increase the lifetime of the sensor network as well as a series of quality standards such as the balance degree the cluster, increasing the number of nodes in the cluster head to cover the entire network were considered. CONCLUSIONS The main purpose of these algorithms to optimize the algorithm LEACH and equipped it with learning automata and also increases the life of the network. At the beginning of each sensor nodes deployed in the environment dedicated learning automata and then start identify to identify their neighboring nodes. With information obtained each node detects its neighbors and is calculated average energy. To determine suitable and balanced cluster head take into account energy metrics and nodes degree and thus the probability of a cluster head node increases or decreases. After selecting a cluster head node, the node that their condition is specified entered to the next stage. At this stage to cover the entire network and connecting nodes that are not neighbors, responsibility of the cluster heading takes place itself. In general, because the choice of a balanced clusters and the use of learning automata network lifetime is increases. 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