A Survey of LEACH and Variants of LEACH Routing Protocols in Wireless Sensor Network Henish Shah 1 , Amit Parmar 2 , Naresh Patel 3 1 Assistant Professor, 2 Assistant Professor,3 Assistant Professor CHARUSAT University , 2 CHARUSAT University, 3CHARUSAT University Changa, Gujarat, Pin no. 388421 1
[email protected],
[email protected],
[email protected] 1
Abstract: Large scale use of wireless sensor network is the main reason for the development of various routing protocol. Day to day improvement in the WSN is most interest for application in different area like Health checking, Vehicular movement, military, space, etc… Sensor nodes can deploy randomly so, routing is the most fundamental and hot research topic. Due to limited energy available on board, it is importan t to reduce power consumption. Radio operations consume more energy per bit than sensing and computation. Hence it is important to reduce number of bits transmitted and received. Various routing protocols are proposed for that. Due to various advantages huge research has been carried out for LEACH and LEACH -C. This paper mainly focuses on recent variants of LEACH and LEACH-C protocols. In this paper protocols are evaluated on the basis of Network Lifetime, Scalability and Stability. Keywords: Wireless Sensor network , LEACH, LEAC H-C, Q-LEAC H, IB-LEACH, LEAC H-CM, MODLECH, ELEACH, V-LEACH, Network Lifetime, Stability.
1. INTRODUCTION The quick growth of technology developed a new class of distributed system known as wireless sensor network [14]. Wireless sensor network have a huge number of low-cost, lo w-power and mult ifunction wireless sensor nodes which has computation, sensing and wireless commun ication ability [15, 16, 20]. These sensor nodes are limited in size, processing power, memory and residual energy [14]. The main task of these nodes is sensing the environment in parameters like heat, pressure with good accuracy. So, it is used in variety of real world applications. Because of their vast usage, and constraints of limited in size, p rocessing power, memory and residual energy of WSN nodes, there is a hot topic of studies in current era. Energy efficient is the most challenging issue in WSN because every sensor node powered by limited battery life and required to work remotely for long time [17, 20]. Many researches are going on saving energy consumption in order to increase life time of wireless sensor network.
The hierarch ically based routing protocols are suited to the energy-saving issue. In these protocols, networks are d ivided into clusters and have a CH node for each cluster [18]. The CH nodes are intermediaries between the sensors nodes in their cluster and BS or sink. The first hierarchical routing protocol is Lo w Energy Adaptive Clustering Hierarchy (LEA CH) and that was introduced in [1]. The LEA CH is considered as one of the most used cluster based routing protocol in order to minimize the energy consumption. In this paper we presents the LEACH protocol and different variant of LEA CH protocols like LEA CH-C, Q-LEA CH, IB-LEA CH, LEA CH-CM, MODLECH, E-LEA CH, V-LEA CH and see how they are differ from original LEACH protocol.
2.
ROUTING PROTOCOL IN WSN: LEACH AND IT’S VARIENTS
2.1 LEACH LEA CH (Lo w Energy Adaptive Clustering hierarchy) [1] is a self-o rganizing adaptive clustering protocol for WSN, It uses the randomization to distribute the
energy load among the sensor nodes . In LEA CH protocol sensor nodes themselves organize in to clusters and some of the nodes become the cluster head (CHs). LEA CH protocol uses round as unit, each round is composite with two phases cluster set up phase and steady state phase. At cluster set up phase a node randomly pick a number between 0 and 1 and co mpare this value with threshold value T(n) , if the number is less than the threshold T(n) then , node become the cluster head for the current round otherwise node is treated as common node. T (n) is calculated by the following formula [1].
( )
{
(
)
Where P = Percentage of cluster head in current round, in LEACH author have fixed the percentage of cluster head which is 5% and 5% is an optimal percentage for all scenarios [1] , r = the current round and G = set of nodes that have not been cluster-head in last 1/P rounds. Each node become cluster head (CH) with probability P when the round start, the nodes which have been head nodes in this round will not be the heads in next 1/P rounds, because the capable nodes in the whole network is slowly reduce. After 1/P round finished, all the nodes will return to the same starting point [11]. Each node that has elected itself as cluster head for this particular round broadcast s an advertisement to the other nodes. After hearing the advertisement all nodes decides the cluster in wh ich they will be belonging for the current round. To do this, Cluster head uses the CSMA MAC protocol [1]. After this cluster formation phase all member node will transmit their data to CHs and then CHs will transmit to BS (Base Station). T( n)r m= (P 1� P_( od1 P)
2.2 LEACH-C In LEA CH there is guarantee or discussion about the placement of cluster head nodes. Since the cluster is adaptive, obtaining a bad clustering. While using the central control system to form a cluster may produce better clusters. LEACH-C (Centralize LEA CH) [5] made changes only in cluster set up phase, steady state phase remain same as in LEACH. In the cluster set up of LEACH-C, every node sends its current location and energy informat ion to the BS (Base Station). Fro m this informat ion BS will calculate the average energy; now the condition is that whichever node has less energy than the average energy, those nodes cannot be CHs (Cluster Head) fo r the current round. Using
the remaining nodes as possible cluster heads , Base Station finds the cluster using Simu lated Annealing algorith m [13]. This algorith m is used to minimizing the total energy required for transmitting the data fro m non-cluster head to cluster heads, by reducing the total sum squared distance between non-cluster head to nearer cluster head. Once the cluster heads and related clusters are found then BS will broadcast the message that consist Cluster Head ID for each node. If Node’s ID is matches with broadcasted cluster head ID’s then the node is cluster head, else nodes will find its TDMA slot for data transmission and goes to sleep until the data transmission time co me. And as author discussed the steady state phase of LEA CH -C is same as steady state phase of LEACH [5].
2.3 LEACH-CM As per the working of LEA CH-C protocol [5], every node sends their coordinates value and energy informat ion to the Base station (BS). BS uses this informat ion to figure out the average energy of the whole network. A deck of nodes that have higher energy than the average energy, those nodes are elig ible to become CHs for current round. In LEA CH-CM (mod ified LEA CH-C) [4]also CH election and cluster formation strategy are same as LEA CH-C but in LEA CH-CM when sensor nodes sending their coordinates value and energy informat ion to BS that time sensor nodes calculate Euclidean Distance between Node and BS and that distance value will be saved in sensor node memory as BSdist [4] . When BS done with CHs election, all the CHs have to make an announcement that it is the CH for current round to other node those who are in communicat ion range of the CHs, all the recip ient member nodes receive CHs announcement they will calculate the Euclidean Distance fro m selected CH to that particular member node and save this again in to sensor node memory as CHdist . If the distance BSdist is less compare to CHdist then member node transmit their data to BS otherwise to selected CH. There are many topologies where Base Station is located in the center at that time many sensor nodes are nearer to BS as compare to the elected CHs. In LEA CH and LEA CH-C assumption is that 5% of nodes become CH is gives the optimal output. Hence in LEA CH-CM 5% o f the alive nodes are become the CHs for each round and also LEA CH-CM takes the ceil value when total number of CHs are less than one otherwise it takes the floor value CHs [4].
2.4 Q-LEACH In Quadrature LEACH (Q-LEACH [2]) network is partitioned in to 4 equal sized sub networks. 100m x 100m area is divided in to 4 sub networks as given in equation 1, 2 and 3. A = a1 + a2 + a3 + a4
(1)
an = A(Xm, Ym) where n=4 and m=10
(2)
+
+
+
(3) For CH selection rando mized clustering [1] is used. CH selection procedure is repeated for each of these four regions individually. Once CHs are defined, non-CH nodes join Cluster by sending request packets. Nodes are allowed to join CH fro m their region only. Nodes use RSSI to find nearest CH fro m its region only. CHs assign TDMA slots to requesting non-cluster nodes. Non-CH nodes will t ransmit during its TDMA slot and during remaining time it will be in sleep mode. CH will co llect data fro m its all the me mber nodes, compresses it and sends it to BS. By Part itioning the network into the equal sized sub network, distance between CHs and BS and between CHs and Cluster member is reduced. Therefore less energy is used during transmission which increases network lifetime and stability period.
2.5 MODLEACH This protocol’s main agenda to solve two issues that existing LEA CH protocol has, (1) In LEA CH every round cluster head (CH) is getting changed without checking their residual energy and once cluster head is formed, it will not get next chance until 1/p round gets over. (2) In LEA CH nodes use same amp lification energy to transmit data regardless of distance between TX and RX. To solve mentioned first issue, MODLEA CH (modified LEA CH)[6] has “efficient cluster head replacement scheme”. If existing cluster heads (CHs) has not spent much energy during in its term and has more energy than the threshold, it will stay as cluster head for next round too. This is how, energy can be preserve, suppose if the cluster head has less energy than the threshold then it will be replace as per LEACH protocol working. To solve mentioned second issue, MODLEA CH [6] divide three transmission categories (i) Intra Cluster
Transmission (ii) Inter Cluster Transmission (iii) Cluster head (CH) to Base Station (BS) Transmission. In Intra Cluster Transmission communicat ion is within the cluster only, In Inter Cluster Transmission communicat ion is between two cluster heads while Cluster head transmitt ing its data straight to Base Station (BS) is known as CH to BS Transmission. A mplification energy requires for inter cluster transmission and for intra cluster transmission or CH to BS transmission are not be the same. Using low energy level for intra cluster transmission compares to CH to BS transmission leads in saving much amount of energy, Moreover, mu lti power levels also reduce the packet drop ratio , collisions and/ or interference for other signals. At the point when node behave as a Cluster head (CH) routing protocol educates it to utilize h igh power amp lification and in next round node behave as cluster member that time routing protocol switches it to low level power amplification[6].
2.6 IB-LEACH Major problem with LEACH is uneven energy consumption among CHs and CMs. Since CHs must keep their receiver on for almost all the time, it loses its energy rapid ly. Intra-Balance LEACH (IBLEA CH)[3] workload is distributed among CMs by selecting one or more than one CMs as CM aggregator. This Protocol is divided to three phases. In first phase (set-up phase), CHs are elected. In second phase (presteady phase) CM aggregator are selecred by CHs. Task of the CM aggregator is to receive packets fro m other CM nodes and send it to BS. Task of the CHs is to elect CM aggregator and prepare TDMA schedule for current round. After each round CM aggregator are re-elected depending on remain ing energy CM aggregator nodes and CMs. Hence CH does not require to keep its receiver on for all the time. A lthough CM aggregator requires to keep its receiver on for all the time, new CM aggregator will be elected by the CH for new round. Hence task of aggregation is distributed among CMs, energy consumption within cluster is mo re uniform. As shown in simulat ion results in [3] it results in prolonged network lifetime. Also, network stability more as compared to LEA CH as it need not require electing CHs often.
2.7 E-LEACH As per E-LEA CH protocol in [7] build cluster in two phases. In first phase, E-LEA CH algorith m use concept of energy threshold. Energy threshold formula: E( ) m (1)
Where E(r) is r-round of an energy threshold; K is factor of an energy threshold. p is the craved percentage of the share of all valid nodes cluster head, Er is the sum of energy of randomly selected node in r-cycle, m is the total nodes of the cluster in the r-round. Before every cluster head selection, compare each cluster head node energy and energy threshold, if node energy is less than the energy threshold then remove that node from cluster head selection [7]. E-LEACH () (
protocol ( ))
use
a
distance
BS that might be located far away fro m it [10]. When the CH dies, the cluster becomes useless because data gathered by the cluster nodes will never reach to the BS.
factor: (2)
Where dm is maximu m d istance from base station to that node, d(i) distance between node i and base station. The distance factor method is useful for finding minimu m d istance between cluster head and base station for data transmission. After the first choice, we have a cluster head candidate set Q. ( )
{
*
( )+
, nϵQ
Fig. 1: V-LEACH [9] (3)
E-LEACH protocol uses cluster head selection algorith m which have global in formation about other sensor nodes [8]. Overall performance of h ierarch ical clustering routing protocol is based on total number of cluster heads. If there are less number of cluster heads then each CH covers larger area then it will trouble for cluster nodes which are far apart fro m their CH consumes more energy. Huge nu mber of cluster heads consumes mo re energy and reduce network lifetime. So, it is necessary to select optimal cluster head has large residual energy in order to increase network lifetime and reduce energy consumption [9]. E-LEA CH selects that node as a CH that have large residual energy. As per simulat ion results in [7] it shows that less energy consumed by E-LEACH protocol compared to LEACH protocol.
2.8 V-LEACH In new version of LEACH protocol each cluster contains; CH which send data that is received fro m the cluster nodes to the BS, vice -CH which become CH of the cluster when CH dies, cluster nodes which sense data fro m environ ment and send it to the CH [10]. In original LEA CH, CH dies earlier because it’s always on receiving data fro m cluster nodes, aggregates these data and then sends these data to the
In V- LEACH the CH and Vice -CH selected on basis of Energy, Residual Energy and Distance [9]. In V-LEACH p rotocol, we have CH and vice-CH that takes responsibilities of CH when CH d ies. By doing above work no need to elect new CH each times the CH dies. This will extend the overall network life time and total communication over the network. As per simulation results in [10] it shows that less energy consumed by V-LEA CH protocol because of that network life t ime is increased by 49.37% compared to LEACH protocol.
3. CONCLUSIONS WORK
AND
FUTURE
Design of energy efficient routing protocol is major challenge. Since radio operation consumes huge energy, number of bits transmitted and received should be minimized. In this paper we have surveyed variants of LEACH and LEA CH-C protocols. Due to drawbacks of LEA CH and LEACH-C many variants are proposed. We have surveyed recently proposed variants of LEA CH and LEA CH-C. These protocols improves network lifetime as compared to LEA CH. The imp rovements are ach ieved by applying various techniques like, elect ing CHs such that it is nearer to center of graph, Distributing work load among CH and CMs, Elect ing Vice CH so that CH election can be avoided when CH dies, and Electing CHs such
that maximu m d istance is reduced. By apply ing these techniques, surveyed protocols are able to improve network lifetime and provide more stability to network. However improvement to QoS, Reliability and Latency are also important. In our future work we will co mb ine more than one techniques (. E.g. IBLEA CH and V-LEA CH can be co mbined) and investigate the improvements in network life t ime along with QoS and Latency
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