27-10-2016, 11:47 AM
1461649608-EJAET2677821.rtf (Size: 845.96 KB / Downloads: 6)
ABSTRACT
A wireless sensor network (WSN) in its simplest form can be defined as a network of sensors, denoted as nodes, that blankets a region and provides information about it. It can sense the environment and communicate the data gathered from the monitored field via wireless links [1]. WSNs have numerous applications ranging from indoor deployment scenarios in the home and office, to outdoor deployment scenarios in natural environment, polyhouses and military settings. In all modern polyhouses, several measurement nodes are required to track down the local climate parameters in different parts of the polyhouse to make the monitoring system work properly. In this paper, we are showing the use of WSN in a polyhouse system. We aim at proving that that the implementation of LEACH protocol to our wireless sensor network would, in fact, reduce the average energy dissipation per node per transmission. Thus leading to a drastic increase in the lifetime of the sensor nodes.
INTRODUCTION
The wireless sensor network is a new hot spot in the field of wireless network. The development of wireless sensor networks (WSNs) has given engineers a new tool for remote monitoring applications. A Wireless Sensor Network (WSN) consisting of small-size wireless sensor nodes equipped with radio and one or more sensors is an attractive and cost efficient option to build the desired measurement system. Determining where to place WSN measurement nodes is an important step in the development of any remote monitoring application. WSN nodes broadcast their link quality, which is dependent on RF environment, and the attached example application can be used to monitor and log the link quality of several WSN nodes, aiding in the deployment of your WSN system.
POLYHOUSE MONITORING USING WSN
Polyhouse farming is an alternative new technique in agriculture, gaining foothold in rural India. It reduces dependency on rainfall and makes the optimum use of land and water resources due to assured system. A typical, traditional farm of 4000 square meters (1 Acre) would generate an estimated annual income from Rs.20,000 to 150,000, (Depending upon type of cultivation i.e. Cereals, Vegetables, and Fruits) whereas estimated annual income from similar sized poly house is Rs.1,00,000 to 5,00,000 [2]. Potentially, polyhouse farming can help the farmer to generate income throughout the year growing multiple crops and fetching premium pricing for off-season vegetables.
In older polyhouses it was enough to have one wired measurement node in the middle to provide the information to the monitoring system. All this has changed in present polyhouses. However, more measurement data is also needed to make this kind of monitoring system work properly. It is possible to easily change the location of the nodes according to the requirement, which vary for different plant, based on the possible changes in the external weather or polyhouse structure. Wireless sensor network (WSN) can form a useful part of the monitoring system architecture in modern polyhouses [3]. Wireless communication can be used to collect the measurements and to communicate between the centralized control and the nodes located to the different parts of the polyhouse.
DIRECT VS MINIMUM TRANSMISSION
Direct Transmission
In a direct communication protocol [5], each sensor node sends a direct message to the base station. In case the base station is located far from the nodes, the communication will utilize a large amount of transmit power from every node. This causes the battery to drain out faster and as a result, the system lifetime of the sensor node is reduced. On the other hand, the only receptions in this protocol occur at the base station, so if either nodes are close to the base station, or the energy required to receive data is great, this may be an adequate method of communication.
The amount of energy spent is defined by:
Ɛamp x k(3d1 + d2)2 (1) where d1 is the distance between successive nodes and d2 is the distance from the node to the base station.
k is a constant. Ɛamp is the energy consumed by the amplifier during transmission.
Minimum Transmission
Another method we can implement is a minimum-energy routing protocol. Data is routed from the nodes to the base station through one or more intermediary nodes. Some nodes act as routers for data messages from other nodes as well as perform the task of sensing the environmental changes. This protocol only considers the energy of the transmitter and disregards the energy dissipation of the receiver in choosing the routes. In this case, the intermediate nodes are chosen such that the energy consumption of the transmitter amplifier is minimized.
The amount of energy spent is defined by:
Ɛamp x k(3d12 + d22) (2) where d1 is the distance between successive nodes and d2 is the distance from the node to the base station.
k is a constant. Ɛamp is the energy consumed by the amplifier during transmission.
LEACH
Low-energy adaptive clustering hierarchy (LEACH) [6] is a widely used energy-efficient clustering algorithm used in wireless sensor networks. The LEACH algorithm randomly selects a few sensor nodes as cluster heads (CH),
and in other subsequent r ounds, reverses this procedure by selecting other nod es instead of the previously selected cluster heads. The task that the cluster head nodes perform is compressing data that it receives from nodes that belong to the respective cluster, and conveying an aggregated packet to the bas e station. A predetermined percentage of nodes, P, are elected as cluster heads in the following manner. A num ber, r is chosen randomly (between 0 and 1) by a sensor node . If this random number is found to be less than a ce rtain threshold value, T(n), the node is elected as a cluster head for the present round. This threshold value is dete rmined by an equation that incorporates the predetermined percentage to become a cluster-head, the present round, and the set of nodes that have not been selected as a cluster-h ead in the last (1/p) rounds, denoted by G. The equation is given by:
_ _ !" _ ∈ $ (3)
____ _ _____ ___ ___
Each elected CH sends a broadcast to the rest of the nodes in the network to notify that it has been elected as the new cluster head. A sensor node wh ich is not a cluster head selects the cluster heads to w hich it is located the nearest to.
LEACH clustering terminates after a finite number of iterations. However, it does not assure good cluster head distribution. A few nodes may choose a cluster so that the distance between its cluster he ad and sink (base station) is greater than the distance between i tself and the sink. According to the LEACH protocol energy model, the energy cost increases as the distance between nodes increases. Since battery power is a constraint in the sensor nodes, it lets the nodes die on complete consumption of energy.
MATLAB SIMULATION
In this work it is assumed that all the sensor nodes are distributed randomly over a sensor field in a polyhouse of the dimensions 100x100 meters. The number of rounds of transmissions completed by the end of the simulation is 100. All sensor data must reach the base station (BS), which is located outside the sensor field, propagated through links selected by random Cluster heads (CH) from a total of 100 nodes. The probability that a sensor node will be selected as a cluster head is denoted by P. We have varied P from 5% to 40% to determine the Optimal Probability (Popt). Nodes that have been cluster heads cannot become cluster heads again for P rounds, where P is the desired percentage of cluster heads. Therefore, each node has a 1/P probability of becoming a cluster head in each round. Once each round is completed, each node that is not a cluster head selects the closest cluster head and joins that cluster (Voronoi tessellation). The cluster head then creates a schedule for each node in its cluster to transmit its data. The following Figs show the varied outputs of average energy of each node and the number of dead nodes at the end of 100 rounds of transmission for P equal to 5% to 40%.
CONCLUSION
The results show that the implementation of LEACH protocol to our wireless sensor network would, in fact, reduce the average energy dissipation per node per transmission by almost half. This would increase the lifetime of the sensor nodes drastically, especially, in a polyhouse network, as tested. In addition to networking for data collecting and monitoring purposes within a polyhouse network, further work may include the development of the automation and control part, in order to complete the wireless control loop. The control commands will be counted and calculated at the base station (coordinator node), and then transmitted wirelessly to the actuators via the motes located in the different parts of the polyhouse. This would help to automatically monitor and control the polyhouse parameters from a remote location. Further power and energy optimization may be tried out using various sensors and devices. Also, there is scope of testing the network in the presence of network interference and greater distances. More number of parameters can be monitored by interfacing and adding other sensors like - Carbon Dioxide Gas Sensor, Humidity Sensor, etc. to the node.