International Journal of Computer Applications (0975 – 8887) Volume 66– No.9, March 2013 15 Merits and Demerits of Existing Energy Efficient Data Gathering Techniques for Wireless Sensor Networks Bhat Geetalaxmi Jayram Associate Professor, Department of Information Science and Engineering, National Institute of Engineering, Mysore, Karnataka, India. D. V. Ashoka, PhD. Professor and Head, Department of Information Science and Engineering, JSS Academy of Technical Education, Banglore, Karnataka, India. ABSTRACT Wireless sensor networks (WSN) are self organized, low cost and low power utilizing network which senses, calculates and communicates the data. The data collection at sensor nodes consumes a lot of energy and sensor nodes have limited energy. Hence most of the data-gathering schemes aim to prolong the lifetime of WSNs by saving power consumption and optimized data transmission. This paper makes an extensive survey of various data gathering techniques in the WSN. The survey is done by dividing the data gathering techniques as static and mobile based on the mobility of the nodes. The data gathering techniques are analyzed in terms of energy conservation, reliability, network life time, cost, data latency and various other parameters. We present a comparison of those existing data gathering techniques along with their advantages and issues. Index Terms Consumption, Efficiency, Latency, Forwarding interruption, Gathering. 1. INTRODUCTION Wireless sensor network is an emerging technology gaining immense attention from the research community recently. Usually, sensor network is self-organizing ad-hoc system with large number of small and low-cost devices. It can monitor the physical environment, consequently collect information and then transmit the collected information to the sink node (also called as control center or base station) [1]. Each node in the wireless sensor network is equipped with sensors, microprocessors, memory, wireless transceiver, and battery [2]. Each sensor node contains one or more sensing devices for monitoring the environment and gathering the data. The processor presented in the sensor node is used to process the gathered data and communicate with the hardware for transmitting the data to other local sensor nodes [3]. The sensor network has wide range of applications in several fields such as healthcare, environmental monitoring, smart homes, military applications etc. It is most suitable for application including structural monitoring, health monitoring, environmental monitoring etc, since it has monitoring abilities and autonomous operation [4]. In sensor networks, the process of sampling the information and transmitting it to central base stations is called data gathering. The information received by base station will be further processed and analyzed [5]. In some data gathering applications such as object tracking and intrusion detection, the time sensitive data is required to be sent back to the station in a near real time manner. The applications like acoustic sensor networks, underwater or ocean sensor networks and environmental monitoring do not need real-time data transmission and access. It can be used in scientific applications by domain scientists to collect scientific data for further analysis [6]. There are three stages in data gathering process: the deployment stage, the control message dissemination stage and the data delivery stage. In the deployment stage, the network deployment issues of the sensing field can be addressed. In the control message dissemination stage, the network setup/management and/or collection command messages can be distributed between the base station and all sensor nodes. In this stage, distributing the messages to all the sensor nodes with low transmission costs and latencies is the challenging task. In the data delivery stage, the data gathering (data collection) process will be completed [7]. In the sensor network, the sensor nodes can generate distributed sites of data, and hens the sensor network is also called as data centric network. The minimization of the energy spent in the transmission of sensor data back to the sink is the key challenge. The data collection techniques are classified into two namely, static node based data collection and Mobile element based data collection [4]. 1.1. Issues of Data Gathering 1) The sink is static node which acts as a gateway between the sensor network and users. The sensor nodes can send the sensing data to this sink node in a multi hop manner. The sensors near to the sink node become the bottleneck, because they should transmit the data of other nodes with more energy consumption [8]. 2) In WSN, energy-efficiency is the major issue. The sensor network requires large number of sensor nodes to operate over a long time period, and hence the energy resources should be managed efficiently. As the data gathering process requires more energy, the designing of energy- efficient communication strategies and its implementation is essential [9]. 3) The reduction in energy consumption and increasing the amount of generated data simultaneously is a big challenge while monitoring an environment. Hence the trade-off between energy consumption and environment observation accuracy is a conflicting goal to achieve. So it remains as a hot topic in wireless sensor networks. 4) In the delay sensitive applications, like battlefield monitoring, the delay between data generation and data processing should be reduced. This is the difficult task due to the distance between the nodes and the Sink. [10].