TREE STRUCTURED TIME SYNCHRONIZATION PROTOCOL IN WIRELESS SENSOR NETWORK Surendra Rahamatkar 1 , Dr. Ajay Agarwal 2 , Vineet Sharma 3 , Pankaj Gupta 4 123 Krishna Institute of Engineering & Technology, Ghaziabad, India 4 Ghyan Bharti Institute of Technology, Meerut, India rahamatkar_s@rediffmail.com ABSTRACT Wireless sensor networks (WSNs) assume a collection of tiny sensing devices connected wirelessly and which are used to observe and monitor a variety of phenomena in the real physical world. Time synchronization is an important issue in wireless sensor networks. Many applications based on these WSNs assume local clocks need to be synchronized to a common view of clock at each sensor node. Some essential limitations of sensor networks such as limited energy resources, storage, computation, and bandwidth, combined with potentially high density of nodes make traditional synchronization methods incompatible for these networks. Hence, an increasing research focus on designing synchronization schemes is required. This paper reviews existing time synchronization protocols and the need for synchronization in sensor networks and then presents the proposed algorithm to construct adhoc tree structure of sensor network along with the process of clock synchronization. Keywords- Wireless sensor networks, Clock synchronization, Tree Structure. 1. INTRODUCTION As the advances in technology have enabled the development of tiny, low power devices capable of performing sensing and communication tasks, sensor networks emerged and received high attention of many researchers. Sensor networks are a special type of ad-hoc networks, where wireless devices (usually referred as nodes in the network) get together and spontaneously form a network without the need for any infrastructure. Wireless sensor networks can be applied to a wide range of applications in domains as diverse as medical, industrial, military, environmental, scientific, and home networks [1]. Since the sensors in a wireless sensor network operate independently, their local clocks may not be synchronized with one another. This can cause difficulties when trying to integrate and interpret information sensed at different nodes. For instance, if a moving car is detected at two different times along a road, before we can even tell in what direction the car is going, the detection times have to be compared meaningfully. In addition, we must be able to transform the two time readings into a common frame of reference before estimating the speed of the vehicle. Estimating time differences across nodes accurately is also important in node localization. For example, many localization algorithms use ranging technologies to estimate internodes distances; in these technologies, synchronization is needed for time-of-flight measurements that are then transformed into distances by multiplying with the medium propagation speed for the type of signal used such as radio frequency or ultrasonic. There are additional examples where cooperative sensing requires the nodes involved to agree on a common time frame such as configuring a beam-forming array and setting a TDMA (Time Division Multiple Access) radio schedule [2]. These situations mandate the necessity of one common notion of time in wireless sensor networks. Therefore, currently there is a huge research interest towards developing efficient clock synchronization protocols to provide a common notion of time. The clock synchronization problem has been studied thoroughly in the areas of Internet and local area networks (LANs) for the last several decades. Many existing synchronization algorithms rely on the clock information from GPS (Global Positioning System). However, GPS-based clock acquisition schemes exhibit some weaknesses: GPS is not ubiquitously available and requires a relatively high- power receiver, which is not possible in tiny and cheap sensor nodes. This is the motivation for developing software-based approaches to achieve innetwork time synchronization. Among many protocols that have been devised for maintaining synchronization in Computer Networks, NTP Special Issue on Ubiquitous Computing Security Systems UbiCC Journal – Volume 4 712