Energy Efficient Protocols for Underwater Sensor network: A Research Review Meenakshi Yadav Research Scholar, CSE Department Banasthali University yadavmeenakshi@gmail.com Komal Malsa Assistant Professor, CSE Department BSAITM erkomalmalsa@gmail.com Chandra Kumar Jha HOD, CSE Department Banasthali University ckjha1@gmail.c Abstract— Recently underwater sensor networks have attracting researchers to discover the underwater environment for using natural resources for different purposes. There are various differences between Terrestrial wireless sensor network & underwater sensor network. Some limitations are high cost, longer time for resulting monitoring and changes in water environment. The deployment of acoustic signals as the communication media imposes many challenges on underwater sensor network. Energy factor is also having same importance like terrestrial wireless sensor network due to effect of water environment on battery. In this paper we study the existing energy efficient protocol for underwater sensor network. We also present the differences and similarities between terrestrial and underwater sensor network.. The main purpose of this study is to explore the area like energy efficiency, battery life, clustering in underwater sensor network. Index Terms— Clustering, underwater sensor network, cluster heads, Batteries I. INTRODUCTION On our earth ¾ area is covered with water and around 100 km population is on coastal areas. Not only it is having most of the useful resources but also used for defense and adventurous purposes. Under water environment is having many limitations such as high cost, unsuitable environment and longer time of accessing the outcome of monitoring water environment and so forth. Underwater networks is having number of applications such as environment monitoring for scientific exploration, disaster prevention, navigation oil/gas monitoring military and so forth [3]. Ground based sensor network are investigated well and many protocols has been introduced. Underwater sensor network owns some different characteristics than the ground level network. Most important one is employment of the acoustic signals in underwater sensor network. The transition from the radio to the acoustic signal is due to the poor performance of radio signals in water. Due to salty characteristics of water it works very low in frequencies and effect of this is requirement of high transmission power and large antennas [11]. Based on these ranges of communications and requirement of various underwater applications two network architecture, short term and long term underwater sensor network has been introduced. Table 1 shows the comparison of both types of applications [2]. Network Requirements ST-UWSNs LT-UWSNs Data Rate Requirement Large Small Transmission Range Short (10m – 1 Km) Short (10m – 1 Km) Deployment Depth Shallow Water Shallow and Deep Water Energy Efficiency Minor concern Major Concern Real-time Delivery Major concern Minor Concern Antenna Size Small Table 1: Comparison of Short term and Long Term UWSN When we are consider underwater sensor network some challenges may occur in the surface environment. At the host side continuous node movement and topology (3D) are major challenges. Some of the underwater application including detection or rescue missions and they are adhoc in nature. Some of them require proper planning and deployment. System those are using for shallow water is not used for deep water. Battery life and Cost of the system is also another challenges for UWSNs [11]. The rest of the paper is organized as follows. Section 2 provides an overview of underwater sensor network with problems. Section 3 gives the differences between terrestrial and underwater sensor network. Section 4 explains the various protocols for energy efficient protocol used for underwater sensor network. Finally Section 5 includes the conclusion part. II. UNDERWATER SENSOR NETWORK During the last decades underwater acoustics network is having much attention by the researchers. For the applications like off-shore ,oil fields monitoring, pollution detection and oceanographic data collection, defense, a highly precise accuracy, continuous monitoring are highly required. So for all these type of application a network need to be build called underwater sensor network. There are several drawbacks in traditional approaches for underwater sensor network like no interactive communication between two ends, retrieval of information at the end,