British Journal of Science 22 January 2013, Vol. 8 (1) © 2013 British Journals ISSN 2047-3745 A New Energy Efficient and Depth based Routing Protocol for Underwater Sensor Networks Reza Javidan (Corresponding Author) Department of Computer Engineering and Information Technology Shiraz University of Technology, Shiraz, Iran E-mail: reza.javidan@gmail.com Tel:00989173159656 Hamideh Rafiee Department of Computer Engineering and Information Technology Payame Noor University, Tehran (PNU), Iran E-mail: hamideh_2022@yahoo.com Abstract Due to certain conditions of underwater environment, providing an efficient and scalable routing protocol in underwater acoustic sensor networks (UWSN), has many challenges. Communication in UWSNs is done through sound that compared with radio; it has lower speed, higher bit error rate, smaller bandwidth and higher and variable propagation delay. Also, in UWSNs, improving the energy efficiency is one of the most important issues since replacement or recharging of nodes batteries has a high cost. Moreover, many proposed routing protocols for UWSNs, use full information about the position of the nodes, that obtaining this information is a fundamental challenge in these networks. In this paper, a new protocol is proposed in which only the depth information of the nodes used in the routing process. Also, to balance the overall energy consumption and thereby increase the network lifetime, residual energy of the nodes considered in the routing calculations. The protocol is compared with DBR protocols using NS2 simulator. Our simulation results show that the proposed method not only improves the overall energy consumption of the network, the end-to-end delay is also reduced. Keywords: underwater sensor networks, routing protocol, energy efficiency. Introduction Various factors such as geological processes in the ocean, study on water characteristics including temperature, salinity, oxygen levels, bacteria and other water contaminants such as water-insoluble material (Heidemann, Stojanovic, & Zorzi, 2011), detecting mines, forecasting and climate change monitoring, study the effects of human activities on marine ecosystems (ISIK, 2007), discovery of underwater oilfields, tracking mammals, fish and other micro-organisms (Deepika, 2005), disaster Prevention: Tsunami (Abdul, & Dongkyun,2012), and many other factors has caused the motivation for the development of underwater wireless sensor networks. UWSN consists of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area. Using radio in UWSN, due to high attenuation and requiring large antenna about 0.5m (Ayaz, Baig, Abdullah, & Faye, 2011), is not suitable. So the sound technology is used in communications. Furthermore, get precise location information of sensor nodes, is another challenge that must be overcome (Ayaz, Baig, Abdullah, & Faye, 2011, Akyildiz, Pompili, & Melodia, 2004, Sehgal, David, & Schonwalder, 2011). GPS that can accurately estimate the position of sensor nodes in wireless networks does not work very well in underwater environments. Because GPS uses 1.5GHz bandwidth and these waves do not propagate in the water (Ovaliadis, Savage, & Kanakaris, 2010, Liu, & Wei, 2011). Many researches have been done about physical layer in UWSN. However, issues related