Developing and Validation Underwater Acoustic Channel in NS2 Simulator Abstract- The Network Simulator (NS2) is simulation tool for networking research purpose. It is an open source code, so it can be modified and extended easily. This paper will present the underwater acoustic channel model and how it has been implemented in NS2 instead of the free-space channel. The acoustic propagation, noise, attenuation and transmission power threshold are discussed. Validation of the developed underwater acoustic model has been presented and compared with analytical results. I. INTRODUCTION Ad Hoc Underwater Acoustic Networks (UANs) are wireless networks that typically consist of multiple sensor nodes that are stationary or mobile and any node that can act as a router. Ad-Hoc UANs are similar to terrestrial wireless networks in terms of auto configuration and the fact that they do not need infrastructure [1]. The sensor nodes gather the data and transmit it - either directly or through a sequence of other nodes - to the gateway, which then forwards the data to other networks or a shipboard data processing centre [2] [3]. To transport data underwater from one point to another radio signals, light, sound or wires can be used. Radio signals require a long antenna (due to the low frequency used) and consume a huge amount of energy [4]. Light can be used for a very short range, but the network needs infrastructure, it is not economic and there is the inconvenience of it being fixed or semi-mobile. In comparison, sound propagates on water in a more efficient manner. Sound travels underwater at 1500 m/s, which is five times lower in magnitude than a radio signal. So to transfer a message over a moderate distance, say 1500 metres, it would take one second, which is a significant amount of propagation delay [5]. Moreover, there are random periods of link discontinuity in which no reception is possible. Therefore, UANs can be placed in the category of Delay Tolerant Networks for which traditional networking protocols may not work well. New approaches are being developed to address the characteristics of such networks [6, 7]. NS2 is an open source simulator and dedicated for networking researches. It is development is supported by the United State’s Defense Advanced Research Projects Agency (DARPA). It is a virtual Internetwork Tested (VINT) project. Ns2 supports the simulation of different network layers such as Transport layer, network layer, data link layer and physical layer. Although the simulator has a considerable self- confidence, bugs are still being discovered and fixed continuously by contributions for the other researchers overall the world. The NS2 website has useful information such insulation, user manual, other researchers’ contributions and documentations. NS2 is implemented in two programming languages, these two programming languages are C++ and Object Tool Command Language (OTCL). The simulator uses C++ language because it is fast to run but it is slow to change, so C++ language used for implanting protocols that need details. OTCL language is fast change but slow to run, so that used where the change required, such as simulation configuration. There are some tutorial materials such as Marc Greis’s tutorial, NS Simulator for beginners by Altman, et al and Ns by examples by Jae Chung, et al give a step by step simulator guide, also give descriptive information and simulation of TCP/IP protocols and some classic queuing and routing models [8] [1]. II. UNDERWATER ACOUSTIC MODEL The physical layer in NS2 is divided into four models: propagation, channel, physical layer and modulation. The propagation model contain the characteristic of the acoustic signals while propagate through underwater channel including the attenuation and ambient noise. The distance dependent attenuation and signal fading in underwater channel are modeled in the propagation model. The channel model is basically designed to handle the propagation delay calculations and make use of the functions from the propagation model. The physical layer model tracks the energy consumption metrics and calculates the transmission times. Finally, the physical model calls the modulation component to calculate the bit error probabilities given received signal strength, modulation scheme and the level of the noise[9] [10]. III. UNDERWATER PROPAGATION MODEL The propagation model in NS2 is designed to calculate the signal to noise ratio at the receiver node. The ambient Omar O. Aldawibi (1) , Esmail M. Ashmila (2) (1) The Higher Polytechnic Institute in Zliten / LIBYA, Email: omar.aldawibi@hpiz.edu.ly (2) Faculty of Science in Zliten Al-Mergab University / LIBYA, E:mail: eashmila@yahoo.co.uk 2012 4th Computer Science and Electronic Engineering Conference (CEEC) University of Essex, UK 978-1-4673-2666-7/12/$31.00 ©2012 IEEE 212