From underwater simulation to at-sea testing using the ns-2 network simulator

Although several network protocols for underwater acoustic wireless sensor networks have been proposed in the past, having a complete and accurate understanding of the performance of these protocols is not an easy task. The unique characteristics of the underwater acoustic communication channel, such as limited capacity, high and variable propagation delays, frequency-dependent attenuation and significant impact of highly variable environmental conditions, motivate the fact it is quite challenging to identify simple but accurate channel models. Such models are instead needed to improve accuracy of simulation results and to be able to derive fundamental results on underwater communications performance. To facilitate the research in underwater sensor networks, it would be really desirable to have a standard platform for simulation, emulation and real-life testing in order to be able to compare and evaluate different network designs, algorithms and protocols in a variety of settings and application scenarios. With this objective in mind, we have developed a framework to seamlessly simulate, emulate and test at sea novel communication protocols, which is based on the open source and well known network simulator ns-2 [1]. Using the proposed framework, anyone willing to implement its solution for simulation experiments using ns-2 can use the same code in emulation mode, adopting real acoustic modem for data transmission. The framework code has also successfully been ported on small portable devices (Gumstix [2]), thus allowing us to embed it inside modem or AUV housings. Therefore, it becomes easy for the research community to write code and evaluate protocols on a real testbed. Different drivers allowing ns-2 to operate with commercial acoustic modems, such as FSK and PSK Micro-Modem [3], Evologics modem [4] and Kongsberg modem [5], have already been implemented.