## 1 Introduction  
Researchers are becoming increasingly interested in underwater wireless sensor networks (UWSN). However, these networks, although sharing the same goals as terrestrial wireless sensor networks, such as network alive time or communication efficiency, present challenging new problems. Underwater communications cannot use radio frequency (RF) signals, since they have an enormous attenuation in the subaquatic medium. Therefore, acoustic signals are used underwater, which present different signal attenuations, depending on distance and frequency. In addition, signal spread is proportional to distance, due to the expansion of the wave-fronts (which may be cylindrical or spherical). Another problem in underwater communication is signal propagation, which is around 1,500 m/s and five orders of magnitude lower than in RF. In radio-frequency networks, this delay is negligible, but in underwater acoustic networks, it is significant. Energy consumption and management is another challenge. Energy consumption is an important problem in sensor networks, as the energy available determines the main operation parameters, such as the sampling frequency, maximum distance between nodes, and so on. Moreover, given the higher energy consumption of underwater nodes, due to the transmission medium, and the difficulty of performing maintenance tasks, such as battery changes, this problem is even more challenging. Until a satisfactory reduction of communication costs is achieved, the best option to compensate for the high energy requirements may be the use of energy harvesting mechanisms that can obtain energy from the environment to extend system operation. The flow of energy produced must fulfill the high demand of communication costs. Therefore, the energetic balance should be carefully examined and dealt with for each application. Given these changes in the communication medium, hardware must be re-designed and new communication protocols proposed. However, several technological challenges should still be investigated for the extensive use of underwater wireless sensor networks. All the previous advances were directed towards the construction of unattended underwater wireless sensor networks, which are of vital importance in difficult access zones, such as offshore underwater installations. New tools and methodologies are needed to tune and improve underwater installations. These new tools and methodologies need to include energy-harvesting and wake-up systems in order to improve the alive time of sensor networks. In addition, these new tools and methodologies must take into account real hardware parameters and the environmental conditions where the system is to be deployed, such as the weather or bathymetry information from the sea bottom. In this paper, a complete UWSN ecosystem for the ns-3 simulator is presented. By extending the currently available energy and underwater frameworks of the ns-3 simulator, we are able to accurately simulate underwater applications before their development. The simulations are fed with real data (such as weather conditions, sound speed profile or bathymetry) from the location where the system will be deployed. The extensions made to the ns-3 simulator include two models based on the implemented hardware: a model of an energy-harvesting module and a model of an underwater low-cost, low-power wake-up modern. In Figure 1, a diagram of this ecosystem with energy-harvesting capabilities and a model of a low-cost, low-power modem is shown. The energy-harvesting module is included in the physical layer, since it is a energy-harvesting hardware model. The wake-up underwater modem implementation is divided between the physical and MAC (Medium Access Control) layers. To test this wake-up modem, different MAC protocols where implemented and adapted to use the wake-up capabilities. The gray highlighted modules are left for future work and include energy-neutral operation algorithms and routing algorithms.