## 1 Introduction  
Underwater Wireless Sensor Networks (UWSN) and terrestrial Wireless Sensor Networks (WSN) share common properties but they have many differences too. These differences necessitate specialized new protocols for underwater communication.  
Cost of the nodes is one of the differences, as underwater wireless sensors are expensive partially because of their more complex transceivers. Another difference relates to the deployment costs. Deployment of underwater sensors, especially in deep waters, can be difficult and expensive. Therefore, an UWSN has to be carefully studied and planed (in terms of performance evaluations, simulations, and tests) before its deployment. Power is another important difference since underwater communications requires higher power than the terrestrial network. But, the most important difference is the communication medium. Underwater communications cannot use Radio Frequency (RF) signals since they have an enormous attenuation in the subaquatic medium. Therefore, acoustic signals are used underwater.  
Acoustic waves present different signal attenuations depending on distance and frequency [1]. In addition, the signal spreading is proportional to the distance due to the expansion of the wave-fronts and can be in a cylindrical or spherical form [2]. Another problem faced by underwater communication comes with the signal propagation, which is 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 important to be considered.  
Given this long propagation delay, the original medium access techniques developed for RF networks, such as TDMA or CSMA, do not perform well underwater [3]. TDMA may need large time-guards to deal with the long propagation delay and the hidden terminal problem is amplified in CSMA networks. The use of a scheduling algorithm to organize the transmissions can, on one hand, avoid collisions, and on the other, reduce or even remove the time-guards, taking advantage of the propagation delay and overlapping transmissions.  
On the other hand, new routing protocols that meet these requirements and offer high energy efficiency are needed. It would also be desirable to submit additional features such as robustness and fault tolerance, which are not currently provided in the proposals made in the literature.  
In this paper, we propose EDETA (Energy-efficient aDaptive hiEarchical and robusT Architecture) as a routing protocol for UWSN, which was recently adapted to this new transmission medium [4]. Moreover, we aim to analyze impacts of different delay-aware and non-delay-aware scheduling and retransmission techniques when applied underwater, in order to optimize the protocol performance in terms of energy consumption, packet delay, number of duplicate packets, and packet loss using simulations in Network Simulator 3 [5]. In addition the paper presents a comparison between the protocols EDETA-e and DBR [6].  
The remaining of this paper is organized as follows. In Section 2, state-of-the-art underwater MAC and routing protocols as well as scheduling algorithms will be presented. Section 3 provides a description of EDETA, while Section 4 introduces different scheduling and retransmission techniques used in the experiments, and describes our simulation, the comparison between EDETA-e _vs._ DBR and the obtained results. Finally, in Section 5 conclusions are drawn and our future work is highlighted.