EDOVE: Energy and Depth Variance-Based Opportunistic Void Avoidance Scheme for Underwater Acoustic Sensor Networks  
[PERSON]  
1 Department of Information and Communication Engineering, DGIST, Daegu 42988, Korea; [EMAIL_ADDRESS] (K-J.P.); [EMAIL_ADDRESS] (Y.E.) School of Computer Science and Engineering, Kyungpook National University, Daegu 41566, Korea; [EMAIL_ADDRESS]  
[PERSON]  
contents due to the limited storage capacity of the node. Sensor nodes in the aquatic environment can communicate using the acoustic [2;3], electromagnetic/radio [4;5], or optical communication modes [6;7]. Sensor nodes commonly use the acoustic communication mode. However, the acoustic communication mode inherits some peculiar characteristics. Acoustic communication has a very long communication range, a very long propagation delay, high absorption and path loss, high energy requirement for the transmission and reception of the acoustic signal, limited bandwidth due to high error rate, and so forth [8;9]. On the other hand, the sink nodes or simply Sinks float over the sea surface. Sinks use multiple interfaces, one interface to communicate with the underwater deployed nodes (e.g., acoustic communication mode) and the other interface to connect with the onshore monitoring and control center (e.g., radio communication mode). The sensor nodes forward or route the sensed data towards the Sink which further relays this data to the onshore monitoring stations. The generic UASN scenario is shown in Figure 1, where multiple sinks are floating over the sea surface. The underwater acoustic sensors are deployed under water with the acoustic transmission range of \(t_{r}\). In that scenario, node \(S\) with transmission range \(t_{r}^{S}\) communicates the sensed data towards the sink through node the nodes \(i\), \(j\), and \(k\) with transmission ranges \(t_{r}^{i}\), \(t_{r}^{j}\), and \(t_{r}^{k}\), respectively. As stated earlier, the electromagnetic or radio and optical communications modes can also be used in the underwater environment; however, they are not suitable due to different aquatic characteristics. Electromagnetic signals at radio frequencies are preferable for the terrestrial communication because they consume low energy, offer high bandwidth, small propagation delay, and fairly low signal attenuation. Hence, the Sinks use the radio communication mode to connect the onshore stations. However, radio communication in the aquatic environment is not suitable because of the high attenuation that results in the severe absorption because of the water conductivity. In result, the radio communication has a limited small transmission range in the aquatic environment. Similarly, the optical communication requires a very precise line of sight between _receiver_ and _Sender_ node pair as well as the clear visibility. These two constraints are difficult to meet because of the water current and its turbidity. Hence, the optical communication fails to achieve the high data rate communication over the long range. Because of these challenges and limitations, the acoustic communication mode is widely used in the underwater networks. However, the data collection and dissemination solutions for the terrestrial networks can not directly be applied in the underwater network due to due to its inherent limitations. There are many routing protocols in the literature that tackle and consider the intrinsic acoustic parameters (e.g., high energy consumption, long propagation delay, large error rate, low bandwidth  
Figure 1: UAN Scenario. and so forth) to perform routing decisions. There are many ways the authors have classified the routing protocols in the literature, however, here we classify those protocols into two main categories, Location or localization-base and depth based routing protocols. In Location or localization based routing protocols, each node knows its own three-dimensional location, the location of the destination node(s) or sink(s), and sometimes the location of the neighboring nodes [10; 11; 12; 13; 14].