# An Energy-Efficient and Obstacle-Avoiding Routing Protocol for Underwater Acoustic Sensor Networks
## 1 Introduction
However, the coexistence of acoustical multi-systems in UASNs brings new challenges, especially obstacle avoidance, to underwater routing protocols. In particular, some marine animals as part of a natural acoustic system also use acoustic signals to communicate, causing interfere to communications among sensor nodes around the marine animals [10; 11]. The routing protocols which are able to avoid the disruption to the routes in UASNs caused by marine animals (considered as obstacles) are called obstacle-avoiding routing protocols, which are special void handling routing protocols. Currently, most of the existing underwater acoustic routing protocols, e.g., VHGOR, focus on prolonging the network lifetime and handling the traditional void area problem, but only a few routing protocols committed to solved the obstacle-avoiding problem. Therefore, propose an effective routing protocol that not only avoids the obstacle but also prolongs the network lifetime, for UASNs, is very crucial. To solve the issues above in UASNs, in this paper, we design an energy-efficient and obstacle-avoiding routing protocol (EOAR), which mainly contains three steps. Firstly, when a current node perceives the presence of marine animals during the underwater communications, the interference area of the animal-nodes and the candidate forwarding relay set are first calculated using the underwater acoustic channel model [12]. Then, the fuzzy logic-based relay selection scheme,taking the propagation delay, the included angle between two neighbor nodes, and the residual energy into consideration, is applied to calculate the forwarding probability of the candidate forwarding relays. Last, a priority-based forwarding method, which can avoid the packet collisions, is applied to schedule the packets transmission towards the destination node. The following are the key contributions of this paper:  
1. In a network where marine animals and sensor nodes coexist, the underwater acoustic channel model is used to determine the interference area of the animal-nodes and then form the candidate forwarding relay set, which can reduce the possibility of those sensor nodes that are interfered by marine animals becoming the candidate forwarding relay set. 2. A new routing protocol call EOAR is proposed in this paper. In EOAR, the forwarding order of the nodes belonging to the candidate forwarding relay set is sorted using a fuzzy logic-based forwarding relay selection scheme. By considering more metrics, including propagation delay, the included angle between two neighbor nodes and the residual energy, the proposed EOAR protocol improves packet delivery ratio and extends network lifetime compared to routing protocols previously applied to fuzzy logic [13]. The simulation results show that our protocol can avoid animals' interference more effectively, increases the packet delivery ratio by 28.4-11.8%, and reduces energy consumption by 53.4-32.7% compared with the classic hop-by-hop vector-based forwarding routing protocol (HHVBF) and void handling using geo-opportunistic routing protocol (VHGOR). The rest of this paper is organized as follows: in Section 2, related work on underwater routing protocols is discussed briefly. In Section 3, the proposed network model is introduced. In Section 4, the EOAR protocol is described in detail. The simulation results are shown and discussed in Section 5. Finally, this paper is concluded in Section 6.