# An Energy-Efficient and Obstacle-Avoiding Routing Protocol for Underwater Acoustic Sensor Networks
## 3 Models
### Network Model  
As shown in Figure 1, we consider a three-dimensional UASN where many sensor nodes coexist with marine animals. The underwater nodes communicate with each other using acoustic signals to complete the collection of oceanographic data. We define the node which generates packets as source node and the packets are transmitted through the network to the destination node. When a source node has a packet to transmit to the destination node which is far away from itself, the entire forwarding process requires many intermediate nodes to participate in forwarding packets. We define the term current node as an intermediate node which has a packet needed to forward. The current node can be an original node which just generated a new packet or a transit node which just received a packet from its neighbor node and itself is not the destination node. However, when marine animals that also use acoustic signals for daily activities are around the sensor nodes that communicate with each other, communication among sensor nodes is disturbed.  
To facilitate the analysis of research objects, the entire network structure is divided into 1000 m \(\times\) 1000 m \(\times\) 1000 m sub-volumes. Each sub-volume contains one common sensor node. Sensor nodes \(N_{j}=\left\{n_{1},n_{2},\ldots n_{j}\right\}\) are deployed in these sub-volumes according to certain deployment strategies that can increase network connectivity rate and network coverage rate. We use a node non-uniform deployment strategy [25] method to deploy the sensor nodes, in which a large number of nodes are mainly deployed in the range centered on the interference area of marine animals, and a small number of nodes are deployed in the path from the interference area to the source node and from the interference area to the destination node. Marine animals such as the Chinese white dolphins are aggregated, so there are a lot of marine animals in a certain area. To simplify the network model, we see many marine animals in a certain area as a whole (one marine animal _Ma_) to study. And the center of the area where the marine animals are located is the geographical location of the marine animal _Ma_. The marine animal _Ma_ is always existed in the network and randomly moves around the network. The EOAR protocol derives the location of the marine animal _Ma_ based on the probability that the marine animal will appear in a certain area. Moreover, the marine animal _Ma_ does not move frequently in a certain area, and the range of movement is not large in a short time. Therefore, we can assume that the location of the marine animal _Ma_ is kept in a certain area within a short period of time. It is assumed that the movement of sensor nodes caused by water currents is slow, and the sensor node is relatively stationary for a certain period of time. Sensor nodes in the network are defined as network nodes, and each sensor node can perceive, receive, and forward packets. In addition, it is also assumed that all the sensor nodes have homogenous transmission range and energy consumption. A sensor node is in the sleep state if it is not working.