# Energy-Efficient Clustering Multi-Hop Routing Protocol in a UWSN
## 2 Related Works
Each node can become the cluster head depending on the set of strategies and set of payoffs for the game. The pay-off function is denoted as the function of residual energy and the path loss of one-hop distance and aims to balance the energy consumption of all nodes. In [15], another clustering protocol scheme was applied for multi-hop routing in UWSNs. The scheme allows nodes to change energy consumption while maintaining excellent network performance. The energy optimization clustering algorithm (EOCA) requires a node to communicate to neighbors within the effective communication range. Each node calculates the total transmission delay between the node and the sink and then elects to become a cluster head according to the value of the total transmission delay. The depth of each node was also used to find a forwarder before sending the packet to the sink. The nodes send data packets to the cluster head or directly to the sink; therefore, the energy consumption at the nodes can be balanced. In [16], an energy-balanced unequal layering clustering (EULC) algorithm was designed for UWSNs to reduce energy consumption in inter-cluster communications. The EULC creates clusters of varying size within the same layer to solve the \"hot spot\" issue. The depth of network deployment is divided into layers based on the communication radius. The sensor nodes calculate the weight with respect to the residual energy of the node, the distance to the sink node, and the node degree. The node with the highest weight elects to become the cluster head. The node stores the information of the neighbor cluster head and then calculates the routing selected function to all the neighbor cluster heads according to the distance between the node and the residual energy. The node selects the next-hop cluster head with the smallest selected routing function value. In [17], the author implemented a simplified balanced energy adaptive routing (S-BEAR) based on a dynamic cluster K-means algorithm. The cluster heads are selected randomly. The nodes join the cluster with the minimum Euclid distance to the cluster head. The cluster head then transmits data to the sink using multi-hop communications. In [18], autonomous unmanned vehicles (AUVs) were deployed underwater for cluster formation, cluster head selection, and scheduling the transmission and wake-up sleep cycle. Since the cluster heads have to wait for the AUVs to collect data, packet delay may increase as a result of the waiting time at the cluster head. In [19], a clustering vector-based forwarding algorithm (CVBF) performed clustering with the assistance of a virtual sink for each cluster. The network space is divided into equal cuboids, each cuboid being considered a cluster in which the node near the sink adopts the role of virtual sink. In [20], the authors presented an energy-optimized path unaware layered routing protocol (E-PULRP) for UWSNs. The network is divided into layers, forming a layered structure around the central sink node. A potential relay node is identified from each layer. The transmission around the sink is divided into a set of concentric shells which produce the layered structure. Communication from the node to the sink follows a multi-hop path through the relay node at each layer. Therefore, the E-PULRP protocol preserves energy consumption. There remains some issues and challenges of clustering protocols in UWSNs. The type of nodes and the depth of nodes should be considered because the nodes may generate different types of data such as temperature, density, acidity, chemicals, conductivity, pH, and hydrogen which are categorized into different types of priority level. Therefore, nodes which generate high traffic priority should have higher priority and higher reliability to transmit data to the sink. In addition, the nodes located near the sink always aggregate data from other nodes which may cause a hot spot and dead nodes. Therefore, nodes should change the cluster head role after some time.