# Energy-Efficient Clustering Multi-Hop Routing Protocol in a UWSN
## 2 Related Works  
UWSNs have attracted many researchers over the last decade because of their enormous variety of application. Many literature reviews of routing protocols for UWSNs categorizing the routing protocols in terms of the routing strategy have been presented [9]. The routing protocol for UWSNs has two types: localization-based and localization-free protocols. The localization-based routing protocol requires the location of nodes to find the routing path from the node to the sink. Despite this, the localization-free protocol uses the depth measurement of the sensor node to establish the routes to the sink. The depth of the sensor node is measured by the pressure sensors equipped on the node. The localization-free protocol has more advantages than the other in terms of scalability. Due to the mobility of nodes, the routes can be constructed by using the depth if the network topology changes. In [7], several cluster protocols for UWSNs are reviewed in terms of cluster stability, delay efficiency, load balancing, and energy efficiency. The network requires a capability of 100% coverage due to the long transmission range and high node mobility. The clustering protocols in UWSNs select the cluster heads and cluster members depending on the location of nodes, types of generated packets, priority of nodes, the energy consumption, and the latency of data. A clustering protocol should achieve high network performance with respect to a high packet delivery ratio, low latency, and a long network lifetime. Some clustering protocols are reviewed in detail in this section. In [10], a clustered-based routing protocol allows the sensors to form clusters according to their depth and energy. The localization-free routing protocol, which is called the energy-efficient routing protocol based on layers and unequal clusters (EERBLC), selects the routing path according to the link quality and residual energy. It presumes that each sensor node does not need its location to set up a cluster. A node calculates a cost according to its residual energy and forwarding ratio. In this protocol, the header nodes selection procedure does not consider the duration of the cluster head and the location of nodes according to the sink. If nodes play the role of the cluster head for a long duration of time, it may become a hot spot, causing a dead node. Another study applied LEACH in UWSNs to establish a cluster [11]. The study also improved LEACH, providing Controlled-LEACH (C-LEACH). C-LEACH deploys a control node at the center of a network's topology, and the control nodes process the clustering protocol, resulting in a longer network lifetime compared to LEACH. The C-LEACH protocol may take a long time to process the cluster algorithm because the control nodes should transmit to all nodes in the network. In [12], the authors developed an adaptive node clustering routing protocol for smart ocean UWSNs based on an optimization technique. The network is divided into a cluster in which the cluster head is selected according to the available energy in the sensor node. The re-transmission may cause high latency or duplicated packets at the receiver while selecting the cluster members. In [13], network deployment is divided into layers in which each layer has a fixed depth value and area width. The multi-layer cluster-based energy-efficient (MLCEE) routing protocol increases network lifetime while reducing the end-to-end delay of a packet. The MLCEE protocol allows the node to calculate its layer; the node then commences broadcasting messages to form a cluster. Since the network is divided into many depth layers, the node adopts the role of forwarder depending on its residual energy and probability. In [14], a topology control energy balance protocol (TCEB) was implemented for UWSNs. The protocol considers the node's energy and path loss as the factors to select a cluster head. The topology control protocol is represented as a non-cooperative game.