# Performance Evaluation of Routing Protocols for Underwater Wireless Sensor Networks
## 2 Literature Review
### Cooperative Energy-Efficient Protocol for Underwater WSNs (Co-UWSN)  
Co-UWSN is a cooperative routing (C.R.) protocol introduced in [14]. The source sensor node transmits data through multiple hops. Each sensor node is designed with only one antenna. As one antenna is insufficient to cover all the areas and provide signals for data communication from source to destination, the relay node concept is used. The relay node works as a repeater, receives the data packets, and retransmits them to the other hop and then to the destination. Multiple factors help in network reliability. One of these is the network topology, and in this scheme, the authors divide the network into different parts. Data transmission between the sender and receiver nodes is done through the cooperation method using the relay route. Co-UWSN routing protocol operation is divided into initialization, cooperation, and routing. In the first stage, it will perform three tasks: (1) the location of the sink node is defined, (2) all the sensor nodes identify their neighbors, and (3) all possible paths to the sink node are estimated. In the second stage, (1) the source node shares its details with the destination and relay nodes, and (2) the forwarder nodes will transfer the received information to the destination node. The receiver node uses the FRC (Fixed Ratio Combining) method to combine these two signals. During the routing and relay selection stage, relay nodes obtain data from the source nodes based on the immediate channel condition, which relies on the weight factor. The weight factor is based on the SNR from the source to each neighboring node, as well as the depth and residual energy (RE). The neighbor whose weight function value is the highest will act as a relay. This protocol's advantages are (i) Better energy consumption, (ii) improved network lifetime, and (iii) reduced end-to-end delay. Reliability Adaptive Cooperation for Energy-Efficient Routing Protocol Using Sink Mobility (RACE-SM)  
The RACE-SM was introduced in [15]. It is an updated version of the cooperative routing protocol for UWSNs called Reliability and Adaptive Cooperation for Efficient (RACE). The RACE-SMs of the sink mobility scheme fixed the problems with a single relay node. All sensor nodes transfer the data directly to the sink if the sink node is within the communication range. The cooperative method transfers packets between the source and the destination when the sink is not in the communication range. GPS-equipped mobile sinks are put in place on the water's surface. The arrival time and speed of the acoustic waves are used to determine how far away these mobile sinks are. The sensor nodes obtain the coordinates by measuring how close the sink is to the surface. The sink nodes are set up in a certain place on the surface or top of the water and then move a pre-defined path. All sink nodes move in the same area, and their memory stores the coordinates of that area so that they can change the direction in which they move. These are the network's mid-boundary, center, and corner. Then, it compares the stored and current coordinates when moving forward. Before exchanging data, a sink node and a sensor node set up a link. Each sink node broadcasts the information packets within a 150 m range. The proposed routing protocol improved the number of live nodes, energy consumption, PDR, and end-to-end delays. Energy-Efficient Regional-Based Cooperative Routing Protocol for Underwater Sensor Networks with Sink Mobility (EERBCR)  
The authors proposed an EERBCR protocol with sink mobility for UWSNs [16] to enhance the network lifetime. In EERBCR, the network area was distributed into 12 zones, three-by-four horizontally and vertically. Four mobile sinks are placed at equal distances from one another, while 100 sensor devices are distributed at random. Each mobile sink traverses a predetermined straight route and services three zones. All sensor nodes are in sleep mode until the sink node arrives in their zone, at which point the sink node broadcasts a hello packet.