# EE-UWSNs: A Joint Energy-Efficient MAC and Routing Protocol for Underwater Sensor Networks
## 2 Related Works
### Energy-Aware MAC Protocols for UWSNs  
The Distance Aware Collision Avoidance Protocol (DACAP) was proposed by [PERSON] and [PERSON] [26]. It was designed specifically for underwater acoustic networks. By using the DACAP algorithm, transmission power is saved by keeping packets away from collisions, using extra waiting periods. In addition, the protocol is based on reducing the handshaking period. Simulation results prove that the DACAP enhances the achievable throughput because it does not wait for the beginning of the next slot to perform transmissions.  
The Hybrid Sender and Receiver (HSR)-initiated protocol was proposed by [PERSON] and [PERSON] in [27]. HSR protocols are based on exchanging handshakes by sending control packets between multiple nodes. HSR can overcome the problem of spatial unfairness among nodes, as well as minimize the signaling overhead.  
[PERSON] et al. [28] proposed a reservation-based protocol known as the Efficient Depth-based MAC protocol (ED-MAC). It aims to avoid collisions and retransmissions by applying a duty cycle mechanism that assigns time slots to each sensor in UWSN in a distributed way. The main goal of the ED-MAC is to save the energy of sensors by putting them into sleep mode at some time slots. Simulation results demonstrate that the ED-MAC has superiority over contention-based MAC protocols in terms of energy consumption, throughput, packet delivery ratio, and fairness.  
In [29], [PERSON] et al. introduced a MAC protocol known as Data-Collection-Oriented MAC (DCO-MAC) for underwater acoustic sensor networks. By using the DCO-MAC algorithm, UWSN is split into two types of sub-networks, based on traffic load. The sub-network with light traffic load uses a contention-based MAC protocol, while the sub-network that has heavy traffic load applies a reservation-based MAC protocol. Simulation results and theoretical analysis prove that the proposed DCO-MAC algorithm has superiority over the other protocols in terms of energy overhead, end-to-end packet delay, the throughput of the network, and fairness.  
[PERSON] et al. proposed a MAC protocol in [30] that aims to decrease the energy consumption of sensors. This goal is achieved by splitting a packet into several sub-packets and each sub-packet is transmitted to the next forwarding sensor. In addition, the sensor isolation issue is solved by depending on the principle of depth adjustment. Numerical results prove that the proposed strategy achieves significant enhancements in terms of energy-saving and packet delivery ratio.  
A reservation-based MAC protocol was proposed by [PERSON] et al. in [31]. It is called the Ordered Contention MAC (OCMAC) algorithm. It is designed for applications that monitor deepwater floors and require low data rates and a sparse topology of UWSN. The main goal of OCMAC is to avoid collisions by scheduling RTS frames. The analysis results show that the proposed protocol saves energy and provides acceptable reliability and throughput.  
In [32], [PERSON] et al. proposed a MAC protocol named Concurrent Scheduling based on Spatial-Temporal Uncertainty MAC (CSSTU-MAC). Concurrent transmission and collision avoidance are performed by the CSSTU-MAC protocol based on temporal-spatial uncertainty and long propagation latency properties of UWSNs. Simulation results demonstrate that the CSSTU-MAC algorithm enhances the mean network throughput and energy consumption compared with other MAC protocols.