## 3 Cooperation in UASNs  
Cooperative communications, in UASNs, remain a challenging concept due to the unique features of UASNs, thus, some of the protocols designed for MANET and WSN cannot be directly applied to the underwater environment. Researchers in [14] conducted an analysis for propagation error in underwater cooperative multi-hop communication, where they examined the expected gains of multi-hop communication. Cooperative multi-hop communication in UASN is illustrated in Figure 4[36]. A data collection method based on coded cooperative OFDM for an underwater dynamic network is developed by [37], where a mechanism of coded cooperation based on selective relay and dynamic  
Figure 3: A Scenario with 32 nodes with 10 malicious nodes. network protocols were proposed. The study of least square cooperative localization for UASNs was proposed by [38]. In their approach, the performance metrics like consistency, coverage and efficiency were analyzed in cooperative localization least square to quantify the localization accuracy deviations. However, the authors proposed distributed algorithms for least square cooperative localization in which the squared-range is integrated by passing the message to a localization network. Moreover, Ref. [39] proposed paths for data collection of mobile node for cooperative UASNs in order to increase the efficiency of data collection for nodes on the surface station. In [17], an autonomous cooperation of mobile sensors in UASN has been studied, where a novel cooperative algorithm is presented in which every autonomous underwater vehicle (AUVs) is equipped with mobile sensors. Moreover, the algorithms take into consideration the maximum communication constrain between the agents based on communication range. A motion algorithm based on the control is decentralized to enable every vehicle to perform some maneuvers in order to achieve minimal error of acoustic source localization. Every autonomous vehicle in an underwater environment is equipped with a hydrophone array custom designed for it to perform some bearing angle measurements between an acoustic source and an array. Acoustic cooperative transmission for underwater communication that utilizes cooperative communication is proposed by [40], where various schemes of transmission for cooperative underwater communication which are specifically designed for communication that uses radio signal were analyzed. By considering the sound speed they also developed a new cooperative scheme for wave transmission, where they applied the concept of AF protocol along source-destination. These cooperative underwater transmission techniques reduce the limitations of the channel and improve the acoustic underwater channel throughput. The acoustic channel is characterized by long propagation delays and high BER. Therefore, it is challenging to design an efficient energy consumption method to achieve reliability in data transfer for time based applications. To overcome this issue authors in [41] proposed the Multi-path Power-control Transmission (MPT) scheme that improves the performance of the network in terms of energy efficiency, delay and low error rate of packet forwarding. MPT uses a scheme that combines the method of power-control with the method of multi-path forwarding. Moreover, the destination combines the packet received and the storage is designed for power-control. As it does not require retransmissions of packets, it uses less energy compared with its counterpart schemes using single path transmission. MPT also achieves less delay since it does not use a hop-by-hop transmission scheme. However, MPT does not solve the long delay problem of UASNs. Figure 4: Cooperative multi-hop UASNs. A cluster method for achieving cooperative communication is studied and analyzed by [42] where they use sensor nodes in every cluster for gathering of data related to a particular deployment area and forward the gathered data to the cluster head (sink) in a collaborative and cooperative manner.