## 3 Cooperation in UASNs
Several sensors are modeled as a dependent variable that are randomly dependent on both realization of noise and channel in which the optimization issues of multi-variable is formulated for minimizing the total consumption of energy. Moreover, an investigation for energy efficiency which is affected by power transmission allocation was conducted. However, the method can only work on a homogeneous network with the same parameters. Acoustic distributed monitoring was implemented in the novel work of [43] that is based on storage of sensors and a trace system of data retrieval for a particular application domain which is designed for recording or storing of data in acoustic networks. They used a scheme of recording in a cooperative pattern and a mechanism of storage balance distribution for resolving the challenges of the large volume of storage and acoustic sampling with high frequency, but this scheme does not solve the unreliability problem for underwater communication. A system of cooperative storage developed by [44] aims to maximize the overall storage of a distributed node system that is disconnected. It uses data mules to forward the data among nodes in an opportunistic network. However, the method does not consider the collaboration of several mules for cooperative underwater monitoring. Moreover, the policies for the replacement of data to have flexibility in the information, not only the data which is already stored, is not considered in the paper. Analysis of multi-hop cooperative propagation is presented in [14] in which they study the most common issues of propagation errors in multi-hop and compared it with its Direct Transmission (DT) counterpart which reviled that Multi-Hop (MH) can provide higher cooperative underwater packet forwarding than DT. This analysis was conducted using a Markov grid and linear networks, however, as the scheme does not work with a multi-channel environment it is inadequate for underwater scenarios. In [45] the authors proposed sensor robot cooperative techniques for underwater monitoring activities. They designed an architectural based system to provide control support for power navigation using cooperative algorithms, mulling data application and cooperative experimental navigation characterization that support long monitoring of underwater robots. A survey of comprehensive localization schemes is presented in [46] that classified the algorithms based on three components of the mobility in the sensor called mobile, stationary and hybrid algorithms. Furthermore, an analysis and comparison of algorithms for localization was performed to determine the direction of future research in underwater. However, they did not cover collaboration among nodes that may result in cooperation that makes it unsuitable to achieve cooperation in UASNs. Location identification of sensor nodes in UASNs is an important aspect of cooperation. In this context the authors in [47] introduced a free anchor localization method for UASNs. They analyzed and concluded that the existing methods using GPS are not suitable for underwater localization. They also designed UASNs active-restrict to solve the problems of GPS which does not require the node information, but uses the node adjacency relationship for localization and is used in dynamic and static networks. However, there is no cooperation between distinct characteristics of communication in underwater and it is also not suitable for reliable cooperative communication in an environment like underwater. In this section, we provided a broad view of cooperation in UASNs. We have discussed some related works and the weaknesses of each method. In the next section, we take a closer look at the cooperation in UASNs by categorizing the existing works and analyzing them in more details.