## 3 Literature Review
The received packets at destination, is checked for BER. If BER exceeds the threshold value, it sends a REQ towards the RLN. The relay sends the desired packet with ACK to the destination. The MRC technique combines the two packets and forwards optimal information towards the final destination. The scheme saves the network energy due to sink mobility, keeps maximum nodes alive and transmits maximum information. However, it consumes high energy and nodes become dead quickly. In [22], three different techniques are used to enhance the PDR and reduce the energy usage as well as ignore void node occurrence. The first scheme is cooperative-based opportunistic hydrocast that helps to minimize the unnecessary contributed nodes during transmission. However, it selects the longer distance paths, due to which energy usage increases. The second approach is improved version of the scheme, while the third one is a cooperative improved version. These techniques minimize dropping effect of information as a result energy usage reduces at the cost of high delay. The cooperative improved technique enables the network to achieve higher RODP. by using cooperation. The route setup criteria are the same for all techniques, the nodes are selected to proceed the information towards nodes which are close to the sink and have fewer hops. The authors proposed a scheme to minimize expended energy in [23]. Four movable sinks are considered, which move according to the sender node position. The movements of the sink are considered only for the horizontal axis. Besides, a cooperation scheme is set among the relay and destination nodes. If any sink node is available in the sender range, then packet is sent to the sink. Otherwise, cooperation is performed. The approach saves the energy of the network. However, it blindly selects the channel link for transmission data which affects the RODP. To minimize the energy consumption, the author proposed a new routing scheme in [13]. In the scheme, the whole network is split into three equal zones. The energy is optimized in such a manner that the upper region nodes consume low energy due to the short transmission range with respect to the sink node. Nodes lie in the mid and bottom region are energized with higher energy. It also considers the lowest depth criteria for the choice of data forwarder nodes. The scheme reduces the energy consumption due to single-path routing and increases the network lifetime. However, due to single-path routing, it reduces the network reliability and throughput. In [24], the authors describe that data packets can be made robust against the different channel factors. In this approach, a cooperation scheme is applied to sensor nodes to send data. In cooperationmode, more than one node is used to transmit data in the direction of the sink using different channel links. In this approach, two different selection criteria are defined for relay nodes selection. Firstly, the authors consider the residual energy and depth and then the SNR of the link with depth and residual energy are considered. This approach has high packet transfer to surface but has high delay as well. To maximize the network reliability, the authors present a cooperative scheme in [14]. The desired function parameters (depth and residual energy) are considered for data forwarder nodes. For cooperation, two relay nodes are used with destination, where the relay and destination nodes are selected by considering the lowest depth criteria. The destination and two relay nodes receive the packet that is sent by the source node. The DSN checks BER and sends a negative acknowledgment (NACK) in case of high BER. The relay node responds over the destination request and retransmits the packet towards the destination along with acknowledgment (ACK). The three received packets are merged by using the diversity technique and optimal information is sent towards the sink node. In case the sink is out of the communication range, multi-hoping is used.