# On Reliable and Efficient Data Gathering Based Routing in Underwater Wireless Sensor Networks
## 2 Related Work
These chains are formed through calculation of optimum paths both locally and globally. A four chain based scheme presents a significant performance in terms of load balancing and energy consumption. LESCA is another protocol that has been proposed in [27]. Under consideration network is clustered using K-ways technique whereas, average energy, distance to BS, and distance to clusters centers are the few parameters that are used in cluster heads determination process. LESCA reduces energy consumption and lifetime gains of the network. WDFAD-DBR is a protocol presented in [28] that implements a technique to avoid the coverage holes creation in a network. Depth difference among nodes is considered as the key factor while selection of forwarding node for data transmission. Furthermore, nodes' forwarding area and nodes' eligible neighbors are also confined to reduce the energy consumption. Whereas, in [29], coverage hole problem has also been addressed in a unique way which is based on minimum critical threshold constraint. BLW-MCT has better performance in network scalability and outperforms counterpart schemes in terms of coverage holes. In [30], a protocol has been presented that adaptively varies the transmission range of nodes hop by hop depending on neighbors' density. Moreover, holding time is also optimized to overcome the end to end delay constraint among network. Above mentioned protocol is proved to perform well if implemented among sparse acoustic networks. Balanced clusters is the core issue been discussed in [31]. A fitness function has been formulated to reduce the overall energy consumption of the network. GAECH is proved to produce better results as compare to the counterpart schemes in terms of network lifetime and stability period. For random deployment scenarios heterogeneous communication ranges could produce better results in terms of network connectivity rate. This is the key motivation being adopted in [32]. In this protocol heterogeneous transmission range is also fused with the concept of aggregate contribution degree. Another protocol has been proposed in [33] that works by dividing the clusters into further smaller clusters. A path-node is selected for data gathering purpose at every sub cluster. Afterwards AUVs take a data gathering tour to visit path-nodes for data gathering. Relay nodes are circulated on the bases of residual energies and are selected out of the member nodes by the cluster head. In [34] GPNC has been suggested that exploits the greedily data forwarding approach. It effectively reduces retransmissions by employing partial network coding moreover, achieves higher packet delivery ratio with efficient energy consumption. Whereas, another routing technique has been proposed in [35] that forwards the packet on a link by carefully observing the link expiration time. Protocol provides reliability to the system through the exchange of acknowledgement messages. Nodes search for alternative link if the link expiration time exceeds packet's delivery time plus the time being consumed in exchange of acknowledgement messages. This protocol achieves better end to end delays in contrast to counterpart schemes. As discussed earlier, AUVs contribute to performance improvements in many ways, however they create new problems too. In [36] a protocol is proposed that is named as LVRP. AUVs causes the rapid changes in network topology which results in protocol overhear. LVRP formulates a mechanism that is benefited by the usage of AUVs besides that minimizes the packet overhead by the employment of a controlled mechanism that reduces the requirement of rapid control packet exchange among nodes. In addition to that there is another protocol called AEDG [37] that also contributes in protocol overhead suppression generated by the movements of AUVs. It associates a set of static nodes with AUVs which are responsible to gather data from surrounding nodes and to track the AUV's current sojourn stop. This technique appears to be an energy conservation method for UWSNs.