## 2 Related Works
### Network Coding Schemes for Underwater Networks  
Availability of an efficient channel model is essential to ensure efficient network performance; however, enhancing transmission mechanisms at both the physical and higher network layers is also inevitable. The network coding (NC) algorithm has emerged as one of the more robust algorithms to support seamless, reliable and computationally efficient transmission. Particularly, NC has justified its robustness for wireless transmission [31]. To reduce the probability of collision among transmitter-receiver, receiver-transmitter and end-to-end delay, in [31], authors developed a protocol named the Practical Coding-based Multi-hop Reliable Date Transfer (PCMRDT) scheme that exhibited reduced delay and retransmission. The authors of [32] studied data transmitting issues over UWSN and investigated the performance based on Automatic Repeat Request (ARQ), NC and erasure coding (EC) schemes. In [32], authors found that NC results in higher throughput than other schemes. In [33], Time Slot based Routing (TSR) was proposed where the NC algorithm was applied to reduce node conflict issues and energy consumption. In [34], VBF-NC was developed, where authors found that amalgamating NC and multi-path routing can enable better UWSN performance. Authors exploited the error-correction nature of NC to strengthen UWSN performance and to significantly enhance error recovery and energy exhaustion. However, nodes in the UWSNs are forced to wait until all the data from all other nodes reaches the destination before initiating the decoding process. Further, the author found NC to be effective in reducing latency and network delay [34]. The authors of [35] combined partial NC and geographic routing protocol with similar intent to enhance network performance. They recommended their approach as capable of ensuring minimised data size, minimal energy consumption and network delays, and later authors [36] backed up the same hypothesis. Exploring different approaches to enhance UWSN reliability and energy optimization, the authors of [37] proposed a multiple-path FEC approach (M-FEC) using Hamming Coding. In [38], authors applied ARQ and FEC to form a segmented data reliable transport (SDRT) model to ensure higher data reliability in UWSN. They used an erasure coding scheme and block-by-block coded data transmission on a multi-hop network.  
In [39], an NC and CDMA-based combined model was developed for UWSN. A butterfly NC model was applied in [40] for UWSN transmission. They used surface nodes, nodes' underwater column and access points to model the network and focused on achieving maximum data delivery from the surface node to the underwater nodes and vice versa. They stated that the ith higher inter-node distance to the access point demand packet relaying mechanism and sequential transmission over loaded networks could make access points vulnerable to the network overloads. To deal with this, they suggested an NC algorithm that can enable multiple packet transmission simultaneously. Considering broadcast nature and flexible computations, the authors of [41] suggested NC for the UWSN routing protocol so as to increase PDR [42]. Various UWSN related issues have been discussed in [43; 44]. A few significant suggestions to enhance UWSN performance can be found in [45; 46; 47; 48]. In [49], authors investigated the usefulness of the multilayered energy harvesting approach to increase the performance of UWSN.