# Investigating Master-Slave Architecture for Underwater Wireless Sensor Network
## 4 System Model
### Restricting Extra Reception of Packets:
Hence in such a scenario, the shortest Accumulated Propagation Distance is considered to be the APD of that specific packet, while the APD is computed through the given equation as shown as:

\[APD=\frac{1}{n\_p}\sum_{j=1}^{n\_p}\sum_{i=1}^{h}dist_{i}^{j} \tag{17}\]

where the number of packets are denoted by n_p, b pertains to the hop count of the packet from the source node to the sink and \(Dist_{j}^{i}\) is the distance measured from the \(i\)th hop to the \(j\)th packet. ### Simulation Results

Simulations are performed in MATLAB (2017a) on the theoretical data to get the plots of the performance metrics to evaluate whether our proposed work is contributing to the main cause of saving energy or not. The main focus is to prolong the network life by saving energy as much as possible; however, we dealt with some trade-offs and compromised some metrics (E2 ED and APD) to gain improvements in PDR and energy tax. We compare ERPMSA-UWSN and WDFAD-DBR based on different parameters including sink numbers variation and node density. #### 5.3.1 Simulation of ERPMSA-UWSN in Comparison with WDFAD

As shown in Figure 12a, the PDR increases with an increase in the number of nodes for both WDFAD-DBR and ERPMSA-UWSN. This is because the increase in the network density also increases the probability of active node occurrence, and reducing the void hole occurrence. ERPMSA-UWSN outclassed WDFAD in terms of PDR in both sparse as well as dense networks. WDFAD selects the next forwarding node based on the difference in weighting depth between the two hops. Alternatively, ERPMSA-UWSN selects the nextforwarding node i.e., the master node based on the depth difference with higher energy and a greater number of PFNs. There are two types of holes in the network--, one is called void hole, while the other is referred to as energy hole. The void hole occurs due to the absence of PFNs in the forwarding area, while the energy hole exists due to the lack of sufficient transmission energy in the potential forwarding node, as shown in Figure 12. The difference of PDR between ERPMSA-UWSN and WDFAD decreases from sparse to dense networks due to the network density. Additionally, WDFAD drops the packet in the absence of PFN in its range i.e., void hole, but ERPMSA-UWSN keeps track of the void hole at the time of selecting the master node for transmission. Therefore, it rarely encounters void holes in its transmission period; however, sometimes there is a chance of an energy hole that occurs due to the additional use of the node. This is also resolved by adopting the 2 nd or 3 rd master in the region. In case, when the 2 nd and 3 rd master do not exist in the vicinity, we divide the PFZ into two portions, the lower PFZ2 portion which is denser in node population, and the upper PFZ1 which is mostly sparse. During the selection process, MSF filters out those masters whose PFZ1 has a minimum of 1 node, and if does not exist, a forwarding node from PFZ2 is selected. In a sparse network, WDFAD drops more packets which broaden the proportional gap between the plot of WDFAD and ERPMSA-UWSN, increases the probability of active nodes, and decreases the void holes, consequently decreases the packet drop as well as the gap in PDR results. To encounter the energy hole, our protocol provides additional support by suppressing redundant transmissions of the packet. This results in reducing the average energy consumption, which prolongs the node and network life, as a result of eliminating the energy holes.The void/energy holes and packet collision affect the network throughput and PDR. Like the WDFAD, we also use the two-hop mechanisms in our proposed protocol (ERPMSA-UWSN) to deal with the void holes. However, in ERPMSA-UWSN, it is ensured that the selected master has no void hole in its range. In addition, the problem of energy hole is significantly highlighted in ERPMSA-UWSN compared to WDFAD, as it mainly focuses on transmission energy economization.