# Retransmission Avoidance for Reliable Data Delivery in Underwater WSNs
## 5 Simulation Results and Performance Evaluation
### Simulation Results
#### 5.2.1 Active Nodes  
It can be observed from Figure 9, as the number of layers increases number of active nodes also increases. Because if the source node lies nearest to surface gateways, it results in less number of duplicate packets and awake less number of nodes. However, if source node resides away from the surface, it results in high number of active nodes. It shows farther the source node is from the surface, higher is the number of active nodes. The number of active nodes increases as the layer number increases in DBR. When the information is obtained up to two hops, the active nodes are high, however, as the hop count increases, means the neighbor information acquired up till three hops, the probability of finding void hole increases. Furthermore, the transmission of data packet from the single path towards destination only involves few number of nodes. While in LMPC and FLMPC multiple routes generated from every cross node results in high number of active nodes. The use of single route is the major reason behind low number of active nodes participating in the data forwarding process. \begin{table}
\begin{tabular}{l c c} \hline
**Option** & \multicolumn{2}{c}{**Value**} \\ \hline  & Scenario-1 & Scenario-2 \\ \hline Area & 2000 m \(\times\) 2000 m & 4000 m \(\times\) 4000 m \\ \hline Noise of Ship & 0.2 dB & 0.8 dB \\ \hline Wind & 5 m/s & 20 m/s \\ \hline Number of Nodes & 150 & 500 \\ \hline Simulation Period & 1000 s \\ \hline Frequency & \(914\times 10^{6}\) Hz \\ \hline Initialized Energy & 1000 J \\ \hline txPower & 0.66 mW \\ \hline rxPower & 0.395 mW \\ \hline idlePower & 0.035 mW \\ \hline \end{tabular}
\end{table} 
Table 4: Simulation Parameters. Figure 9 shows that initially the number of active nodes in scenario one of LMPC is high due to tree generation from source node resulting in high number of duplicate copies. Later, the increment is gradual because higher depth nodes forward data packets through the relay nodes which are already awake in the upper layers and also awake few more sensor nodes. Less number of active nodes save network energy. Number of active nodes in FLMPC-One is lower as compared to LMPC. FLMPC-One generates less copies of packets which reduces the chances of collision. Packet collision is very critical factor in sensor networks which effects energy and delay of the network. If collision increases, it affects network's performance and results in loss of data. All the active nodes not only relay data packets of higher depth nodes but also sense their own data and forward it. Two hops neighbor information of FLMPC-One reduces number of active nodes and also reduces the probability of data packet entrance in void region. FLMPC-One acquires neighbor information to avoid the awakening of sleeping nodes leading to void regions. Active nodes of FLMPC-Two in scenario one are less than both LMPC and FLMPC-One because of finding \(PFN\) after using three hops information. It saves data packet from entering in void region. If sensor node is lying in the sparse region, this mechanism reduces the probability of data packet drop. When a sensor node forwards data packet to its \(PFN\) using three hops information. The receiver node needs not to forward that data packet to the node found by its previous forwarder during \(PFN\) finding mechanism. Because previous node information may lead data packet to void region. So, current forwarder locates its \(PFN\) by running \(PFN\) selection mechanism. In this way, data packets loss is avoided. In scenario two, initially increment in the number of active nodes of LMPC and FLMPC-One is rapid. Later, FLMPC-One makes smart decision by detecting void holes and changes the path of the data packet. In this way, FLMPC-Two awakes suitable nodes which results in gradual increment. Although, two hops neighbor information reduces active nodes of FLMPC-One, however, three hops information reduces them more. FLMPC-Two has more data to forward and already awake nodes are not enough.