## 4 Simulation Analysis  
In this section, the detailed simulation analysis of the proposed scheme in contrast to the conventional AHH-VBR scheme is presented. To fairly evaluate the performance of both the schemes, we simulated an underwater 3D network of 2 km \(\times\) 2 km \(\times\) 4 km area, where \(X_{max}=Y_{max}=2\) km and depth of \(Z_{max}=4\) km. The network size of 200 to 450 nodes has been simulated with the varying transmission ranges, ranging from 500 m to 900 m to demonstrate the sparse and dense network scenarios. In each simulation trial, the nodes are deployed randomly in the said network area and every individual sensor node acts as a data source (generates data packets) as well as a forwarder node. The position of the Sink node is static during the whole simulation course. Sink node is positioned at the water surface and at the center of the network area with coordinates (\(X_{max}/2\), \(Y_{max}/2\), 0). All nodes are homogeneous in terms of transmission range in every trial and are assigned initial energy \(E_{0}\) as \(E_{min}+rand(E_{rand})\), where \(E_{min}=50j\) and \(E_{rand}=30j\). A single network scenario for a given transmission range and network size is simulated 100 times. Therefore, all distinct points in the graphs of the simulation results are an average of 100 simulation trials. The payload size of the data packet, neighbor request, and acknowledgment packets are \(70\times 8\) bits, 64 bits, and 112 bits, respectively. The common header of 88 bits is used for all packet types in simulation. In addition to that, the data rate of \(16\times 10^{3}\) bits per second and the underwater acoustic delay propagation delay of 1500 m has been set in the simulations. Network is static during the complete simulation period. In last, the pure ALOHA is used at MAC layer because it is not susceptible to delays and does not use any collision detection and the avoidance mechanism. As stated earlier in a brief discussion about the conventional AHH-VBF, it ensures the packet forwarding reliability by setting the minimum forwarder threshold, \(\tau\), which depends upon the error probability, the packet collision rate, and the size of the packet. However, in simulations, AHH-VBF considered \(\tau\geq 2\), which indicates that there should be at least two or more than two forwarders in the forwarding region. This ensures the reliability as well as the collision probability at the next hop forwarder(s). Additionally, it consumes more energy and utilizes more bandwidth, which is the scarce resource of the UASN. This situation can easily arise when the holding time difference between two or more than two forwarders is very negligible or smaller than the propagation delay between them. On the contrary, our proposed scheme intends to avoid multiple transmissions of the data message towards the upstream direction, to save energy and avoid collision at upstream receivers. In short, the proposed scheme not only selects the spatially suitable but also the energy-rich acoustic node among the forwarders pool. Hence, the fair performance comparison is achieved by setting \(\tau=1\) and analyzing the packet suppression count or the number of forwarders count and energy consumption. During all simulation scenarios, there are 200 data sources that generate data packets destined to Sink node. The same number of data sources is used for the large network size scenarios with the intention to find the impact of identical data traffic on network performance. The simulation results are analyzed for two underwater network scenarios: One with the static Sink, which is placed on the sea surface at the fixed location and the other where the Sink is mobile. In the static Sink scenario, the Sink is placed at \((X_{max}/2,Y_{max}/2,Z=0)\) coordinates. On the contrary, in the mobile Sink network scenario, the sink moves vertically from the sea surface towards the seabed with a constant speed, \(sp=5\) m/s. However, its \(X\) and \(Y\) coordinates remain constant.