# Towards Efficient Sink Mobility in Underwater Wireless Sensor Networks
## 5 Simulation Results  
In this section, performance of the proposed scheme is compared with already existing depth based routing protocols of UWSNs: DBR, EEDBR and SEEC. Simulations are performed by creating a complete UWSN environment using MATLAB [28]. For simulation, 2200 rounds are run with the same parameters. All 100 of the sensor nodes are randomly deployed in the network field of 100 m \(\times\) 100 m. The initial energy of each sensor node is 5 J [11]. The transmission range of each sensor node is 50 m and depth threshold is 15 m. The sending and receiving power consumption of the sensor node is set to 2 W and 0.1 W, respectively [7]. The size of the packet is 50 bytes [7]. Simulation parameters are summarized in Table 1.  
To evaluate the performance of routing protocols, network lifetime, network residual energy, packets received per round, total packets received at sink, stability period and packet drop ratio are primary metrics. Besides these common metrics, we introduced a new metric: MUR. The definitions are given below:  
**Network lifetime** is a total period (number of rounds) in which all the sensor nodes in the network die.  
**Network residual energy** is defined as the total energy of each sensor node at specific intervals (rounds). It can be computed using Equation (8):  
\[\mathbf{N}_{res}=\sum_{i=1}^{n}\mathbf{E}_{res_{i}}, \tag{8}\]  
where \(\mathbf{N}_{res}\) is the calculated network residual energy, \(\mathbf{E}_{r_{i}}\) is the residual energy of \(\mathbf{i}_{th}\) sensor node and \(\mathbf{n}\) is the total number of sensor nodes.  
**Total packets received at sink** is also known as throughput. It is a summation of total packets received by all the sinks. It can be computed using Equation (9):  
\[\mathbf{Tp}=\sum_{i=1}^{n}\mathbf{TPack}_{i}, \tag{9}\]  
where \(\mathbf{Tp}\) is total number of packets received by all sinks, \(\mathbf{TPack}_{i}\) is the total packets received by the \(\mathbf{i}_{th}\) sink and \(\mathbf{n}\) is the total number of sinks.  
**Stability period** is defined as the round in which the first sensor node of the network die.  
**Packet drop ratio** is a ratio of number of packets dropped by the sensor nodes to the total packets sent by the source nodes in any specific round (\(r\)). The computation of the packet drop ratio in any specific round (\(r\)) can be done using Equation (10):  
\[\mathbf{PDrop}_{r}=1-\frac{\mathbf{PktRev}_{r}}{\mathbf{PktSent}_{r}}, \tag{10}\]  
where \(\mathbf{PktRev}_{r}\) denotes the packets received in that specific round and \(\mathbf{PktSent}\) refers to the total packets sent in that specific round.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Number of nodes & 100 \\ Initial energy of nodes & 5 J \\ Data rate & 16 Kbps \\ Center frequency & 30 KHz \\ Packet size & 50 Bytes \\ Packet reception power & 0.1 W \\ Packet transmission power & 2 W \\ Transmission range & 50 m \\ Running rounds & 2200 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation parameters.  
MUR is the new metric that is used to analyze the utilization of mobile sink in the routing protocol. Many routing protocols have been using mobile sink together with multi-hopping. This ratio tell us that how much of the total packets are gathered by the mobile sink. The equation to calculate MUR is defined as follows:  
\[\textbf{{MUR}}_{r}=\frac{\textbf{{PktMS}}_{r}}{\textbf{{PktSent}}_{r}}, \tag{11}\]  
where \(\textbf{{PktMS}}_{r}\) is the number of packets received by the mobile sink in any specific round and \(\textbf{{PktSent}}_{r}\) refers to the total packets sent in that particular round.