# An Energy Balanced and Lifetime Extended Routing Protocol for Underwater Sensor Networks
## 5 Simulations
### Regular Node Distribution  
In this part, we analyze the performance in the regular node distribution case. If not specified, the network is divided into five concentric circular rings and each ring contains four nodes. The radius \(R\) of each ring equals 500 m. Here we assume that each sensor node generates a data packet and forwards it to the sink in each round. A more realistic data load distribution will be analyzed in the next section. First, we discuss the effect of maximal EL to our proposed algorithm. Figure 6 presents the sending rounds when different percentages of sensor nodes deplete their battery power. We simulate seven cases and the maximal EL varies from 2 to 500. From this figure we can see that the maximal EL can affect the network life to some extent. When the maximal EL becomes very large (e.g., 500), the sensor nodes consume a lot of energy on broadcasting and upon receiving EL changes. Therefore, the sensor nodes are unable to send more data packets. However, when the maximal EL becomes very small (e.g., 2), the sensor nodes are unable to distinguish remaining energy changes among neighborhood nodes and a lot of energy is wasted on long range transmissions. When the first node in the network is dead, the network sends the largest number of data packets at the case of maximal EL = 20 and maximal EL = 30. In addition, in the case that maximal EL = 20 performs better after 20% of nodes in the network are dead when compared with the case of maximal EL = 30. So in the next simulations, we set maximal EL = 20. It should be noted that the energy consumption of broadcasting residual energy level information and determining relative distance makes up only a small proportion of the total energy consumption. The reasons are listed as follows:  
* The network structure we consider here is a quasi-stationary one which means the sensor nodes rarely move after deployment. So nodes need to broadcast beacon messages only once to obtain the relative distance towards the sink node and their neighborhood nodes. In addition, the cost of broadcasting beacon messages becomes relatively low when comparing with continuous data transmissions. * Although each sensor node needs to broadcast its EL changes 19 times (maximal EL = 20) before it depletes all its energy, the frame length of beacon messages and EL change notice packet is small as these control packets have no data load. So the total energy consumption for transmitting control packets is low. In order to further present the cost for control packets, we calculate the percentage of energy consumption for different transmitting phases. In this regular node distribution case, the result shows that the sum of energy consumption in broadcasting/receiving EL notice packets and beacon packets \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Data Rate & 10 kbps \\ Center Frequency & 20 kHz \\ Bandwidth & 10 kHz \\ Receiving Power & 0.03 W \\ Transmitting Power & 0.17–29 W \\ Mode Type & FSK \\ Packet Error Rate Model & ns3::UanPhyPerDefault \\ Signal Noise Model & ns3:UanPhyCalcSintDefault \\ Acoustic Propagation Speed & 1500 m/s \\ UAN Propagation Model & ns3:UanPropModelThorp \\ MAC Model & CWMAC \\ Required SNR for Signal Acquisition & 20 dB neuPa \\ Payload of DATA & 200 Bytes \\ Network Radius & 1–2 km \\ Initial Energy per Node & 200 J \\ Node Number & 20–50 \\ Number of Concentric Circular Rings & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation Settings. makes up 3.48% of the total energy consumption (maximal EL = 20). In addition, this small part of energy consumption can prolong the network lifetime significantly by energy balancing. Figure 7 shows the percentage of node residual energy at different sending rounds for different protocols. It can be seen that the direct one-hop transmission protocol (Figure 7b) is not suitable for long time transmissions because the sensor nodes far away from the sink consume their battery power at a high speed.