## 6 Performance Evaluations
### Simulation Results
#### 4.2.2 Network lifetime evaluation under the second scenario  
In this set of experiments, the network lifetime is studied under the second scenario concerning the average traffic rate and the number of sink nodes.  
The first experiment studies network lifetime under the second scenario. In this experiment, traffic averages three to 11 packets per second while fixing the number of sink nodes in the network to three nodes. Figure 14 displays the second scenario's network lifetime vs. average traffic rate. The figure indicates that the proposed approach increases network lifetime with increasing traffic volume. In addition to the reasons mentioned above, which made the proposed approach outperforms the other algorithms in the first scenario, the rest of the reasons for such improvement can be justified as follows. As the environmental conditions in this scenario are assumed to be outside the normal range, the routing paths are vulnerable to environmental factors. This increases the number of paths cut off for environmental reasons, and thus data transmission will become more and more concentrated. This further aggravates the energy imbalance of the network. Compared with SMRP, the proposed algorithm can achieve effective energy balance across the network in a harsh environment. At the same time, the proposed approach effectively bypasses the danger zones and discovers safer paths for data transmission through its modified environmental impact metric. On the other hand, in the case of EERP, its routing paths would inevitably cross the danger zones as the environmental impact on the routing performance is not taken into consideration, making the routing paths be cut off due to environmental reasons, causing more energy wastage as a result of retransmission of lost packets. Therefore, EERP algorithm has the worst performance compared with the others.  
Figure 13: Influence of increasing the number of sink nodes on network lifetime under the first scenario.  
The second experiment of this set studies the network lifetime while varying the number of sink nodes under the second scenario. This experiment was conducted by increasing the number of sink nodes in the network from one to three and maintaining the average traffic rate \(\lambda\) at three packets per second. Figure 15 shows the variation of network lifetime with respect to a different number of sink nodes. The figure shows that introducing more sink nodes in the network increases the network lifetime. This is because deploying more sink nodes in the network can effectively alleviate the energy-hole problem, which helps to balance network energy consumption. However, it can also be seen from the figure that the proposed algorithm improves the network lifetime compared to the other algorithms, even with an increase in the number of sink nodes. Compared to the SMRP and EERP algorithms, the proposed approach can better use its energy-balance feature due to its new proposed metrics, namely the nodes' energy consumption load metric and the sink load metric. It reveals the first reason behind such results. The second reason is that the proposed environment-aware routing as SMRP algorithm can avoid danger zones, and thus the routing paths are much less likely to be cut off due to environmental reasons. This explains the reason why the EERP gives the worst results, as it does not consider environmental impact. Finally, the SMRP and EERP do not take into consideration the link quality to make the routing decisions, which leads to packet loss and, thus, more energy consumption due to the retransmission of lost packets.