# An Energy-Efficient and Robust Multipath Routing Protocol for Cognitive Radio Ad Hoc Networks
## 5 Performance Evaluation
### Simulation Results and Discussion
#### 5.3.1 Varying the Number of Sessions  
The number of active sessions is increased from 4 to 16 with a step size of 2, and its impact on the network throughput, PDR, average energy consumption per bit, and average end-to-end delay are observed and analyzed. The SUs are subjected to a random velocity between 0 and 5 m/s, and the pause time is set to 30 s, whereas the number of SUs is fixed to 30. That is, we evaluate the impact of different traffic scenarios on the performance of the routing protocols.  
Figure 6 shows the average network throughput as a function considering the number of active sessions. As shown in the figure, the throughput of both protocols is enhanced with increasing number of sessions. This is because the greater the number of source-destination pairs, the greater the number of packets successfully delivered to their destinations within the specified time. In addition, with a smaller number of connections, the throughput difference between ERMR and L2 ER is small. Nevertheless, the proposed ERMR outperforms L2 ER significantly with the greater number of sessions. ERMR has up to 25% higher throughput than L2 ER. The proposed protocol with multiple paths has a better tendency to combat the dynamic environment and the stress of heavy traffic.  
Figure 7 shows the PDR as a function considering the number of active sessions. It should be noted that the increases in the number of sessions has dual effects on PDR. That is, PDR increases with increasing number of active sessions, and it reaches its peak value at 10 active sessions. Thereafter, PDR decreases owing to the traffic congestion in the network. The proposed ERMR depicts better PDR by a healthy margin of 20-25% in all cases, proving its robustness in CRAHNs. The provision of backup paths for responding to route failures and the availability of more stable channels contribute to the improvement in the data delivery percentage.  
Figure 6: Network throughput vs. the number of sessions.  
Figure 8 shows the average energy consumed per bit as a function considering the number of active sessions. It is found that the energy consumption per bit is sharply decreased until the number of sessions is 10 and thereafter attains almost steady consumption. In fact, the amount at which average energy consumed per SU increases with additional sessions is considerably low compared to the number of packets reaching the destinations. This is what leads to the trend of the graph in the figure. Furthermore, we find that the proposed routing protocols exhibit uniformly low energy consumption throughout the process. Basically, both routing protocols are energy-efficient routing protocols designed for CRAHNs. However, L2 ER does not consider the channel switching energy, which is inevitable in multichannel networks. In addition, a significant amount of energy can be saved for each route discovery process that takes place in mobile networks. Consequently, using the backup path preserves the improvident energy consumption in discovering a new routing path at every route failure. Likewise, the channel selection policy in the proposed ERMR avoids frequent channel switching by ensuring a stable channel for data communication, resulting in improved energy conservation.  
Figure 9 shows the average end-to-end delay as a function considering the number of active sessions. For both protocols, the average end-to-end delay increases almost linearly with increasing number of sessions. It is also obvious that the end-to-end delay of the proposed ERMR is lower  
Figure 8: Energy consumption per bit vs. the number of sessions.  
Figure 7: Packet delivery ratio vs. the number of sessions.  
than that of L2 ER. This results from the better adjustment to the dynamic network and spectrum heterogeneity in ERMR.