# Enhancing Reliability of Tactical MANETs by Improving Routing Decisions
## 5 Performance Evaluation
### Performance Metrics and Simulation Results  
The choice of appropriate performance metrics is important for effective design process. The ns-2 simulator allows choosing from a large set of available performance metrics. For our simulations, we have assumed throughout, packet delivery rate (PDR) and end-to-end delay metrics to analyze the performance of our proposed protocol, and compare it with other similar protocols. Furthermore, each performance metric is simulated assuming the following 3 key parameters: network diameter, node speed, and the number of network nodes.  
The throughput metric is defined as the average number of successfully delivered bits per unit of time. Modern tactical MANETs in digitalized battlefield need to support high throughput applications utilizing services such as real-time video. The throughput is affected by the use of heterogeneous network components, and often by jamming and interference. Figure 5(a) compares the average throughput and the node speed. We observe that AOMDV and LQA-AODV protocols have similar performance, however, when the speed is increased (i.e., over 20 m/s) in a tactical mission scenario, the throughput of AOMDV becomes inferior to LQA-AODV. Figure 5(b) shows the throughput with different values of the network diameter. Link quality-based routing allows the LQA-AODV protocol to differentiate between strong and weak links, even when the network is large. Even better throughput is observed in Figure 5(c), especially when the number of nodes is again increased.  
Figure 6: _Cont._Packet Delivery Ratio (PDR) is a fraction of successfully delivered packets. This metric is often used to estimate link quality small tactical MANETs where network load is a vital QoS constraint to consider. The performance for PDR is evaluated similarly as for the throughput. All results in Figure 7a,b demonstrate that the proposed LQA-AODV protocol can effectively improve the PDR at the destination node. Figure 7c shows that network loads can differ significantly when the network deployment area is larger than 3000 m\({}^{2}\). Clearly, the maximum capacity of MANET as well as PDR are directly related to the achievable RSS or SINR.  
Figure 6: (**a**) Throughput vs. node speed. (**b**) Throughput vs. network diameter. (**c**) Throughput vs. node density.  
Figure 7: **(a)** PDR vs. node speed. **(b)** PDR vs. network diameter. **(c)** PDR vs. node density.  
Finally, the end-to-end delay is defined as the time required for the packet to be fully received at the destination. It is another important QoS performance metric often considered in tactical MANETs, especially for time-sensitive and mission-critical applications such as remote drone operations. The simulations were carried out assuming varying node speeds, densities and the network deployment area size. The obtained results are presented in Figure 8a,c. The proposed LQA-AODV protocol always outperforms all other AODV based protocols considered. Interestingly, the LQA-AODV protocol yields the best performance improvement over other protocols when used for large area coverage. This shows that link quality measurements are beneficial for routing, especially over large areas.  
Figure 8: _Cont._