# Pipe Routing with Topology Control for Decentralized and Autonomous UAV Networks +
## 8 Simulation Results and Discussion
### Performance Evaluation
#### 8.3.1 Routing Performance  
Figures 8-12 show the routing performance (measured by the average route length, PDR, route up time, and number of route breaks) of different schemes (TC-Pipe, Pipe, ConCov-Pipe, AODV, and Relay) for single and multiple data flow scenarios. For single data flow settings, we report results for the three locations (\(C_{1}\), \(C_{2}\), and \(C_{3}\)). Similarly, for multi-flow settings, we test on settings \(C_{4}\)-\(C_{6}\), each having three flows. We also evaluated two different node densities (30 and 50 UAVs) and two node speeds (20 and 40 m/s). Multiple targets, and thus flows, can create interference and congestion, especially at higher data rates. The TC-Pipe and Pipe routing schemes consider congestion and interfering links between different routes when selecting a route or proactively switching the current routes, leading to better performance. Using the TC-Pipe scheme to maintain a robust pipe (with alternate routes) around each current route allows the network to select high-quality routes to the BS, with less interference and congestion. Without topology control, the Pipe routing alone selects less interfering or congested routes if/when they are available. AODV, on the other hand, only considers the shortest route and thus may select routes with congested or interfering links. _Average Route Length:_ Figure 8 shows the average route length achieved by all the routing schemes for three data flows at both densities and both speeds. A shorter route length often provides better data throughput and shorter delays. We observe that the route length increases with distance between the target and BS nodes, but it does not vary noticeably when the node density and/or speed change. Across all target distance settings, we find that TC-Pipe achieves the shortest average route length, while AODV has the longest. This shows the method's ability to establish stable, shorter routes using the pipe region. We observed a similar trend in route length for single data flow settings, \(C_{1}\ldots C_{3}\). _Average PDR:_ Figures 9 and 10 show the average PDR of each routing scheme for a single flow and multiple flows, respectively, across several target distances, node densities, and speeds. The average PDR of a routing scheme improves at smaller target distances, since longer routes are more likely to break due to node mobility. The average PDR also increases at higher densities because there are more opportunities to find a good route. In contrast, the average PDR decreases with node speed because more route breaks occur. For different network settings and target locations, our proposed TC-Pipe scheme achieves higher average PDR than the Pipe, AODV, and ConCov-Pipe schemes. By building a more robust pipe, it can select better quality routes (i.e., stable routes with low interference and congestion). We next expand on these points. In the single-target long-range setting \(C_{1}\), the PDR at different data rates for both UAV densities and speeds is shown in Figure 9a,d. At this route length, TC-Pipe provides significant increases in PDR; for example, it improves up to 63%, 105%, and 129% over Pipe, AODV, and ConCov-Pipe, respectively, for 30 UAVs at 20 m/s, with similar values at 40 m/s. At a higher density or using a closer target location, we observe similar trends but with reduced gains, since all methods experience improved PDR. For three distant targets (setting \(C_{4}\)), the PDR trends for low and high density are shown in Figure 10a and 10d, respectively. We see that for 30 nodes at 20 m/s, TC-Pipe gives  
Figure 8: Average route length for three-target locations. up to 50%, 71%, and 112% increases in PDR compared to Pipe, AODV, and ConCov-Pipe, respectively. Even at higher UAV speeds, where route breaks are more frequent, TC-Pipe improves PDR significantly compared to Pipe and the other schemes, since topology control helps to create alternate routes. Again, at a higher density or for closer targets, we observe similar trends but with reduced impact, since all methods give a higher PDR.