## 5 Performance Evaluation
### Experimental Study  
#### 5.2.1 Impact of Node Positions  
In this part, two network topologies have been set up to test the impact of the position of the nodes on the performance of the network.  
OSCAR is flexible because the rank delimitations for each class are readily configurable. Accordingly, the impact of the physical position of the nodes was not a focus of this work. Instead, the impact of different link configurations and initial node class groupings on the performance of OSCAR was investigated. The first and second topologies are those illustrated, respectively, in Figures 1 and 4. In both cases, the nodes are distributed over different layers depending on their proximity to the root. Thus, the second form of network is more condensed and close to the root, while the other is more spaced-out and distant from the root.  
The first metric tested is the radio duty cycle. Figure 5 shows the time period during which the node is active for the first topology. In this figure, we can see that OSCAR's average service cycle is lower than that of Orchestra. For OSCAR, nodes 1-3 correspond to those most in demand because they benefit from a larger number of allocated slots and are therefore more active. While nodes 8-10 are the least in demand and thus least active. As such, the cell scheduling mechanisms efficiently use slot allocation to remove slots from inactive nodes. Orchestra in contrast has a relatively flat radio duty cycle for all nodes, as it does not modulate slots allocation.  
The result for the second topology is also shown in Figure 5, indicating a slightly higher average duty cycle compared to the first arrangement. It is roughly equivalent to Orchestra's average duty cycle and is due to Algorithm 2's duty cycle adjustment. This is explained by the fact that the nodes benefit from a greater number of allocated slots due to their position close to the root node.  
Figure 6 illustrates the results obtained in terms of latency for the first and second topology, respectively. We can see that OSCAR's average latency is smaller than Orchestra's in Figure 6. We notice that most nodes show less latency except classes 4 and 5 (i.e., nodes 8-10), a slightly greater end-to-end delay is present. Nonetheless, the global impact of this delay profile results in a reduced average latency, and the nodes close to the root have half the latency. Regarding the second arrangement, OSCAR again exhibits less average latency than Orchestra and the performance gain becomes greater for the first nodes in class 0. The average latency is 42% shorter. This is explained because these nodes have more opportunities to dump traffic, which can solve the conflict problem.  
Figure 4: Second network topology used in the performance evaluation.  
Figure 7 illustrates the average packet delivery rate for OSCAR and Orchestra. In this experiment, each node sent 2000 packets to the root, for a total of 20,000 packets sent across the network. Additionally, the data rate has been set to 5 pkts/min. For the first and second topology, OSCAR has a better delivery rate compared to Orchestra. With OSCAR, we  
Figure 5: Average duty cycle of OSCAR and Orchestra for the first and second topology.  
Figure 6: Average end-to-end delay of OSCAR and Orchestra for the first and second topology.  
notice that nodes 8-10 have higher packet delivery rates when the topology is condensed. Indeed, these nodes are in class 3, whereas when the topology is more dispersed, these nodes belong to classes 4 and 5. For example, node 10 displays a rate of 88.5% for the first topology and 95.7% for the second topology. This demonstrates that the allocation of slots according to the class of the node plays an important role in the performance of the network. The packet delivery rate for Orchestra remains roughly equivalent in each of the two network layouts. This can be explained because Orchestra allocates the same number of slots to all nodes, regardless of the position of that node.