# Traffic Aware Scheduler for Time-Slotted Channel-Hopping-Based IPv6 Wireless Sensor Networks
## 6 Discussion of Simulation Results
### Impact of Number of Nodes--Comparison with OSCAR  
We compare our implementation with OSCAR, an adaptive approach described in Section 3.2. Similar to OSCAR, the design principles of our scheduler are based on the idea that the nodes that suffer the most in convergecast traffic are the children of the root. When there is little traffic, OSCAR and our scheduler behave like RBS Orchestra. In  
Figure 14: We observe that when it comes to average radio duty cycle, the new scheduler performs better than Orchestra in a high-traffic situation.  
Figure 15: We observe that when it comes to stability, the new scheduler performs better than Orchestra, in high traffic situations.  
OSCAR, the number of additional allocated cells is correlated to the rank of the node, in our implementation it is correlated with the subtree size, which makes our solution more suitable for unbalanced networks. Moreover, we only adapt the scheduler for the root and its children. To analyze the differences of the two schedulers, we study the impact of the number of nodes on the average delay, average PDR and average radio duty cycle (Figure 16).  
We consider the same performance parameters as the authors of OSCAR. The desired number of nodes are placed on a \(200\,\mathrm{m}\times 200\,\mathrm{m}\) grid. The sender nodes are placed uniformly around the root node. We vary the number of sender nodes from 20 to 100 nodes. Each sender in the network transmits 2000 packets to the root. The traffic load is 1 pkt/minute, same as in [13]. To complete our figures and compare the schedulers, we took the values from the article that describes OSCAR, in Figure 9a-c, Section 5.3.2 of [13]. This also means we were restricted by the placement of nodes the authors used for analyzing the performance of OSCAR, and we could not compare the schedulers in unbalanced networks.  
Figure 16: _Cont._  
The authors of OSCAR use the rank of the node to attribute resources to the nodes. In OSCAR, each root's child is allocated 1 cell every 6 cells. We consider the subtree size of the root's children when allocating resources, thus in our case, the number of allocated cells can vary depending on the subtree size. We allocate 0.7, 1.06 or 1.4 cells every 6 cell. Considering the high number of nodes, we suspect each child of the root is allocated the maximum number of cells, 1.4 cells every 6 cells. We expect our scheduler to increase the average PDR, decrease the delay and increase the radio duty cycle when compared to OSCAR.  
As expected, we see a 70% decrease in average delay and a slightly higher PDR for our scheduler, if the number of nodes in the network is less or equal to 80 (Figure 16a,b). This happens because, on one hand, we allocate more transmission opportunities for the root's children than they do in OSCAR. On the other hand, we only adapt the scheduler of the root and the root's children to tackle congestion. If the network has a high number of nodes, the performance of our scheduler will start decreasing because the congestion will become significant also for nodes farther from the root (Figure 16a).  
In Figure 16c, one can see that the new scheduler has a higher average duty cycle, regardless of the number of nodes in the network. This can be explained by the fact that we allocate more transmission opportunities for the root's children.