# A Reconfigurable Formation and Disjoint Hierarchical Routing for Reshapeable Bluetooth Networks
## 6 Scatternet Performance
### Routing Performance  
In the simulation scenario, the scatternet topologies were constructed using the scatternet formation algorithms described in Section 3. Overall, 10 topologies were simulated, each with 60 nodes randomly distributed in the same geographical area. The optimum layer \(k\) is determined as three by the peak-search method for the 60-node samples. Table 1 summarizes the simulation parameters. The average packet throughput is defined as the ratio of the total number of successfully completed routing packets over the total simulation time in seconds. This parameter reflects the transmission capacity of a scatternet. The simulation results for the average packet throughput comparison between the reconfigurable mesh-tree and BlueHRT are presented in Figure 11. In BlueHRT, the throughput initially increases as the packet generation rate increases. However, this throughput slowly increases as the packet generation rate increases beyond three packets/node/s. This is because in a ring with tree-shaped  
Figure 10: Average number of formation packets. Figure 9: Average path length in a scatternet. architecture, packets tend to be queued at the nodes of the ring-subnet, and scatternet congestion is more likely to occur earlier. In a mesh-tree topology, the average packet throughput increases continuously as the routing packet generation rate increases. In general, the mesh-tree has much better throughput performance than BlueHRT in layer \(k\) = 2, 3 and 4 cases. This is because the hierarchical routing method, together with the mesh-subnet, significantly enhances the system performance. From the observation of the simulation, the throughput increases as the size of the mesh subnet increases. When the packet generation rate is greater than six, the \(k\) = 3 and 4 cases achieve better throughput performance than the \(k\) = 2 case since they generate more return links to increase the size of the mesh-subnet. In addition, the \(k\) = 5 case achieves the worst throughput performance as BlueHRT since this case almost achieves the tree structure and is not suitable for the reconfigurable mesh-tree network. The average packet delay metric is defined as the average packet transmission time from the first transmitted bit at the source node to the last received bit at the destination node for every routing packet. The average packet delay for any two node pair in the scatternet is mainly governed by three factors, which include average path length, average intra-piconet scheduling delay and average inter-piconet switching delay in the scatternet. Figure 12 shows the average packet delay performance of the reconfigurable mesh-tree and BlueHRT. In BlueHRT, the delay metric rapidly increases as the packet generation rate increases above two packets/nodes, and saturates when the packet generation rate increases above four packets/nodes. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Time (s)** & **20** \\ \hline Number of nodes & 60 \\ Optimum layer for 60-node samples & 3 \\ \(N\)-tier in all masters & 4 \\ Traffic pattern & Poisson arrival \\ Scheduling scheme & Round robin \\ Routing protocols & Hierarchical Routing \\ Packet transmission & Source routing \\ FIFO buffer size & 400 Packets \\ Source-destination pair & Randomly selected \\ Query or reply packet & 1 Time slot \\ Data packet (for each routing session) & 5 Time slots \\ Each routing session & 1 Data packet \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The simulation parameters. Figure 11: Average packet throughput of mesh-tree and BlueHRT. It is observed from the simulation that a buffer overflow phenomenon propagates from the nodes of the ring-subnet to neighboring master nodes, and this contributes to a large average packet delay in the scatternet. This phenomenon is due to the fact that the nodes in the ring-subnet are the transmission bottleneck, which results in congested packets waiting in the FIFO (first input first output) queues of neighboring master nodes.