# A Reconfigurable Mesh-Ring Topology for Bluetooth Sensor Networks
## 4 Performance Results  
In this Section, a discrete event simulator is written by Matlab to investigate the network routing performance, and the configuration parameters for routing performance simulation are defined as follows. For the packet transmission of each node, each packet was generated in accordance with a Poisson arrival pattern. In addition, it was assumed that a single packet was sent in each routing session, and that each data packet had duration of five time slots. A first in first out (FIFO) queue was provided with a length of 80 packets for each node. When the buffer is in overflow, a FIFO buffer is used in each node, and a tail drop mechanism is designed to drop the packets. In each routing session, the source-destination pair was randomly selected, the time division duplexing (TDD) scheme was adopted for both piconet and scatternet scheduling, and packets were forwarded using the RMR with the designed routing protocol. The overall simulated nodes are 100, which are uniformly distributed in a specific area. From Equations (1) and (2), the resulting number of piconets is \(p=15\) and the number of mesh links is \(ml=5\). Three simulation configurations are simulated, as in Figure 6. In the ring configuration, 15 masters with red color are interconnected by an intra-bridge with green color, which is a slave node to relay packets between interconnected piconets. Figure 6a is the piconet case, which is assumed to have 5 available mesh links in master 3. Figure 6b is the scatternet case with a uniformly distribution for mesh links among masters 3, 6, 9, 12, and 15. Figure 6c is the hybrid configuration of piconet and scatternet cases. In the hybrid case, it is assumed that there are two mesh links at master 3 and three mesh links distributed at 7, 11, and 15. Figure 6: The piconet case of Mesh-Ring topology (**a**); the scatternet case of Mesh-Ring topology (**b**); the hybrid case of Mesh-Ring topology (**c**). In Figure 6a of master 3, there exist various connection opportunities for the 5 mesh links via a bridge node from ID 16 to 30. Each bridge node is sequentially connected and simulated by master 3 to determine the highest throughput point. With a peak-search method, the 5 determined bridge nodes with highest throughput performance for the piconet case are shown as Figure 7. The first peak point is generated at bridge 25, which is shown by the blue line. The other determined peak points are 24, 16, 19, and 20. The simulation results demonstrate that the peak-search method works well to determine the optimal placement for each mesh link connection with the best throughput performance. With the determined mesh links, three configurations are simulated, and their performances are shown in Figure 8. For the piconet case, three mesh links achieve the maximum throughput performance. For the scatternet and hybrid cases, the throughput performance increases as the mesh link increases. In addition, more mesh links achieve better throughput performances. As a result, the scatternet case achieves better throughput performance than the other two cases as the packet generation rate increases. The packet generation rate is defined as the number of packets generated in each node at a given time slot. In [15], the cluster-based mesh topology demonstrates better routing performance than the conventional full mesh topology with the on-demand routing protocol. Our proposed Mesh-Ring topology is a type of cluster-based mesh architecture, and the ring routing protocol can operate for a larger network. After the RMR determines the optimal Mesh-Ring configuration, Figure 9 demonstrates the packet successful probability (PSP) for RMR with three cases, Ring and Mesh topologies. The RMR achieves almost 100% packet delivery ratio when the packet generation rate in each node is smaller than 4. The PSP in each node is defined as the total successful reception packets over the total network generated packets. The piconet case achieves better PSP than the Ring network when the packet generation rate is greater than 5.