# A Cooperative MAC Protocol for a M2M Heterogeneous Area Network
## 6 Simulation Model and Results
### Performance Analysis  
This section evaluates the performance of the proposed M2M heterogeneous area network and the effectiveness of the proposed Blank Burst algorithm. Simulation results are used to compare the performance of two M2M area networks. Using simulation models, we evaluate the performance of the proposed algorithm by using the following metrics: packet success rate (PSR), end-to-end delay, and the number of collisions. The PSR is defined as the ratio of the number of packets successfully received by the data sink to the total number of packets generated by the end devices. The first two metrics are also used to compare the performance of homogeneous and heterogeneous M2M area networks. Simulation models were used to obtain results from three different networking scenarios. In the first scenario, a homogeneous network is used where the network elements are 802.15.4 end devices, routers, and a data sink node. Thirty-two end devices are used using four 6 LoWPAN clusters. A six-hop network is simulated that has the same end device to data sink transmission distance used in the heterogeneous network. In the second scenario, 64 end devices are used where a multi-frequency heterogeneous network architecture is simulated without implementing the BB signaling algorithm; this may result in inter-domain (802.11/802.15.4) collisions. In this case, once a 6 LoWPAN payload arrives at the buffer, immediately a WLAN packet is generated and transmitted using the CSMA/CA protocol without the BB algorithm. In the third scenario, 6 LoWPAN payloads are aggregated to generate a WLAN packet using a preset aggregation factor. Once a WLAN packet is generated, the BB signal is used to transmit the packet in an interference-free mode. Figure 10 shows the packet success rate of the three networking scenarios and demonstrates the marked differences in PSR values among these three scenarios. The PSR of the heterogeneous network with the BB signaling (scenario 3) algorithm decreases gradually with the offered load; where the PSR drops from 97% to 53%. The PSR value of the heterogeneous network (scenario 2) without the BB algorithm drops from 75% to 30% with the increasing load. The homogeneous network (scenario 1) experiences the lowest PSR whose value reduces from 48% to 8%. The PSR value for these networks depends on the total number of collisions and network congestion levels. Figure 11 illustrates the link-by-link PSR rate of the homogeneous network. The plot shows that the PSR value progressively decreases from the end devices mainly due to collisions and network congestion. As more packets are accumulated in the routers, the network throughput decreases due to congestion and collisions. Although we have used a staggered link design to avoid collisions between neighboring 6 LoWPAN clusters in the multi-hop network, the congestion level increases non-linearly with the load due to the use of the CSMA/CA protocol. For limiting the paper size we are not describing the staggered link design which can be found in [28]. Figure 10: Packet success rate (PSR) for three simulation scenarios for different offered load conditions. Comparing the PSR values of the heterogeneous network with and without the BB signaling algorithm shows that the BB signaling algorithm significantly increases the throughput. Improved performance is achieved due to the absence of inter-network collisions and lower network congestion. The heterogeneous network has the advantage of fewer hops, as well as a high data rate MFDRR to the data sink link. In this simulation, a 6 Mbits/s MFDRR to the data sink link was used. Figure 12 shows packet loss rates for all network simulation scenarios. Packets are dropped when the retransmission threshold is exceeded after multiple collisions; in this simulation, a retransmission threshold of four was used. For the homogeneous network, the packet drop rate is always high and remains steady due to lower network capacity and congestion; recall this scenario also experiences the lowest PSR.