# A Cooperative MAC Protocol for a M2M Heterogeneous Area Network
## 6 Simulation Model and Results
### Performance Analysis
The plot shows the significant improvement of the heterogeneous network performance when the BB signaling is used. As shown in the figure for scenario 3 with traffic load up to 1.5 packets/s/node, the overall packet loss rate remains very low. Compared to scenario 3, scenario 2 results in a much higher packet loss rate even at low network traffic loads. In the heterogeneous network when BB signaling is not used, then both intra and inter network collisions increase due to the mutual interference between data packets as well as interference between data and ACK packets. Results clearly show that packet loss rate increases exponentially with incoming traffic without the BB signaling. The proposed signaling mechanism offers significant QoS gain by using the cooperative MAC protocol, which allows the sharing of the transmission channel in a fair non-collision mode. In heterogeneous networks, one must consider the transmission ranges of the two different networks. The 802.11 transmitter covers a longer transmission range, as well as transmits at a higher transmission power, compared to 802.15.4 devices. Hence, any 802.11 packet could collide with a large number of end device packets when an omnidirectional antenna is used in the MFDRR. Use of the uniquely-proposed BB signaling completely eliminates the inter-network collisions. End-to-end delay plays a significant role in evaluating network performance. Figure 13 shows the end-to-end packet delay for the three simulation scenarios. The plot shows that the homogeneous network introduces very high packet delay due to the higher number of collisions and network congestion in a multi-hop network. Simulation results show that the largest component of the delay is the queuing delay at the router due to the congestion. Comparing the delay of the heterogeneous network, it can be seen that the heterogeneous network without the packet aggregation and the  
Figure 11: Link-by-link packet success rate of the simulated homogeneous network. BB signaling offers a lower delay at a low offered load, but the delay increases significantly as the load increases. One of the reasons for the lower delay is the shorter queuing delay because packet aggregation is not used. However, this advantage diminishes as the load increases due to high collision rates. On the other hand, the network with BB signaling maintains a stable end-to-end delay for all load conditions. At low traffic load, the delay is higher compared to scenario 2 due to the longer wait period caused by the BB signal propagation delay. Over the multihop network, the MFDR needs to wait several superframe periods to allow the BB packets to propagate to all end devices. On the other hand, at higher load, the scenario 3 delay is lower compared to scenario 2 due to absence of interdomain collisions. The end-to-end packet delay for an \(N\) hop network using the proposed heterogeneous network can be expressed by Equation (5) where \(T_{a,i}\) is the link access delay, \(T_{Q}\) is the queuing delay at the router, \(T_{agg}\) is the packet aggregation delay at the MFDRR, and \(T_{BB}\) is the blank burst delay which absorbs the WLAN packet transmission time. A higher packet arrival rate could increase the total access delay in the 6 LoWPAN clusters, but this delay is compensated for by the lower aggregation delay. Additionally, the BB signaling technique completely eliminates the inter-domain collisions; hence, performance at higher load is not affected by the co-existence issue. \[T_{ee}=\sum_{i=1}^{N}T_{a,i}+\sum_{i=1}^{N-1}T_{Q}+T_{agg}+T_{BB} \tag{5}\]  
Figure 14 shows the BB signaling frequency for different aggregation factors at the highest considered network traffic load. The results show that end devices are enforced into the sleep state between 3.6 times/s and 4 times/s when devices cannot transmit any packets. In this simulation, a 2.7 ms BB duration is used. In this case, end devices remain silent for a maximum of 10.8 ms/s.