## 5 Results
### Analysis  
#### 5.2.1 Normalized Throughput  
Figure 6 of the throughput analysis shows the performance of the multi-channel MAC (MMAC) protocols including the IEEE 802.11 as a base reference to compare with the single-channel protocol. It is clear that multi-channel MAC protocols (in the case of high-load scenarios) have significantly better throughput results than IEEE 802.11. The concurrency of data packets delivered by multi-channel MAC protocols explains the large margin of difference in performance.  
Figure 5: Simulation of IEEE 802.11, AMMAC, BiMMAC, and SA-MMAC.  
The figures compare the MMAC protocols in configurations of 3, 4, and 12 channels with the number of stations varying by steps of 2 nodes from 5 to 70 nodes. In Figure 6a, it can be seen that bidirectional MMAC (BiMMAC) outperforms the other protocols initially with a low number of stations in a three-channel network. However, once the number of stations increases, the performance decreases in BiMMAC as it saturates early while other protocols continue to improve the network throughput. This can be explained by the lack of control channel utilization for data transmissions by the BiMMAC protocol.  
Both of the proposed protocols, E-SA-MMAC and Max-E-SA-MMAC, outperformed all other protocols in this scenario. This can be explained by the fact that in high-load situations, where every station has a packet to send all of the time, maximizing each RTS-CTS handshake by using the bidirectional packet transfer has a significant impact on the number of successfully transmitted data packets. In the proposed protocols, this includes the use of a control channel to send data packets in both directions when other dedicated data channels are currently unavailable.  
In Figure 6b, the throughput pattern changes significantly. BiMMAC has a better throughput initially; however, with a larger number of stations, the proposed protocol is able to match BiMMAC as it saturates due to the lack of control channel utilization for data transmission. The multi-channel MAC protocols using data transfer on the control channel perform poorly due to the extra overhead and longer backoff timers in the control channel. The fairness index of the former protocol, BiMMAC, falls sharply after approximately 40 stations while E-SA-MMAC and Max-E-SA-MMAC remain more fair and consistent, which will be explained under JFI analysis.  
In Figure 6c, the multi-channel MAC protocols of 12 channels suffer similarly to 4 channels due to the extra overhead and longer backoff timers in the control channel as the station numbers increase. Therefore, protocols not using data transfers in the control channel are able to negotiate more promptly the RTS-CTS demands and keep their data  
Figure 6: Normalized throughput comparison of the two MMAC protocols, E-SA-MMAC and Max-E-SA-MMAC, versus others; (**a**) 3, (**b**) 4, and (**c**) 12 channels.  
channels occupied. After a certain point, however, it is expected that the number of stations contending in a dedicated control channel will eventually collide more often than successfully negotiating a data channel; thereby, we expect a decrease in the overall network throughput. This is a disadvantage of a dedicated control channel.