# SINR-Based MCS Level Adaptation in CSMA/CA Wireless Networks to Embrace IoT Devices
## 5 Performance Evaluation
### Fixed Number of Users  
In this section, we consider a scenario in which an increasing number of APs is introduced to serve a fixed number of wireless devices in CSMA/CA wireless networks. For this, we fix the number of wireless devices at 60 and increase the number of APs from 2 to 60 (i.e., 2, 4, 6, 10, 20, 30, 40, and 60) in a circular area with a radius of 1000 m.  
In Figure 14, we show the total throughputs achieved by the 60 wireless devices when different MCS levels are used for different PPP densities of APs for 2 s of simulation time. From the simulation results in the figure, we can see a pattern of higher total achieved throughputs with higher MCS levels and higher densities of APs, similarly to the results in Figure 9. The figure also shows the total  
Figure 12: Cumulative distributions of user throughputs.  
Figure 13: Fairness among user throughputs.  
throughputs achieved by the 60 wireless devices when all APs use the proposed automatic MCS level adaption algorithm. From the results, we can see that the 60 wireless devices achieve throughputs comparable to those achieved when all APs use the highest MCS level.  
In Figure 15, we show the retry limit ratios of all the packets sent by APs for 2 s of simulation time. Similarly to the results in Figure 10, the simulation results in Figure 15 also show that the proposed algorithm keeps the retry limit ratios comparable to those of the lowest MCS level in most cases. However, the simulation results in Figure 15 show higher retry limits ratios for low densities of APs compared to those in Figure 10. This is partly because many wireless devices are located outside the minimum distances (The minimum distances for the MCS levels can be calculated using the minimum SINR requirements of the MCS levels and the transmit power by assuming no interference.) for their MCS levels but inside the packet delivery ranges (i.e., power monitoring ranges) from their serving APs when only small numbers of APs exist in the relatively large area we simulated.  
In Figure 16, we show the throughput fairness among the 60 wireless devices with different MCS levels for different densities of APs. The results show that users achieve better fairness with the proposed algorithm than with the highest MCS level, similarly to the results in Figure 13.  
Figure 14: Total throughputs achieved by 60 wireless devices.  
Figure 15: Ratios of retry limits to sent packets.  
In Figure 19, we show the throughput fairness among the varying numbers of the wireless devices with different MCS levels when the number of APs is fixed at 30. The results in the figure show that users achieve better fairness with the proposed algorithm than with the highest MCS level, similarly to the results in Figures 13 and 16. However, the results show high fairness for low densities of users compared to the results in Figures 13 and 16. This is partly because, when there are only small numbers of wireless devices in the area we simulated, the APs associated with them are located relatively far from each other because of the PPP density of the APs.