# SINR-Based MCS Level Adaptation in CSMA/CA Wireless Networks to Embrace IoT Devices
## 4 Demonstrations Using Simulations
### Multiple Users in Multiple Cells  
To demonstrate the behavior of the proposed algorithm in an environment with multiple cells (i.e., multiple APs) and multiple users, in Figure 5, we show a Voronoi diagram [33] where 10 APs and 10 wireless devices are located in an area of \(2000\times 2000\) m. The APs and the wireless devices in the figure are randomly distributed in the area using two independent homogeneous PPPs of the same density. The solid arrow lines in the figure show connectivities between APs and wireless devices. The lines also represent the CBR traffic flows from APs to their associated wireless devices. In the figure, notice that some APs (e.g., AP5, AP6, and AP9) do not have any wireless devices associated with them. However, for demonstration purposes, we deliberately change the serving AP for WD10 from AP8 to AP0 and change that for WD13 from AP0 to AP2. As shown with the dashed arrow line in the figure, WD10 moves from its initial location of \((681,240)\) to its final location of \((1800,1800)\) during 10 s of simulation time. AP0 is located at the same position as in Figure 2.  
Figure 4: (**a**) changes of the MCS level in AP0 for WD1; (**b**) changes of the achieved throughputs obtained by WD1. In Figure 6a,b, we show the changes of the received signal strengths and SNRs of ACK frames from WD10 arrived at AP0, respectively, during 10 s of simulation time. The received signal strengths of packets are calculated using Equation (1) by AP0 for every received ACK frame from WD10. The SNRs of ACK frames are calculated using Equation (2) by ignoring interference (i.e., the indicator function is set to 0) when ACK frames from WD10 are received (Note that the SNRs can be obtained by simply deducting the thermal noise power (i.e., \(-\)126 dBW) from the received signal strengths). In Figure 6b, we also show the minimum SINR requirements of the four MCS levels in Table 1 with dashed lines (Note that the minimum SINR requirements are the same as the minimum SNR requirements if no interference is assumed). By comparing the simulation results in Figure 6b with the changes of SINRs of ACK frames shown in Figure 3a, we can see that they are similar to each other. This is because WD10 is moving along the same path and its serving access point (AP0) is located at the same position in both Figures 2 and 5. The simulation results in Figure 6 also show that AP0 receives less ACK frames from WD10 than in Figure 3a. This is because some of the packets sent by AP0 to WD10 are not received successfully by  
Figure 5: Voronoi diagram of multiple cells and multiple users. Figure 6: (a) changes of received signal strengths of ACK frames; (b) changes of SNRs of ACK frames. WD10 due to the interference by other nodes in Figure 5 (Note that the proposed algorithm utilizes the absence of ACK frames as shown in Algorithm 1). However, notice that, with the received signal strengths or SNRs of ACK frames, it is hard to capture the intensity of interference in multi-cell, multi-user environments. In Figure 7a,b, we show the changes of SINRs of ACK frames from WD10 received at AP0 and the moving averaged SINRs calculated by AP0 for WD10 using the SINRs of the ACK frames, respectively, during 10 s of simulation time. The graphs in Figure 7 show that the SINRs and the moving averaged SINRs of ACK frames experience fluctuations caused by interfering packets from other nodes while WD10 moves. However, from the results, we can see that the moving averaged SINRs fluctuate less than the instantaneous SINRs as expected. We also show the changes of the MCS level in AP0 for WD10 and the changes of the achieved throughputs by WD10 during 10 s of simulation time in Figure 8a,b, respectively. By comparing the graphs of the moving averaged SINRs in Figure 7b with the changes of the MCS level in Figure 8a, we can see that the MCS level at AP0 for WD10 reflects the changes of the moving averaged SINRs for WD10. Figure 8: (**a**) changes of the MCS level in AP0 for WD10; (**b**) changes of the achieved throughputs obtained by WD10.