# An Admission Control Mechanism for 5G LWA
## 4 Numerical Results  
In this section, we present simulation results to validate the performance of the introduced LWA admission control algorithm in terms of system throughput. We use Matlab simulator in order to assess the network performance. The performance evaluation was conducted in an enterprise scenario of 200 m \(\times\) 200 m, where there is an LTE small cell eNB located at the center and a WLAN AP within it. The LTE and WLAN UEs are distributed uniformly within the coverage area of the LTE network and WLAN network, respectively. We adopted the IEEE 802.11 ax protocol with Request to Send/Clear to Send (RTS/CTS) access mechanism on 5 GHz in the simulations. Most simulation assumptions follow the 3 GPP recommendations. A detailed description of the simulation parameters is given in Table 2. In the simulation, we considered the conventional LTE-only and WLAN-only technology as benchmark technology (without LWA), with system throughput representing the aggregated downlink throughput of LTE and WLAN networks. We also compared our results with random transfer and LTE-W [20]. A number of the random LTE UEs were selected for LWA activation in a random transfer. UEs were selected for activation of LWA service on LTE-W based on the lowest LTE throughput. Figure 4a shows the system throughput for a variable number of WLAN-only UEs. We considered a scenario where the LTE network is crowded with LTE UEs, while the WLAN network is uncrowded. In this scenario, if we increase the number of WLAN-only UEs, we can see an increase in system throughput for the benchmark technology. This gain is contributed by the increase in utilization of the uncrowded WLAN system. However, this gain decreases as the number of WLAN UEs increases towards the saturation point of the system, as shown in Figure 4a. In the same figure, with LWA technologies, we considered offloading some of the LTE users to the WLAN. As discussed earlier in Section 3.3, the throughput gain in an LWA network constitutes the gain from the WLAN and LTE networks. The gain from the WLAN network is mainly due to utilization of the underloaded WLAN AP, whereas for the LTE network, it is from the remaining LTE UEs occupying more resources after offloading to the WLAN network. In other words, the per-user data rate of the remaining LTE users  
Figure 3: An overview of the LWA procedure. increases after offloading. However, as WLAN UEs increase, our algorithm limits the number of LTE users being offloaded to the WLAN, as shown in Figure 4b. Consequently, the system throughput gain achieved in both the WLAN and LTE networks decreases significantly. As a result, a decreasing trend in the overall throughput of the LWA network is observed. Figure 5 shows that the system throughput decreases as the number of LTE UEs increases. As discussed earlier, our algorithm limits the amount of LWA offloading based on the accepting capacity of the WLAN network. Hence, increasing LTE users above the WLAN capacity will cause a further increase in resource sharing among LTE users, i.e., the per-user data rate decreases. \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameters** & **Values** \\ \hline BS and AP distance & 50–100 m \\ Downlink bandwidth & 20 MHz \\ Noise power & \(-\)174 dBm \\ Path loss for cellular links & 15.3 + 37.6 log\({}_{10}\)(d)m \\ Path loss for unlicensed band & 15.3 + 50 log\({}_{10}\)(d)m \\ Transmission power of eNB & 36 dBm \\ Transmission power of AP & 24 dBm \\ Number of WLAN UEs & 2–10 \\ Number of LTE UEs & 20–40 \\ E[P] & 1500 bytes \\ CWmin & 16 \\ CWmax & 1024 \\ WLAN bit rate & 1 Gbps \\ PHY Header & 192 bits \\ MAC Header & 224 bits \\ Delay & 20 us \\ SIFS & 16 us \\ DIFS & 50 us \\ Slot time & 9 μs \\ ACK & 112 bits + PHY header \\ RTS & 160 bits + PHY header \\ CTS & 112 bits + PHY header \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. Figure 4: (**a**) System throughput with variable numbers of WLAN-only UEs; and (**b**) the number of LTE UEs transferred with variable numbers of WLAN-only UEs.