## 3 System Model  
### VLC Heterogeneous Networking Architecture  
The VLC-RF heterogeneous network is depicted in Figure 1. It comprises multiple VLC access points (APs) and a single RF AP. Specifically, each VLC AP consists of several low-power light-emitting diodes (LEDs) interconnected with the control center through a power cable. On the other hand, the RF network is connected to a femto-base station, and a photosensitive receiver (PD) is situated at the user's end. RF communication signals span across the entire room, whereas individual VLC APs cover a smaller area. Each region covered by a VLC AP is referred to as an optical cell. Typically, VLC APs are deployed in an overlapping manner to fulfill both communication and lighting requirements. The main parameters covered in this paper are shown in Table 2.  
The VLC-RF network topology, depicted in Figure 2, leverages VLC as the downlink and RF as the complementary uplink and downlink solution to mitigate the instability of the VLC link uplink. Figure 1: Composition of VLC/RF HetNet. \begin{table}
\begin{tabular}{c c} \hline \hline
**Definition** & **Symbol** \\ \hline Lambert series & ML \\ DC channel gain & H \\ Receive power & R\({}_{p,c}\) \\ Signal-to-interference-plus-noise power ratio & SINR \\ Probability distribution of active RTAs & A \\ Probability distribution of specific types of RTA being active & Ac \\ QoE value for the video-based RTA & MOS\({}_{\text{video}}\) \\ QoE value for the VoIP-based RTA & MOS\({}_{\text{VoIP}}\) \\ QoE value for the web/text-based RTA & MOS\({}_{\text{Web}}\) \\ VLC link blocking probability & P\({}_{\text{block}}\) \\ Handover dwell time & T\({}_{\text{dwell}}\) \\ Comprehensive QoE values & QoE\({}_{\text{all}}\) \\ MT movement pause time & t\({}_{\text{w}}\) \\ MT movement duration & t \\ VLC link recovery rate & \(\beta\) \\ VLC average interruption duration & \(\gamma\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main parameters of this paper. Based on the half-power angle of the transmitter source, the Lambert series _ML_[14] can be calculated. The distribution of the DC channel gain \(H\) in this VLC architecture and the received power \(R_{p,c}\) in the indoor space can be found as follows:  
\[ML=\frac{\log_{10}2}{\log_{10}\cos\alpha}, \tag{1}\]  
\[H=\frac{(ML+1)+A\text{det}\times Ph^{ML+1}}{2\pi\times D^{2}}, \tag{2}\]  
\[R_{p,c}=P_{t}\times H\times T_{s}\times G_{cont}, \tag{3}\]  
where \(\alpha\) represents the half-power angle, _Adet_ denotes the area of the PD, \(D\) signifies the distance vector from the receiving plane to the LED light source, _Ph_ represents the angle vector representing the ratio of the height to the receiving plane and the distance vector \(D\), \(P_{t}\) denotes the emitted power, \(T_{s}\) represents the optical filter gain, and \(G_{cont}\) signifies the collector gain. In our experiment, we defined the half-power angle \(\alpha\) of the visible LED to be 50 degrees. The contact area _Adet_ of the photodetector surface was set to 0.0001. Additionally, we determined the angle vector _Ph_ to be the ratio of the light source's height \(h\) to the distance vector \(D\) between the light source and the receiving terminal. To provide context, we selected a room with a height of 3 m, and the height of the light source \(h\) was set to 1.5 m. Lastly, we configured the emission power of a single LED to be 250 watts. The received power distribution of the VLC APs depicted in Figure 3 can be determined using Equations (1)-(3). Figure 3 illustrates the received power distribution and coverage of nine VLC access points in an indoor space of \(6\times 6\times 3\) cubic meters. The obvious overlapping area between each VLC AP unit is caused by the coexistence of optical signals emitted by adjacent LED transmitters operating within the same optical wave bandwidth. Intrusion into this region causes the appearance of CCL, resulting in the degradation of VLC link performance.