## 1 Introduction  
Most wireless protocols and technologies are currently based on the use of the Radio Frequency (RF) spectrum, such as 5G, WiFi, Bluetooth, etc. The current overuse of the spectrum and projected growth of users and data rates [1, 2] have led to an increasing interest on finding new wireless technologies to either complement or replace current wireless networks. One of the most promising alternatives in the recent years has been Visible Light Communication (VLC) technology [3, 4, 5, 6]. VLC uses the visible light spectrum (from 380 nm to 780 nm) and takes advantage of the widespread use of High-Brightness LEDs (HB-LEDs) in Solid-State Lighting (SSL). The capability of HB-LEDs to rapidly change the light emitted makes them suitable for incorporating communication capability in SSL systems. To use HB-LEDs in VLC systems, the VLC driver needs to do two things: the bias tasks (i.e., lighting) and the communication tasks. In a traditional lighting application based on HB-LEDs, the driver needs to perform the bias task by maintaining a desired Q-point (i.e., bias point). This means that the HB-LED driver controls the average illumination level and counteracts any temperature-related effects on the HB-LEDs. The temperature behaviour of the HB-LED and its control is illustrated in Figure 1. This figure shows the effect of temperature on the HB-LED in the I-V-Flux characteristic at two different temperatures, T\({}_{1}\) and T\({}_{2}\), where T\({}_{2}\) is greater than T\({}_{1}\). The most notable effect is observed in the threshold voltage, making the V-I characteristic of the HB-LED shift to lower voltages as the temperature rises. Even though the temperature also affects the I-Flux characteristic, the effects are negligible and have less impact on communication performance than the threshold voltage shift [7; 8; 9]. The voltage applied to the HB-LED is v\({}_{0}\)(t) Its average value, V\({}_{\text{bias}}\)(T), must be controlled to keep the average value of io(t), b\({}_{\text{bias}}\), constant and controlled. Note that the temperature dependency is shown by the (T) at the end of the names. The bias task is normally performed by means of a feedback loop implemented throughout the HB-LED driver. Lighting-level control (i.e., dimming) and temperature-effect mitigation are also expected in VLC applications, necessitating average output current control. The communication tasks are what make the traditional HB-LED driver into a VLC driver. To implement communication capability, a high frequency communication signal must be applied around the Q-point. This is also depicted in Figure 1, with an example of a communication. To minimize the distortion, the HB-LED must work in its linear region, avoiding the vicinity of the threshold voltage V\({}_{\text{th}}\)(T). Another limit is the maximum current of the HB-LED, I\({}_{\text{max}}\). This current defines a maximum voltage V\({}_{\text{max}}\)(T), which depends on the temperature, as shown in Figure 1. Therefore, the working voltage region of the HB-LED, as a load of the VLC driver is derived: V\({}_{\Omega}\) = V\({}_{\text{max}}\)(T) - V\({}_{\text{th}}\)(T). It is worth noting that V\({}_{\Omega}\) is not temperature-dependent, which this work will take full advantage of. The peak-to-peak amplitude of the communication signal, V\({}_{\text{pp}}\), and its average value, V\({}_{\text{bias}}\)(T), are selected following a certain criteria. In this case, the criterion is maximizing the communication signal amplitude, making  
\[V_{pp}=V_{\Omega}, \tag{1}\]  
This need means that the Q-point is fixed in the middle of the linear region, leading to  
\[V_{bias}(T)=V_{th}(T)+\frac{V_{\Omega}}{2}, \tag{2}\]  
Figure 1: Temperature effects on the I-V-Flux characteristic of the HB-LED. and  
\[I_{bias}=\frac{I_{max}}{2}. \tag{3}\]  
It is important to note that the maximization of the communication signal amplitude (i.e., to maximize the communication distance range) constrains the value of the Q-point, (i.e., the value of \(\rm I_{bias}\)).