## 3 Numerical Results
### Effect of Available Emitted Power  
Considering that VLC performance highly depends on the power budget at the transmitter, the effect of available signal power on the performance for distinct emission beams-based drone VLC is evaluated for the representative side position of the receiver in this \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{4}{*}{**Position of Receiver**} & \multicolumn{2}{c}{\begin{tabular}{c} **Energy Efficiency of** \\ **Lambertian Drone VLC** \\ **(Bits/J/Hz)** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Energy Efficiency of Z-Power** \\ **Non-Lambertian Drone VLC** \\ **(Bits/J/Hz)** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Energy Efficiency of NSPW** \\ **Non-Lambertian Drone VLC** \\ **Non-Lambertian Drone VLC (Bits/J/Hz)** \\ \end{tabular} } \\ \cline{2-9}  & \begin{tabular}{c} **Receiver** \\ **Altitude of 0 m** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Altitude of** \\ **2.95 m** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Altitude of 0 m** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Altitude of** **0 m** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Altitude of** **0 m** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Altitude of** **0 m** \\ \end{tabular} & \begin{tabular}{c} **Receiver** \\ **Altitude of** **0 m** \\ \end{tabular} \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Side position \\ \end{tabular} } & Upward orientation & 13.04 & 0.002 & 11.31 & 4.99 & 11.53 (side position), 14.40 (side position 2) & 0.00 (side position) \\ \cline{2-9}  & Horizontal orientation & 12.82 & 6.40 & 11.11 & 15.64 & 11.32 (side position), 14.19 (side position 2) & 1.76 (side position) & 8.68 (side position 2) \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Corner position \\ \end{tabular} } & Upward orientation & 10.83 & 0.00 & 10.00 & 2.00 & 9.64 & 0.00 \\ \cline{1-1} \cline{2-9}  & Horizontal orientation & 11.62 & 3.40 & 10.79 & 13.60 & 10.43 & 0.55 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results summary of the drone altitude effect for Lambertian and non-Lambertian drone VLC. subsection. Generally speaking, the achievable rate of drone VLC under different light beam configurations is enhanced to some extent separately, as shown in Figure 6a. Particularly, for the situation of receiver altitude of 0.85 m, in other word, the receiver is located on the working plane of terrestrial receiver, the achievable rate performance of baseline Lambertian light beam configuration based drone VLC is enhanced to 13.03 Bits/Hz from the initial 6.38 Bits/Hz, when the total available signal power at the transmitter of drone VLC is increased to 1000 mW from the initial 100 mW. At the same time, the achievable rate performance metric is enhanced to 11.31 Bits/Hz, 11.53 Bits/Hz, and 14.40 Bits/Hz, from the initial 4.67 Bits/Hz, 4.89 Bits/Hz, and 7.76 Bits/Hz for the non-Lambertian Z-Power drone VLC, NSPW drone VLC (side position), and NSPW drone VLC (side position 2), respectively. It indicates that compared with the baseline Lambertian drone VLC, the achievable rate gain achieved by the NSPW drone VLC (side position 2) is varied to 1.37 Bits/Hz from the initial 1.38 Bits/Hz, when the total available signal power at the transmitter of drone VLC is increased to 1000 mW from the initial 100 mW, since the more intensive radiation is successfully projected to the side position 2 by the distinct asymmetric spatial emission characteristic of the non-Lambertian NSPW light beam. Similarly, for the situation of receiver altitude of 2.5 m, in other words, the receiver is located on the typical height of aerial receiver, the achievable rate performance of baseline Lambertian light beam configuration-based drone VLC is enhanced to 8.69 Bits/Hz from the initial 2.09 Bits/Hz, when the total available signal power at the transmitter of drone VLC is increased to 1000 mW from the initial 100 mW.