## 1 Introduction
\begin{table}
\begin{tabular}{l l} \hline \(N\) & Number of sub-carriers \\ \hline \(P_{max}\) & Maximum Optical Power \\ \hline \(I_{H}\) & Higher level current \\ \hline \(\Delta fm\) & Measurement bandwidth \\ \hline \(G(\overline{\mathbf{v}}_{c})\) & Gain of hemispherical concentrator \\ \hline \(\overline{\mathbf{v}}_{c}\) & Field of View \\ \hline \(\frac{\Delta\lambda}{2}\) & Spectral half-power bandwidth \\ \hline \(\lambda(\varphi;\hat{\varphi})\) & Shifting to shorter wavelength at non normal incidences \\ \hline \(n_{i}\) & Effective index of the input layer \\ \hline \(K\) & Number of users \\ \hline \(E_{i}\) & Incident energy in W/cm\({}^{2}\) \\ \hline \(y^{[k]}(t)\) & Received signal by user \(k\) at time \(t\) \\ \hline \(h^{[k]}(t)\) & Channel response vector between the \(M\)-th optical transmitter and user \(k\) at time \(t\) \\ \hline \(h^{[k]}_{LOS,m}\) & LoS channel component from optical AP \(m\)-th to user \(k\) \\ \hline \(h_{fe}(t)\) & Time-domain CIR for the front-end \\ \hline \(X[n]\) & Frequency-domain data in \(n\)-th sub-carrier \\ \hline \(H^{\text{SR}}\) & Reflection-based channel \\ \hline \(H^{\text{SD}}_{\text{NLoS}}\) & Channel from source to destination (NLoS component) \\ \hline \(H^{\text{RD}}_{\text{NLoS}}\) & Channel from relay to destination (NLoS component) \\ \hline \(t\) & Time instant \\ \hline \(\varphi^{[k]}_{m}\) & Incident angle for user \(k\) from AP \(m\) \\ \hline \(\gamma\) & Responsivity of PD \\ \hline \(\rho_{1}\) & Reflectivity of the main region \\ \hline \(\sigma^{2}_{z}\) & Variance of Gaussian noise \\ \(|\mathcal{F}|\) & Number of frequency sub-bands per color \\ \hline \(Q\) & Cluster size \\ \hline \end{tabular}
\end{table} 
Table 2: List of variables in this survey. \begin{table}
\begin{tabular}{l l} \hline \hline \(w^{[k]}\) & Precoding vector associated to user \(k\) \\ \hline \(\theta_{ep}\) & Resources allocated for channel estimation \\ \hline \(\theta_{fb}\) & Resources allocated for feedback \\ \hline \(L_{CP}\) & Number of samples of Cyclic Prefix \\ \hline \(I_{L}\) & Lower level current \\ \hline \(A_{PD}\) & Area of detection of PD \\ \hline \(T_{\phi}\) & Time for peak transmission \\ \hline \(\varphi\) & Generic angle of incidence \\ \hline \(\lambda_{0}\) & Wavelength of transmitted signal \\ \hline \(v\) & Lambertian radiation index \\ \hline \(n_{s}\) & Effective index of the sparcer layer \\ \hline \(M\) & Number of Access Points \\ \hline \(C^{[k]}\) & Lower bound capacity for user \(k\) \\ \hline \(d_{[m]}^{[k]}\) & Distance between \(m\)-th AP and user \(k\) \\ \hline \(h_{m}^{[k]}(t)\) & Channel response for user \(k\) from Access Point \(m\) at instant \(t\) \\ \hline \(h_{diff}\) & Contribution of the nLoS components \\ \hline \(h_{fs}(t)\) & Time-domain free-space channel component \\ \hline \(H_{fe}\) & Frequency-domain CIR for the front-end \\ \hline \(\hat{n}^{[k,p]}\) & Orientation vector of p-th PD of user k-th \\ \hline \(H_{\text{LoS}}^{\text{SD}}\) & Channel from source to destination (LoS component) \\ \hline \(H_{\text{LoS}}^{\text{RD}}\) & Channel from relay to destination (LoS component) \\ \hline \(s^{[k]}\) & Time-domain symbol to user \(k\) \\ \hline \(\phi_{m}^{[k]}\) & Irradiance angle for user \(k\) from AP \(m\) \\ \hline \(\phi_{1/2}\) & Radiation semi-angle \\ \hline \(A_{\text{room}}\) & Area of the room \\ \hline \(\rho\) & Average reflectivity \\ \hline \(|\mathcal{C}|\) & Number of chip colors \\ \hline \(|\mathcal{G}|\) & Number of resources \\ \hline \(|\mathcal{S}|\) & Number of sector per cell \\ \hline \(P\) & Number of orthogonal Pilots \\ \hline \(\theta_{cd}\) & Resources allocated for coherence detection \\ \hline \(T_{S}\) & Symbol Period \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cont. (LED) that are present in the new lighting infrastructures and are being the replacement of previous lighting infrastructures due to their efficiency, which makes this technology low-cost and accessible everywhere.