## 5 Conclusions  
In this work, we focus on indoor successive interference cancellation detection of optical uplink NOMA based on a fluorescent concentrator and downlink NOMA based on interference coefficient estimation. To investigate the performance of uplink NOMA, we consider fast-response fluorescent material to ensure a wide-coverage QD concentrator with an effective coverage area. Since NOMA has emerged as a promising candidate for practical band-limited multi-user VLC systems, our experiments demonstrate that the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Reference** & **Materials** & **Light Source** & \begin{tabular}{c} **Modulation** \\ **Scheme** \\ \end{tabular} & \
\begin{tabular}{c} **BER** \\ **(Mbps)** \\ \end{tabular} &
\begin{tabular}{c} **Data Rate** \\ **(Mbps)** \\ \end{tabular} & **Distance (m)** \\ \hline
[17] &
\begin{tabular}{c} CdZnSe/ZnSe\({}_{1.3}\) \\ \end{tabular} & QD blue \(\mu\)LEDs & NOMA & \(3.24\times 10^{-3}\) & 120 & 1.5 underwater \\ \hline
[18] & Cm6 and DCM &
\begin{tabular}{c} Blue and \\ green LEDs \\ \end{tabular} & OOK & \(4\times 10^{-3}\) & 12 & Not provided \\ \hline
[20] & Conjugated polymer & Blue LEDs & OFDM & \(<\)FEC & 400 & 0.5 air \\ \hline
[22] & Cm6 & White LEDs & OOK & \(<\)FEC & 32 & 0.3 air \\ \hline Our work & \
\begin{tabular}{c} Material-1 \\ (CdSe/ZnS) \\ \end{tabular} & Blue LD & NOMA & \(<\)FEC & 40 & 1.5 air \\ \hline Our work &
\begin{tabular}{c} Material-2 \\ (CsPbBr\({}_{3}\)-50) \\ \end{tabular} & Blue LD & NOMA & \(<\)FEC & 40 & 1.5 air \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Luminescent concentrator-based MISO VLC systems reported in different works. Figure 18: BERs at optimal power allocation ratio of 0.93 with interference estimation optimization. high-speed MISO NOMA-VLC is suitable for free-space channel communication. The QD concentrator-empowered MISO NOMA-VLC system can support an aggregate data rate of 40 Mbps by 2 LDs over a 1.5 m free-space distance, which ensures a unique connectivity approach for indoor IoT applications. Furthermore, the LS-SIC and LSTM-SIC algorithms are proposed in the downlink NOMA communication system. We also propose a recurrent neural network-based guided frequency interference coefficient estimation algorithm in the NOMA-VLC communication system, which improves the accuracy of interference estimation by introducing interference coefficients. Numerical results demonstrate that our proposed algorithm is effective in providing more accurate reconstruction and in weakening the influence of error propagation. Using NOMA technology, the power multiplexing and rate doubling for two users with the same link is achieved. Interesting work to be further explored is to study the power multiplexing and interference detection algorithms in uplink and downlink NOMA to further enhance the system capacity. In the future, we will focus on improving the channel capacity with fast-response material. Furthermore, we will investigate the feasibility of the QD-based MISO-NOMA VLC system in an underwater environment. In addition, in future work, we would like to extend the two-user case to a multiple-user case for the MIMO-NOMA VLC system. Conceptualization, S.A.H.M. and Y.L. ; methodology, S.A.H.M. and Y.L. ; formal analysis, S.A.H.M., Y.L. and Z.Z. ; investigation, S.A.H.M., Y.L., Z.Z. and A.A.; resources, Z.Z. and J.X. ; data curation, Y.L., Z.Z. and A.A.; writing--original draft preparation, S.A.H.M., Y.L., Z.Z. and J.X. ; writing--review and editing, S.A.H.M., Y.L., Z.Z., A.A. and J.X. ; visualization, Y.L., Z.Z. and J.X. ; supervision, J.X. ; project administration, J.X. ; funding acquisition, J.X. All authors have read and agreed to the published version of the manuscript. Supported by the Science Foundation of Donghai Laboratory (DH-202 XF01015); the National Natural Science Foundation of China (NSFC) (61971378); the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA2030208); and the Zhoushan-Zhejiang University Joint Research Project (2019 CS1081). Not applicable.