## 1 Introduction
Moreover, the authors in [20] proposed a nanopatterned fluorophore on a flexible matrix to achieve higher optical gain without affecting the FoV. They developed nanopatterned luminescent solar concentrators (LSCs) as VLC detectors to double the optical gain compared to conventional rectangular counterparts. This was also proposed to expand the receiving spectral range of conventional silicon (Si) photodetectors for high-speed solar-blind ultra-violet (UV) communication [21]. It validated the feasibility of a high-speed photoreceiver structure with a composition-tunable perovskite-based phosphor and a low-cost Si-based photodetector. Because of its wide FoV, the authors in [22] used a novel fluorescent concentrator in a \(2\times 2\) MIMO indoor VLC system providing a corresponding data rate of 32 Mbps through conventional on-off keying (OOK). It potentially enabled a high degree of spatial multiplexing to be attained through a simple receiver design with a wide FoV. However, most of the MIMO systems have limited data rates of 10-40 Mbps due to narrow bandwidths and low SNRs. In addition, multiple access technologies are classified into two categories, namely, orthogonal multiple access (OMA) and NOMA, according to different methods of resource division. NOMA technology divides time, code, and power dimensional resources in a non-orthogonal way. The resources are used to carry out data bearing-transmission, which can support flexible connectivity and allow for more efficient use with limited resources [23; 24]. To guarantee the effective utilization of resources and enhanced capacity of the access system, the NOMA-VLC system is designed in uplink and downlink data transmission. It can also offer several other enticing merits, such as high spectral efficiency, low transmission latency, and fast access with few interactions. However, there are certain challenges that limit the performance of NOMA-VLC systems such as the error propagation issue together with the nonlinear distortion caused by limited modulation bandwidth, multipath effect, and nonlinearity of optical sources, e.g., light-emitting diodes (LEDs). Moreover, securing accurate channel state information, which is essential to recover the non-orthogonally synthesized signal, is also challenging in NOMA-VLC systems. NOMA systems utilize the sophisticated successive interference cancellation (SIC) technique at the receiver side for data detection and multiple access interference suppression [25], which makes it possible to transmit information from multiple users overlapping on the same resource unit simultaneously. However, the multi-user data detection problem is a bottleneck for its further performance improvement. NOMA-VLC systems are prone to two major drawbacks, which are (i) availability of the line-of-sight (LOS) link, and (ii) overall complexity and overhead of the feedback mechanism involving channel quality. The drawback of the LOS link usually arises in VLC systems with mobile users due to random receiver orientations, which is highlighted in [26; 27; 28]. A novel metric for the access point adoption problem has been investigated for receivers with random orientations [29]. For a downlink VLC system, the handover issue is discussed in [30], where device rotation is kept into consideration to compute the handover probability. A generic mechanism for the random receiver orientation is designed in [31], where the square-channel gain distribution is computed analytically. The proposed mechanism applies to any prior distribution for the receiver orientation, which is further developed for multi-LED scenarios in [26]. The effect of titling the receiver angle on the BER performance is investigated in [32]. To overcome the challenge of the LOS link, a potential solution is to use QDs with wide FoVs, which is the key motivation of our work.