## 2 Literature Survey  
Current research related to the indoor MIMO-VLC systems is presented in this section along with its advantages and limitations. The existing studies are given as follows:  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [16] presented the \(3\times 3\) MIMO-VLC system for enhancing the data rate. The pre-equalizer circuit is utilized to improve the LED transmitter bandwidth over VLC communications. Here, the channel matrix computation is simplified by a MIMO training sequence that depends on the time-multiplexing. The SNR decides the order of the modulation through the data transfer of VLC communications. Moreover, the spectral efficiency is improved by using OFDM. The phosphor LED utilized in the VLC communications has the narrow modulation bandwidth that creates the issues in high speed communication. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [17] developed the design of a linear transceiver for an indoor VLC with various LEDs. There are two different VLC systems that are analyzed, such as VLC with white LED and VLC with Red/Green/Blue (RGB) LEDs. The Additive White Gaussian Noise (AWGN) is considered as the noise model in this MIMO-VLC system. The lighting constraints are considered to jointly optimize the transmitter precoding and the offset. The lighting constraints are color illumination, optical power and non-negativeness. The MSE is reduced and transmission reliability is improved by formulating the non-convex transceiver design problems. Here, the communication performances are evaluated only under AWGN noise; it doesn't consider the shot and thermal noise for VLC communications. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [18] presented the design of the Mirror Diversity Receiver (MDR) in a \(2\times 2\) MIMO-VLC system. The modulation and demodulation considered in this \(2\times 2\) MIMO-VLC system is the ID-MM scheme. This MDR design minimizes the channel correlation by stopping the incoming light from one direction and enhancing the channel gain from the light obtained from the other direction. Besides, the channel gain is enhanced by positioning a double-sided mirror among the PD of the receiver. The channel gains of the MDR are analyzed in various locations of the receiver. Additionally, the channel capacity is improved by formulating the optimization problem based on the height of the mirrors. If PD receives more light from the LED, this results in intensity loss in the communication. [PERSON] and [PERSON] [19] analyzed the communication of the Distributed MIMO (D-MIMO)-relaying VLC scheme. This D-MIMO-relaying VLC scheme relays the optical signals from the MIMO VLC system to the secluded indoor area. Here, the AWGN is assumed as background noise to evaluate VLC communications. The channel capacity's tight upper bound is derived by utilizing the multiple access relay channels and sum rate. This work selects the optimum relay parameters such as distance among relays, amount of LED-PD pairs in a relay and height of relays. The selection of optimum relay parameters helps to achieve improved channel capacity through the MIMO-VLC communication. It fails to analyse the error rate during the data transmission. [PERSON] and [PERSON] [20] presented the MIMO in a VLC system for enhancing the BER and spectral efficiency of carrierless amplitude and phase modulation (CAP). The signals of CAP are generated by mapping the information bits into Quadrature Amplitude Modulation (QAM). The noise model considered in this MIMO CAP system is AWGN with double-sided power spectral density and zero mean. Moreover, each LED's emitted intensity is scaled with weighting factor to develop an effective precoding technique, namely the Power Factor Imbalance (PFI). The PFI-based precoding enhances the power efficiency and infuses the dissimilarity.