# Indoor Wavelet OFDM VLC-MIMO System: Performance Evaluation
## 1 Introduction  
### State of the Art Regarding FFT-OFDM and DWT-OFDM  
White light-emitting diodes (LEDs) are considered a successful technology for the next decade. Due to low energy consumption, high performance, and high durability, white LEDs can be used in a large variety of communication systems to increase performance and minimize costs. Visible Light Communication (VLC) has the ability to carry data by modulating light. This limits the extra cost of VLC techniques which use LEDs. Additionally, these benefits enable people to access the Internet through the same visible light. Consequently, the demand for VLC has increased rapidly with the increase of LED power. Major research was undertaken to establish high data indoor VLC systems [1]. VLC has an uncontrolled spectrum, precisely from 400 to 700 \(\upmu\)m, providing a huge bandwidth of communication that leads to high data rates. The VLC spectrum in adjacent communication cells can be reused. Intensity modulation/direct detection (IM/DD) is added to VLC systems, where the transmit messages can be modulated by light without taking phase information into account. Besides, it can be directly sensed by the detector. The essential properties of light made VLC more effective, more power-efficient because the LEDs are used in illumination and simultaneously are used in communication. Moreover, the VLC is more secure, does not need license and has the ability to deliver high data rates compared to RF communication. Hence, the proposed system has the above-mentioned properties and consequently has superiority over radio frequency systems. Several VLC studies are involved in efficient modulation schemes like Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) to raise the data rate by maximizing the bandwidth. MIMO is used in many new technologies to increase data rate capacity and spectral efficiency [2; 3; 4]. MIMO systems contain multiple transmitter antennas and multiple receiver antennas. There are many types of MIMO techniques that are used for transmitting data over an indoor optical wireless channel to provide high link capacity and spectral efficiency, including spatial modulation (SM) and spatial multiplexing (SMP) [5]. The bandwidth limitation of LEDs is considered as one of the big challenges of achieving high efficiency in VLC systems [6]. Optical MIMO could be willing to offer a large data transmission rate by transferring data in the transponder and spatial spectrum [7]. Different pre-frequency domain equalization (Pre-FDE) mechanisms could be reported to improve LEDs bandwidth, such as analog Pre-FDE [6], digital Pre-FDE [8] in addition to the adaptive digital Pre-FDE [9]. VLC OFDM MIMO technique requires a detector for separating data from specific LEDs. Generally, there are two types of receivers with different concentrator designs that can be used in VLC-MIMO systems to increase VLC systems capacity [10]. These are categorized into two major optical categories; one of them is referred to imaging receiver (ImR) and the other is called a non-imaging receiver (NImR). The space division multiplexing VLC (SDM-VLC) technique is a promising technique for high speed indoor wireless communication. [PERSON] et al. [11] suggested two protocols to boost an indoor SDM-VLC contour. There are two VLC link configurations: line-of-sight (LoS) which is mostly used in commercial systems and non-line-of-sight (Non-LoS) [12]. Thanks to OFDM for its high spectral efficiency, high capacity, and its ability to resolve multi-path channels. However, OFDM suffers from sensitivity to carrier frequency offset and synchronization errors. There is a lot of work that has been done to develop this, such as the short-time Fourier transform (STFT), the wavelet transform (WT), and wavelet packets (WP). The traditional OFDM techniques utilize inverse fast Fourier transform/fast Fourier transform (IFFT/FFT) systems at the transceiver for data multiplexing to simultaneously relay them through subcarrier numbers.