# Ambient LED Light Noise Reduction Using Adaptive Differential Equalization in Li-Fi Wireless Link
## 1 Introduction  
The multimedia services of the 5G network have begun since 2019, and a 6G network, which is expected to increase 100 times more than the transmission rate of the 5G network, will be implemented soon [1; 2; 3]. It is easy to predict that the transmission capacity of the wired network will increase in line with the establishment of the 6G wireless network [4; 5; 6]. In such a wired/wireless network environment, a massive Internet of things (IoT) service in which a large number of mobile devices and smart sensors are connected is being partially operated and is evolving further [7; 8; 9]. It is important that these massive IoT services are implemented in various environments in order to spread to various fields and stabilize quickly. In most environments, it is possible to implement mobile services using RF(radio frequency) signals. However, it is necessary to use other types of signals in spaces where RF signals are not sufficiently transmitted or difficult to use. In particular, it may be difficult to use an RF signal-based wireless service in both an industrial facility where high security is required and a medical facility where there is no electromagnetic interference. In addition, since it is expected that RF frequency resources with a frequency band of up to 300 GHz will be gradually depleted in the future, it is expected that auxiliary services through other transmission media will be needed in order to fully support these IoT services. Among these auxiliary technologies, a light fidelity (Li-Fi) transmission technology, which transmits data wirelessly using light emitted from a white light-emitting diode (LED), is capable of operating IoT services within a special environment such as a hospital and national security facilities [10; 11]. In the past 20 years, Li-Fi related research has shown great growth and potential [12]. Until now, the Li-Fi transmission system has generally shown atransmission rate of about 1 Gb/s at a wireless transmission length of 10 m in a building environment [13; 14; 15; 16]. In general, the transmission rate is determined by the signal-to-noise ratio (SNR) of the received signal. Furthermore, the important thing is that the SNR is determined according to the ambient noise [17]. In the case of Li-Fi, the cause of reducing transmission performance is known as noise generated by ambient light sources [18; 19; 20; 21]. There are two types of noise generated from ambient light sources. The first is a shot noise generated by a random change in the number of photons incident on the optical receiver. The second is interference noise that changes with time generated by an electronic circuit driving a light source [19; 20]. The impact of noise from the above-mentioned ambient light sources on Li-Fi transmission performance has been reported in [18; 20]. [PERSON] et al. have studied the impact of interference noise generated from fluorescent and incandescent lamps on the transmission performance of optical signals in infrared wireless links. However, the effect of contemporary white light sources such as white LEDs, dimmable LEDs, and energy-saving bulbs on the visible light communication channel is not covered [18]. [PERSON]. [PERSON] analyzed the RF spectrum of interference noise generated from various artificial light sources in indoor wireless optical links based on the IR range, including tungsten bulbs, IR headphones, TV remotes, and non-visual daylight [22]. [PERSON] analyzed the shot and interference noise generated from white LEDs, dimmable LEDs, and energy-saving light bulbs, which are recently used as lighting, and implemented relevant modeling [20]. However, a few techniques have been proposed to reduce shot and interference noise from these ambient light sources [23; 24; 25]. [PERSON] designed and implemented a high-frequency filter based on a DC offset remover circuit to reduce interference noise from ambient light sources [23]. However, no data transmission experiment was performed, and only the noise reduction was experimentally verified.