# A Novel 4 \(\times\) 1 MISO-VLC System with FBMC-OQAM Downlink Signals
## 1 Introduction  
With the advent of the 5G era, various types of access services are rapidly developing. There is a growing demand for high-speed, low-power consumption, and secure-access systems. Currently, indoor short-range wireless communication technologies include traditional Wi-Fi, Bluetooth, infrared communication, and wireless telephone communication. However, they all have disadvantages, such as slow communication speed, high power consumption, and low security. Visible-light communication (VLC) is an emerging indoor technology that has captured the attention of researchers because of its low cost, high data rates, frequency-free operation, and high security [1; 2; 3]. It uses LEDs as the light source and the primary device for transmitting data signals, while also serving as indoor lighting. One of the most common problems faced by the VLC application is the limitation of access bandwidth [4].  
In recent years, a few researchers have proposed a variety of techniques to enhance the transmission rate and frequency-band utilization in the indoor access system. One of the most common methods is using the multicarrier modulation technique, which divides high-speed data streams into multiple low-speed sub-streams. This method effectively improves spectral efficiency [5; 6; 7; 8]. It has been widely applied in many optical access systems, such as multi-carrier modulation passive optical network systems, optical wireless communication systems, and indoor visible-light communication systems [9; 10; 11]. However, the traditional multi-carrier modulation technique, such as orthogonal frequency division multiplexing (OFDM), adds a cyclic prefix (CP) to effectively reduce the impact of inter-symbol interference (ISI). Nevertheless, it reduces the data transmission rate and leadsto the wastage of spectrum resources [12; 13]. In addition, using rectangular functions as filters in OFDM systems results in large and slow-decaying side lobes, which easily cause interference between subcarriers [14]. In [15], we propose and design a RoF system for downlink 4/16/64 QAM-OFDM signals. Although this scheme provides a flexible access method, it wastes bandwidth resources and leads to a certain degree of out-of-band leakage. In [16], although the FBMC system based on frequency-domain expansion can solve the problem of spectrum resource waste caused by the OFDM system, its implementation complexity is high. To resolve the above issues, we propose the integration scheme of filter bank multicarrier (FBMC) and offset quadrature amplitude modulation (OQAM) techniques based on a multiphase network in VLC systems to effectively reduce out-of-band leakage and inter-symbol interference. In addition, to further enhance the downlink bandwidth capacity, 4 \(\times\) 1 multiple-input-single-output (MISO) access channels are introduced.  
In this paper, a novel VLC system with 4 \(\times\) 1 MISO FBMC-OQAM downlink signals is proposed. We analyze the indoor optical intensity and power-distribution characteristics when four LEDs are used as light sources and modulation signal transmitters. Meanwhile, we test the bit-error-rate (BER) performance of traditional OFDM and FBMC-OQAM signals. The results show that FBMC-OQAM signals have better visible-light signal-reception performance than OFDM signals, and the 4 \(\times\) 1 MISO system used has a larger downlink bandwidth capacity than the 1 \(\times\) 1 single-input-single-output (SISO) system. Compared to using conventional OFDM access signals, we use FBMC-OQAM downlink signals as access signals. One advantage of using this scheme is that there is less out-of-band leakage in signal transmission, resulting in higher frequency-band utilization of the system. Moreover, using this access signal can resist the negative impact of frequency offset. Based on this research work, we will consider introducing some machine-learning algorithms in artificial intelligence (AI) technology to further improve the transmission and reception performance of FBMC-OQAM access signals in the future.