## 1 Introduction
With VLC/LiFi, photodiodes receive LEDs' intensity based on the switching ON/OFF statuses from LEDs [12]. Refs [13; 14] implemented an ultra-high-speed pulse density modulation with extremely effective spectral properties using photodiodes. The multiple-input multiple-output (MIMO) technique is applied to transmit high-speed data with ultra-high-speed multi-channels for the VLC and LiFi system [15; 16]. Because a photodiode is used as the detector, the VLC and LiFi techniques have some disadvantages: the communication distance is short, making them compatible with indoor applications only. In an outdoor environment, the channel distortion obstructs the LED signal receiving photodiodes. However, the OCC system, which deploys an image sensor as the receiver, then the OCC can operate at a distance of up to 200 m [17]. [PERSON] et al. [18] presented the effect of image sensor types on OCC performance. When we use a global shutter camera for OCC system, the camera frame rate and packet rate must be considered carefully based on Nyquist's law. When we use a rolling shutter camera, the sampling rate should be considered based on the camera frame rate and the rolling shutter speed. The signal-to-noise ratio (SNR) should be considered to transmit data with long communication distance besides the focal length of the camera and exposure time. LiFi technology can now achieve a maximum communication distance of 10 m using a photodiode lens [19]. With OCC techniques, the MIMO technique can operate efficiently, resolving simultaneous links with multiple-light sources and the camera. However, with photodiodes, the MIMO technique is not feasible for multiple connections. Region of interest (RoI) signaling is a popular algorithm that can be applied to detect multi-light sources in an OCC system. The authors in [20] proposed the camera on-off keying (OOK) with a high data rate based on the rolling shutter effect. Still, this scheme has some drawbacks, including a limited communication distance and low performance. In [21], the authors proposed combining the orthogonal frequency-division multiplexing (OFDM) waveform and rolling shutter effect (rolling-OFDM) for a high-data-rate OCC system. Because intensity modulation/direct detection (IM/DD) modulation is deployed, the rolling-OFDM scheme requires suitable LED materials. A 2D-OFDM scheme based on the screen code with a high data rate is proposed by [PERSON] et al. [22]. However, its drawbacks include the large transmitter size, the short communication distance, and the expensive transmitter. In [23], the authors proposed a color intensity modulation-MIMO scheme to transmit data using a global shutter camera, which has a frame rate of 330 frames per second. Because it uses color intensity modulation, a maximum communication distance is just 1.4 m with high BER value (BER of \(10^{-1}\)). This scheme is just compatible with the global shutter camera, which is expensive and not widely used. Moreover, using colors to transmit data has some drawbacks compared with OOK schemes, such as the limited communication distance and high bit error rate. In [24], the authors proposed a rolling-shutter-based MIMO scheme with an LED matrix. This scheme can resolve the flicker effect, but there are some disadvantages: a short communication distance (1.4 m) and non-rotation support (such support is essential when using 2D-code for the OCC technique for IoT systems). In this paper, we will propose a monitoring system using an LED-array-based OCC system. The MIMO technique, RoI signaling, and matched filter are deployed to improve the performance of the OCC system. The rolling shutter camera and global shutter camera can easily to implement with the proposed scheme in the OCC system, especially in closed-circuit television (CCTV), which is commonly used; thus, this scheme can be applied to an environment monitoring system that uses CCTV as a receiver. The proposed approach can achieve a long communication distance of 20 m with a low bit error rate. The remainder of this paper is divided into four sections.