## 1 Introduction  
In recent years, visible light communication (VLC) has attracted a lot of interest as a novel technology in short-range wireless communication [1; 2; 3; 4; 5]. VLC is one of the free-space optics research fields that use visible light between 375 and 780 nm as the variant in data communication [6; 7; 8]. VLC is a particularly advantageous communication method, as it can offer a high data rate and is environmentally friendly, nonhazardous, reliable, and particularly secure because of line-of-sight propagation, which makes VLC a potential alternative to radio frequency (RF) technology for wireless communication. Light-emitting diodes (LEDs) have been employed not only for lighting, but also utilized as transmitters in most VLC systems because of their high performance, energy efficient properties, low cost and fast response relative to the traditional incandescent and fluorescent lamps [9]. In addition, image sensors [10; 11; 12; 13; 14] or photodiodes (PDs) [15; 16; 17] are typically used as receivers. Our experiment was conducted using an LED-PD. With PD and complex modulation methods, such as quadrature amplitude modulation (QAM), orthogonal frequency-division multiplexing (OFDM) or a combination of QAM and OFDM, the speed in the VLC system was demonstrated to reach as high as a few tens of gigabits per second [18; 19]. Nevertheless, the gigabit per second speed has only been conducted in laboratory environment with offline modulation and demodulation (signal processing with Matlab). For wider applications, we must consider VLC in real-time operating systems and variable signal-to-noise ratio (SNR) conditions. On the PD-receiver side, there are three main sources of noise for indoor VLC systems, such as ambient noise, shot noise, and electrical pre-amplifier noise (thermal noise). The noises have a distortion effect on the received signal. The offset voltage is generated by noise and amplified along with the original signal in the data demodulating process. If the offset voltage is considerably large, amplifier saturation may occur because of the circuit limitations. Therefore, a low SNR is a challenge that must be overcome before implementing and deploying indoor VLC systems on a larger scale. Typically, in conventional methods, a high-pass filter (HPF) is adapted to block direct current (DC) voltage signals affected by noise [20; 21]. However, contrary to RF, with the On-Off Keying (OOK) modulation, the signals received by a photo-detector are DC voltages as square waveforms; therefore, if we use an HPF, the phase and amplitude responses of the circuit change significantly and produce a signal known as a differentiator. In addition, transmissions are unstable at the beginning because of the relaxation time effect, which even causes data loss [22]. Therefore, for the OOK modulation with this method, in theory, it requires SNR = 13.6 dB for it to be error-free [9]. As [PERSON] et al. reported [20], an SNR of 5.4 dB was required to achieve a bit error rate (BER) of \(5\times 10^{-4}\). With coding for the balance of 0 bits and 1 bits, a BER of \(10^{-6}\) needs an SNR of 2.5 dB [3]. Thus, under the low-SNR condition, the HFP does not have a good performance. With this motivation in mind, we proposed a novel VLC receiver design to solve the problem. More specifically, the average-voltage tracking (AVT) circuit is implemented at the receiving circuit to detect the average voltage value produced by noise and then to eliminate this voltage to demodulate the original data. In this paper, we will discuss the SNR analysis and the performance enhancement technique for the receiver at a low SNR. The rest of this paper is organized as follows. In Section 2, the impact of light interference on the receiver and the impact of the HPF on the performance of the VLC systems are discussed, following which a novel receiver design is proposed. In Section 3, the experimental setup is presented along with the results, and the advantages of the receiver design are analyzed. Finally, conclusions are provided in Section 4.