# Research Progress on Modulation Format Recognition Technology for Visible Light Communication  
[PERSON]  
1 Guangxi Key Laboratory of Functional Information Materials and Intelligent Information Processing, Nanning Normal University,  
data by modulating the brightness of LED light sources, enabling high-speed communication while simultaneously fulfilling lighting functions. This technology is particularly suitable for specialized coverage scenarios, including indoor positioning, vehicular communication, and underwater link, thus contributing to the realization of the 6G vision of \"integrated space-air-ground-sea\" communication coverage. VLC systems utilizing multi-color integrated LEDs have achieved transmission rates of 23.43 Gb/s [3], while underwater visible light communication (UVLC) systems can also facilitate the real-time transmission of 25 Gb/s in turbid waters [4], thereby demonstrating the technical potential of VLC. The performance of VLC systems is significantly influenced by the design and optimization of modulation techniques. Various modulation formats have been effectively applied in VLC systems, including on-off Keying (OOK) [5], pulse amplitude modulation (PAM) [6], quadrature amplitude modulation (QAM) [7], orthogonal frequency division multiplexing (OFDM) [8], etc. Each modulation format possesses distinct advantages and disadvantages regarding spectral efficiency, bandwidth capacity, noise resistance, and implementation complexity. While OOK is straightforward, it suffers from low spectral efficiency, whereas high-order QAM can enhance capacity but requires more rigorous channel equalization [9]. Consequently, it is essential to adopt adaptive modulation format-switching methods tailored to different application scenarios and complex channel environments, such as dynamically adjusting modulation orders or encoding methods to optimize transmission efficiency and enhance robustness under low signal-to-noise ratio (SNR) conditions. Modulation format recognition (MFR) technology serves as a core prerequisite for enabling adaptive demodulation. Its fundamental principle involves analyzing and processing received signals to capture underlying patterns or characteristics, which are then used to determine the signal's modulation format through threshold-based decision making or classifier-based judgments. Essentially, MFR is a form of pattern recognition. The basic principle of MFR technology in VLC is illustrated in Figure 1. Common signal analysis methods include likelihood functions and their maximum likelihood estimation, as well as feature construction based on time-frequency representations, constellation diagrams, and statistical measures, etc. In recent years, with the advancement of deep learning, automatic feature learning has become feasible. MFR technology provides the necessary foundation for subsequent adaptive demodulation, playing a pivotal role in optimizing the performance of VLC systems. It is noteworthy that MFR technology has been widely applied in traditional radio communication domains, such as spectrum sensing, cognitive radio [10], the Internet of Things (IoT) [11], and electronic warfare [12]. However, research on MFR in the VLC domain is still relatively limited. Therefore, advancing MFR technology research within the VLC field is crucial, as it can further enhance VLC communication capacity and spectral efficiency. A systematic review of the fundamental architecture, developmental trajectory, and unique challenges associated with modulation format recognition techniques in VLC systems will facilitate the identification of future research directions for this technology. Modulation format identification in current VLC systems grapples with challenges arising from channel complexities, including LED nonlinearity [13], multipath scattering, and background noise.