High-Efficient and Low-Cost Biased Multilevel Modulation Technique for IM/DD-Based VLP Systems

In recent times, several indoor positioning systems have been actively studied for environments where satellite signals are typically degraded and disrupted. Among them, visible light positioning (VLP) has attracted wide interest owing to its advantages of high energy efficiency, broad bandwidth availability, and electromagnetic interference rejection. The performance of a VLP system highly depends on its ability to distinguish between individual signals for each channel. In this paper, we propose a new optical signal modulation technique suitable for intensity-modulation/direct-detection (IM/DD)-based VLP systems. Furthermore, we present major considerations and some constraints for evaluating the modulation technique, and show the superiority of the proposed method through comparison with various conventional schemes. The comparion simulations reported that the proposed scheme improves signal-to-noise ratio (SNR) by more than 4.6 dB, reduces channel error by 3.5 times or more, and reduces peak-to-average power ratio (PAPR) by more than 6 dB excluding time division multiple access (TDMA). The performance was also verified by the positioning experiment using an field-programmable gate array (FPGA) and simple transmission/reception hardware in a 2.0 m x 0.8 m x 1.6 m region.