Interleaved Binary Demodulation Technique for Low-Cost and Fast-Response Visible Light Positioning Using Palindromic Sequences

Abstract

Recent advancements in visible light positioning (VLP) systems have continuously improved positioning accuracy, extending the application fields in Internet-of-things and factory automation technologies. However, their multiplexing and modulation methods still limit the applicability of VLP systems. Multi-level driving and sensing techniques that use orthogonal frequencies increase the design complexity and are strictly constrained by the bandwidths of the illuminators and sensor devices. Existing binary modulations require additional amendments to the code synchronization. In addition, real-time VLP is fundamentally affected by the distorted signal after orthogonal demultiplexing. Herein, we present a low-cost expansion of VLP that employs binary demodulation in code-division multiplexing. The proposed method utilizes DC-biased binary sequences using the palindromic variant of the Hadamard matrix, which provides perfectly orthogonal sequences while maintaining robustness to signal changes. The proposed demodulation regroups the signal collections of orthogonal sequences in an interleaved manner and determines the source signals via re-modulation. Compared with existing methods, it does not require extra-synchronizing structures and naturally compensates for dynamic sensor signals solely via binary operations. Following its implementation in an FPGA using commercial LEDs and a PIN-PD, we validated that the method achieved 48 dB SNR at a source-to-sensor distance of 10 m. The experiments showed that the proposed method eliminates 45–66% of signal errors and 33–43% of positional displacement during the sensor movements at 800 mm/s. Combined with trilateration, the static positioning error is 0.0158 m on average in 1.31, 0.91, 2.36 m, whereas the standard deviation of the raw position is limited to 0.0016 m.