A Study on Hybrid PWM/PAM Dimming Control for Digital Color Shift Keying Using RGB-LED Array

摘要

In this paper, we consider a hybrid pulse width modulation / pulse amplitude modulation (PWM/PAM) system for digital color shift keying (DCSK) using RGB-LED array as a method of dimming support for visible light communication. DCSK is an optical intensity modulation scheme which transmits data imperceptibly through the variation of the color emitted by red, green and blue light emitting diodes. In DCSK, the variation can be represented by the digitally controlled "on-off" intensities of multiple RGB-LEDs. Generally, for the dimming control system of DCSK, two kinds of scheme are considered. One is the dimming control by PWM which changes the duty cycle of optical transmit signals, and the other is the dimming control by digitally controlled PAM with coordinated multiple RGB-LEDs usage. In the proposed system, PWM and PAM are combined to realize wider dimming range than PAM and higher spectral efficiency than PWM. We evaluate the error performances of the proposed system, DCSK with PWM and DCSK with PAM from simulation analysis under several measured light dimming levels. Consequently, the proposed system can improve the averaged received signal energy-to-noise ratio per symbol compared with DCSK with PWM and DCSK with PAM.