Experimental Evaluation of Hybrid PWM/DPAM Dimming Control Method for Digital Color Shift Keying Using RGB-LED Array

Abstract

In this work, we focus on digital color shift keying (DCSK), which is one of the modulation schemes of visible light communication (VLC). DCSK is an extended version of IEEE 802.15.7 color shift keying (CSK) that transmits data through the intensity ratios of red, green, and blue. Digitally controlled LED drivers of DCSK can also reduce the nonlinearity effect caused by the shift of the intensity amplitude. DCSK supports lighting functions such as flicker mitigation, target color control, and dimming control. For the dimming control method of DCSK, two schemes have been considered. One is pulse width modulation (PWM), which changes the duty cycle of optical transmit signals, and the other is digital pulse amplitude modulation (DPAM), which changes the number of red, green, and blue LEDs (RGB-LEDs) being used. In a previous analysis, a hybrid scheme of PWM and DPAM was proposed that could achieve both a wider dimming range than DPAM and a higher spectral efficiency than PWM. Unlike in theoretical analysis, with actual LED drivers, the dimming level (DL) obtained by PWM, DPAM, and hybrid PWM/DPAM may cause errors due to individual differences in the dimming method and LED drive current. In this work, we experimentally evaluate the accuracy of DL and the symbol error rate (SER) of DCSK with PWM, DPAM, and hybrid PWM/DPAM.