Implementation of dimming control scheme based on joint coding and modulation

To realize the function of flicker mitigation and dimming control in visible light communication system, a scheme of dimming control using joint coding modulation was proposed. In the scheme, the pulse width modulation (PWM) and the run length limited code (RLL) were adopted to match the duty cycle between the intra-frame and the inter-frame as well as to achieve the flicker mitigation respectively, and also the multi-pulse position modulation (MPPM) and the overlapped pulse position modulation (OPPM) were utilized to achieve light intensity adjustment for the purpose of improving the power efficiency or spectral efficiency. Theoretical analysis demonstrates that compared with a typical variable pulse position modulation (VPPM), the normalized power of the MPPM with a duty ratio of 0.9 can save 2.24 dB, and the spectrum utilization of the OPPM with a duty ratio of 0.5 is higher than 0.8 bps/Hz, which means OPPM has a higher spectrum efficiency. In addition, two modulation schemes based on the FPGA platform were implemented. The experimental results verify that the joint modulation dimming scheme can support the light source flicker mitigation and high-precision dimming control under the condition of ensuring the effective data transmission.