MPPM dimming control for OFDM-based visible light communication systems

In conventional dimming control systems utilizing pulse width modulation (PWM) scheme, when duty cycle is reduced the receiver sensitivity requirement will be increased to keep data rate constant, which makes it hard to achieve error-free transmission. In this paper, we investigate a new mechanism of dimming control by reducing the transmitted data rate to adapt for receiver sensitivity. The mechanism can keep transmitted data rate maximum while satisfying communication quality. In order to compensate for the increased receiver sensitivity, we propose a new dimming control method combining adaptive M-QAM orthogonal frequency division multiplexing (OFDM) signals and multi-pulse position modulation (MPPM) light pulse. By utilizing the pattern effect of MPPM, excess information bits can be transmitted and thus both the symbol rate of M-QAM symbols and the receiver sensitivity requirement can be reduced, which makes error-free transmission at high data rate easier to be implemented.