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Excess signal transmission with dimming control pattern in indoor visible light communication systems

In traditional dimming control system using pulse width modulation (PWM) combined with M-QAM OFDM scheme, OFDM signal is only transmitted during “on” period. To guarantee the communication quality, reduction of duty cycle will cause increased symbol rate or added LED power. This means system BER performance degradation and power consumption. In order to solve the defects of the traditional dimming scheme, we propose a new dimming control scheme in indoor visible light communication, which combines OFDM signal and multi-pulse position modulation (MPPM) light pulse well with each other. By means of dividing traditional PWM pulses into MPPM pulses with the same duty cycle, the pattern effect of MPPM pulses is utilized, which makes excess signal transmission possible. Simulation results show that when reducing the brightness of LED the achievable symbol rate using dimming control patterns is not higher than the traditional PWM scheme and the LED power is also reduced, which satisfies both system reliability and energy effectiveness under constant high data rate and BER less than 10-3.