Separately transmitted optical OFDM for visible light communication with dimming control

In visible light communication (VLC) systems, optical orthogonal frequency division multiplexing (O-OFDM) is an appealing modulation. However, it suffers from high peak-to-average ratio (PAPR). When considering the dimming function, the high PAPR of O-OFDM signal limits its system performance. In this paper, a new scheme, termed separately transmitted optical OFDM (ST-OFDM), is proposed. In ST-OFDM, the PAPR of O-OFDM signals are effectively reduced by separating conventional direct current optical OFDM (DCO-OFDM) signal into two signals with much lower PAPR. The two separated signals are then simultaneously transmitted by different LEDs and constructively added in space. In this way, ST-OFDM does not alter the structure of the conventional OFDM receiver, which makes it easy to implement. The theoretical model for ST-OFDM is also studied, and the closed-form expression for effective SNR is obtained. In addition, in order to provide the dimming function, both the spatial dimming and analog dimming are used. Simulation results show that both the bit error rate (BER) and the spectral efficiency performance of the proposed ST-OFDM scheme are better than that of spatial dimmable OFDM (SD-OFDM) scheme and the conventional DCO-OFDM scheme.