Hybrid diversity combined OFDM for LiFi

Orthogonal Frequency Division Multiplexing (OFDM) based light fidelity (LiFi) scheme provides the opportunity of high speed data transmission along with room illumination. This paper proposes Hybrid Diversity Combined OFDM (HDC-OFDM) for LiFi by combining the aspects of existing diversity-combined asymmetrically clipped optical OFDM (DACO-OFDM) and direct current biased optical OFDM (DCO-OFDM). The proposed HDC-OFDM has the benefits of power efficiency of DACO-OFDM and the dimming flexibility of DCO-OFDM. In HDC-OFDM transmitter, the lower subcarriers are modulated with DACO-OFDM, and the higher subcarriers with DCO-OFDM. In order to remove the impact of DCO-OFDM clipping noise on DACO-OFDM component, a high DC bias is applied on DCO-OFDM. On the other hand, the effect of DACO-OFDM clipping noise on DCO-OFDM element is reduced by estimating the DACO-OFDM clipping noise and then deducting the noise from the received signal of DCO-OFDM. In order to obtain the optimum bit error rate performance of HDC-OFDM, the percentage of subcarriers and the ratio of power levels for DACO-OFDM and DCO-OFDM components are varied. Simulation results show that the dimming flexible HDC-OFDM is 5 dB better than DCO-OFDM and only 1.5 dB inferior to DACO-OFDM in terms of optical power efficiency.