Adaptively Biased OFDM for IM/DD-Aided Optical Wireless Communication Systems

In direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM), a constant DC bias is introduced to render the bipolar signal non-negative. However, due to the inherent disadvantage of high peak-to-average power ratio (PAPR), the DC bias should be set to a relatively high level to suppress the clipping distortion, resulting in power inefficiency. Therefore, we conceive a novel adaptively biased optical OFDM (ABO-OFDM) for optical wireless communication (OWC), where the bias is dynamically optimized according to the signal magnitude to enhance the power efficiency. Meanwhile, the interference induced by the adaptive bias is placed on the reserved subcarriers, which avoids contaminating the legitimately transmitted information data. The implementation complexity of the ABO-OFDM transceiver is almost the same as asymmetrically clipped optical OFDM (ACO-OFDM), which is notably lower than the superimposed OFDM schemes. Numerical results have demonstrated that the proposed ABO-OFDM outperforms the conventional DCO-OFDM and ACO-OFDM in terms of power efficiency.