Adaptive Resource Assignment for Multi-user VLC based on Pre-Distorted ADO-OFDM

VLC needs to support multiuser connectivity due to the popularization of 5G, it is an important issue to improve the performance of multi-user VLC systems. Among several methods have been proposed for intensity modulation/direct detection (IM/DD) VLC. One is asymmetrically clipped and DC biased optical OFDM (ADO-OFDM), which combines DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM). ADO-OFDM has many excellent points to compare with DCO-OFDM. However, it is difficult to implement in a multi-user environment due to inter-user interference from clipping noise. Thus we focus on Pre-Distorted ADO-OFDM, which can suppress the inter-user interference caused by clipping noise with pre-distortion signals. Thanks to this, we are able to implement ADO-OFDM in a multi-user VLC environment. In addition, this paper introduces a scheme combining Hadamard code spreading and adaptive modulation order into a multi-user ADO-OFDM system to achieve an improved throughput performance over a multi-user DCO-OFDM system.