CitationTan J D, Wang Q, Wang Z C. Modified PTS-based PAPR reduction for ACO-OFDM in visible light communications. Sci China Inf Sci, 2015, : xxxxxx(3), doi: xxxxxxxxxxxxxx Dear editor,Visible light communication (VLC) has raised great interests since it supplements the unlicensed spectrum resource for ultra-high data rate transmission [1]. In order to resist time dispersion and guarantee the real-valued and non-negative constraint in VLC channel, DC-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM) techniques have been utilized in VLC systems [2]. Unlike DCO-OFDM which requires high DC bias [3], ACO-OFDM enjoys an advantage of high power efficiency and wide light emitting diodes (LED) dynamic region.The inherent peak-to-average power ratio (PAPR) issue of VLC OFDM leads to severe LED nonlinear distortion, which deteriorates the bit error rate (BER) performance [1]. Several methods reported in [4][5][6][7] have been investigated to reduce PAPR and mitigate LED nonlinear distortion of OFDM-based VLC systems. However, the costs such as data rate and performance loss induced by the above algorithms could not be neglected.As an effective method for PAPR reduction, partial transmit sequence (PTS) technique has an advantage of negligible performance degradation and no power increase. However, side information is required at the receiver, which results in data throughput loss [8]. In this letter, we propose a modified PTS-based PAPR reduction scheme for ACO-OFDM in VLC systems by exploiting the unoccupied subcarriers to transmit side information. A novel transmitter is presented to apply the PTS technique in ACO-OFDM VLC system without data throughput loss and an original power allocation method is also proposed to mitigate the power efficiency loss induced by the side information signals. Simulation results demonstrate that the proposed scheme achieves a significant PAPR reduction performance without data throughput loss as well as an improved BER performance when LED nonlinearity exists.Methodology. At the transmitter, the quadrature amplitude modulation (QAM) symbols X ACO of N -point ACO-OFDM block is divided into V disjoint clusters { X