Performance analysis of filtered ACO-OFDM for visible light communication systems

Abstract Visible light communication (VLC) is considered a promising complementary wireless technology that utilizes the unlicensed visible-light spectrum to support high-data-rate indoor communication. Orthogonal frequency-division multiplexing (OFDM) is widely adopted in VLC systems because of its high spectral efficiency and robustness against multipath effects. However, applying OFDM in intensity modulation/direct detection (IM/DD) VLC systems introduces inherent limitations, including high peak-to-average power ratio (PAPR), nonlinear distortion, and noticeable out-of-band (OOB) emissions resulting from rectangular pulse shaping and signal clipping. Asymmetrically clipped optical OFDM (ACO-OFDM) is used to ensure signal non-negativity and improve power efficiency, yet conventional ACO-OFDM still exhibits considerable OOB radiation, leading to spectral leakage and reduced spectral efficiency. This work investigates filtered ACO-OFDM techniques to suppress OOB emissions and improve bit error rate (BER) performance. A standard ACO-OFDM system is used as a reference and compared with raised-cosine (RCOS) windowing and subband finite-impulse-response (FIR) filtering combined with frequency-domain equalization. Simulation results over an IM/DD VLC channel with additive white Gaussian noise show that RCOS windowing provides limited OOB reduction with some BER degradation. In contrast, subband FIR filtering with minimum means square error (MMSE) equalization significantly improves spectral confinement and reduces BER from 6.0 × 10 −3 to 1.6 × 10 −4 at 14 dB.