Research On OOK Visible Light Communication System With Low Flicker

Visible light communication（VLC）is superior to traditional radio frequency for its characteristics of high data rate,reliable security and unlicensed frequency bands.Therefore,visible light communication has become a research hotspot in the field of wireless communication.With the development of low-cost solid-state lighting devices,such as white light emitting diodes（White LEDs）,the system can realize low energy consumption lighting while transmitting data.However,the generation of modulated visible light signals causes variation to the LED intensity in intensity modulation/direct detection（IM/DD）transmission,which may cause flickering.Flicker may cause migraines,headaches,and even repetitive behavior among persons with autism.Therefore,flicking mitigation approaches must be applied for the visible light communication system that combines illumination and communication.While the optimization of the LED driving circuit and encoding can be employed to reduce flickering,bulb driving circuit dramatically increase the system cost and communication requirements are usually excluded.As to encoding methods,they will result in reduced data rate and hardware overhead,leading to performance bottlenecks.In this dissertation,we proposed a frequency-domain signal processing method to mitigate LED flickering.First,modulated signals are transformed into frequency domain by Fourier transform,where the low-frequency components（3-70Hz）are extracted,and inversely restored into time domain for transmission.Then,we study the influence of low-frequency components elimination on time-domain signal distortion,and explore the methods to reduce the distortion caused by low-frequency loss.Then,the interference models of different kinds of artificial light sources are analyzed,and noise and artificial light source interference are introduced into the channel to simulate the actual indoor environment.Finally,at the receiving end,the artificial light source is processed in the same way with the flicker processing method,which effectively reduces the channel interference and improves the communication quality.Simulation results show that by applying the proposed frequency-domain signal processing technique,performance of the VLC system is enhanced with the cancellation of interference while flicker is reduced significantly.Under the condition of a 13d B signal-to-noise（SNR）ratio,the bit error rate is below the 10^-3 threshold.