Research Of Visible Light Communication System Based On Modified OFDM

With the development of high-power LED(Light Emitting Diode),Visible Light Communications(VLC)technology has paid more and more attention.However,many of the current researches only move RF technology into the VLC,and do not combine the VLC channel characteristics to improve the corresponding technology.Based on this,this paper studies the channel model that is more suitable for the VLC system application environment.Based on the channel research,this paper studies and improves the OFDM(Orthogonal Frequency Division Multiplexing)technology which is more suitable for VLC systems.The improved modulation technique is more suitable for the intensity modulation/direct detection mode of the VLC system,which not only can effectively overcome the influence of multipath channels,but also has higher spectral efficiency.It can provide technical support for engineering implementation and application promotion of VLC systems.Firstly,based on the basic channel model and the indoor VLC application environment,this paper introduces the illuminating delay factor and multi-reflection path,and proposes a modified channel model that is more in line with the working condition of the VLC system.In order to compare the similarities and differences between the two,this paper carried out a simulation experiment.The simulation results show that the basic channel model underestimates the degree of multipath delay.After introducing the illuminance delay factor and multiple reflection paths,the multipath delay will be more severe.In order to overcome the multipath effects,this paper studies the DCO-OFDM(Direct Current biased optical OFDM)and ACO-OFDM for VLC systems.By adding special signal processing such as shunt,flip,and superposition,this paper proposed a modified ACOOFDM modulation scheme,which can effectively utilize each subcarrier resource and greatly improve the spectrum efficiency.Compared to the DCO-OFDM,the modified ACOOFDM has lower BER(Bit Error Rate).Compared to the ACO-OFDM,it's spectrum efficiency is doubled.Therefore,the modified ACO-OFDM performance is optimal.In order to verify the superiority of the modified ACO-OFDM,this paper constructs a VLC system,analyzes each module of the system,and tests the different modulation schemes in the system application.Experiments show that the 16-QAM(Quadrature Amplitude Modulation)system has a high BER(Bit Error Rate)and it is difficult to maintain normal networking.The BER of the DCO-OFDM system is slightly improved,but the network rate fluctuates drastically.ACO-OFDM and modified ACO-OFDM are adopted.Both have low BER and stable networking,but the modified ACO-OFDM has higher spectral efficiency and performs best in four modulations.