Performance Research Of Outdoor Visible Light Communication In Atmospheric Channel

Visible light communication(VLC),as a new short-range wireless communication technology,has the advantages of rich frequency spectrum resources,strong antielectromagnetic interference ability,good confidentiality,convenient installation of free application band,and so on.Known as "the most sufficient green energy for one kilometer," it has rapidly become a research hotspot in the field of wireless optical communication.In addition to its applications to indoor high-speed communications,Outdoor visible light communication(OVLC)is affected by atmospheric turbulence,atmospheric attenuation and other factors,resulting in random changes in light intensity.The transmission performance of the system is seriously affected.In this paper,the outdoor visible light communication system is taken as the research object.The main research contents and results are summarized as follows:(1)Introduction of on-off key(OOK)critical control and orthogonal frequency division multiplexing orthogonal frequency division multiplexing(OFDM)to outdoor visible light communication systems.by adding a DC bias to the OFDM signal,At the same time,the detailed system block diagrams of two modulation techniques are given.In this paper,a model of gamma-gamma atmospheric channel with weak,medium and strong turbulence intensity is proposed,which is more in line with the actual turbulence situation and satisfies the weak,medium and strong turbulence intensity.Then the mathematical expressions of BER of OOK intensity modulation system and DCO-OFDM modulation system in gamma-gamma atmospheric turbulence channel are derived in detail.Finally,different modulation techniques are compared and analyzed by using Matlab tool to carry out numerical simulation.Error rate performance under different turbulence intensity,It is concluded that the DCO-OFDM subcarrier 4QAM-DCO-OFDM modulation system can ca effectively suppress the influence of atmospheric turbulence on the signal intensity.(2)In the visible light communication,4QAM-DCO-OFDM modulation optical signal is adopted to effectively suppress the effect of medium intensity atmospheric turbulence on the signal intensity,but OFDM belongs to the multi-carrier modulation system.Therefore,it inevitably brings about peak to average power ratio of optical signals.In order to reduce the PAPR of DCO-OFDM optical signals in visible light communication,the selective mapping(SLM)method and orthogonal cosine transform(DCT)are introduced into VLC.The principle of reducing PAPR is introduced and analyzed in detail.Considering the complexity of the system and the PAPR performance,the single method can not achieve the best results.In the end,a scheme of combining DCT with SLM method is put forward.The results show that DCTSLM method is helpful to decrease the PAPR of VLC-OFDM system.