The Research Of Adaptive Modulation Technique In Visible Light Communication System

With the wireless spectrum resources have becoming increasingly strained,visible light communication as a new type of wireless communications technology has came into being.It has two functions: illumination photosource and data communication.Compared with traditional wireless communication technology,it is featured by higher safety and reliability,non-electromagnetic noise,no electromagnetic spectrum authorization,and has the advantages of low communication cost,wide application field etc.It is an important expansion of the existing wireless communication technology,which has a great research potential.Traditional visible light communication technology generally uses single and fixed modulation mode.By analyzing visible light communication channel capacity and bit error rate curves in fixed modulation mode,it can find that the spectrum resources of visible light communication in this modulation mode can not be fully utilized,which restrict the data transmission rate of visible light communication.Therefore,based on the combination of orthogonal frequency division multiplexing technology and quadrature amplitude modulation,an adaptive modulation scheme was proposed to improve spectrum utilization rate of visible light communication system.Adaptive modulation obtains the state information of channel from channel estimation.It auto-adapted selects orthogonal amplitude modulation order according to the channel condition parameter.When the channel condition is good,it uses high order modulation improving the transmission rate in the process of communication;when the channel condition is poor,it adjusts the modulation mode with low order appropriate modulation modes.This paper mainly studies the effects of the visible light communication system of modulation system BER on transmission error rate and system frequency utilization rate,and proposes an adaptive modulation technology with the combination of quadrature amplitude modulation(QAM)and orthogonal frequency division multiplexing(OFDM)technology.Among them,quadrature amplitude modulation uses two independent baseband signals with the same carrier frequency of two orthogonal to each other by double-sideband suppressed-carrier modulation,which has the advantages of making full use of bandwidth,and strong anti-noise ability.Orthogonal frequency division multiplexing is a new type of multi carrier modulation and technology,which plays an important role in making sure the reliability and antimultipath effect data transmission.As various kinds of modulating techniques used,the signal will have a slight distortion.But equalization technologies can reduce the distortion of the demodulated signal.Therefore,using equalization technology can compensate signal distortion after the visible light communication signals going through the adaptive modulation.And finally through the analysis of simulation results,it is verified that the adaptive modulation scheme can make visible light communication system obtain high transmission rate and low packet error rate.