Research On Equalization Algorithm In Visible Light Communication System

Under the background of resources shortage,because of low power consumption,high reliability and high brightness,light emitting diodes(LED)will generally take place of the traditional light as an ideal recourse of the next generation.In particular,the response time of LED is very short,which can be used in the high-speed communication.Visible light communication(VLC)is the LED lighting combined with wireless communication technology,using LEDs rapid flashing light and shade of light to transmit signals,which provide a new short-range wireless communication method.Visible light communication has the advantages of having no electromagnetic interference,needing no applying for radio frequency spectrum,having big emission power and safe communication.But the multipath effect and frequency selective fading in the visible light communication will cause inter-symbol interference,which increases the bit error rate and affects the communication quality.Therefore,based on the analysis of visible light channel and OFDM modulation technology,this paper carries on corresponding research and simulation for the equalization technology of visible light communication system receiver.We proposes an equalization method using the minimum mean square error(MMSE)equalizer based on the frequency domain oversampling and symbol reconstruction techniques to eliminate the inter-symbol interference(ISI).Thus,we can effectively solve the inter-symbol interference caused by multipath fading and frequency selective fading caused by delay spread to improve the BER performance of the system and to achieve efficient reuse of source signals.In this paper,the main works are as following:1.Aiming at the inter-symbol interference caused by multipath propagation in the visible light wireless channel.This paper using equalizing technology to eliminate inter-symbol interference in the VLC system receiver.Through the analysis and comparison of zero-forcing equalization,MMSE equalization,decision feedback equalization and maximum likelihood sequence estimation,we can determine the equalization algorithm of this paper.The innovation point lies on introducing the frequency domain oversampling into the MMSE equalization technology,which avoids the spectrum aliasing caused by under-sampling.Through inserting protection interval,the sender signal and discrete channel impulse response of a linearconvolution transform into cyclic convolution,and then perform FFT transform into frequency domain to MMSE equalization.The received signal spectrum contains frequency domain channel matrix,we can effectively compensate and correct the channel distortion and improve the SNR performance of the VLC system.2.In the traditional system,generally the guard interval is inserted when the transmitter modulation,and in the receiver directly remove guard interval to reduce inter-symbol interference.In order to use the useful information of guard interval parts and make full use of the whole OFDM symbols,this paper reconstructs the received symbols including the guard interval parts.And then the reconstructed symbol are equalized by the proposed FDO MMSE equalization.Finally,the numerical analysis and experimental simulation prove that the MMSE equalization is based on FDO and symbols reconstruction have better BER performance than the traditional equalization algorithm,thus,increased the signal reuse of the VLC system.