| Visible light communication is a new type of wireless communication method in which the information bits to be transmitted are coded and modulated,and the visible light of 385THZ-789THZ is used as a carrier to transmit information quickly by LED light.The technology needs to take into account illumination and communication in practical applications.Therefore,multi-LED array layout is needed to ensure illumination,and multi-array cooperative transmission coding technology is used to ensure communication effectiveness and reliability.In this paper,the light source layout,information space and time domain coding,cascade coding and other technologies are studied in depth.The specific work contents can be seen as follows:Firstly,the indoor room of 4m×4m×3m is taken as the experimental simulation model,the transmission channel model of visible light indoor is established by studying the luminous principle of LED lamp and referring to Lambert attenuation model.The illumination distribution and uniformity of indoor receiving plane are calculated numerically.It is concluded that the illumination uniformity of 4LED array layout is 15.7%higher than that of 3LED array under the same power consumption condition.Moreover,the illumination value of 4LED is distributed between 348.28-462.5 11x,which meets the international lighting standards of 300-1500Lx.In addition,the adaptive criterion for MIMO channel is established in a large area.The results show that the power uniformity,average signal-to-noise ratio(SNR)and channel capacity of the adaptive channel are increased by 13.75%,1.3032dB and 17 bit/s/11z respectively,and the average bit error rate(BER)of the adaptive channel is reduced by three orders of magnitude compared with that of the random channel.Secondly,on the premise of meeting the indoor lighting standards,space-time block coding is carried out for the transmition information bits,and the orthogonal coding matrices of different number of LED arrays are designed,and its system reliability is simulated experimentally.The experimental results show that space-time block coding can achieve high quality of information transmission,but its effectiveness is poor.In 4×4 MIMO system,when SNR? 8dB time,the error performance of the system is better than 10-6,but the spectral efficiency is only 1.5 bit/s/Hz.Thirdly,in order to improve the effectiveness of the system,spatial modulation coding is applied to transmition information bits,and the position information is used to carry the transmission bits to improve the information transmission rate.The experimental results show that the spectrum utilization of spatial modulation coding can reach 4 bit/S/Hz,which is 167%higher than that of space-time block coding.But its reliability is poor.In SNR=20dB time,the bit error rate of 4X4 MIMO system can only be achieved 10 4.Even if RS coding and spatial modulation coding with good selectivity are cascaded,the reliability of the system cannot be effectively guaranteed.Finally,combining the advantages of space-time block coding with spatial modulation coding in system reliability and validity,space-time block-spatial modulation cascade coding was designed for visible light MIMO communication.The experimental results show that STBC-SM concatenated coding system reliability is slightly reduced compared with the space-time block coding,but the spectrum utilization of the system can be increased by more than 50%.Compared with spatial modulation coding,the system efficiency is reduced by 25%,but the system reliability is improved by more than 11dB gain.Therefore,STBC-SM concatenated coding effectively alleviates the contradiction between transmission rate and transmission quality in visible light MIMO communication system. |
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