Visible Light Modulation Technology Based On Space-time Combination

With the development of Visible Light Communication(VLC)technology,it has become a research hotspot to search for spectrum efficient short-distance transmission technology.In order to further improve transmission performance of indoor VLC system and make full use of spatial resources of VLC system,modulation technology based on space-time combination is studied in this thesis.By introducing spatial modulation into signal domain mixed modulation,high transmission efficiency and good power utilization can be obtained.The specific research work is as follows:The characteristics and modeling methods of indoor VLC transmission channel are studied,and the modeling and simulation results of indoor VLC transmission characteristics and channel fading characteristics are given.On the basis of the frequency spectrum efficient Carrierless amplitude-phase Modulation(CAP),power efficient Digital Pulse Interval Modulation(Digital Pulse Interval Modulation),DPIM and Spatial Modulation(SM)are summarized and analyzed.A modified hard decision detection algorithm is proposed for DPIM signal demodulation,and the performance of the algorithm is proved to be low complexity and close to maximum likelihood sequence detection(MLSD).Aiming at the joint modulation of VLC signal domain,a hybrid modulation scheme(CAP-DPIM)combining CAP and DPIM was proposed.By loading CAP signal onto DPIM timeslot pulse,the mixed modulation signal was constructed,which could obtain higher frequency spectrum and power utilization without reducing system reliability.And then by introducing Dual Header Pulse Interval Modulation(DHPIM),the system spectrum efficiency can be further improved.The theoretical expression of frame error rate for cap-DPIM/DHPIM hybrid modulation in visible light Gaussian channel and fading channel is derived respectively.The simulation results show that the hybrid modulation scheme has better bit error performance than the traditional single modulation at the same frequency band efficiency,and the diversity of modulation parameters can provide more flexible design choices.In order to utilize the spatial dimension of VLC,a space-time mixed modulation scheme was proposed.In the traditional SM modulation mode,the signal domain was driven by DC bias CAP(DCO-Cap)or DCO-Cap-DPIM signal,and the space-time mixed modulation transmission mode,namely SM-Cap-DPIM,was constructed.The spectrum efficiency,power utilization and error code performance of the system can be improved respectively,and a good compromise of the above performance can be obtained.In order to further utilize optical Spatial resources,GSM-CAP-DPIM hybrid Modulation is constructed by Generalised Spatial Modulation(GSM).The theoretical expressions of bit error rate(BER)and frame error rate(FRR)of space-time mixed modulation in visible light Gaussian channel are derived,and the influence of different space-time parameter selection on the performance of hybrid modulation system is explored.The accuracy of theoretical analysis and effectiveness of hybrid modulation implementation scheme are verified by simulation.