Research On Indoor LED Visible Light Communication System Based On MIMO-SCMA Technology

With the rapid development of the mobile communication industry,the requirements for the transmission rate and quality of communication data are becoming higher and higher.Traditional radio frequency communication has the problem of limited spectrum resources.Visible light communication has become an important supplementary technology for 5G due to its advantages such as greenness,high security,and abundant frequency band resources.This thesis builds a visible light communication system,and on this basis,introduces new code modulation technologys,which effectively enhances the VLC's bit error rate performance and system capacity to meet the needs of future high-speed,large-scale connections and low-latency5G communication scenarios.The main research contents and results of this thesis include:?1?The basic principle and system composition of indoor visible light communication are described.Based on the link model and channel model,the visible light communication system is modeled and analyzed and the experimental system of visible light communication is built.?2?The sparse code division multiple access technology is applied to visible light communication.For the special modulation of VLC,the complex signal is converted into a real signal using mapping.Using Huawei's codebook and MPA decoding algorithm,a simulation scheme is designed.Simulation results show that when SCMA is used in VLC,six users share four physical resource blocks,and the system capacity is increased by 50%.However,due to the non-orthogonality of the codebook and the interference of ambient light in the VLC channel,its bit error rate performance is reduced.When the bit error rate is 10^-3,the signal-to-noise ratio increases compared to the AWGN channel about 17d B.At the same time,an offline experiment based on SCMA is designed.?3?Multi-input multi-output technology is applied to visible light communication,mainly including space-time coding technology and receiving diversity technology.For the layout problem of MIMO indoor light sources,consider the standard deviation of the illuminance and the average signal-to-noise ratio of the system including direct links and primary reflection links.On the premise of meeting the international standard illumination,a function combining illumination uniformity and signal-to-noise ratio is established.When the room model is 4m×4m×4m,the symmetrical distribution of 4 groups of LED arrays is adopted.Simulation results show that the power consumption of the MIMO structure is reduced by 17.4%compared with SISO.When the distance between the LED array and the roof edge is 1m,and the distance between each lamp bead in the LED array is 0.025m,it is the optimal light source layout.At this time,the overall performance of VLC is optimal.?4?It is proposed to combine SCMA technology and MIMO technology in visible light communication.Based on the above optimal MIMO light source layout,a MIMO-SCMA VLC system model is built and simulated.Introduce STBC transmit diversity and receive diversity technologies into the system,and compare the error performance of different space-time coding matrices,different receive diversity technologies,and different numbers of received diversity.Simulation results show that the maximum combining ratio technology?MRC?has the best reception performance.With the increase in the number of transmitting and receiving ends,the bit error rate performance of the VLC system has greatly improved.When the bit error rate is10^-2 compared with the SISO-SCMA system,the MIMO-SCMA system with 4 transmissions and 4 receptions has a gain of about 12d B.The MIMO-SCMA VLC system improves the stability of the transmitted information while increasing the system capacity.