| Visible Light Communication(VLC)has become one of the most potential and promising technical means in the field of wireless communication in the future by virtue of ultra-wide spectrum resources,confidentiality and safety,and no electromagnetic interference.It is very popular in the application scenarios of perception integration.Sparse Code Multiple Access(SCMA)is a non-orthogonal multiple access(NOMA)technology based on the code domain.Compared with the existing NOMA technology,it has Excellent shaping coding gain and error-free propagation characteristics;compared with Orthogonal Frequency Division Multiple Access(OFDMA)schemes,it provides overload gains in the number of supported users and improves spectrum utilization.This paper focuses on the VLC system based on SCMA technology,the main contents are as follows:1.This paper first summarizes the application of multiple access technology and SCMA technology in VLC,and finds that there is very little research on SCMA technology in VLC.Then,the relevant theories of SCMA technology,LED characteristics and VLC system are introduced,and the volt-ampere characteristics,P-I characteristics and modulation bandwidth of multi-primary silicon-based LEDs are tested experimentally,which lays the foundation for the design of analog circuits and system modules in the following.2.Considering that it is very difficult to realize the real-time VLC system based on SCMA technology,this paper conducts research from three aspects: system design,frame synchronization and channel estimation.In terms of system design: propose a SCMA-OFDM structure model suitable for VLC,and analyze the characteristics of the structure,such as overload capability,robustness,and high spectrum efficiency;design and test VLC’s transceiver analog front-end link to ensure SCMA signal Transmit in the linear range of the VLC link;build an experimental platform based on Keysight equipment to analyze the transmission process of SCMA signals in VLC.Frame synchronization: compare and analyze the deficiencies of classic frame synchronization algorithms,and propose a system frame synchronization structure scheme based on ZC sequence.Channel estimation: In point-to-point VLC systems,channel estimation can compensate for the frequency-selective fading of the VLC channel on the one hand,and on the other hand can provide fixed input parameters required by the Message Passing Algorithm(MPA)in SCMA to improve reception terminal demodulation performance.Therefore,this paper proposes a channel estimation scheme based on pilots and reconstructed signals.Experiments show that this scheme significantly reduces the number of iterations of MPA at the receiving end under the same bit error rate performance,thereby reducing the detection complexity.3.After offline data processing and analysis on the experimental platform based on Keysight equipment,it is concluded that compared with the OFDMA scheme,the SCMA scheme in the VLC system improves the system capacity and performance at the expense of system bit error rate performance and at the cost of transmission distance.Therefore,in order to improve the overall performance of the system,this paper proposes an adaptive SCMA codebook allocation scheme.The scheme performs adaptive subcarrier grouping and SCMA codebook allocation according to the SNR of each subcarrier in the system bandwidth.The results show that the system rate and bit error rate are both obtained.improve.Finally,in the case of a transmission distance of 40 cm and below the limit of forward error correction,the data transmission rate of single primary color reaches 103.6Mbit/s,and parallel transmission of four primary colors achieves a total data transmission rate of412Mbit/s. |
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