| With the continuous advancement of science and technology,it is an increasing demand for high-speed communications.The current communication transmission rate is far from meeting people's needs.At the same time,the shortage of spectrum resources has become more and more serious.All of this forced people to seek new ways to achieve transmission rates.With the rise of light emitting diode(LED)energy-saving lighting,Visible Light Communication(VLC)has gradually entered the people's field of vision.VLC can satisfy people's demand for high-speed communications while satisfying people's lighting needs.Moreover,VLC has attracted a large number of scientific researchers to conduct related research because of its huge spectrum resources,well confidentiality,no pollution and no interference with existing communication systems.On the other hand,as an efficient modulation technology in the field of moderm communications,Multiple Input Multiple Output(MIMO)technology can use multiple antennas simultaneously at the transmitter and receiver sides of the system to increase the spatial dimension of the system.MIMO technology can significantly improve system performance and transmission rate without increasing system bandwidth and power by multi-antenna transmission achieved spatial multiplexing and diversity gain.In order to improving the VLC performance,MIMO is an important technology.However,because the performance of MIMO technology is greatly affected by the channel correlation,and the light channel has high correlation,spatial modulation(SM)technology based on MIMO technology can effectively avoid inter-channel interference.SM becomes a key technology for realization of high-speed optical communications.In order to realize the efficient modulation design of VLC,the research work of this paper is as follows:First,we performed an optimization analysis of Direct-code Space Shift Keying(DC-SSK)in VLC.This modulation scheme makes full use of the spatial information of each activated LED and inactive LED to obtain a higher transmission rate.We add the mapping criteria of the analysis signal under the transmission power parameter and give the corresponding mapping table.One closed-form expression of the system error rate is given.The simulation results show rthat the scheme improves the system transmission rate and the accuracy of the theoretical expression.Secondly,based on the DC-SSK scheme,the influence of channel correlation on system performance is studied,and a high-complexity optimal power allocation scheme and a low-complexity suboptimal power distribution scheme are proposed to enable the system to have high channel correlation.Which make the system can obtain better system reliability while improving the transmission rate.Simulation analysis of the optimization scheme confirmed that the proposed power allocation scheme can effectively reduce the impact of high channel correlation on the system and improve system performance.At the same time,we also analyze the influence of LED position and half-power angle on the performance of DC-SSK system.The results showed that they have a strong guiding role for practical applications.Finally,we designed and optimized the Quad-LED Complex Spatial Modulation(QCSM)scheme in VLC to make full use of the space modulation technology and the unique color modulation technology in VLC to improve the transmission rate of the system.Through the spatial information and color information to achieve high-speed information transmission.We further simplify the traditional system bit error rate expression for system performance analysis to obtain more simple theoretical results.The simulation results confirm the correctness of the analysis results and verifies that the proposed scheme improves system performance and achieves high-speed transmission and system reliability.The influence of LED position and half-power angle on the performance of QCSM system is analyzed and the results are verified by simulation. |
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