Research On Multi-level Modulation Technology Of Non-empty Indoor Optical Wireless Communication System

Visible Light Communication?VLC?is a novel technique,and it modulate electrical signals to visible light emitted by a light-emitting diode?LED?for transmission.This technology is a new type of wireless optical communication technology with both lighting and communication functions.It has the a lot of advantages,such as wide modulation bandwidth,no electromagnetic radiation and strong transmission at high speed.It can be widely used in indoor wireless signal access.Therefore,it is technically feasible and necessary to study the multi-level modulation format in the visible light access system for an indoor environment.This paper analyzes the modulation/demodulation principle of phase-shift keying modulation,quadrature amplitude modulation and orthogonal frequency division multiplexing?OFDM?modulated signals.It also analyzes the indoor visible light communication link channel model by numerical simulation experiments.The transmission application characteristics of additive white Gaussian noise channel and Rayleigh fading channel are explored.On this basis,the theoretical analysis,simulation research and some experiments on the application of multi-order modulation technology in non-empty indoor optical-borne wireless communication system are carried out.The main research results obtained are.For QAM/PSK-OFDM visible light access systems,the higher the signal-to-noise ratio is,the better the bit error rate performance of QAM/PSK-OFDM visible light access system will be s,the higher the modulation order of optical signals is?the more complex the system modulation?,the worse the bit error rate performance will be.Under the the same modulation order and condition of receiving signal-to-noise ratio,the BER code rate performance under the single-path Rayleigh fading channel is lower than that under the two-path Rayleigh fading channel.The indoor visible light system adopting the QAM-OFDM modulation format exhibits better performance than the system adopting the PSK-OFDM modulation format,which is embodied in the optimal BER performance.In addition,after comparative research,the8QAM-OFDM visible light signal can communicate at high speed in the single-path Rayleigh fading channel and the 2-path Rayleigh fading channel with a bit error rate lower than 10^-3,which not only has the best BER performance and higher band utilization after transmission through the channel,but also can achieve the high-speed stable transmission of signals.Finally,the feasibility of the simulation experiment was verified by illumination analysis.The visible channel in practical applications is often complicated,and the natural or human factors will affect visible light signal transmission.In addition,in the above simulation study,only the influence of Rayleigh scattering in the visible channel is considered.Therefore,the conclusions obtained in this paper are only considering the influence of Rayleigh channel.In the future,we will consider studying the channel model that is closer to reality,so that the research results are universal.