| With the rapid development of Solid-State-Lighting technology,white Light-Emitting Diodes（LEDs）have been widely used.As an emerging wireless optical communication technology,white-LEDs-based visible light communication（VLC）has extensive application prospects because of the advantages of high-capacity,enhanced security,anti-electromagnetic interference,free spectrum application and green energy-saving.For indoor VLC systems,full-duplex mode,multipath interference,multi-users access interference and networking schemes are research hotspots.To solve these problems,a reasonable channel model is the basis.The traditional indoor VLC channel model focuses on the multipath effect and the immobile obstructions,however,few studies account for the shadowing resulting from the non-quantitative and randomly mobile obstructions.In practice,especially for the mobile multi-users communication systems nowadays,the random shadowing is ubiquitous and has great effect on the performance of communication.First of all,the research background and significance of indoor VLC systems are introduced in this paper,followed by its research status around the world.Then,the composition and rationale of indoor VLC systems are discussed primarily.In addition,the channel model of indoor VLC systems is analyzed emphatically in terms of the characteristics of optical sources,photodetectors,and communication channel.In order to quantify the shadowing resulting from the non-quantitative and randomly mobile obstructions,the Poisson process is introduced to describe the entrance of the mobile obstructions into indoor VLC systems,and the probability density function is introduced to characterize the size and the position of the obstructions,then a weighting function of the shadowing is proposed based on the principle of mathematic statistics and geometry.Furthermore,by combining the traditional indoor VLC channel model with our weighting function,we set up a new model to account for the shadowing resulting from the non-quantitative obstructions with random movement.In addition,the expressions of the received optical power,the horizontal illuminance and the impulse response are also given.The feasibility and superiority of the channel model is verified through the simulation.In the end,based on the proposed channel model,the distribution of the received optical power is simulated.In addition,focusing on the signal-noise ratio（SNR）and bit error rate（BER）,a simulation and analysis of the communication quality of the indoor VLC system,which utilizes the new channel model,is conducted.The results show that the existence of the mobile obstructions degrades the communication performance indeed.When the parameter of the Poisson process is ten per minute and the duration is five minutes,the average SNR decreases by2.5d B,and the distribution of the received optical power is not smooth any more,and so is the distribution of SNR.However,SNR on the entire receiving plane is higher than the threshold of 13.6d B,which results in a bit error rate below1?10-6.In other words,the indoor VLC system is still reliable.On a deeper level,this paper simulates the maximum available bandwidth in different communication environment based on the new channel model respectively.A simulation optimization of the LEDs’direction and the photodetectors’field of view is also presented focusing on the SNR’s coefficient of variation.The results show that the optimal values of the LEDs’elevation angle and the photodetectors’field of view are 90 degrees and 60 degrees respectively. |
