Research On Novel Multiple Access Technologies For Indoor High-speed Visible Light Communication Networks

Recent years,the semiconductor lighting technology,which is known as "green lighting",is developing rapidly.It uses the characters that semiconductor devices can flicker at high speed and transmit the modulated visible light signals in the free space.This makes that semiconductor light emitting diode(LED)lamps can be used to communicate when lighting and brings up a new way of broadband access for wireless communication.LED is one of the most promising green solid light sources.Compared with the traditional light source,LED light source has lower power consumption,smaller size,longer service life,green environmental protection and also has the advantages of shorter response time,better modulation performance etc...At the same time,the LED light source belongs to the frequency band without supervision registration,so it can alleviate the current shortage of the traditional wireless communication spectrum shortage.As long as the traditional incandescent lamps change to LED lights,we can make the lighting into a wireless network transmitter.The visible light communication technology based on LED lighting system is a new type of wireless optical communication method which uses visible light as carriers and is developing rapidly.However,the light emitting mechanism of white light LED makes its bandwidth limited,so the transmission rate of visible light communication network is not very high in the current application scenarios.The research on visible light communication is mainly focused on advanced modulation and equalization of signals,and has made a series of breakthroughs at present.With the further development of the research,the transmission rate will no longer be an obstacle to visible light communication.However,as a kind of wireless communication technology,the realization of multiple access is a severe ordeal during the popularity of development process.Because the scenario of visible light communication network is indoor,where there will be a lot of users,if each user is assigned a network access point,it will cause a lot of resources waste.Therefore,the implementation of multiple access is very important for the development of visible light communication.For this reason,this paper studies this problem,proposes a multiple access scheme for visible light networks and a power allocation scheme for non-orthogonal multiple access in visible light networks.· A multi access scheme for indoor high speed visible light communication based on color and code division is proposed.Considering the modulation bandwidth of RGB LED is larger than ordinary white LED,and CDMA has the advantages of strong anti-interference ability and high frequency spectrum utilization,we can combine RGB LED and CDMA technology to achieve multiple access optical system.The traditional orthogonal code sequence will be transformed to be used in visible light system.We also built an experiment platform.It realized when two users accessed under the red and blue LED transmitting lights,the total transmission rate could reach 32Mbps,and the error rate of each user was also lower than 3.8×10-3 and met basic communication requirements.· A dynamic power allocation scheme based on non-orthogonal multiple access(NOMA)is proposed.NOMA distinguishes users in the power domain,allocates different powers to different users,and uses the successive interference canceller(SIC)to demodulate the signals at the receiver.This is in agreement with the intensity modulation direct detection of visible light communication,so it can be used in visible light systems.Although the jamming information is introduced into the NOMA signal,and the receiver becomes much complicated,the spectrum efficiency can be improved.In this paper,the transmission rate of the user and the total throughput were analyzed.Currently,most power allocation schemes are static power allocation,and the power between users is a fixed ratio.In the indoor visible light network,movement of users would lead to the change of channel state information,so,using the static power allocation scheme could reduce the throughput.This paper proposed a dynamic power allocation scheme based on the channel state information.The simulation results showed that when the number of users was 6,the average bit error rate of the network was below 3.8e-3 by using the dynamic power allocation scheme,and the average bit error rate of the network was close to 0.01 when the static power allocation scheme with the allocation ratio of 0.4 and 0.3 were adopted.In terms of throughput,the dynamic power allocation scheme could improve the throughput by 20%.