Theory And Technology Of Visible Light Communication Based On Spatial Modulation

Visible light communications(VLC)not only combines the two functions of illumination and communication,but also has a lot of advantages such as rich spectrum resources,high security,no electromagnetic radiation as well as the properties of energy conservation and environmental protection.Optical spatial modulation(OSM)combines spatial modulation(SM)with VLC,which has attracted extensive attention of the academic and industrial circles.In OSM,the transmitter is light-emitting diodes(LEDs)and the receiver is photodiodes(PDs).At any given time instant,only one transmitter is activated to transmit information while the others are idle.Thus,SM can avoid the inter-channel interference(ICI)and synchronization problems in multi-input multi-output(MIMO)technology.This paper focuses on the theoretical research and analysis,and studies the VLC system based on spatial modulation.The main contents of this paper are as follows:Firstly,some spatial modulation techniques,including space shift keying(SSK),generalized space shift keying(GSSK),spatial modulation(SM),are analyzed.The system model,basic principle and detection algorithm of the above three techniques are studied and compared in detail.Secondly,the average signal error rate(SER)of the VLC system based on SM is investigated.According to the basic principle of SM,the average SER analysis is divided into two aspects:one is the error probability of the spatial domain and the other is the error probability of the signal domain when the estimation of the spatial domain is correct.Based on the two aspects,the theoretical expression of the average SER is derived.By comparing the theoretical value with the simulation value,it is found that the derived theoretical expression of the average SER and the simulation can reach a good agreement in high signal to noise ratio(SNR),which can verify the accuracy of the deduced expression of the SER.Thirdly,the application of constellation optimization in VLC system is studied.The constellation optimization aims to obtain the appropriate modulation order for each LED by using the channel state information(CSI)at transmitters.Two different ways of constellation optimization are introduced in detail.The first one is to use the derived theoretical expression of the average SER and minimize the SER to obtain the optimal modulation order combination.The second one is to maximize the minimum Euclidean distance to optimize the constellation orders.The two constellation optimization methods are simulated and the results show that the performance of VLC system which uses the constellation optimization is better?At last,the bit mapping scheme for SM based VLC with an arbitrary number of transmitters is investigated.An adaptive bit mapping scheme is proposed which is described in detail into three steps.The first step is the bit mapping in signal domain and the second one is the bit mapping in signal domain.Finally,the CSI is taken into consideration to obtain adaptive bit mapping.Simulation results on bit error rate performance are provided and substantiate that the adaptive bit mapping scheme can achieve better performance.