Research On Adaptive Spatial Modulation Based On Random Direction Model In Indoor Visible Light Communication System

With the growing maturity of light emitting diode(LED)manufacturing technology,visible light communication(VLC)can provide indoor lighting and communication,which has attracted extensive attention.In indoor environment,it is necessary to configure multiple white LED arrays as light sources to maintain sufficient illumination brightness.Therefore,multiple input multiple output(MIMO)technology is considered as one of the most potential applications in broadband high-speed transmission of indoor VLC system.However,inter channel interference(ICI)in the MIMO-VLC system might degrade the system performance.Therefore,it is important to eliminate the ICI in the MIMO-VLC system.In this work,we develop the adaptive spatial modulation scheme to eliminate ICI.In the traditional spatial modulation only one antenna is activated at a time to eliminate the interference between users,which however results in low spectral efficiency.In order to solve this problem,higher spectral efficiency can be achieved by adaptively selecting different modulation modes according to the received SNR feedback.Considering that the users can move around in the indoor environment in practice,we introduce the random direction mobility model for the user,and derives the probability density function(PDF)and cumulative distribution function(CDF)of the instantaneous signal-to-noise ratio.The simulation results show that the adaptive spatial modulation scheme can eliminate the ICI,improve the spectral efficiency of the system and achieve lower bit error rate.Moreover,in order to further make use of the channel state information from the receiver PD,a channel adaptive spatial modulation scheme is proposed,which can select the active antenna with the best channel gain through the feedback channel state information of the receiver,and further improve the bit error rate performance.Meanwhile,based on the random direction mobility model,the closed-form expression for the PDF and CDF formulas of the indoor SNR are derived.In addition,two adaptive mechanisms are developed according to received SNR.Simulation results show that thethe channel adaptive spatial modulation scheme can balance the trade-off between link robustness and spectral efficiency,and achieve a better system performance.