Application Of Non-orthogonal Multiple Access Technique In Indoor Visible Light Communication

Recently,motivated by the demand of applications in many special scenarios,visible light communication(VLC)has been emerged and rapidly developed.As in conventional wireless communication systems,VLC systems also need to provide multiple services to multiple users simultaneously.Therefore,multiple access strategies are crucial for VLC.A number of multiple access schemes have been proposed and widely adopted in VLC,including TDMA,CDMA,and OFDMA.However,these schemes only provide orthogonal access for users by means of different time slots,different frequency bands or different codes.However,by using the Non-Orthogonal Multiple Access(NOMA)technique,each user can be distinguished according to different power levels.Therefore,in NOMA systems,different users can convey data information within the same band as well as the same time,which means a higher utilization of communication resource.Firstly,this paper will investigate the basic principle of conventional indoor VLC systems and its channel modeling.The theory of NOMA will be introduced in detail.The research will be focused on the differences between OFDMA and NOMA schemes.Secondly,orthogonal frequency division multiplexing(OFDM)will be studied in VLC,thus the concept of optical OFDM.This paper will propose a novel scheme which combines NOMA with OFDM in VLC systems.The signal processing procedures of NOMA-OFDM in VLC uplink and downlink will be investigated,respectively.Successive interference cancellation(SIC)signal detection and the demodulation process in NOMA-OFDM VLC systems will be described.The influence of different channel estimation methods on optical NOMA-OFDM will be compared by numerical simulation,in terms of BER performance,SNR and power allocated ratio(PAR),respectively.In addition,the P-I characteristic and 3dB bandwidth of the LED used in this paper will be measured.Experimental results verify the feasibility of NOMA.Finally,a novel single carrier division multiplexing(SCFDM)based NOMA will be proposed to alleviate the high PAPR of NOMA-OFDM.Experiment results show that the PAPR amplitude of NOMA-SCFDM can be reduced by nearly 25% compared to NOMA-OFDM.Therefore,NOMA-SCFDM can achieve better BER performance than NOMA-OFDM.The constellations of NOMA-SCFDM and NOMA-OFDM will be further compared,respectively.