Coverage Performance Analysis Of User-Centric Indoor Visible Light Communication System

Visible light communication(VLC)is a technology that couples communication and lighting,it uses light-emitting diodes(LEDs)to provide green energy-saving lighting while modulating the visible light signal emitted by the LED to realize high-speed data transmission without occupying the existing radio frequency(RF)spectrum resources,reducing the burden on the existing wireless communication systems.However,visible light has the characteristics of line of sight(LOS)propagation,which makes it difficult to achieve full indoor coverage and satisfactory communication transmission services,transmitted power,the number of user equipments(UEs),multiple access scheme,will have certain impact on coverage performance.This paper proposes a user-centric quality of experience(QoE)probability coverage model based on non-orthogonal multiple access(NOMA)VLC system,and introduces QoE as the system performance evaluation index.The LED coverage performance in indoor multi-user scenarios is analyzed,and the effecting factors such as the number of UEs,transmitted power and power allocation methods on the coverage probability is studied.For the visible light multi-cell indoor communication system,the effect of three modulation methods,on-off keying(OOK),variable on-off keying(VOOK),multiple pulse position modulation(MPPM)along with the Boolean model and the Elfes model on coverage performance is discussed.The simulation results can provide a research basis for designing multiple access protocols and mobile handover technologies in the VLC network.The main work and innovations of this paper are as follows:1.This paper employs user-centric QoE as an evaluation index to propose the QoE probability coverage model.User-centric QoE is different from network-centric Quality of Service(QoS).QoS implements various basic technologies for business management from the perspective of the network,which only evaluates the performance of the network transmission layer,ignores the user's subjective factors,and cannot directly reflect the user's recognition of the service.While QoE is an evaluation method that takes the user's recognition as the standard,and considers the whole performance of the network from the user's perspective,which can better reflect the user's satisfaction with the network service.In this paper,QoE is used as asystem performance evaluation index to propose the QoE probability coverage model,which is defined as the LED coverage area projecting on the ground with a certain probability to make the UE have a satisfactory QoE.Based on the model,this paper analyzes the factors that affect the indoor VLC network coverage performance,such as multiple access scheme,number of UEs,and power allocation methods.The simulation results show that appropriate selection of relevant factors in specific scenarios will effectively improve the VLC systems coverage performance.2.NOMA scheme and user pairing strategy are utilized to analyze the indoor VLC network coverage performance.NOMA refers to the implementation of a non-orthogonal transmission strategy to simultaneously serves multiple UEs with different channel qualities on the same optical waveband,so that multiple UEs simultaneously share the entire available frequency and time resources.However,using NOMA to serve a large number of UEs at the same time will cause interference between co-channels,especially in smaller cells,that is,using NOMA in VLC system is also difficult to handle more UEs at the receiver side at the same time.The user pairing strategy is the combination of both orthogonal multiple access(OMA)and NOMA,pairs and processes UEs within the coverage area,which not only user fairness and system capacity are enhanced,but also a better balance between capacity and reliability is obtained.The simulation results demonstrate that the coverage preformance of the user pairing strategy which integrates OMA and NOMA is better than NOMA.3.This paper studies the effect of three modulation modes,OOK,VOOK,MPPM,and two coverage models,Boolean and Elfes,on the indoor VLC network coverage performance under multiple cells.According to the characteristics of the three modulation modes OOK,VOOK and MPPM,calculating the coverage rate in the case of multiple cells to analyze the related factors that affect the coverage performance,the impact of the Boolean and Elfes models on the coverage performance is also considered.The simulation results imply that the factors which affecting the coverage performance are linearly related to the multi-cell coverage rate.The results of the analysis provide the effective reference for further research on other problems of the indoor VLC system network,such as LED layout and network handover.