Research On The Performance Of Multi-cell Multi-user Visible Light Communication System

With the current surge in the number of emerging services and wireless devices,the demand for wireless data traffic,especially indoor data traffic,is growing rapidly.However,the problem of the shortage of traditional radio frequency spectrum resources is becoming increasingly prominent,and it's no longer able to meet the increasing demand of data traffic in the future.In recent years,the new lighting technology represented by light-emitting diode(LED)is becoming increasingly popular.Visible light communication(VLC)technology provides new methods and ideas to meet the needs of indoor high-speed communication.However,due to the increasing number of indoor user equipment,the existing point-to-point visible light communication has been unable to meet the future high-speed communication requirements of indoor multi-user.Indoor visible light communication has the characteristics of short transmission distance,which makes the division of optical cells particularly important.At the same time,the division of optical cells can reuse space resources and improve the overall communication rate of the system.Multiple input multiple output(MIMO)technology and non-orthogonal multiple access(NOMA)technology,as the key technologies of 5G,have become the research Hotspots.These two technologies can improve the spectral efficiency of the system by spatial.reuse of spectrum resources in optical cells.This paper mainly focuses on the research of indoor multi-cell multi-user visible light communication system based on MIMO technology and NOMA technology.For an effective compact aperture-based angular diversity receiver in MIMO-VLC system,a large channel gain is added by adding a non-aperture receiving unit in the middle of the receiver without changing the size of the original receiver,which enhances the receiving ability of the receiver for the incident light in the vertical downward direction.The improved aperture-based angular diversity receiver is applied to the multi-cell multi-user MIMO-VLC system.In order to solve the problem that the close distance of multiple users may cause the rank of overall MIMO channel matrix to be not full,a photodetector selection(PDS)method based on the maximum minimum singular value(MMSV)criterion is considered.To solve the problem of how to eliminate inter-cell interference,the interference area is optimized by the tilt of LEDs firstly,and then two multi-cell implementation schems are discussed:the first is dynamic cell division,and the second is PDS to eliminate inter-cell interference.The simulation results show that both schemes can successfully eliminate the influence of inter-cell interference.A simple user grouping and pairing strategy in the NOMA VLC system is studied,and the advantages of this scheme over OMA scheme are analyzed in terms of system coverage probability and ergodic sum rate.This simple user grouping and pairing strategy is applied to multi-cell joint transmission system.In order to avoid the interference between overlapping and non-overlapping areas in the cell,two subcarrier allocation schemes are considered:one is area based subcarrier allocation,the other is user based subcarrier allocation.The performance of the two schemes is analyzed through simulation and compared with a NOMA multi-cell scheme with a frequency reuse factor of 2.The simulation results show that the user based subcarrier allocation scheme has the best performance,and the area based subcarrier allocation scheme performs better than the NOMA scheme with a frequency reuse factor of 2 for large number of users.