| Intelligent reflecting surface(IRS)aided wireless communication technology is the frontier in B5G/6G research.IRS promises to reconfigure intelligently radio frequency(RF)wave propagation environment to meet requirements of efficiency in both spectrum and energy.IRS consists of a large array of passive antennas,which makes it possible to control beamforming of reflected RF signals.IRS can increase the received signal power of the intended user,but it has potential interference enhancement to its non-serving users and non-serving systems.This thesis focuses on the spatial distribution,carrier frequency ratio and technological attributes of interference induced by IRS.Firstly,the recent research of IRS communication technology and application is comprehensively discussed.Typical IRS channel models and interference models,including free-space path loss,far field beamforming case and small-scale fading,are analyzed.Based on the theoretical analysis methods of automatic interference cancellation(AIC),the inter-cell interference cancellation(IIC)property in IRS-assisted Wireless Communications is explored,and it is showed that IRS becomes asymptotically interference-free to its non-serving users.Then,the spatial distribution of multipath interference induced by cross-system IRSs is studied.Based on the IRS cascade channel and the optimal phase design method of reflecting elements,the beamforming gain matrix of the induced multipath interference is analyzed and the computational expression of the channel model is given.The quantitative relationship between signal to interference ratio(SIR)and the azimuth & elevation angles of the IRS reflected signal is deduced,and the spatial distribution of induced multipath interference is analyzed in terms of carrier frequency,azimuth &elevation angles and the number of reflecting elements.Finally,IIC and the spatial distribution of induced multipath interference is observed and verified through numerical simulation.It is found that inter-cell interference and induced multipath interference should not be ignored unless user moves to a specific location.The beamforming gain of induced multipath interference is related to the carrier frequency ratio.Specifically,when the carrier frequency ratio is less than or equal to 1,the induced multipath interference can be effectively suppressed by increasing the number of reflecting elements;when the carrier frequency ratio is greater than 1,the spatial region of induced multipath interference is further dispersed as the carrier frequency ratio increases. |
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