Performance Optimization Of Intelligent Reflecting Surface Assisted Non-orthogonal Multiple Access Networks

The sixth generation wireless communication network puts forward higher requirements for delay,connection density and rate.Both intelligent reflecting surface(IRS)technology and non-orthogonal multiple access(NOMA)technology have been recognized as key technologies for the sixth generation wireless communication networks.This thesis mainly studies the performance optimization of IRS assisted NOMA networks,and applies IRS to cooperative NOMA networks and cooperative mobile edge computing(MEC)networks.The main research contents of this thesis are as follows:Firstly,an IRS assisted cooperative NOMA network with simultaneous wireless information and power transfer(SWIPT)is proposed.This thesis mainly studies the optimization problems of minimizing transmit power and maximizing user fairness.An iterative optimization algorithm based on successive convex approximation techniques is proposed to jointly optimize the passive beamforming vector of IRS,the power splitting ratio and the transmit beamforming vectors of the base station.The results show that the power consumption and user fairness of IRS assisted cooperative NOMA networks with SWIPT proposed in this thesis are better than conventional IRS-NOMA networks without SWIPT and IRS-orthogonal multiple access(OMA)networks.Then,an IRS assisted cooperative NOMA-MEC network with SWIPT is proposed,in which each mobile user offloads some or all computing tasks to the MEC server for remote execution based on IRS and half duplex decoding-and-forwarding relay.An iterative optimization algorithm based on penalty method is proposed to minimize the task delay between users by jointly optimizing the power splitting ratio,the reflection coefficient matrix of IRS,the offloading task ratio and the offloading transmit power.The results show that for network delay,the IRS assisted cooperative NOMA-MEC network with SWIPT proposed in this thesis is superior to conventional IRS assisted NOMA-MEC networks without SWIPT and IRS assisted OMA-MEC networks.