School of Communication and Information Engineering University of Posts and Telecommunications 400065;
Department of Electronic and Electrical Engineering College London WC1E 6BT;
College of Information Science and Electronic Engineering University 310027;
Engineering Product Development Pillar University of Technology and Design 487372;
College of Telecommunications and Information Engineering University of Posts and Telecommunications 210003;
heterogeneous networks; non-orthogonal multiple access; reconfigurable intelligent surface; resource allocation;