School of Computer and Communication Engineering,University of Science and Technology Beijing,Beijing,100083,China;
Dawning Information Industry(Beijing)Co.,Ltd.,Beijing,100083,China;
Higon Austin R&D Center,Austin,TX 78746,USA;
School of Computer Science,Chengdu University of Information Technology,Chengdu,610225,China;
College of Computer Science,Sichuan University,Chengdu,610041,China;
Relay selection; outage probability; NOMA; QoS; signal-to-interference-plus-noise rate(SINR); beam-forming;