Research On Cooperative Power Domain Non-Orthogonal Multiple Access Technology

With the application of advanced multimedia and the access of massiver users,the demand for wireless capacity and spectral efficiency is rapidly increasing.Non-orthogonal multiple access(NOMA),which has been recently proposed for the3 rd generation partnership projects long-term evolution advanced(3GPP LTE-A),constitutes a key technology to improve spectrum efficiency,user access ability and user fairness in the fifth generation and beyond(5G/B5G)mobile communication networks.In addition,cooperative communication technology can effectively improve the communication range and system diversity gain;Hence this thesis combines NOMA with cooperative communication technology,focusing on the research of power-domain NOMA technology in the cooperative systems.In order to continuously improve the diversity gain of the system,this paper studies the cooperative NOMA system in the form of user relay,single dedicated relay and multiple relays;In response to the related problems in these cooperative NOMA systems,in order to further improve the system's communication reliability and throughput;This paper proposes new cooperative NOMA systems,namely Self-energy Recycling Full-duplex cooperative NOMA system,Incremental-relay cooperative NOMA system,Multi-relay cooperative NOMA system with an eavesdropper and relay selection(RS)to enhance physical layer security.Then the performance analysis and verification of the proposed system are carried out respectively.The specific research work and results are as follows:Aiming at the energy restricts the user relay working time and the effect of loop self-interference(LI)signal on the system performance for the Full-duplex user relay NOMA system,this thesis proposes a Self-energy Recycling Full-duplex cooperative NOMA system,where the relay harvests energy from dedicated energy signal sent by a base station,while it reuses energy from LI signal.The outage performance and system throughput in delay-limited mode of Self-energy Recycling Full-duplexcooperative NOMA system using DF,AF and QMF relay are analyzed respectively,and the diversity order of nearby user and distant user is further derived.The simulation results of the system performance demonstrate that the Self-energy Recycling Full-duplex cooperative NOMA system can effectively use the loop interference signal and improve the outage performance of users,diversity gain and throughput.Aiming at the low freedom-degree of the channel in the Half-duplex conventional cooperative NOMA system,which leads to a decrease in spectrum efficiency,this thesis proposes an incremental-relay cooperative NOMA system.The outage performance for the system is fully analyzed,where the closed solution expression of the outage probability for two NOMA users and the system throughput expression in delay-limited mode are derived.In addition,the analysis of the conventional cooperative NOMA system performance is used as a benchmark of the proposed system performance.The system performance simulation can be concluded as follows: Compared with the performance of the conventional cooperative NOMA system,the outage performance of the distant user in the proposed system has been significantly enhanced;In low SNR,the outage performance of the nearby user and the throughput of the proposed system in the limited delay mode also significantly improved.The proposed system can effectively improve the system spectrum efficiency,user outage performance and system throughput.Aiming at the physical layer security problem in the multi-relay cooperative NOMA system,a multi-relay cooperative NOMA system with eavesdroppers is proposed;TRS and ORS schemes are also proposed to improve system secrecy outage performance.The closed form expressions of the secrecy outage probability and the secrecy diversity order for the proposed system under the TRS / ORS schemes are derived.The secrecy outage performance of the proposed system under the RRS scheme is also analyzed,which is used as a benchmark of the system performance under the TRS and ORS mechanisms.The secrecy performance simulation results ofthe system show that: Based on the proposed TRS and ORS scheme,the secrecy outage performance and secrecy diversity gain of the proposed multi-relay cooperative NOMA system increase as the number of relays increases;i.e.,it significantly improves secrecy diversity gain and secrecy outage performance.