Research On Opportunistic Transmission Techniques For NOMA Relaying Systems

At present,we are stepping into the era of intelligence that people are closely connected with all things.In the new period,mobile data traffic has increased explosively,the total number of devices connected by communication networks is huge,and users' requirements for spectral efficiency,reliability and power consumption are more and more stringent.In the face of the current situation of billions of connections and a serious shortage of available spectrum resources in communication network,non-orthogonal multiple access(NOMA)technology has demonstrated its unique advantages and becomes one of the key technologies to deal with the access of massive equipment and improve spectral efficiency.Based on NOMA,this article will be dedicated to the downlink transmission scheme for the future communications network to improve system reliability and spectrum utilization.This paper focuses on the application of full duplex technology in NOMA based on orthogonal frequency division multiplexing(OFDM)technology.And combing with the relay selection(RS),power allocation(PA),and antenna selection(AS),we are aiming at designing a reliable opportunistic transmission scheme which can increase the system capacity and network coverage while providing users with reliable and effective communication.The main research results can be summarized as follows:1? For the NOMA half duplex(HD)relay system,this paper studies a two-stage relay selection scheme which guarantees the quality of service(Qo S)for the weak user firstly,and then maximizes the system capacity.whereafter,when relays perform at different forwarding protocols,the system outage probability and the obtained diversity gain are derived in the Rayleigh fading channel.The simulation results show that this scheme can ensure the reliability of the system while improving the fairness of NOMA users.2?Aiming at the NOMA relay system which is power constrained,in order to enhance the utilization of spectrum resources and energy resources effectively,and improve the communication quality of the edge users,an improved joint power allocation and relay selection scheme(Sub-OPA-RS)is proposed based on the traditional equal power allocation joint scheme(EPA-RS)with full duplex(FD)technology.First,different optimization methods are used to determine the transmission power of the base station and the relay,and then the optimal node is selected from multiple relays to maximize the rate of the system.Subsequently,the outage probability and the performance of different joint schemes are analyzed and compared.The simulation results show that the stability and effectiveness of the SubOPA-RS scheme are better than that of the EPA-RS scheme.3? For the single antenna NOMA full duplex relay system,multi-antenna technology is introduced to improve the performance of the system,and two multi-stage antenna selection schemes have been proposed successively.Those schemes use a hierarchical antenna selection technique to select one or more receiving antennas at the receiver,and select an optimal transmission antenna at the transmitter.They can reduce the operation complexity of the multi-antenna system while improving the performance of the system.In order to be more practical,based on the Nakagami-m fading model,the closed expressions and asymptotic values of outage probability under different schemes are derived through complex mathematical derivation,which can provide guidance for the performance analysis of the multi-antenna NOMA full duplex relay system.Finally,the performance of the two schemes is verified through theoretical and simulation analysis.