Research On Full Duplex Relay And Energy Harvesting For Cooperative NOMA Systems

Different from the previous generations,5G mobile system is under standardization in terms of spectral efficiency,energy efficiency,connect density and mobility.5G network is expected to support unprecedented numbers of connected devices as well as considerably larger volumes of data traffic.Non-orthogonal multiple access(NOMA)and full-duplex have been recognized as promising techniques to alleviate spectral resources shortage.To further enhance user fairness and accept reliability,cooperative NOMA drawn wide attention in academia.In addition,many literatures indicate that the combination of NOMA and full-duplex relay can further improve spectral efficiency.However,numbers of wireless devices are energy-limited in future 5G and Internet of things systems,which influences sustainability of communication system.As green communication technique,energy harvesting provides promising solution for prolonging the lifetime of energy-limited communication networks by powering wireless devices,which has lately gained a lot of attention.Motivated by the above,the paper focus on the application of full-duplex relay and energy harvesting technology to NOMA system.Under the assumption of system model,we make a comprehensive analysis and optimization of system performace.The main contributions are listed as below.The application of simultaneous wireless information and power transfer(SWIPT)to downlink non-orthogonal multiple access system is studied.A novel cooperative NOMA protocol for high communication reliability and user fairness is proposed,where a near NOMA user acts as a full-duplex(FD)energy-harvesting relay to help transmission from the source node S to the far NOMA user.The power splitting(PS)architecture is adopted at the relay to perform SWIPT.The aim is to maximize the data rate of the near NOMA user while satisfying the QoS requirement of the far NOMA user and the energy causality condition of the near NOMA user.The formulated problem is a non-convex fractional programming.By jointly optimizing the power allocation factor,the PS ratio,the receiver filter and the transmit beamforming,we propose alternative optimization(AO)based algorithm to obtain optimal solution.In addition,a low complexity suboptimal scheme is proposed and the semi-closed form solution is derived to characterize the performance of our proposed design.Simulation results verify the correctness of theoretical analysis and show performance gain of our proposed protocol over the existing transmission protocols.A downlink cooperative non-orthogonal multiple access(CNOMA)system is investigated,wherein the near user acts as a full-duplex(FD)relay to assist the far user.The energy efficiency is to be maximized subject to QoS requirement of the far user and power budget constraints of the base station and the near user.Since the formulated problem is highly nonconvex,it is computationally challenging to be addressed.A low-complexity path-following algorithm is proposed,which invokes only one convex quadratic problem at each iteration.Numerical results demonstrate that the proposed algorithm outperforms the conventional iterative method.We consider a full-duplex wireless powered cooperative NOMA system,where a dedicated relay assists the far NOMA user by employing DF protocol.In the first slot,the base station(BS)and the relay harvest energy from a dedicated power beacon.In the second slot,with the harvested energy,BS communicates with the near NOMA user directly and the far NOMA user via the relay.To maximize the data rate of the near user under the QoS requirement of the far user and power constraint of the power beacon,we formulate a joint optimization of time allocation coefficient,power allocation coefficient and energy beamforming vector.An optimal beamforming design for problem solution is proposed,which converts the original problem into semi-definite programming(SDP)problem.Simulation results demonstrate that the proposed scheme outperforms other benchmark strategies.