Researches On Energy Efficiency Optimization And Reliability Analysis For Wireless Power Transfer-Based NOMA Networks

With the rapid development of fields such as mobile and smart device manufacturing,immersive mobile applications,artificial intelligence(AI),online games,three-dimensional media,virtual and augmented reality,Internet of Things(IoT)and big data analytics,mobile data traffic is experiencing explosive growth.These diverse applications require beyond fifth-generation(B5G)and six-generation(6G)wireless networks to support high reliability,low latency and high data rate transmission,diverse service requirements,and ubiquitous connectivity.In order to cope with the above challenges brought by the surging data traffic,improve the network performance index and the quality of user service experience,a variety of new wireless communication technologies have been widely studied by the academic and industrial circles.Nonorthogonal multiple access(NOMA)is considered as a promising wireless access technology in the envisioned future,which allows allocating one frequency channel to multiple users at the same time within the same cell,thus providing services to multiple users in the same resource block.In this way,NOMA schemes tend to offer several advantages over orthogonal multiple access(OMA)schemes such as improved user fairness and spectral efficiency,higher cell-edge throughput,massive connectivity support,and low transmission latency.In the dissertation,the validity and reliability of NOMA technology based on power-domain superposition coding are fully considered,and energy efficient resource allocation strategies are proposed.From different perspectives,the dissertation completes the reasonable resource allocation,and achieves a great improvement in energy efficiency(EE),transmission delay,as well as reliability in a variety of NOMA-based transmission scenarios.The main contributions and innovations of the dissertation are summarized as follows:Firstly,an energy-efficient resource allocation strategy for massive multipleinput multiple-output(MIMO)NOMA network scenarios is proposed.To ensure the continuous energy supply of user devices and achieve efficient and energy-saving resource allocation,wireless power transfer(WPT)technology is introduced into massive MIMO NOMA systems,and the EE optimization problem of massive MIMO NOMA systems with WPT-powered multicell is further proposed.To maximize the EE of the network,we propose a novel joint power,time,antenna selection,and subcarrier resource allocation scheme,which can properly allocate the time for energy harvesting and data transmission.Considering the difference of channel state information(CSI),the dissertation derives the expression of EE,a key indicator,from the perspective of perfect CSI and imperfect CSI.Then,under the joint constraints of transmitting power,WPT time,antenna number,subcarriers and quality-of-service(QoS),an EE maximization problem is formulated.The EE maximization problem is effectively solved by an energy-efficient resource allocation algorithm based on distributed alternating direction method of multipliers(ADMM).Secondly,an energy-efficient UAV placement and resource allocation strategy in multi-user NOMA network is proposed.In the dissertation,a new NOMA system is studied,where WPT technique is used to charge a multi-antenna unmanned aerial vehicle(UAV)while the UAV acts as a base station(BS),providing services to multiple pairs of ground users(GUs)via NOMA transmission mode.To maximize the EE of the whole system,a joint optimization problem of the allocation of the UAV’s transmit power between different NOMA user pairs and within each pair,the WPT time,and the placement for the UAV is proposed under multivariable constraints.To efficiently solve this nonconvex problem,we decompose the problem into three subproblems using block coordinate descent(BCD).For the subproblem of intra-pair power allocation within each NOMA user pair,we construct a supermodular game with confirmed convergence to a Nash equilibrium.Given the intra-pair power allocation,successive convex approximation is applied to convexify and solve the subproblem of WPT time allocation and inter-pair power allocation between the user pairs.Then,we solve the subproblem of UAV placement by using the Lagrange multiplier method.Thirdly,the outage probability(OP)of WPT-powered ultra-reliable lowlatency NOMA system is derived.The dissertation considers an uplink shortpacket URLLC system with finite block length(FBL)in a quasi-static Rayleigh fading channel.To extend the life cycle of energy-constrained user equipment(UE)and guarantee the data packets transmission of UE,WPT technique is employed in the system.To meet the stringent reliability and latency requirements for emerging applications in B5G and 6G networks,the dissertation proposes a WPT-powered NOMA scheme based on FBL.Furthermore,OP is adopted as an important URLLC metric,and two closed-form approximate bounds of system OP for finite and infinite battery capacities are deduced by means of stochastic process theory and Taylor series expansion formula of function,to characterize the relationship between reliability and latency.Finally,an energy-efficient resource allocation strategy for massive MIMO NOMA networks based on nonlinear energy harvesting(EH)model is proposed.The dissertation investigates the massive MIMO NOMA systems based on practical nonlinear EH model,in which a multi-antenna BS transfers power to the IoT devices to two single-antenna IoT devices via energy beamforming in the downlink,followed by the IoT devices sending their data simultaneously in the uplink by consuming the harvested energy.A time division protocol is designed for this system to adequately allocation the EH time and wireless information transmission time.By jointly optimizing the transmit power of BS,nonlinear EH time and the antenna selection variables,an EE optimization problem is proposed to effectively determine the optimal resource allocation strategies under the constraints of guaranteeing the minimum information rate of the IoT devices and the transmit power of BS.The problem is nonconvex due to the user interference and nonlinear characteristic of EH model.A nonlinear fraction programming method is applied to convert the problem into a subtractive convex optimization problem,and then we solve it by Lagrange dual decomposition approach.In conclusion,the theoretical results of energy efficiency optimization and reliability analysis studied in the above NOMA-based scenarios can better improve the theoretical framework,technical solutions and optimization algorithms of NOMA communication in the future,and accelerate the application process of NOMA key technologies in the future wireless communication network.