Transmission Design And Optimization For Non-orthogonal Multiple Access In Power Domain

The development of wireless communications is further driving deep societal changes with tremendous economic,cultural and technological impact to a society that is becoming more networked and connected.In order to support the exponential growth of existing mobile traffic and emergence of new wireless applications and services,the fifth-generation(5G)of wireless networks have been set out to be developed.To meet the challenging requirements in 5G networks,a mere evolution of the current networks is not sufficient and fundamentally new multiple access technologies are required.To coordinate and guarantee the service in 5G,a research on the transmission design for non-orthogonal multiple access(NOMA)is conducted in this dissertation.In order to improve the spectral efficiency,manage interference,decrease the transmission delay and guarantee secure communications,the combinations of NOMA with other 5G candidate technologies such as multiple-input multiple-output(MIMO),coordinated multi-point(CoMP),short-packet communications,and unmanned aerial vehicle(UAV)-aided wireless communications are to be investigated.The main contributions of the dissertation include:1)The application of MIMO to NOMA downlink communication systems is investigated in this dissertation,which allows for overloading the spectrum and beamformer by multiplexing the users in the power domain.Moreover,based on the direction and distance from the BS,a low complexity user clustering algorithm is proposed,which enhances the compatibility of NOMA and MIMO technologies.Furthermore,a sum-rate maximization problem is formulated for improving the spectral efficiency.Then,two iterative algorithms based on weighted minimum mean square error and convex optimization are proposed to perform the design of beamforming vectors and power allocation coefficients.Finally,simulation results demonstrate the advantage brought by NOMA in terms of improving spectral efficiency.2)A novel joint design of beamforming and power allocation for a multi-cell MIMO-NOMA network is proposed in this dissertation,in which base stations adopt CoMP for downlink transmission.Moreover,a new scenario is studied where the users are divided into two groups according to their quality-of-service requirements,rather than their channel qualities as investigated in the literature.The proposed joint design aims to manage inter-cell interference and improve spectral efficiency and is formulated as a non-convex NP-hard problem.To make the problem tractable,a series of transformations is adopted to simplify the design problem.Then,an iterative suboptimal resource allocation algorithm based on successive convex approximation is proposed.In each iteration,a rank-constrained optimization problem is solved optimally via semidefinite program relaxation.Numerical results reveal that the proposed scheme offers significant sumrate gains compared to the existing schemes and converges fast to a suboptimal solution.3)Downlink NOMA is introduced into short-packet communications and its benefits in achieving a lower transmission latency relative to OMA is thoroughly examined in this dissertation.Taking into account the impact of the non-zero decoding error probability caused by finite blocklength,the effective throughput is adopted as the metric to evaluate the system performance.Moreover,this dissertation investigates the trade-off among the transmission rate,decoding error probability,and the trans-mission latency measured in blocklength.Furthermore,the transmission rates and power allocation are optimized to improve the spectral efficiency while subject to a finite blocklength constraint.Finally,the simulation results show that NOMA significantly outperforms OMA in terms of achieving a higher effective throughput subject to the same finite blocklength constraint,or incurring a lower latency to achieve the same effective throughput target.4)The physical layer security is enhanced in this dissertation by exploiting the maneuverability enabled by UAV in NOMA systems.In the considered scenario,users are assumed with different security clearance levels.To improve energy efficiency of the UAV,a flight duration minimization problem is investigated via jointly designing resource allocation and UAV trajectory.Moreover,some insights related to the secure transmission and the position of UAV are provided to simplify the maximization problem.Furthermore,a computationally efficient iterative algorithm based on the successive convex approximation(SCA)technique is proposed to facilitate the joint design.Finally,simulation results are presented to demonstrate that the UAV-aided rely can significantly enhance secret transmissions.