Investigation Of Non-Orthogonal Multiple Access Technique In Millimeter Wave Communication Networks

With the wireless service demand explosively increasing,there are many challenges in 5G and beyond wireless networks,such as extremely high data rates,massive connectivity and ultra-high traffic density.Millimeter wave(mmWave)communications and non-orthogonal multiple access(NOMA)in power domain have been recognized as two promising enabling technologies.Compared with traditional sub-6 GHz wireless communication networks,mm Wave communications promise a much higher capacity thanks to abundant spectrum resource.NOMA is able to multiplex multiple users in power domain and provide massive connectivity and a superior spectrum efficiency.In this thesis,we focus on performance analysis of mm Wave NOMA system in several scenarios.Our investigations shall be conducted for single cell mm Wave NOMA networks in terrestrial,an unmanned aerial vehicle(UAV)-assisted mm Wave NOMA networks,and multi-cell mm Wave NOMA networks with base station cooperation.Firstly,in the case of single cell in terrestrial,an agile-beam NOMA scheme in mm Wave communication networks is proposed,which can flexibly switch between the single/multi-beam transmission modes.This scheme overcomes the constraints of user distribution in fixed single-beam NOMA and fixed multi-beam NOMA schemes,and it is applicable to a wide range of scenarios.Considering the sparsity of mm Wave signal in angle domain,a novel user pairing strategy employing both distance and angle information is designed to facilitate the agile-beam NOMA transmission.In the proposed agile-beam NOMA scheme,the base station has an adaptive capability to flexibly switch between the single-bam and multi-beam transmission depending on the user pairing results.With the tool of stochastic geometry,an in-depth performance analysis is carried out,and then the analytical expressions of outage probability and sum rate are derived.Furthermore,the agile-beam NOMA scheme is extended to a multiple-radio frequency(RF)chain system,and the performance of the multiple-RF chain system is analyzed.Moreover,simulation results demonstrate the superiority of the proposed agile-beam NOMA scheme in mmWave communication networks.Then,the sum rate of agile-beam mm Wave NOMA networks is maximized by optimizing the switching point and resource allocation.With equal resource allocation strategy,the asymptotic expression of transmission mode switching point is derived.Furthermore,based on the asymptotic switching point,the optimization problem of maximizing the sum rate in agile-beam NOMA scheme is formulated and then decomposed into two subproblems,i.e.,maximizing the sum rate in single-beam case and multi-beam case.The optimal solution of power and antenna allocation is provided.Moreover,the optimization of agile-beam mmWave NOMA system is extended to more general multi-user case.Simulation results verify the effectiveness of the asymptotic switching point and validate the optimal solution of optimization problem.In addition,the superiority of the agile-beam NOMA scheme over fixed single-beam or multi-beam NOMA schemes is demonstrated in simulation.Further,considering the sensitivity of mmWave signal to blockages,we propose a UAV-assisted mmWave NOMA scheme.A general performance analysis framework is established over Nakagami-m fading channel.Considering the randomness of blockages,the characteristic of directional transmission and dynamic user decoding ordering,the analytical expressions of outage probability,sum rate and ergodic rate are derived with the tool of stochastic geometry.Simulation results demonstrate the accuracy of the theoretical analysis and the superiority of NOMA over OMA in the considered UAV-assisted mmWave networks.In addition,the importance of user pairing and UAV hovering altitude on the system performance is confirmed in simulations.Finally,in multi-cell mmWave NOMA networks,the cell-edge users suffer from severe inter-cell interference.To enhance the performance of cell-edge users,we propose a mm Wave NOMA scheme with base station cooperation in multi-cell networks,in which multiple cooperative base stations employ non-coherent joint transmission to serve a cell-edge user and each base station serve a near user with NOMA scheme.Subsequently,the outage probability,sum rate and energy efficiency of system are derived with stochastic geometry tool.Furthermore,simulation results are provided to verify the correctness of analytical derivation and demonstrate cell-edge users' performance improvement with coordinated multipoint transmission.In addition,the superiority of NOMA scheme in multi-cell mmWave networks with base station cooperation is verified.In this paper,we focus on performance analysis of mmWave NOMA system in these scenarios,and the optimization design is conducted only in agile-beam mmWave NOMA system.In the future work,we will further investigate the optimization design of UAV-assisted mmWave NOMA system and multi-cell mmWave NOMA system with base station cooperation.