Research On Non-orthogonal Multiple Access Technology Based On Unmanned Aerial Vehicle

With the developments of mobile internet networks and internet-of-things,there are great challenges for the fifth generation(5G)mobile communication to support massive connectivity and seamless connection under limited spectrum.In order to solve the above problems,non-orthogonal multiple access(NOMA)technology came into being.NOMA has gradually attracted the attention of academia and industry due to its advantages of high spectral efficiency,large-scale connection and low latency.Meanwhile,unmanned aerial vehicles(UAV)communication has become an important supplement to terrestrial communication systems owing to its advantages of flexibility,high mobility,low latency and easy deployment.In order to obtain the advantages of both technologies,this thesis mainly investigates the UAV-assisted NOMA communication technologies.Traditional UAV-NOMA systems usually consider system performance under ideal hardware conditions.However,in actual wireless communication scenarios,due to the limitations of cost and production process,radio frequency(RF)front-end devices may be affected by phase noise,nonlinearity power amplifier,or in-phase/quadrature-phse imbalance(IQI).Because of the existence of hardware impairments,the signal will be distorted in the transmission process,so that the expected signals do not match the actual transmission signals.Although some signal processing and compensation algorithms can mitigate harmful impacts of hardware impairments,there are still residual hardware impairments(RHIs).In addition,obtaining perfect channel state information(CSI)is a great challenge in practice.The common method is that the transmitter sends the training sequence known by transceivers,and the receiver estimates the CSI by the received pilot sequence.However,due to the influence of the channel estimation algorithm and various noises,there is an error between the estimated channel and actual channel,namely channel estimation errors(CEEs).Therefore,it is of great significance to investigate the influence of RHIs and CEEs on the reliability of UAV-NOMA systems.Considering non-ideal hardware conditions and CEEs,this thesis takes cooperative communication transmission as the research object and studies the influence of the combination of UAV communication and NOMA technology on the system performance under different scenarios and different fading channels.The main contributions of this thesis are summarized as follows:Firstly,a novel hybrid satellite/UAV-NOMA system is proposed,which random geometry method is used to model the random location of NOMA users on the ground.The existence of CEEs is considered in the system modeling,and the linear minimum mean square error is used to estimate the channel.In order to analyze the performance of the considered system,the analytical expressions of outage probability(OP)of the far user and near user under imperfect CSI are derived.To further improve the system sum rate,the optimal position of the UAV is obtained by minimizing the average distance between the UAV and the user.Secondly,extending to two UAVs,a ground-air-ground system is considered that the two UAVs are served as relays.The whole communication process is divided into uplink NOMA communication,point-to-point communication and downlink NOMA communication.Considering imperfect successive interference cancellation(ip SIC),the outage performance of randomly deployed NOMA users is investigated.By obtaining the approximate OP at high SNR region,the diversity gain is further obtained.In addition,the analytical expression of throughput in time-delay limited transmission mode is derived.Finally,considering a multi-way relay network,this thesis proposes a model where multiple NOMA users mutually exchange their information with the aid of an amplified-and-forwarded(AF)UAV relay.The achievable sum rate(ASR)of systems is derived when the transceivers are limited by RHIs.The effects of RHIs of transmitter and receiver on ASR of the network is also studied.In addition,this study carries out the asymptotic analysis by invoking the affine expansion of the ASR in terms of high signal-to-noise ratio(SNR)slope and high SNR power offset.There are 26 figures,2tables and 88 references in this thesis.