On The Design Of Multiple Access Schemes Under Massive MIMO Deployment

With the rapid development of the mobile Internet and the Internet of Things,the future 5G mobile communication will face a more complex access scenario: it can accommodate largescale connected devices and support more diverse user service requirements.This poses a great challenge to the design of the access protocol.Non-orthogonal multiple access technology and millimeter wave communication have also become research hotspots because they can effectively solve the above challenges.In this paper,the non-orthogonal access technology under the deployment of large-scale antenna arrays is mainly studied in combination with some existing technologies.The main contents are summarized as follows:Firstly,a joint time and angle domain sparse code division multiple access scheme for millimeter wave communication systems is proposed.It has been proved that the effective integration of millimeter wave communication,massive multi-input multi-output and non-orthogonal multiple access technology can significantly improve the system capacity.The Power domain non-orthogonal multiple access and successive interference cancellation receive detection techniques are mostly used in the currently relevant studies.However,successive interference cancellation algorithm is faced with serious error propagation problems,and complex power allocation and user pairing algorithms are needed.In order to cope with this problem,we propose the joint time and angle domain sparse code division multiple access scheme,this proposed scheme mainly includes three processes: sparse spreading,beam mapping and beamforming,which are coordinated by the base station(BS).The spreading process is conducted over time domain by associating a specific sparse spreading vector with each user according to its location,while the beam mapping and beamforming processes are conducted over angle domain to superimpose the user signals in a beam to further achieve the multiplexing gain.At each user,it spreads its signal with its own spreading sequence and then sends the spreading signal to the mm Wave channel,at the BS receiver,first the receive beamforming is performed and then a corresponding factor graph is constructed,based on which,message passing algorithm(MPA)is performed to recover all users' transmitted messages.The simulation results show that the proposed transmission mechanism is feasible,and our proposed beamforming scheme has better performance than some existing beamforming schemes.Secondly,a multiple access scheme for small packets based on Bilinear Generalized Approximate Message Passing for massive machine type communication scenarios is designed.A typical application scenario faced by 5G mobile communication is the massive machine type communication.The existing LTE access scheme is no longer suitable for this application scenario because of the large signaling overhead.In this paper,we adopt the grant-free access mechanisms used in some current study,and use the Bilinear Generalized Approximate Message Passing Algorithm to solve the above problems.However,during the research,we found that the Bilinear Generalized Approximate Message Passing Algorithm will result in the reception detection performance deterioration in the case of high signal-to-noise ratio.In response to this finding,we improved the Bilinear Generalized Approximate Message Passing Algorithm and the simulation results show that our detection algorithm has better user detection success rate and system symbol error rate performance than the existing detection scheme.Finally,we propose a beam space modulation scheme in 3D scenarios and extend a new access mechanism through the beam space modulation scheme.Here,we use a beam space modulation scheme based on index modulation.First,we design a beam selection algorithm.Next we design a factor graph construction algorithm and get a sparse factor graph bringing the low detection complexity.Finally,we proposed a new detection algorithm which combines the successive interference cancellation and message passing detection algorithms,where the proportional shrinkage method is used to deal with the problem of inter-beam interference.The simulation results show that our detection algorithm can get a good performance and the proposed transmission mechanism is feasible and our receiving detection scheme has better performance.