Research On 5G Uplink Non-orthogonal Multiple Access And Transmission Technology

The 1st to 4th generation mobile communication system mainly used Orthogonal Multiple Access(OMA)as the multiple access method.However,due to the shortcomings of low spectrum utilization of the OMA system,it cannot fulfill the requirements of the 5th Generation Mobile Communication System(5G)for larger system capacity and faster transmission rate.Therefore,new multiple access scheme Non-Orthogonal Multiple Access(NOMA)has gradually attracted the attention of experts and scholars in the field of communications.Multi-User Shared Access(MUSA)proposed by ZTE Corporation is one of the 5G candidate NOMA schemes.This system mainly based on spread technology and Successive Interference Cancellation(SIC)technology.In this paper,MUSA system is studied in depth from the evaluation of the system,the improvement of the traditional SIC receiver,and the design of the pilot-free system under the Grant-Free(GF)transmission.Prototype verification of the pilot-free MUSA system is implemented by building a hardware test platform through Universal Software Radio Peripheral(USRP).Firstly,this paper evaluates MUSA system from the user overload performance and system throughput and the influence of the near-far effect and the length of the spread code on the system performance.The evaluation results show that the MUSA system can maintain good user overload performance and system throughput when transmitting packets of different typical sizes.In addition,difference in power between users caused by the near-far effect can further improve the performance of the system,and the longspreading sequence can significantly improve the overload performance of the MUSA system.For the traditional SIC receiver of MUSA system has the disadvantages of low decoding efficiency,poor decoding performance,unequal user decoding opportunities and large propagation.This paper introduces Hybrid Interference Cancellation(HIC),Enhanced Successive Interference Cancellation(eSIC),Enhanced Hybrid Interference Cancellation(eHIC)and data-based channel estimation refinement technique.The simulation results under 1TX2 RX antenna configuration and 500% user overload show that the HIC receiver can bring 1?1.5 dB performance improvement and the eSIC and eHIC receiver can bring 1.5?2 dB performance improvements.At the same time,the simulation results show that data-based channel estimation refinement technique can effectively reduce propagation errors.The estimated value of channel response under this method is closer to the actual value as the number of successfully decoded users increases.Secondly,this paper discusses the pilot-free MUSA system under Grant-Free(GF)transmission.Aiming at the problem that the system cannot avoid pilot collision in GF transmission mode,this paper focuses on the pilot-free MUSA system under GF transmission,and proposes a blind equalization algorithm based on K-Means clustering.This algorithm can perform phase compensation according to the clustering result,thereby achieving signal equalization.Simulation results show that the pilot-free MUSA system can support 200% user overload under the 1TX1 RX antenna configuration and Quadrature Phase Shift Keying(QPSK)modulation.For the pilot-free MUSA system,the channel estimation cannot be performed so that the traditional receiving antenna diversity technique cannot be used.This paper proposes a group of pre-set spatial bisector linear combining vectors to pre-combine receiving signals to achieve blind receive diversity.The simulation results show that the pilot-free MUSA system of 1TX2 RX antenna configuration can achieve 350% user overload under this method.Finally,this paper realizes the prototype verification of the pilot-free MUSA system through the construction of the hardware test platform for the 2-user pilotless access system.This platform maily uses the Laboratory Virtual Instrumentation Engineering Workbench(LabVIEW)software to process the modulation and demodulation of the MUSA system,and simulates the uplink “UE-BS” communication process through the USRP.The test results show that 2 users can realize the shared access of text data under the pilot-free MUSA system.