Low Latency And High Reliability Scheme Design For 5G High Frequency System

While information technology is changing our lives,Many new types of services arise,which require lower latency and higher reliability.In 2017,the International Telecommunication Union defined uRLLC as one of the three representative services of 5G to meet the needs of such scenarios as self-car driving and industrial automation.Besides,the application of millimeter wave and MIMO has become inevitable in 5G.The hybrid beamforming technology composed of digital precoding and analog beamforming can provide better performance for the system and will be widely used in 5G systems.The characteristics of uRLLC arise great challenges for physical layer.Its user-plane latency requirement is less than 1ms,and packet error rate in 1ms must be less than 10'5.these requirements are 100 times more stringent than that in LTE.How to support high qulity transmission of uRLLC and reduce its impact on traditional services has become a research hotspot,which requires not only a new frame structure but also a new coexistence mechanism between uRLLC and traditional services.In addition,strict latency requirement also plague beam training in hybrid beamforming.Large-scale antenna arrays increase the number of beams and transceivers,leading to rapidly increasing of beam training complexity.It is necessary to find a new method to complete beam training in a very short time.To solve above problems,this paper studies uRLLC frame structure design,uRLLC coexistence with other services and beam training algorithm.Firstly,DMRS allocation and slot length are discussed based on mini-slot,and a reasonable frame structure of uRLLC is designed.The latency and reliability performance of uRLLC are verified by simulation,and the target of 3 GPP can be achieved.Secondly,aiming at the coexistence of uRLLC and eMBB,a mechanism based on the idaea of code division multiplexing is proposed,which can effectively avoid the conflicts between different services.It can not only complete reliable transmission of uRLLC,but also has not great impact on eMBB.Finally,a low redundancy beam training algorithm based on gradient descent is designed by observing the beam gain under sub-array structure.By this algorithm the latency is lower than other existing algorithms while performance loss is not more than 8%.