Research On Key Technologies For 5G Ultra-reliable And Low-latency Communications

Ultra-reliable and low-latency communication(URLLC)is one of the three major application scenarios of 5G proposed by ITU.URLLC has extremely high requirements on delay and reliability,which can meet the requirements for applications such as automation,driverless,and telemedicine.The previous communication systems mainly focus on the improvement of communication rate and bandwidth,but URLLC puts forward new requirements on delay and reliability,which brought huge challenges to the design and construction of 5G system.This thesis has studied the key technologies of low-latency and ultra-reliability communication in 5G system.Including the classification and selection of preambles in the competition-based random access process,and the design and optimization of uplink grant-free transmission schemes.Finally,LDPC encoder in URLLC scenarios has been implemented.In the competition-based random access process,considering the competitive access of two types of devices,e MBB and URLLC devices,different preamble selection schemes will have different effects on the devices' successful access probability and delay.In order to improve the successful access probability of URLLC devices,this thesis has proposed two optimization schemes based on the studies of the three traditional schemes,unclassified scheme,non-overlapping classification scheme and overlapping classification scheme.The optimization scheme which based on the adjustment factor enables the URLLC devices to select from a set of specially reserved preambles firstly,which can increase the probability of successful access of the URLLC devices when the load of the access request is low.And the joint optimization scheme based on adjustment and restriction factors can guarantee the access request of the URLLC devices preferentially by restricting some e MBB devices when the access load of the URLLC devices is high.Simulation results show that the proposed optimization schemes can effectively increase the successful access probability of URLLC devices.In the uplink grant-free transmission mode,since the data packets are directly sent without the scheduling process by the base station,collision of data packets between different users may occur during the transmission process,which makes bad effects on the reliability of transmission.To solve the problem,this thesis studies the collision probability of data packets in different uplink grant-free transmission schemes,then has proposed a dynamic parallel transmission scheme.In the reserved frequency domain transmission channels,multiple channels are selected to transmit several replicas of the same packet at the same timeslot.The parallel scheme can fully utilize the reserved transmission resources under the sporadic data arrival rate,improving the reliability of transmission and reducing the transmission delay.The simulation results show that the proposed dynamic parallel transmission scheme can effectively improve the transmission reliability.Finally,according to the service characteristics of URLLC communication small data packets and high reliability,this thesis studies the FPGA design and implementation of LDPC encoder suitable for URLLC scenarios,and performs board-level verification.The encoder has the advantages of low resource consumption,simple structure and low complexity.