| In order to create and accomplish the future space-aerial-terrestrial integrated network vision of broad-band mobile communication,the 5th Generation(5G)mobile communication system breaks through the limi-tation of terrestrial network and brings satellite communication technique into 5G standard framework for the first time.In the low earth orbits(LEO)satellite mobile communication channel,high-speed relative motion between the satellite and the terrestrial terminal will cause problems such as dynamic doppler frequency shift and dynamic time delay,which brings challenges to the unified air interface signal processing of the terrestrial terminal.This paper focuses on the downlink time-frequency synchronization and experimental verification for broadband 5G integrated LEO satellite mobile communication system,designs a 5G-integrated broadband LEO satellite mobile communication ground experimental system,completes the design and implementation of the multi-beam LEO satellite channel simulator,and also completes the downlink time-frequency synchro-nization algorithm design,hardware implementation and verification of the ground terminal simulator.Firstly,the 5G integrated LEO satellite mobile communication is studied from the perspectives of ap-plication scenarios,network architecture and physical layer protocol architecture.The 5G NR downlink syn-chronization signal generation method and the basic steps of user cell access are studied.The application scenarios,network architecture and the difficult problems to be solved of the 5G integrated satellite mobile communication system are reviewed.From the aspect of the physical layer protocol architecture,the 5G in-tegrated satellite mobile communication system is introduced,and the basic steps for cell access are given.Starting from the frame structure and time-frequency resources,the 5G NR downlink synchronization signal generation method is introduced in detail,and the role of the synchronized signal block and the synchronized signal block set as well as the 5G NR cell search process are discussed.Secondly,in view of the high cost and complexity of field experiments of LEO satellites,a design scheme of 5G-integrated broadband LEO satellite mobile communication ground experimental system is proposed.Starting from the requirements of the ground experimental system,the function of each component of the system is analyzed in combination with the design indicators.On the basis of subsystem functions and tech-nical indicators,the overall architecture design of the ground experimental system is proposed,including three parts: the beam domain 5G satellite base station simulator,the multi-beam LEO satellite channel simulator and the 5G satellite terminal simulator.According to the proposed system architecture,the digital signal processing platform scheme is analyzed and compared,and the selection of subsystem equipment,chips and communication interfaces is completed.Then,the hardware design and implementation scheme of the multi-beam LEO satellite channel simu-lator in the ground experimental system is carried out.Starting from the analysis of LEO satellite channel characteristics including channel fading,dynamic long delay and Doppler frequency offset,the broadband multi-beam LEO satellite antenna domain,beam domain and dynamic long-delay signal transmission models are established,and the satellite channel performance is simulated by using these models.Based on the signal transmission model,the architecture of the multi-beam LEO satellite channel simulator is designed and the functions of each sub-module are defined.The entire system is divided into software platform and hardware platform for implementation.After giving the overall system architecture,the detailed logic design of each sub-module is carried out,including sub-module internal architecture design,input and output interface signal design,internal data flow design and low-complexity circuit design,and then the resource consumption of the sub-module is evaluated accordingly.Finally,the downlink time-frequency synchronization algorithm design,hardware implementation and verification of the terminal simulator in the ground experimental system is completed,which can support5 G NR 400 MHz bandwidth transmission mode.First,the synchronization signal transmission model of the integrated satellite-terrestrial communication system is established,and based on the time-frequency synchro-nization algorithm of 5G integrated satellite communication system,the algorithm implementation process of downlink time-frequency synchronization is designed.According to the design process,the specific hardware architecture of downlink time-frequency synchronization is proposed,and the functions of each sub-module and the data flow relationship between the sub-modules are designed.Then the data calibration design,cir-cuit logic design,interface signal design and signal timing design are carried out for the sub-modules in-volved in signal data calculation.In the end,the Verilog code,timing simulation and hardware verification are completed on Field Programmable Gate Array(FPGA)hardware platform,and the hardware resource consumption of downlink time-frequency synchronization is given. |
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