Research And Implementation Of Key Technology Of Integrated Baseband System Based On FPGA

Aerospace telemetry?track and command(TT&C)is an important part of the aerospace technology.It studies the remote control,telemetry,ranging,and digital transmission of spacecraft to ensure normal communication between the ground command station and the spacecraft.The space measurement and command system is the institutional system of the TT&C process,which is the premise to ensure the compatibility of the system.It focuses on the research of the Unified S-Band system.The integrated baseband system is based on the aerospace measurement and command system to modulate the remote control signal,demodulate the telemetry signal,and at the same time realize the requirements of ranging,speed measurement and other requirements.With the increase of space missions and the requirements for technical indicators related to ground command equipment,the original equipment has more problems,such as single function,complex structure and difficult development.In summary,it is required to design an integrated baseband system based on USB with simple structure,sub-module and adjustable function parameters,which makes the system integrate remote control and telemetry functions and improve overall performance.The research content includes:(1)Combining the requirements of the subject and the problems of the existing equipment,a system based on "FPGA + RF board" and PC host computer is built.FPGA is used as the core algorithm chip to realize the main function of the integrated baseband system.(2)The research and design of the transmitter is completed,including data preprocessing,main carrier modulation and output.The key technology focuses on the phase modulation of the multiple subcarriers and ranging signals to the main carrier.With the increase of satellite communication data and the need for high-speed transmission,the main carrier frequency has been improved from 70 MHz of existing equipment to 500 MHz.Due to the increase of carrier frequency,the serial processing scheme is no longer applicable.The methods of multi-channel parallel processing,the high and low-frequency signal decomposition in the FPGA are introduced to implement the carrier modulation.It increases the main carrier frequency,reduces the frequency difference between the IF and the RF,and reduces the difficulty of implementing the frequency conversion.(3)The research and design of the receiver is completed,including input link,synchronization and demodulation.The key technologies focus on the band-pass sampling and carrier synchronization of telemetry signals.The main carrier frequency of the telemetry signal is high.When twice the highest frequency is selected as the sampling frequency,the configuration of the analog-to-digital converter and the processing clock of FPGA are very high.Therefore,the band-pass under-sampling scheme is introduced,and the optimal sampling frequency is designed by the method of spectrum shifting,which reduces the frequency of the main carrier and the complexity of subsequent FPGA designs.Due to the complex satellite communication environment,long transmission distance and Doppler frequency shift,the received main carrier frequency has a certain frequency deviation.Based on the traditional Costas loop,combined with the FFT frequency offset estimation algorithm,the acquisition of the center frequency and synchronization of the main carrier are realized.(4)The system self-test is realized.Through the self-loop of the transmitter and receiver,this system implements comprehensive test.After software simulation and hardware measurement,combined with the state indication of the PC host computer,the design of the integrated baseband system is realized,and the correctness and reliability of the design scheme are verified.On the basis of the original equipment,the indicators have been improved,the functions of remote control and telemetry have been unified,which reduces the complexity of the equipment.It provides a test platform for the ground command station,a research program for software and hardware collaborative design,and research experience for modulation and demodulation of high-speed signals.