Development Of Test System For A Transponder Based On LabVIEW FPGA

Transponder is an important equipment for aircraft to realize information interaction with ground TT&C station.Its reliability is of great significance for the stable operation of aircraft.Therefore,it is necessary to conduct a test for the transponder in every stage of its design,production,and service.However,traditional transponder test equipment composed of discrete instruments generally has problems such as large size,fixed working frequency band,and poor performance of real-time signal processing,which makes it difficult to conduct automatic and comprehensive test for the transponder.To solve the above problems,this paper develops a test system for a certain type of aircraft transponder based on LabVIEW FPGA platform and PXIe modular instruments,which provides a more complete scheme for the comprehensive test of the transponder.Firstly,according to the test functions and specifications of the transponder,the overall design scheme is determined,which takes PXIe modular instruments as the hardware platform and LabVIEW FPGA as the main development tool.In this system,the vector signal generator is used to generate and transmit the uplink signal to the transponder,the vector signal analyzer is used to realize the reception and processing of the downlink signal of the transponder,the digital multimeter and oscilloscope are used to realize the electrical and waveform test of the transponder,and the serial communication board is used to realize the simulation of the aircraft computer.The baseband signal generator,IF signal receiver,local oscillator,mixer and other modules in the hardware platform are all implemented by independent PXIe modules,which improves the system’s upgradability.In addition,the LabVIEW FPGA development environment is used to realize the local processing of the test signal in the test system,which greatly improves the signal real-time processing ability and test coverage of the test system.On this basis,this paper focuses on the key technologies and implementation methods of the uplink and downlink communication link,which is the core part of the transponder test system.The design of the uplink communication link includes convolutional coding,interleaving,spread spectrum modulation,DQPSK modulation and so on.The design of downlink communication link includes digital down converter,DQPSK demodulation,spread spectrum demodulation,frame synchronization,deinterleaving,Viterbi decoding and so on.The FPGA design of parallel digital down convertor based on CORDIC algorithm and joint synchronization algorithm based on Costas carrier synchronization algorithm and Gardner symbol synchronization algorithm are mainly studied,which improves the processing performance of the system.The design of each algorithm module is realized by using LabVIEW FPGA platform and Vivado development environment,and each module is simulated to verify its correctness.This paper designs the upper computer software of the system,and uses desktop oscilloscope,transponder simulator,and real transponder to verify the correctness of all parts.Finally,the overall function of the test system is verified.The results show that the transponder test system designed in this paper meets the requirements of functions and specifications.