Research On The Technology Of Data Transmission Of Air-ground Datalink In AFDX Avionics

As the standard equipment of civil aircrafts, the Air-Ground Datalink System has been widely usedwith ACARS which is Aircraft Communication Addressing and Reporting System regarded as themost widespread part. It has acquired a good effect in our civil aviation, but the core technology hasbeen monopolized by Western Countries until now and there are only several corporations abroad whosupply the equiments and architechture of Air-Ground Datalink System. With localization of thedatalink advised by CAAC and the development requirents of our large aircraft, the research on thetechnology of Air-Ground Datalink System shall be promoted with a tough requisite. Considering ofthe instability and little accumulation interval, a research on the data transmission was made based onthe specification of ARINC-618, combined with the development requirements of our large aircraft. Aground system was developed to accomplish the receipt and transmission of ACARS messages for thepurpose of providing the intertrasmisson data link for the test of avionics and flight in the future.Although the ACARS signal is Minimum Shift Keying (MSK) modulated, it is incompletely assame as the tradition. After the system analysis of the ARINC-618protocol, a data acquisitionplatform was set up to collect the real-time ACARS signal. Through the analysis of the signal, thedesign schematic and implementation flow chart of the message transmission system were presentedto fullfil the modulation of ACARS signal, and some experiments were done to verify the justifiabilityof system design.As for the reception system, against the analysis of traditional MSK signal, the zero-crossingdetection method was adopted to realize the decoing of ACARS messages. However, in considerationof the signal distortion, the processing shall be made to improve the signal quality. A number ofsimulations were done and an effective means was sought out and a zero-crossing detection methodbased on Bis-Code Element was proposed to decode the ACARS signal with relevant experiments.Through the analysis of the data and a contrast with the standard datalink equipment-PATS, theBis-Code Element zero-crossing detection algorithms showed a good performance.At the last of this article, an analysis on the input-output waveform of each module andexperiment results, the reasonability of system design and module design was shown to demonstratethe ground system of Air-Ground Datalink System has a good performance.