The Research Of Signal Detection Method For Physical Layer Of Airborne Electronic System's BIT

With the wide application of information technology, the degree of informationization of all kinds of aviation equipments and systems is improved greatly. Built-in test(BIT, for short) for aircraft avionics is a kind of important technology improving the testability and diagnostic capability of system and equipments obviously. BIT can not only monitor the main working parameters of avionics for maintaining and repairing, but also predict the possible fault in future, and even conduct the redundancy management and restructure the systems of aircraft avionics with fault.The paper takes very high frequency( VHF, for short) communication system as research subject, and discusses the BITE system of VHF by analyzing the function structure and working principle and hardware system in detail. As the audio system and working principle of VHF receiver is similar to AM receiver, the superheterodyne is taken as the experiment subject in detecting the signal. By analyzing the working principle and function structure and circuit principle diagram of superheterodyne, the general selection principle of test points for signal acquisition is discussed, and on this base, the detection method of typical fault of no sound in superheterodyne is summarized.According to the requirements of test points for BIT, a kind of practical method of selecting the test points is given by analyzing the k node fault method of BIT fault analyzing method, and on this base, the optimal selection principle and validity principle of test points in the physical layer of aircraft avionics systems are summarized.Finally, on the base of functional block diagram of the audio processing system and the signal flow graph of BIT for VHF receiver in aircraft A320, the fault information matrix is constructed and considering comprehensively the reliability and the cost of test and aiming at the optimal selection, a kind of method of optimal selecting test points is provided based on fault diagnosis value measure with the theory of information entropy. The fault of no sound in superheterodyne is taken as the typical fault for verification, and the result of experiment shows that the influence of test cost and diagnosis profit on test points selection is considered comprehensively in this method, which could judge the value of test points on fault diagnosis overall and the objective of detecting the signal with the least amount of test points and the lowest measuring cost is achieved.