Research Of Improving The Reliability Of Air Traffic Control Communication System

With the rapid developing of China's civil aviation, flights frequency and density are continually growing, and bring higher demands on flight control like higher quality requirements on Air-Ground communications. As the equipments and the frequency points for Air Traffic Control system (ATC), Very High Frequency (VHF) communications system, and other wireless communication systems, appear more and more, then the radio frequency interference become a severe problem on ATC. Therefore, how to reasonable select the new frequency on ground-air communications and eliminate the radio frequency interference become a difficulty that must be solved.This paper introduces the related knowledge of aviation Air-Ground communications, summarizes the kinds and characteristics of communication interference on the current Very High Frequency (VHF) communications system of ATC, and studies two aspects on solution of the problems above: The first aspect is focusing on the interference of frequency points, takes technical analysis on the allocation of additional frequency, which calculate the derivative frequency from the inter-modulation firstly, and find out the derivative frequency that exactly drop on the working frequency (or nearby but may interfere with working frequency). Then, according to the theory of VHF inter-modulation interference establishes a mathematical model that can be applied with computer programs, and according to the model completes the main program; This program applies Delphi integrated development environment, and provided with the necessary DLLs, so that program can be operated independently without the Delphi development environment, and tries to give a simple and appropriate window interface and menu. The program has been tested in Jinan and Qingdao Airport. The test results were satisfactory. This program is developed by aim at the characteristics of the VHF of aviation. Applying this program may improve the preparation for the inter-modulation interference, especially in timely finding out the inter-modulation interference due to the equipment performance declining gradually, and can guide to improve the equipment to avoid the interference. Computation considers the impact of ATTIS frequency. The computation results are useful on practice, which can timely detect the potential interference that can induce transmitters detuning, greatly reduce the failure rate due to reduce the power of transmitter. It has a higher applied value on the current civil aviation communications system.Another aspect is focusing on the various inferences among various types of VHF communications, to discuss the Blind Source Separation. According to the principle of independent component analysis, using blind signal separation, the nature of the inference can be not considered. If only the signal is separate with the working signal, they will be able to distinguished from the useful signal, and then extracted the useful signal. By analyzing the joint probability distribution, and studying the ICA algorithm, select one of the fastest algorithm and apply to separate useful signal and the interference signal on the ATC system. The simulation results show that this algorithm has a good separation performance with small computation scale, fast speed, and not be affected with the long of the step. But it is a fixed-point algorithm only applied to the stable interference environment, but cannot automatically adjust the weight of separation vector following the difference of the interference environmental. The last part takes a summary for all the working. It shows the creative points, the practice value on civil aviation communication, discuses the shortage of the present work, and the struggling direction on the future.