Analysis Of Interferences In VHF 3 Off-set Carrier Overlapping Area

In order to solve the problem that kinds of interference occur frequently in the VHF off-set carrier overlapping area, improve the quality of the air-ground communication and ensure the security of civil aviation, the phenomenon and mechanism of common and special interference are analyzed, the corresponding solutions for common interference are researched and the solutions together with optimized measure for special interference are proposed.On the base of elements and framework of civil aviation VHF air-ground communication system, the mechanism and problems of the off-set carrier system are analyzed. The statistics of typical cases in latest two years are analyzed based on the mechanism of the interference. The causes and mechanism of interference in overlapping area are analyzed by combining with typical cases in Beijing area control center from the kinds of phenomenon. The corresponding solutions for common interference are also proposed. To one of the special interference in overlapping area—the co-channel interference, the characteristic features of signal transmitted by multi-transmitters setting different off-set frequency are tested, and the setting method of the frequency is analyzed. Then the optimized setting of the frequency and transmitters is gained. To another special interference in overlapping area—the time-lag interference, the reason why current solution is inapplicable in our nation is gained from the experiment in Beijing area controlling center. And then the synchronization solution using GPS is introduced.The results indicate that more than three off-set carriers are not advised in a sector. The off-set carrier frequency differences should be above 7.5K and the more the better. The signal transmitted by transmitters at different place can be synchronous on time and frequency in the synchronization solution using GPS. The time-lag interference is resolved and frequency stability of transmitters at different place is ameliorated. The synchronization solution using GPS reaches the anticipative effect in test.