Research On The Signal Detection And Estimation Based On Cyclostationary Theory For Broadband Aviation Data Link System

L-Band Digital Aeronautical Communication System1(L-DACS1) is a main technical method for future aviation mobile communication system. Aiming at the problem of the civil aviation VHF communication frequency resource scarcity, L-DACS1 employs the spectrum gaps between two adjacent channels of Distance Measure Equipment(DME) and works as an inlay system. However, the DME pulse interference signal makes deleterious influence on the OFDM receiver of L-DACS1 inevitably. In order to solve this problem, based on cyclostationary theory, DME interference detection and estimation methods in the OFDM receiver of L-DACS1 are carried out. The main research contents of this paper are as follows:Firstly, the characteristic parameters of L-DACS1 system, the model of forward link system and the signal model of DME are introduced. The simulation indicates that DME pulse interference makes deleterious influence on L-DACS1 link transmission performance.Secondly, according to the relevant cyclic statistics theory, the criteria to determine a cyclostationary signal, the mathematical description of cyclic autocorrelation function and cyclic spectrum density are given. Then the cyclic spectrum of amplitude modulated signal are researched by simulation. On this basis, the cyclostationary characteristics of OFDM signal and carrier offset DME signal are proved, and the mathematical expression of DME cyclic spectrum is deduced in detail. Simulation results show that OFDM signal and DME signal have peak value at specified cyclic frequency in each of their cyclic spectrum. This theoretical analysis result is verified by simulation.Thirdly, according to the differences between the cyclic spectrums of OFDM signal and carrier offset DME signal, DME signal's detection is made in L-DACS1 system OFDM receiver. Then the location of carrier offset DME among the received signal can be determined by using the correlation property of Gauss pulse pairs.Finally, after the existence of DME interference is determined, the method of using the peak value of carrier offset DME signal's cyclic spectrum to estimate its average power is put forward. The accuracy of this method is studied by simulation. Simulation results demonstrate that DME interference can be detected effectively in L-DACS1 system OFDM receiver and its average power can be estimated accurately using the methods proposed in this paper.