Research Of Carrier Synchronization Key Technology In Satellite-Based AIS

The satellite-based Automatic Identification System(AIS) is a maritime navigation safety communications system with the potential to provide AIS detection service coverage in a worldwide range, which is extremely important in the field of military, economic, and political. Carrier synchronization as a key technology of satellite-based AIS is related to the correctness of the receiver decoding directly and it will affect the reliable of communication. In the thesis, the algorithms of time delay and frequency-offset in the carrier synchronization are discussed. It applied the cross-correlation operation, Fast Fourier Transform(FFT) and maximum likelihood theory to expend estimate range and improve the precision.(1) An improved time delay estimation method base on M&M algorithm is proposed. By setting the auxiliary factor to remove the value which is effects by noise most. Computer simulations are used to illustrate that aiming to AIS signals, time delay MSE of the modified method is lower two orders of magnitude. A joint frequency and timing recovery algorithm based on cross-correlation function is proposed in this thesis. A stepwise searching method is adopted to set reference frequency to eliminate the influence of frequency offset, the argument at which correlation value achieves a maximum is the delay and frequency offset estimator. Simulation results show this proposed algorithm can estimate time delay and frequency-offset, the range of frequency estimation can reach-4000Hz~4000Hz.(2)This thesis proposes an improved algorithm based on FFT. By changing the scope of periodgram peak position, the algorithm expands the range of positive frequency offset estimation and uses the angle information to fix the estimated result. Simulation results show that the range of improved algorithm can be doubled in a high precise. An improved method of frequency estimation based on training sequence is proposed. By analyzing the problem of phase ambiguity, it gives a possible value and uses the theory of maximum likelihood to determine the exactly estimation. The results of the experiment show that the estimation range is expanded four times with a high precision.(3)The experiment platform of programming controlling is established to detect real signals. It connects the computer and instrument by local area network to realize programming controlling. The experiment results show that the proposed algorithms can estimate the parameter of signals in a high accuracy and the correct information can be acquired finally.