Research On Carrier Acquisition Technology Based On Discrete Matching Fourier Transform

Big Doppler frequency shift is a remarkable character of the low orbit satellite communications, which will cause the deterioration of output SNR of the acquisition circuit result from Doppler frequency. Auto frequency control (AFC) loop is introduced in known Doppler frequency shift compensate scheme, but big Doppler frequency shift greatly exceed the estimate range, reach about士l00kHz. The most pivotal question to solve the synchronization of carrier wave is acquisition, namely, approximately estimate of Doppler frequency. satellite communications signal is similar to Linear Frequency Modulated Signal, we should get much of the satellite Doppler shift through time-frequency presentation which should adapt bigger frequency movement. Matching Fourier Transform is proposed in this paper to estimate Doppler frequency shift and linearity frequency for the characteristic of high dynamic signal, then presents a improved method, combine changeable sample ratio processing technology with"changeable center frequency filtering"to realize the high dynamic signal's acquisition which is exacter and faster.First, some tradition track projects are introduced, including MLE,ALS,AFC and EKF. Then, these methods are compared and sumed up.Next, time-frequency presentation (TFR) is introduced including the linear short-time Fourier transform (STFT) and the quadratic Wigner-Ville and Cohen. Then put forward Fourier transform which is a special example of Matching Fourier Transform. And Matching Fourier Transform could estimate the parameter of Linear Frequency Modulated Signal.Then, author studies the fast arithmetic and restaining noise in Matching Fourier Transform. changeable sample ratio processing technology and"changeable center frequency filtering"are introduced to acquire high dynamic signal under low SNR.Finally, high dynamic signal is dealt by changeable sample ratio processing technology and"changeable center frequency filtering"through Matlab emulate. The result make out that Matching Fourier Transform reduces much operation in virtue of FFT, and has well capability of restaining noise.