A Study On Signals Acquisition Method Of High Dynamic Vehicles

In recent years, high dynamic vehicles have been widely studied by many countries, and telecommunication is an important safeguard. Signal acquisition is the first step to communication systems. Whether the acquisition is fast and effective determines the performance of whole communication system. Owing to the high speed and high acceleration of high dynamic vehicles, Doppler effect will be caused and result in Doppler frequency shift and Doppler rate of frequency change, which is different with other communication systems. Acquisition method of signal affected by Doppler effect is studied in this paper.Firstly, the background of high dynamic vehicles was introduced and physical model was analyzed. According to the physical model, Doppler effect to the signals was discussed and a signal model was built.Secondly, the paper described current acquisition methods of spread spectrum with Doppler effect, such as methods based on sliding correlation, matched filter and fast Fourier transformation. With the shift theorem of DFT, a spectrum shift was used to replace multiplication between carrier with the received signal, which has the same performance with traditional algorithm but cost less time. A cascaded FFT algorithm based on the correlation of spectrum was provided to realize the faster acquisition and corresponding performance on accuracy and computational complexity was widely analyzed by simulation.Finally, the paper introduced the concept of fractional Fourier transformation(FRFT) and the realization of its fast computation. Then traditional acquisition methods of carrier with Doppler rate of frequency change, based on rate searching, were introduced. The application of FRFT to capture the carrier was discussed and simulated. Two strategies improved from simple FRFT algorithm were provide, one of which is combine two dimensions FFT and FRFT and the other one is splitting the searching interval to smaller one by step. These two strategies can have better performance in accuracy and lower the computational complexity. Application to the modulated signal or other signals rather than to simple carrier was discussed and a good prospect acquisition of interference signal with FRFT was proved feasible.