Research Of Several Key Technologies In Samrt GPS System

The term "smart antenna" appeared in the field of communication and this technology was applied widely and quickly. It can carry out a best result by modifying parameters according the environment. Based on the current status of the research on GPS interference suppression system in the world, the smart antenna technology is applied to solve the problems of the puny GPS signals received and interference easily happened in GPS receiver system and to improve the performance of interference suppression. Several key technologies in smart GPS receiver system are investigated in this dissertation. The main work and contributions are as follows.1) An array with circular polarized quadrifilar helix antenna is adopted in the dissertation, making use of the cross polarization of it. This scheme decreases the mutual coupling effects of the elements in the array and improves the performance of interference suppression of the smart GPS receiver system. The measurements of the S scatter matrix show small coefficients less than-30 dB, and simulation results match the experimental data very well. The mutual coupling impedance matrix resulting from the S scatter matrix is applied to the compensation for the mutual coupling effects. The results after compensation show that the presented method is effective to remove the mutual coupling effect and the un-roundness of the pattern of one antenna in array is reduced about 1.8dB.2) The effects in the presence of channel mismatching on the performance of the array are anatomizzed in this dissertation and are found remarkable on interference suppression. And an approximately linear relationship is found between sensor phase perturbations and the warp of the average absolute value of the maximal gain or of the direction when the sensor gain and phase perturbations are less than 2dB and 30 degree respectively. Practical measurements on the mismatching channel are performed and compensations for the mismatching channel by all-pass filter for phase perturbations and digital for sensor gain perturbations are carried out to testify the feasibility and the capability. A scheme for calibration is advanced with a RF switch or a coupler. The calibration equipment with a RF switch is built and the practical measurements testify its validity.3) An approach of dummy moving is proposed to suppress interference of correlative signals according to the spatial smoothing of MUSIC and a physical implement moving array is raised accordingly. The validity of this method dealing with the two kinds of signals is illuminated by computer simulations that the approach causes the full orders of the covariance matrix with correlative or coherent signals. This approach is also applied in DOA estimation and in beamforming for interference suppression. The simulations on the effects of mutual coupling and the mismatching channel on DOA estimation are performed, which illuminate a obviously effects on DOA estimation. The mutual coupling impedance matrix is applied to compensate the mutual coupling effects in DOA estimation and in beamforming for interference suppression of a practical system.4) The method of RLS (Recursive Least Square) is applied in smart GPS system based on the characters of the GPS signals that they are submerging in the environmental noise. It realizes a performance similar with power inversion with noise serves as an expectation signal and suppresses the interferences which are more larger than the GPS signals The performance of interference suppression in the presence of channel mismatching and mutual coupling is researched, and a more than 30 dB performance of interference suppression comes into being with the sensor gain and phase perturbations less than 0.5dB and 5 degree correspondingly.5) Based on the practice requirements, a digital smart GPS system scheme is designed and built. Its principle,frame and related important specification and parameters are proposed. The function simulations of the system are performed. And the measurements of the system carry out to testify the feasibility and the capability of the method for smart GPS system, with an improvement of SNR over 17dB.All the results in the dissertation demonstrate the validity of the scheme of applying the technology of smart antenna into the GPS system, which improves the performance of interference suppression of the system. We find the effects of channel mismatching and mutual coupling of the array on the performance of system, which are worth more researches. The achievements received in this dissertation are valuable in theory and applications for further research in smart digital GPS system.