The Research And Implementation Of An Interference Suppression Technology For A Satellite Communication System

With the development of satellite technology, the anti-interference method for satellite communications draws international attention, and now has become a hot topic of anti-interference studies. A certain type of satellite communication system uses the phased array antenna technology to strengthen the useful signal by controlling the main lobe direction of the array beam pattern, so as to improve the communication effect.Now, in order to enhance the system ability for interference suppression, especially for the blanket jamming entering from side lobes of the array beam pattern, an analog and digital mixed method which do the minimum changes to the original system structure is used to improve the system. The main content of this thesis is designing and implementing the analog and digital method on a simplified system of the original system, and testing the performance of this method. This provides a reference for whether it can be applied to the practical satellite communication system.Firstly, this thesis introduces the related theories of phased array adaptive beamforming, including the principles and implementation algorithm of beamforming, and the theory of side-lobe cancellation(SLC) method in detail particularly. These theories lay a foundation for the research of our analog and digital mixed method.Secondly, the specific design scheme of the analog and digital mixed method is given. The hardware structure of the system used in the experiment is presented and the working principle of system is analyzed. The system is divided into two parts by this method, the analog part and the digital part. The digital part uses an un-normal(called non-blocking matrix) SLC method to calculate the weights for anti-interference, and make them close to the optimal weights of system through an iterative method. Then the analog part applies the previous weights to a so called amplitude and phase weighting module which consists of digital attenuators and digital phase shifters, in order to suppress the interference directly in radio frequency.Thirdly, a series of simulations are conducted for the analog and digital mixed method. The reasons for using the non-blocking matrix SLC method is explained by comparing its performance with that of the conventional SLC method. The correctness of the iterative method for weights calculation is verified and the convergence property of the iterative method is researched according to corresponding simulation results. And then a combine method of the SMI algorithm and the LMS algorithm is chosen by analyzing the performance of common algorithms for weights calculation to implement the calculation in the digital part. And furthermore, the influence for interference suppression taken by the restrictive performance of attenuator and phase shifter is discussed refer to the simulation results.Finally, this thesis introduces the detail implementation process of the digital part of system in FPGA, including the verilog designs and Modelsim simulation results of the DC cancellation and DDC, the interference detection, the SMI and LMS algorithms, the weights conversion(main containing the Cordic algorithm) and the RS-232 interface communication. And according to the test results on the experimental system, this analog and digital mixed method is proved to be effective on interference suppression.