Research On Anti-jam Based On Space-time Processing Under Multi Uavs Cooperative Navigation System

With the development of satellite navigation applications in various industries, and the trend of the development of single UAV system to multi UAVs cooperative system, multi UAVs cooperative navigation system has become the inevitable development orbit. Therefore, the problem of anti-jam of multi UAVs cooperative navigation has become one of the urgent issues to be solved. In this thesis, the thesis proposes two points to improve the anti-jamming capability of navigation system based on the research of the existing anti-jamming technology of the satellite navigation, and the characteristics of the application environment of multi UAVs cooperative system. The one is multi antenna cooperative model of UAVs system, the other is the application of CLMS(Constrained Least Mean Square) algorithm for space-time model, and improves the adaptive step size of the algorithm. The main work of this thesis is as follows:Firstly, the thesis proposes the idea of multi cooperative antennas under one single UAV unit equipped with one single antenna based on the flexibility and controllability of multi UAV cooperative system. Within this assumption, a multi UAVs cooperative system can realize adjustability which fixed antenna doesn't have, based on its flight formation adjustability. In this thesis, according to the simulation results of beam effect of three basic array antenna structures, linear array, area array and Y circular array, under different interference environments and different array spacing, the thesis summarizes the anti-jamming performance of different antenna formation in different array element spacing, and studies the influence of weight disturbance caused by the cooperative antenna array.Secondly, the thesis proposes the idea of applying Constrained LMS algorithm to the model of space-time processing, and the problem of step size is derived which involves the convergence of the algorithm. This method inherits the small amount of computation which is the original algorithm's characteristic, makes it suitable for the low computational power of UAV. And the algorithm ensures the strong constraints on the satellite signal at the same time. Simulation results illustrate its effectiveness.Thirdly, the thesis proposes the improvement method of the step factor of the Constrained LMS algorithm under space-time processing model by summarizing the original variable step size of LMS algorithm, based on the research of the original CLMS algorithm step size. This improvement can make the algorithm have better convergence rate at the initial stage of algorithm, simulation results illustrate its effectiveness.Through the above work, the results were summarized as follows: Y type circular array usually has strong zero sinking for interfering signals, which is suitable for general interference environment. Area array is more suitable for the case of interference concentration in the airspace. The linear array has good effect only in the case of interference fits its zero sinking direction. The optimal antenna spacing is usually not in the vicinity of the half wave spacing, and the multi UAVs cooperative antenna can be slightly increased or decreased to obtain the best antenna receiving distance based on the half wave spacing. When the CLMS algorithm is applied to the space-time model, it can be used to improve the ratio of signal in case of 60 d B four interference transmission. Although it cannot completely suppress the interference, it guarantees the satellite signal constraints and has the characteristics of small calculation, which is very suitable for UAV application background. The improvement method of the step factor of the Constrained LMS algorithm trades the effect of the convergence for initial faster convergence, which has strong application significance for the navigation of unmanned aerial vehicles.