| With the rapid development of satellite communications, the number of satellite interferences which caused by radiant point intentionally and unintentionally is keeping on the increase, impacting on operation of communication satellites. First, it is necessary to determine the transmitter's location to deal with the interferences. From the satellite interference events, there are potential dangers of communication satellites safety. Interference localization for satellite is becoming one of the important contents of the anti-jamming ability of satellite communication systems, Research on the relative problems is springing up in china.Determine the location of interference, the original analysis is the basic nature of unlawful interference signal, mainly spectrum and appearance, Then inquiries satellite transponder resources databases, as well as various satellite uplink station carrier frequency database, to identify possible location of interference. But, this method is low efficiency. From a technical point of view, this method has its limitations.When the interference source located on the ground transmit interference signals. The satellite which was interfered by the antenna main lobe is the main satellite; Meanwhile, there are some disturbing energy leakage in antenna side lobe, affecting nearby supplementary satellite. Side lobe signal has low power, will not impact on the supplementary satellite But the side lobe signal's characteristics are the same with the characteristics of main lobe signal. Time different of arrival is generated through satellite interference's main lobe and side lobe signal transmitting from the different satellite transponder and different downlink or uplink lines, and frequency different of arrival is the doppler frequency offset which is generated through the main satellite and secondary satellite's different perturbations phenomena in orbit.Interference localization for satellites are achieved through measuring time difference of arrival and frequency difference of arrival between two signals which traverse the different uplink/downlink paths of two satellites and through acquiring the orbit references of two satellites and the geographical locating data of ground station.This dissertation has studied key technology for interference localization for satellites with twin satellites or with three satellites, especially the time difference of arrival and frequency difference of arrival estimation algorithms.This dissertation has introduced some basic theories for the work and summarized the basic methods and principles of satellite interference location technique. The locating principle on TDOA&FDOA with twin satellites is discussed in this dissertation. A commonly used method of calculating time difference of arrival and frequency difference of arrival is the cross ambiguity function in joint estimation of time delay and frequency offset. In this dissertation, different algorithms and their application conditions and performance of two models are described and analyzed. This dissertation has studied the methods calculating a pair of time difference of arrival or a pair of frequency difference of arrival with three satellites. This dissertation has studied the time estimation methods of GCC algorithm and Cross- Bispectrum algorithm. It has studied time delay estimation based on cyclic correlation parametric approach, taking into account the multi-channels disturbance and noises with the non-stationary characteristic. Multi-path time delays are estimated precisely with this method, and disturbances and noises can be refrained effectively.There are six chapters in this dissertation.Chapter 1 has recounted the purpose for satellite interference location system of this dissertation and the application of the satellite interference location system, it also introduced the history and current situation of location methods. At the end of this chapter the parameters time difference of arrival and frequency difference of arrival is introduced.Chapter 2 has introduced some basic theories for the work in the dissertation, such as some characteristics of high order cumulants and cycle stationary.Chapter 3 has summarized the basic methods and principles of satellite interference location technique. The locating principle on TDOA&FDOA with twin satellites is discussed in this dissertation. A commonly used method of calculating time difference of arrival and frequency difference of arrival is the CAF (cross ambiguity function) in joint estimation of time delay and frequency offset. Narrowband model and wideband model are calculation models of the CAF. Both of them have different algorithm and estimation performance respectively. In this dissertation, different algorithms and their application conditions and performance of two models are described and analyzed.Chapter 4 has studied the methods calculating a pair of time difference of arrival or a pair of frequency difference of arrival with three satellites. Thus, satellite interference location has realized. This dissertation has studied the signal model with three satellites and the time estimation methods of GCC algorithm based on the second order statistics and Cross- Bispectrum algorithm based on the third order statistics. Emulation experiments have been performed in the end.Chapter 5 has studied time delay estimation based on cyclic correlation parametric approach, taking into account the multi-channels disturbance and noises with the non-stationary characteristic. Multi-path time delays are estimated precisely with this method, and disturbances and noises can be refrained effectively. This method has better performance than the time delay estimation based on correlative and has less calculating amount and more wide applicability than the estimation based on the higher-order cumulant approach. The relevant conclusions are got and verified by the simulation experiments.It has great significance to study on the location method using the cycle stationary characteristics of signal with non-cooperative radiant point signal location.Chapter 6 has summarized the work content of this dissertation, and made further prospects according to the status of the research work now.The main works and contributions of this dissertation are as following:Based on the principles of twin satellites location method, In this paper, we propose an improved algorithm to estimate parameter time different of arrival and frequency different of arrival, using cross ambiguity function to joint estimation, further development of the short-related operations, a new combination of the sum of CAF efficient algorithm, Algorithm is aimed at the elimination of the dependence of resampling. Then the simulation and experiment results are obtained for the traditional calculation method and the improved method. Experiment shows that the improved method of calculating a higher resolution of the estimated parameters time different of arrival and frequency different of arrival, improve the positioning accuracy of the measurement parameters.Based on the current correlative principles of locating satellite interference parameter estimation into a two-dimensional locating problem of estimating parameters, thereby reducing the amount of computation and improve locating accuracy of the measurement parameters and improve measurement speed. Based on the higher-order spectrum, cycle stationary theory and other modern signal processing theory, dissertation has studied the multi-path delay parameter estimation methods with noise and interference.The dissertation has studied the characteristics of high order cumulants, analyzed GCC and Cross- Bispectrum algorithms applied in the signal model of fixed time delay concretely, and made simulations under the condition of single path propagation and multi-path propagation.Taking into account the multi-channels disturbance and noises with the non-stationary characteristic, time delay estimation based on cyclic correlation parametric approach is studied in this dissertation. Multi-path time delays are estimated precisely with this method, and disturbances and noises can be refrained effectively. This method has better performance than the time delay estimation based on correlative and has less calculating amount and more wide applicability than the estimation based on the higher-order cumulant approach. The relevant conclusions are got and verified by the simulation experiments. |
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