Research On Non-cooperative Satellite Signal Parameter Estimation Methods

Signal perception represents an important means of space situational awareness.Through the analysis of satellite downlink signals,satellite the signal source can be detected,identified,tracked,and monitored.Signal perception plays a crucial role in the accurate determination of characteristics,position,status,and other parameters of the signal source.With the development of modern communication technology,the design of a satellite signal source has become more complicated.Due to a lack of prior information,signal detection and analysis of a complex noise floor and low signal-tonoise ratio have become challenging.In view of the above difficulties and challenges,this thesis addresses the following topics:(1)Research on automatic detection and separation methods of complex noise floor wideband signalsAccording to the amplitude distribution characteristics of a sub-band signal in the frequency domain,a broadband local power spectrum detection method with a complex noise floor,a distributed local expansion(DLE)method are proposed.This thesis develops a way of optimal parameter thresholds setting based on the probability theory,which is verified by experiment with actual maritime satellite data.The results show that under the same parameter setting,the false alarm rate of DLE method is 75% lower than the LADACC method.(2)Instantaneous synchronization parameter estimation of short-term discontinuous signalThe carrier frequency,carrier phase,code frequency,and code phase synchronization parameter estimation methods of a short-term signal are studied,and the influences of signal-to-noise ratio and other factors on the estimation accuracy of each method are simulated and analyzed.Based on the joint code frequency and code phase construction optimization function,a code frequency method is proposed.The simulation verifies that this joint optimization function method has more than ten times better accuracy than the wavelet-based method.When the code frequency is known,the joint code frequency and phase optimization function is used to obtain the mathematical derivation of the code phase analytical solution.The proposed method is verified by simulation,and the simulation result shows that at a low signal-to-noise ratio,the proposed method has approximately five times better accuracy than the logarithmic nonlinearity(LOGN)method.Moreover,the estimation accuracy of the proposed method is less affected by the oversampling rate,convolution factor,and other factors.In addition,at a high signal-to-noise ratio,the performance of the proposed method approached the Modified Cramer-Rao Lower Bound.(3)Research on the estimation method of signal modulation characteristic parametersThe QPSK signal orthogonal deviation estimation method based on the highprecision constellation coordinate estimation and the USB measurement and control signal modulation index estimation method based on the spectrum analysis are proposed.The theoretical analysis of the proposed methods accuracy are conducted,and the correctness of the theoretical derivation are verified by the Monte Carlo simulation.The simulation results show that stable results are obtained by estimating the characteristic parameters of the actual collected data.The frequency analysis of the consistency between the regeneration signal based on the USB measurement and control signal modulation index estimation results and the actual signal verifies the correctness and practicability of the proposed method.(4)Research on high-precision tracking method of synchronization parameters of noncooperative continuous signalsThe high-precision carrier and code tracking methods of a non-cooperative continuous signal are studied.First,a high-precision carrier tracking method of a noncooperative signal based on the co-orthogonal loop model is proposed.This method represents an extended in-phase-orthogonal loop method,and it is combined with a long-term cumulative feed-forward carrier synchronization model to improve the carrier phase accuracy.At the same time,the phase correction feedback method is employed to increase the tolerance range of the initial frequency deviation by more than twice.Next,a lead-delay piecewise integral code loop tracking method based on the spreading signal code tracking model is proposed;this method uses the code frequency and phase joint optimization function to construct a code phase detector.Due to the introduction of the code frequency into the loop filter,the proposed method has the characteristic of the anti-code frequency deviation.At the same time,the code synchronization parameter tracking accuracy is more than ten times better than that of the traditional M-GAD method,and also,the proposed method performance is less affected by the change in the convolution factor.Finally,the innovation points of this thesis can be summarized as follows:1)A distributed local expansion spectrum detection method based on the frequency domain detection is proposed;2)A high-precision code frequency estimation method and a code phase estimation method based on code frequency and joint code-phase optimization function are proposed;3)The estimation method of QPSK signal orthogonal deviation based on the constellation coordinate estimation and the estimation method of USB measurement and control signal modulation index based on the spectrum analysis are proposed;4)The carrier tracking method of a non-cooperative signal based on the co-orthogonal loop structure and the code tracking method of a noncooperative signal based on the spreading code loop structure are proposed.