Research On Direct Position Determination Methods Joint Signal Waveform Characteristics

Accurate location estimation is of great significance in many engineering applications.The development of passive positioning technology is closely related to the development of active devices such as radar and modern radio communication technologies.Signal characteristics and the ability of equipment to process signals determine the use of positioning methods.Direct Position Determination(DPD)algorithm has higher positioning accuracy and robustness in low signal-to-noise ratio and complex environment than traditional two-step positioning method.It has been demonstrated to achieve a better accuracy with known signal waveforms.However,the signal waveform is difficult to be completely known especially in the actual passive positioning process.The accuracy of the DPD algorithm for unknown signal waveform is limited,which limits the DPD method to some extent.According to the actual demand of defense programs,this paper focuses on an in-depth study of DPD algorithm based on signal waveform characteristics,proposes a novel DPD algorithm for digital modulation signal with unknown symbols(MDPD),and provides a certain theoretical support for DPD algorithm in the further application of passive positioning systems.The main works are summarized as follows:1.The existing DPD algorithm based on the prior signal information is analyzed.The basic principles of the DPD algorithm with known and unknown waveforms,as well as the DPD algorithm for constant mode signals,OFDM signals and cyclostationary signals is analyzed.2.The Direct Position Determination algorithm in the over-the-horizon scene is studied.Direct Position Determination(DPD)algorithm is usually proposed for line-of-sight target,aiming at the problems that the two-step model in the traditional radio positioning technology is difficult to obtain the optimal estimation accuracy,and the accuracy of the over-the-horizon target is suboptimal,an over-the-horizon target DPD method on known radiation source waveforms is proposed.On this basis,the positioning error covariance matrix considering the height error is deduced and the positioning performance is analyzed by Monte Carlo simulation.3.The Direct Position Determination algorithm for digital modulation signal with unknown symbols is studied.Regardless of fact that the advantages of the Direct Positioning Determination(DPD)algorithm outweighs the traditional two-step positioning method,the current DPD algorithms are often limited in the actual scene due to its focus on totally unknown or known signal waveforms.Considering the signal waveform is difficult to be completely known especially in passive location,a novel direct position determination algorithm for digital modulation signal with unknown symbols(MDPD)is proposed in this paper based on maximum likelihood criterion.Monte Carlo simulations validate that the MDPD algorithm outperforms both the DPD with unknown signals and the common indirect approach particularly in low signal-to-noise ratio(SNR),while those methods converge to the Cramér-Rao low bound in high SNR.4.The MDPD method based on particle swarm optimization algorithm is studied.as the optimization of the cost function is a nonlinear integer optimization problem,an improved Particle Swarm Optimization(PSO)algorithm is considered for the optimal symbol search.Simulations are carried out to show the higher position accuracy of the proposed DPD method and the convergence of the fitness function under different inertia weight and population size.On the one hand,the proposed algorithm can take full advantage of the signal feature to improve the positioning accuracy.On the other hand,the improved PSO algorithm can improve the efficiency of symbol search by nearly one hundred times to achieve a global optimal solution.5.The MDPD method combined with waveform reconstruction is studied.Considering the digital modulation signals exist commonly in passive location system with unknown symbol information,this paper proposes a method of DPD for digital Modulation signals(MDPD)combined with waveform reconstruction.The simulation results verify the feasibility of MDPD algorithm with waveform reconstruction.Meanwhile,compared with two existing localization algorithms,the proposed MDPD is proved to achieve higher positioning accuracy and converge to asymptotic optimality positioning accuracy.