Direct Position Determination for Digital Modulation Signals with Unknown Symbols

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. The MDPD is a centralized location approach combining the symbol estimation and position determination to further improve the positioning precision of the partially known signals. 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 Cramer-Rao low bound in high SNR.