A Time Delay Estimation Method of LFM Hybrid Signals Based on Hough Transform

In actual passive positioning systems, linear frequency modulation (LFM) hybrid signals at low signal-to-noise ratios (SNRs) are often received by communication devices. Because of the pseudo correlation peaks and peak matching problems, the time delay cannot be accurately estimated by the traditional basic correlation method (BCM) and generalized correlation method (GCM). Thus, a peak detection method based on Hough transform is proposed in this paper. By cyclic correlation, peak detection, and line fitting, the time delays are determined as the intercepts on the cycle frequency coordinate axis. In addition, the signals with different frequency modulation (FM) slopes can be distinguished by the signal slopes, and the signal delays can be matched. Monte Carlo simulation results show that the accuracy ratio and minimum mean square error (MMSE) of the proposed method perform better than the traditional BCM and GCM at low SNRs.