MEDLL-based method of ground-wave and cycle identification for Loran-C signal

Ground-wave and cycle identification is significant technology of Loran-C signal processing. Due to fast attenuation of the Loran-C signal in inland areas and small difference between sky-wave delay and ground-wave delay, ground-wave and cycle identification cannot be carried out well by the methods of general optimized envelope correlation and peak detection. To address this problem, a method based on Multipath Estimation Delay Lock Loop (MEDLL) is proposed to perform ground-wave and cycle identification for Loran-C signal. The algorithm computes measured correlation function by optimal Loran-C envelope and extracts estimated delay value of ground-wave by MEDLL. Moreover, all the pulse signals in two complementary cycles (16 in total) are used to obtain 16 cycle identification results, respectively, and the result with highest confidence is selected as final identification output. Results demonstrate that the proposed method identifies the ground-wave and cycle of Loran-C signal accurately when sky-wave delay is 30 mu s more than ground-wave delay, which meet the performance requirements of Loran-C receiver in wide inland areas. The method is robust to environmental noise and sky-wave interference.