Technology Automatic Identification System Co-channel Interference Suppression

With the rapid development of society, maritime safety has attracted more and more attention around the world. Automatic identification system (AIS) has been widely used in the shipping field, because it realized the mutual communication between ship and ship, ship and shore. The satellite-based AIS is becoming one of the hotspots of the future shipping system, because of its wide coverage. However, the satellite receiver can receive signals from different cells with the same frequency band and these signals will form co-channel interference (CCI). Suppressing CCI is one of the most challenging issues of the satellite-based AIS. In view of this, this paper mainly investigates AIS signal detection and focuses on satellite-based AIS CCI suppression. The main contents are as follows:(1) To investigate the interference suppression capabilities of different detection algorithms for the gaussian filtered minimum shift keying (GMSK) modulation in AIS, firstly, the GMSK principle is introduced, and then one-bit differential detection, two-bit differential detection, differential detection with feedback and six-order of combined differential detection (CDD-6) algorithms are studied and compared. The simulation results show that the CDD-6algorithm is optimal in terms of bit error rate (BER) performance, but their CCI suppression capabilities are not good.(2) To solve the problem of CCI, a novel serial receiver structure based receive beamforming is proposed. In this structure, all incident angles of all desired and interference signals are estimated by estimation of signal parameters via rotational invariance techniques or rooting multiple signal classification. Then one of minimum mean square error, minimum variance distortionless response (MVDR) and matched filter beamforming algorithms is employed to make the steering vector align with the incident angle of desired signal to suppress interference signals. Finally, a two-bit differential detection algorithm is applied to detect the useful signal. The simulation results show that the proposed structure, compared with the case of single receiving antenna without beamforming, significantly suppresses the CCI and notably improves the BER performance of GMSK.(3) To make the receiver structure in (2) simple, a receiver structure based constant modulu receive blind beamforming is proposed. In this structure, a blind beamforming algorithm is firstly employed to recover the desired signal, and then a two-bit differential detector is applied to detect the useful signal. Three constant modulu blind beamforming algorithms including steepest descent constant modulu algorithm (CMA), least square CMA and analytical CMA are investigated. The simulation results show that the proposed structure, compared with the case of single receiving antenna without beamforming, effectively suppresses the CCI; but its performance is worse than that of MVDR beamforming receiver in (2).