In order to use the existing automatic identification system (AIS) to provide additional\nnavigation and positioning services, a complete pseudorange measurements solution is presented\nin this paper. Through the mathematical analysis of the AIS signal, the bit-0-phases in the digital\nsequences were determined as the timestamps. Monte Carlo simulation was carried out to compare\nthe accuracy of the zero-crossing and differential peak, which are two timestamp detection methods\nin the additive white Gaussian noise (AWGN) channel. Considering the low-speed and low-dynamic\nmotion characteristics of ships, an optimal estimation method based on the minimum mean square\nerror is proposed to improve detection accuracy. Furthermore, the Ã?± difference filter algorithm was\nused to achieve the fusion of the optimal estimation results of the two detection methods. The results\nshow that the algorithm can greatly improve the accuracy of pseudorange estimation under low\nsignal-to-noise ratio (SNR) conditions. In order to verify the effectiveness of the scheme, prototypes\ncontaining the measurement scheme were developed and field tests in Xinghai Bay of Dalian (China)\nwere performed. The test results show that the pseudorange measurement accuracy was better than\n28 m (ÃÆ?) without any modification of the existing AIS system.
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