山区航道AIS信号场强分布特性

船舶自动识别系统(Automatic Identification System, AIS) 在内河应用中, 由于山区遮挡产生大量的信号盲区, 使其效用受限, 使用Okumura-Hata模型研究了AIS通信系统在这些地区的可靠性。在长江三峡坝区航段上基于坝河口、石牌、西坝3个基站设置了29个测点, 其中山区地带为13个测点, 开阔地带为16个测点。测量了所有测点的实际场强, 并与理论场强进行对比分析。使用线性回归法对Okumura-Hata模型的修正参数进行优化, 计算了山区地带13个测点和开阔地带16个测点中距离大于2.9 km的9个测点的修正场强。为验证修正模型的准确性, 在重庆永川航段设置6个测点进行验证试验。分析结果表明: AIS信号在传播过程中3 km为临界距离, AIS信号传播距离小于3 km时, 曲线较平缓, 信号较好, 传播距离大于3 km时, 曲线较陡峭, 信号质量急剧变差。Okumura-Hata模型计算的理论场强与实际场强分布趋势吻合, 但在具体数值上存在差距。验证试验中6个测点的实际场强平均值为-106.636 dBm, 理论场强平均值为-100.982 dBm, 修正场强平均值为-107.710 dBm, Okumura-Hata模型计算结果的平均误差为5.654 dBm, 平均准确率为94.615%, 修正模型计算结果的平均误差为1.071 dBm, 平均准确率为98.329%。

Distribution characteristic of AIS signal field intensity along mountainous waterway

Due to the shadowing effect of AIS mountains signals, there were many blind areas along mountainous waterways limiting the application of AIS.Okumura-Hata model was used to study the reliability of AIS communication system in those areas.29 test points, which were primarily served by three base stations at Bahekou, Shipai, and Xiba located along the Three Gorges Dam segment, were set.Among the 29 test points, 13 test points were in mountainous areas and 16 test points were in open areas.The actual field intensities of the 29 test points were measured and compared with theoretical field intensities.A linear regression model was used to optimize the corrected parameter of Okumura-Hata model.The correcting field intensities at the 13 test points in mountainous areas and at 9 out of 16 test points in open areas, having a distancegreater than 2.9 km from the base stations, were calculated.In order to verify the correctness of modified model, verification test was carried out for 6 test points along Chongqing—Yongchuan segment.Analysis result indicates that a distance of 3 km is a critical threshold for AIS signal transmission.When the propagation distance is less than 3 km, the AIS signal is good and the AIS field intensity curve is smooth.However, when the propagation distance is more than 3 km, the AIS signal quality reduces sharply and the curve is steep.The distribution trend of theoretical field intensity calculated by Okumura-Hata model is consistent with that of actual field intensity, but there are still gaps between the theoretical values and the actual values.In verification test, the average values of actual field intensity, theoretical field intensity, and correcting field intensity at 6 test points are-106.636, -100.982, -107.710 dBm, respectively.The average error and precision rate of calculated result of Okumura-Hata model are 5.654 dBm and 94.615% respectively, and the values of correcting model are 1.071 dBm and 98.329% respectively.