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摘要:
以数量庞大的低轨非导航卫星播发的信号作为导航源可不依赖全球导航卫星系统(GNSS)提供定位、导航、授时(PNT)服务能力。对于全球星低轨通信星座播发的机会信号，针对其信噪比低且使用多种扩频码进行复合正交扩频调制的特点导致难以提取多普勒的问题，开展基于全球星机会信号的多普勒定位技术研究。通过实测数据对全球星导频信号进行分析，针对性地提出利用平方交谐项实现全球星的导频扩频信号的解码方法，并利用解码结果通过并行码相位搜索捕获算法提取多普勒观测量，建立粗时多普勒定位数学模型并实现定位。实测验证结果表明：利用2颗全球星的实际信号能够达到精度优于100 m的水平定位性能。
Abstract:Using signals broadcast by a large number of non-navigation low Earth orbit satellites as navigation sources can provide positioning, navigation, and timing (PNT) services independently of global navigation satellite system (GNSS). Due to the low signal-to-noise ratio and compound orthogonal spread spectrum modulation using multiple spread spectrum codes, it is difficult to extract Doppler from the opportunity signals broadcasted by the Globalstar low Earth orbit communication constellation. Therefore, the research on Doppler positioning technology based on Globalstar opportunity signals was carried out. By analyzing the Globalstar pilot signal through measured data, the decoding method of the Globalstar pilot spread spectrum signal using square cross-term was proposed, and the decoding results were further used to extract Doppler observation by parallel code phase search acquisition algorithm. Finally, a mathematical model of coarse-time Doppler positioning was established, and the positioning was realized. The results of the experiments show that horizontal positioning performance with an accuracy of better than 100 m can be achieved by using the actual signals of two Globalstars.
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Key words:
- positioning /
- opportunity signal /
- low Earth orbit satellites /
- Globalstar /
- Doppler /
- spread spectrum communication
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图 1 前向链路导频通道QPSK调制扩频
Figure 1. Forward link pilot channel QPSK modulation and spread spectrum
图 5 解码序列与导频信号平方进行滑动互相关结果
Figure 5. Result of sliding cross-correlation between decoding sequence and squared pilot signal
图 7 全球星M090-38044估计多普勒与预测多普勒
Figure 7. Globalstar M090-38044 estimated Doppler and predicted Doppler
图 8 全球星M092-38043估计多普勒与预测多普勒
Figure 8. Globalstar M092-38043 estimated Doppler and predicted Doppler
表 1 导频信号扩频调制使用PN码参数
Table 1. Parameters of PN code for pilot signal spread spectrum modulation
PN码种类 码速率/（码片·s−1） 码片个数 码周期/s 导频短PN码 1.2288 ×10632768 2/75 外PN码 1200 288 0.24 内PN码（一对） 1.2288 ×1061024 1/ 1200 
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