面向复杂海况和北斗卫星接收机的极化敏感阵列自适应信号处理算法研究

BeiDou satellite navigation system (BDS) can provide positioning, short message, differential correlations service simultaneously, and has a wide application in marine detection field. However, the rapid changing ocean environment can attenuate the satellite signal and have a multipath effect on BDS receiver. The traditional weak signal enhancement method and anti-multipath interference technology do not fully consider the application environment of the ocean, so it has some limitations in the application of the ocean buoys and submersible vehicles. This project intends to study the mechanism of the Beidou satellite navigation signal propagation in complex sea conditions, and analyst the essence cause and law of the effects from marine environment on satellite signals. A new algorithm which estimates the polarization state of the incoming wave is proposed. The polarization state estimation results will compare with the prior information obtained from the analysis of BDS signal propagation. And the polarizations state then finally is determined. Combined with direction of arrival (DOA) estimation and time delay estimation, a polarization-space-time adaptive algorithm is proposed. The algorithm can remove the reflected and scattered wave effectively from polarization, space and time domain, which will improve the performance of the Beidou receiver. Considering there is no satellite signal under the bad sea conditions, the DOA estimation method which is according to the prior information in the receiver (such as ephemeris data, antenna array platform attitude, array element position and etc.) is also proposed, which then support the adaptive algorithm to beamforming, and the satellite signal will be enhanced. The polarization sensitive antenna array technology based on prior information is expected to be effective against the sea clutter in marine environment. The BDS receiver with the technology will has certain ability against the bad sea condition.

北斗卫星导航系统能同时提供定位、短报文、差分增强服务，在海洋探测领域有广泛应用。然而多变的海洋环境会使信号衰减，并产生多径效应，严重干扰北斗接收机的性能。传统弱信号增强及抗多径干扰技术未充分考虑海洋应用环境，在海洋浮标、潜器等中应用具有局限性。本课题拟研究复杂海况下北斗卫星导航信号海面传播机理，分析海洋环境对卫星信号的影响规律，并提出来波极化状态估计算法，与信号极化特性先验信息匹配，确定来波的极化状态。结合来波方向估计、时延估计，形成极化敏感阵列自适应信号处理算法。从极化域-空域-时域去除杂波，提高北斗接收机海上应用的性能。并考虑恶劣海况无卫星信号条件下，根据接收机先验信息（如星历数据、阵列平台姿态及阵元位置等）估计信号来向，从而辅助自适应算法进行波束形成，增强卫星信号。本课题提出的极化敏感阵列自适应信号处理算法，预期能有效对抗海洋环境产生的杂波，使北斗接收机具有一定对抗恶劣海况的能力。

本项目针对复杂海洋环境下北斗卫星信号较弱易受多径干扰以及其他电磁干扰的情况，提出采用极化敏感阵列从极化域、空域、时域三方面对接收信号进行处理，使阵列指向有用卫星信号，削弱或零陷其他干扰信号，从而提高卫星接收机捕获、跟踪的性能。. 项目从两方面开展研究，首先研究了复杂海况下北斗卫星信号传播特性，得到不同海况下北斗卫星信号极化特性及反射信号功率损耗变化情况，仿真结果表明，光滑海面以及低海况情况下，反射信号以左旋圆极化波为主，在大入射角的情况以右旋圆极化波为主，总体反射损耗较小，反射多径信号对接收机影响较明显。在高海况小入射角情况下反射信号主要为左旋圆极化波，且损耗较大，对卫星接收机影响不是很明显，但大入射角情况下反射极化特性转为右旋圆极化，损耗随之减少，对北斗入射信号会形成较大影响。同时研究了不同多径干扰信号对北斗接收机影响机制，总结出1个码片延时内的短延时多径信号对接收机影响较大，该结果为北斗卫星接收机抗干扰设计提供理论基础及指导。. 其次针对非相干与相干多径干扰，研究了极化敏感阵列多参数估计算法及不同阵型的波束形成算法。多参数估计以MUSIC算法为基础，利用降维的方法分步估计空间角度和极化域角度，实验结果表明基于MUSIC算法的极化-空域多参数估计算法无论在线阵还是L阵上，空间入射角、极化域角度估计误差均在1°以内。同时提出采用改进 MUSIC算法来应对相干干扰或者低信噪比、波达角度间隔较小情况下传统MUSIC算法失效问题，拓展极化敏感阵的适用范围。另外，研究了不同阵型下极化域-空域波束形成算法，结果表明线阵和圆阵采用极化-空域LMS算法波束形成效果较好，为实际阵列设计提供理论指导。. 为降低极化阵列硬件及算法复杂度，提出采用交替极化敏感阵替代全极化敏感阵，信干噪比可提高15-20dB，为实现适用于海洋环境的小型化、低功耗北斗卫星接收机提供理论基础和思路。