面向北斗B1信号利用阵列天线抑制极近多径的算法研究

Over the past decades GNSS receiver technologies have got remarkable developments. The performance on positioning accuracy, tracking sensitivity, first fix time and power consumption, etc., is greatly enhanced. However the multipath-induced error is still a major error source for GNSS receiver and has not obtained properly resolved yet, especially for those delayed less than 100 nanosecond with respect to the line-of-sight signal. Stemming from Beidou B1 signal and based on the characteristics that the angle-of-arrival of multipath signal is different than that of line-of-sight signal, this proposal suggests using antenna array signal processing technology as well as signal angle-of-arrival fast estimation iMLE algorithm and vector signal space projection technique, in order to mitigate the multipath errors within 100 nanosecond by forming the null on multipath direction whereas the gain on line-of-sight direction. It is expected that this algorithm can improve the performance of mitigating near-in multipath error by more than 50% with respect to the current multipath mitigation methods. It can also be combined with other mitigation methods to simultaneously mitigation near, middle and far multipath signals, significantly enhancing the receiver's positioning accuracy.

GNSS接收机技术经过过去近三十年的发展已经得到了长足的进步，在定位精度、跟踪灵敏度、首次定位时间以及功耗等方面得到了极大地提高，但是多径信号干扰却一直是困扰GNSS接收机定位精度的一个主要问题。尤其是对于延迟小于100纳秒的近多径信号目前还没有很好的抑制方法。本课题面向北斗B1信号，根据卫星直达信号和多径信号的入射角不同的特点，结合信号入射角快速估计iMLE算法和矢量信号空间投影技术，提出利用天线阵列信号处理技术在多径信号入射方向形成增益零点而卫星直达信号入射方向增益不变，从而抑制延迟小于100纳秒以内的近多径信号。和目前国内外同类算法相比对近多径误差抑制能力预计提高50%以上。本课题的天线阵列算法也能够和其他多径抑制算法结合，有效抑制近、中、远各级多径，大幅提高接收机的定位精度。

复杂环境下的精确定位问题具有迫切的应用需求。但是卫星定位信号会受到信号遮挡、多径干扰等因素影响，卫星定位精度严重下降，极端情况下会恶化1~2个数量级。其中多径信号干扰是最主要的影响因素。目前国际上主流方法分为组合相关器技术（Strobe correlator）和多径误差能量抑制技术（Multipath-energy Mitigation Technology（MMT））。Strobe技术优点是计算量较小、实现简单，缺点是多径误差抑制比较低；MMT技术利用最大似然原理能够实现70%的多径误差抑制比，缺点是搜索算法效率太低、计算量较大。本项目创新性的提出了利用天线阵子空间迭代投影技术和码相位幅度联合估计技术，用于多径误差的抑制和消除。通过信号空间域的搜索代替信号参数的搜索，提高了信号估计精度的同时简化了计算复杂度。实现多径误差抑制比优于90%，多径延迟抑制能力达到50ns，多径估计准确率比MUSIC和MDL算法提升15%，入射角估计精度提升50%。通过城市峡谷、林荫、海上平台等10多种环境下的大量测试证明该技术比国际同类算法定位精度提高20%以上，实现复杂环境单点定位精度0.8米，载波相位实时差分定位精度5厘米。本项目成果对于复杂环境高精度定位有着重要的应用价值。