摘要
随着全球定位系统(GPS)在军用和民用领域的应用范围和数量日益扩大,GPS接收机的抗干扰问题受到国内外学者的广泛关注,同时基于阵列信号处理的GPS抗干扰技术则逐渐成为目前的一个研究热点。在对GPS信号的干扰中,压制式干扰是最大的威胁,而抑制多径干扰则是高精度定位的有效保障。本课题围绕两种不同应用环境下的基于阵列信号处理的GPS接收机抗干扰技术和GPS的多径抑制技术展开深入讨论。
为顺利开展GPS接收机抗干扰技术的深入研究,采用直接模拟数字中频GPS信号方式建立GPS接收机软件研究平台,利用GPS C/A码的频谱特性讨论连续波干扰频率对接收机捕获性能的影响,详细分析调频-调幅、宽带噪声干扰信号的相关参数及相干、非相干积分时间对捕获噪声电平的影响,并采用蒙特卡罗误码率仿真模型研究各种干扰信号对输出误码率的影响。
传统的波束形成技术计算复杂度为O(n3),并且干扰波达方向角的估计误差对其性能有很大影响,多级维纳滤波器结构的空时降维GPS接收机抗干扰方案虽然将计算复杂度降低到了O(n2),但该方案需要以期望信号作为参考信号,而GPS子空间抗干扰方案则只需要获得期望卫星的波达方向角。深入分析FAPI子空间跟踪算法后发现该算法比同类子空间跟踪算法具有更好的估计性能和收敛性能,通过讨论干扰个数估计值对子空间跟踪类GPS接收机抗干扰方案的影响,提出一种适用于该类抗干扰方案的“有效”干扰个数估计方法和一种新的抗干扰方案,将新的抗干扰方案与传统波束形成技术、多级维纳滤波器技术及同类子空间抗干扰技术进行比较发现新方案具有优越性。
针对GPS C/A码信号的恒模属性,详细分析基于恒模算法的GPS接收机盲抗干扰方案原理,重点解决其实际应用中存在的关于C/A码数字化、计算量和收敛时间问题,提出一种改进的GPS接收机恒模盲抗干扰方案并仿真验证其抗干扰性能。方案采用10ms的解扩数据,将收敛时间缩短到约0.2毫秒,该类盲抗干扰方案更适用于跟踪状态下的GPS接收机。
深入讨论GPS多径信号引起的码相位和载波相位误差性能,分析比较经典的窄相关器、MEDLL、Strobe相关器、改进的Strobe相关器及E1/E2 GPS多径抑制技术,发现当存在短多径信号时这些方法均没有表现出很好的性能。多径信号引起的码相位误差有时正时负,文章着重分析自适应多径估计与抑制技术,提出一种修正的自适应滤波多径估计与抑制方案,抽头间隔时间直接决定了该方案的多径抑制性能,文中方案优于其它经典方法,并且对短多径信号有很好的抑制效果。
Along with the increasing quantity and extension of application in the military and civil field, the scholars inside and outside have been paid more and more attentions to the anti-jamming problem of GPS receiver, simultaneously, the GPS anti-jamming technology based on array signal processing gradually becomes a research focus now. The blanket jamming is the supreme menace among the interferences for GPS, while the suppression of GPS multipath signal ensures the high-accuracy positioning availably. The thesis makes an in-depth research on the GPS anti-jamming technologies used in two different application conditions based on array signal processing and the GPS multipath rejection.
A GPS research platform is designed by adopting software simulator to generate IF GPS signals, the GPS C/A code spectral characteristic is utilized to discuss the affection on the performance of acquisition by CW interference, and the effects to the noise power in acquisition of the parameters of FM-AM, wideband noise signal and the coherent integration time, non-coherent integration time are analysed in detail, and the Monte Carlo model is adopted for the research on the effects to the output bit error rate of these interferences.
The computational complexity of the conventional beamforming is O(n3), and the estimation error of the interference DOA effects the performance deeply, although the rank-reduced STAP of Multistage Wiener Filter(MWF) reduces the computational complexity to O(n2), it needs the reference signal, while the GPS anti-jamming based on the subspace tracking technique only requires the DOA of the signal of interest(SOI). It is discovered that the FAPI algorithm has better subspace estimation performace and convergence performace, by discussing the effect of the interference number to this kind of GPS anti-jamming methods. An estimation method of the effective interference number that is suitable for the methods and a novel anti-jamming scheme are proposed. By comparing it with the conventional beamforming and MWF, the advantage of the novel one is obtained.
Aiming at the property of the GPS C/A code, the technique of blind GPS anti-jamming receiver based on constant modulusalgorithm (CMA) is analysed in detail, and the problems which are about digital code, computational complexity and convergence time are solved. A modified blind GPS anti-jamming receiver is proposed, and the computer simulations validate it. In the modified scheme,10ms' data is adopted for despread, and the convergence time is reduced to 0.2ms. This method is very suitable for the receiver which is in the tracking condition.
The code phase error and the carrier phase error performances caused by the GPS multiputh signal in-depth are discussed. By analysing the GPS multiputh suppression based on narrow correlator, MEDLL, Strobe correlator, enhanced Strobe correlator and E1/E2 correlator, it is known that all of them have a weak capability when short multiputh signals exist. Sometimes the code phase error is positive, and sometimes it is negative. the adaptive multipath estimation and elimination technique are analysed, and a modified scheme is proposed. The time between the two taps determine its performance straightly. The modified adaptive multipath estimation and elimination technique is better than the classical methods, and it can give a better suppression performance for short multiputh signals.
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