电离层多径信道均衡方法研究

发布时间：2018-05-14 18:42

本文选题：电离层 + 多径效应　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：随着现代战争中各种新型武器的应用和发展,主要受地球曲率限制的常规雷达已无法适应对远距离、超低空等目标的探测需求,因此各种体制的超视距雷达成为世界各国争相研究的重要探测设备之一。其中,利用电磁波经电离层折射的高频天波超视距雷达以其特有的大范围远距离探测、多目标探测、隐身和超低空目标探测等特点成为许多国家的研究重点。然而,由于高频天波超视距雷达利用后向返回散射传播机理对远距离目标进行下视探测,其采用高频段的电磁波,信号通道为电离层媒质,因此其性能必定会受到高频段内的外部有源干扰、电离层媒质和下视探测方式等引入的无源干扰等因素的影响。其中,电离层媒质信道引起的电磁波多径效应会严重影响雷达的检测精度。因此,研究天波超视距雷达多径信道均衡方法,消除或降低多径效应引起的信号污染,进而提高雷达检测性能具有重要的现实意义和实用价值。本文针对高频天波超视距雷达应用中的多径效应对雷达检测性能的影响现实,首先通过分析作为雷达信道的电离层的基本特性、利用电离层传播的传播模式和传播特性等,讨论了多径效应对雷达回波(距离、多普勒频移和多普勒展宽)的影响情况。然后,为了抑制或减小多径效应对雷达回波的影响,采用了信道卷积来对消其影响的信道估计和均衡方法。在信道估计与信道均衡中通过建立信道估计与信道均衡的信号模型,采用了基于训练序列的多径信道估计方法与以最小均方误差为准则的信道均衡方法,仿真并分析了信道估计与信道均衡的效果和性能。针对信道均衡后出现的输出信号旁瓣较高的情况,采用了增加失配滤波器的方法来进行旁瓣抑制,并通过加权迭代最小二乘算法来求解失配滤波器参数,同时也对多径信道均衡后再增加失配滤波器后的输出信号的响应和效果进行了仿真和分析。之后,提出通过增加均衡长度进行旁瓣抑制并与失配滤波器法进行效果对比仿真,并针对多径信道估计、信道均衡和失配滤波器等过程中可能出现的误差,分别从信道均衡参数变化、失配滤波器参数变化和多径信道读取误差等方面对输出信号的影响进行了仿真和分析,以便于所提出的信道均衡方法在实际工程中的有效应用。最后,给出了本文研究的结论,并提出了今后进一步研究的方向。利用本文提出的多径信道均衡方法,可以达到减小多径效应对天波超视距雷达回波信号影响的目的,提高雷达对目标的检测能力。
[Abstract]:With the application and development of various new types of weapons in modern warfare, conventional radars, which are mainly limited by the curvature of the earth, have been unable to meet the detection needs of targets such as long-range, ultra-low altitude, etc. Therefore, various systems of OTH radar have become one of the most important detection equipments in the world. Among them, the high frequency sky-wave over-the-horizon radar, which is refracted by the ionosphere, has become the research focus in many countries because of its unique characteristics of large range long-range detection, multi-target detection, stealth and ultra-low altitude target detection. However, because the high frequency sky-wave over-the-horizon radar uses the backward backscattering propagation mechanism to detect the long-range target, it uses the electromagnetic wave in the high frequency band, and the signal channel is the ionospheric medium. Therefore, its performance is bound to be affected by the external active interference in the high frequency band, the passive interference introduced by ionospheric media and the down-looking detection method, and so on. The multipath effect of electromagnetic wave caused by ionospheric medium channel will seriously affect the detection accuracy of radar. Therefore, it is of great practical significance and practical value to study the multipath channel equalization method of sky-wave over-the-horizon radar, to eliminate or reduce the signal pollution caused by multipath effect and to improve radar detection performance. In this paper, the influence of multipath effect on radar detection performance in the application of high-frequency sky wave over-the-horizon radar is discussed. Firstly, the basic characteristics of ionosphere as radar channel are analyzed, and the propagation mode and propagation characteristics of ionospheric propagation are used. The influence of multipath effect on radar echo (range, Doppler shift and Doppler broadening) is discussed. Then, in order to suppress or reduce the influence of multipath effect on radar echo, channel convolution is used to eliminate the influence of channel estimation and equalization. In channel estimation and channel equalization, the signal model of channel estimation and channel equalization is established, and the multipath channel estimation method based on training sequence and the channel equalization method based on minimum mean square error are adopted. The effect and performance of channel estimation and channel equalization are simulated and analyzed. In view of the high sidelobe of output signal after channel equalization, the method of adding mismatched filter is used to suppress the sidelobe, and the parameters of the mismatched filter are solved by the weighted iterative least square algorithm. At the same time, the response and effect of output signal after multipath channel equalization are simulated and analyzed. Then, the sidelobe suppression is proposed by increasing the equalization length and the simulation results are compared with the mismatched filter method, and the possible errors in the multipath channel estimation, channel equalization and mismatch filter are analyzed. The effects of channel equalization parameters, mismatched filter parameters and multipath channel reading errors are simulated and analyzed, respectively, in order to facilitate the effective application of the proposed channel equalization method in practical engineering. Finally, the conclusion of this paper is given, and the direction of further research is proposed. The multipath channel equalization method proposed in this paper can reduce the influence of multipath effect on the echo signal of sky-wave over-the-horizon radar and improve the detection ability of radar to target.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN958.93

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