【作者】 刘小飞；

【导师】 王秉中；

【作者基本信息】 电子科技大学 ， 无线电物理， 2010， 博士

【摘要】 本文研究了基于电磁时间反演技术的高分辨率雷达成像方法和自适应超宽带无线传输方案。一方面,针对复杂环境下雷达成像系统所要求的远作用距离、高灵敏度、高分辨率和高稳定性等重要性能指标,深入研究了电磁时间反演算子分解(DORT,法语缩写)成像方法和传输模式的时间反演多信号分类(TR-MUSIC)成像方法。另一方面,考虑到大容量、高数据率、强自适应能力的无线通信系统的发展需求,本文提出了两种基于电磁时间反演技术的自适应超宽带无线传输方案,分别是时间反演SISO/MISO脉冲超宽带传输方案和后置时间反演MIMO超宽带传输方案。首先,论文对电磁DORT算法进行了进一步深入研究,对其在电磁探测和成像问题中的全波矢量理论和应用模型进行了研究和讨论。论证了DORT在实现高效选择性目标定位和高分辨率成像方面的优势。显示其在地下目标探测、穿墙雷达成像、医疗检测等领域的应用潜力。随后,论文将该算法扩展到多频点和宽带情形,提出宽带电磁DORT成像技术。由于宽带系统能捕捉到目标对不同频率的不同响应,因此可以更精确、更全面地探测、定位和成像目标。进一步,本文提出了传输模式的电磁TR-MUSIC成像方法。对存在多散射的模型进行了全波分析,并详细讨论了其特征值系统和伪谱定义。该算法相对于DORT的优势在于其成像分辨率显著提高,可以探测间距小于一个波长的多目标。与回波模式的TR-MUSIC算法相比,该传输模式方法由于等效阵列孔径的增大进一步提高了成像分辨率,扩大了成像区域有效范围,解决了回波模式下阵列平面法线方向上重叠的多目标分辨困难的问题。随后,一种基于时间反演技术的超宽带脉冲SISO/MISO通信方案在本文提出并用于提高接收端信噪比。由于基于时间反演的传输方案的接收端不需要采用Rake接收机,明显简化了接收机结构。在该方案的基础上,本文分析了时间反演脉冲信号的功率优化问题,提出了补偿系数提取的一种有效方法。然后,进一步验证了功率补偿后的时间反演通信系统在满足美国联邦通信委员会(FCC)规定的辐射要求的同时,仍能保证其相对于传统超宽带脉冲通信的性能优势。这对实际工程中的电磁兼容设计具有重要意义。最后,本文提出一种后置时间反演MIMO超宽带无线传输方案。得益于时间反演技术的空时聚焦特性,该方案的理论分析和数值实验都显示了它在有效利用复杂环境下的多径效应、获取高信噪比方面的显著优势。同时,基于确定信道模型的通信系统分析显示,该方案的抗信道估计误差的鲁棒性明显提高。这证实了时间反演技术的引入有利于低误码率、高传输速率、高抗信道估计误差和抗多径效应的无线传输系统的实现。更多还原

【Abstract】 This dissertation investigates high-resolution radar imaging methods and self-adaptive ultra-wideband wireless transmission schemes based on the electromagnetic time reversal technique. On one hand, aiming at the important performance targets, such as the distant detection range, high sensitivity, high resolution and high stability, which are demanded for radar imaging system in complex environment, the imaging methods with decomposition of the time reversal operator (DORT , Abbreviation in French) and with the time reversal multiple signals classification (TR-MUSIC) are investigated in great depth. On the other hand, considering the developmental requirements of the large capability, high data rate, and robust self-adaptability of wireless communication systems, the dissertation proposes two self-adaptive ultra-wideband wireless transmission schemes based on the electromagnetic time reversal technique. They are time-reversed SISO/MISO impulse ultra-wideband transmission scheme and post- time-reversed MIMO ultra-wideband transmission shceme.Firstly, the dissertation further investigates the electromagnetic DORT algorithm, the full-wave vector theory and its application model of electromagnetic DORT in electromagnetic detection and imaging problems are investigated and discussed. It verifies the advantages of DORT in terms of realizing the efficient selective-localization and high resolution imaging. It demonstrates the potential in its applications on the areas of subsurface targets detection, through-wall radar imaging and medical examinations. Then, the algorithm is extended to multiple frequencies and wideband cases. The wideband electromagnetic DORT imaging technique is proposed. Since the wideband system can capture different responses from the targets in different frequency points, it can perform the detection, localization and imaging for the targets more accurately and completely.Furthermore, the imaging method with transmit-mode electromagnetic TR-MUSIC is proposed. The full-wave analysis of the multiple scattering models is carried out, and its egienvalue system and pesudospectrum definition are discussed in detail. Compared with the DORT method, the superiority is the great improvement on imaging resolution. It can distinguish the targets with distance smaller than one wavelength. Compared with the echo-mode TR-MUSIC, the transmit-mode method futher improves the resolution due to the improved effective array aperture, and the coverage of imaging domain is enlarged. It overcomes the problem with echo-mode scenario, which is an obstacle occurred in the detection of multiple targets overlapping in the direction of normal line of the array plane.Subsequently, a time reversal technique based ultra-wideband impulse SISO/MISO communication scheme is proposed in this dissertation and employed to improve the signal-noise-ratio of the receiver. Since the reveiver of the time reversal based transmission scheme needs no Rake receiver any more, the structure is obviously simplified. Based on this shceme, the dissertation analyzes the power optimization of the time reversal impulse signals and proposes an effective method of extracting the compensated coefficient. And then it is futher proved that the time reversed communication system can meet Federal Communication Commission (FCC)’s regulation of radiation requirement and at the same time keep the performance superiority over the classical ultra-wideband impulse communication, when the power is compensated. This is significant for the electromagnetic compatibility design in practical engineering.The last part of the dissertation proposes a post- time-reversed MIMO ultra-wideband wireless transmission shceme. Taking advantages of the spatial-temporal focusing characteristics of the time reversal technique, both the theoretical analysis and numerical experiments of this scheme show the great superiority on effectively utilizing the mluti-path effect under complex environment and achieving higher signal-noise-ratio. Meanwhile, the communication system analysis based on determinate channel model demonstrates that the robustness against the channel estimate error is evidently enhanced. It is verified that the introduction of time reversal technique is helpful for realization of the low bit-error-rate, high data rate, and high robustness against the channel estimate error and malti-path effect in wireless transmission systems.更多还原