Research On High-resolution Imaging And Self-adaptive Wireless Transmission Based On The Electromagnetic Time Reversal

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.