| As a technique to focus signals both temporally and spatially in complex media, time reversal (TR) was first applied in acoustics, and in recent years it was introduced into electromagnetic wave field. Because of the high-definition focusing both in time and space, if TR is applied to ultra-wideband (UWB) wireless communication, it will tremendously increase the capacity of the channel, reduce the co-channel interference, reduce inter-symbol interference, increase the information transmission rate, improve the signal-to-noise rate, and realize low-cost, secret communications in military. So TR has attracted a lot of wireless communication researchers.This paper comprehensively investigates the research progress of TR-based wireless communications, develops a UWB antenna for UWB wireless communications, constructs a TR-UWB wireless transmission experiment platform, and then experimentally studies the TR-UWB wireless transmissions under the environments of multipath-free anechoic chamber, sparse-multipath anechoic chamber and a small office. As far as we know, this is the first time full time domain method is used to fully investigate TR-based UWB wireless transmission allocated by FCC.Chapter 1 introduces the development history of UWB wireless communications, problems to be solved, present solutions and the advantages of TR technique. Then we investigate the research progress of TR-based wireless communications, theoretically explain the temporal and spatial focusing of TR, and finally introduce the development status of UWB antennas.Chapter 2 introduces the principle of TR-UWB wireless transmissions, utilizes advanced instruments to construct a TR-UWB wireless transmission experiment platform, introduces the parameters of all the hardware, and proposes demands for the antennas to be used in the experiment system.Chapter 3 develops a UWB bow-tie aperture antenna for UWB wireless communications and accomplishes the corresponding measurements both in frequency domain and in time domain. The measurement results show that the impedance bandwidth of the antenna covers the UWB band of 3.1~10.6 GHz allocated by FCC. The radiation patterns are relatively stable in the operation band. The temporal characteristic of the antenna is good and distortion caused by antenna is not severe. The antenna basically meets the demands of UWB wireless communications.Chapter 4 applies the full time domain method to investigate the TR-UWB wireless transmissions under the environments of multipath-free anechoic chamber, sparse-multipath anechoic chamber and a small office. The investigations include the recovering of the signal waveform, the multi-path effect suppression ability of TR, the energy focusing characteristic of TR, as well as the transmission rate of the experiment system, impacts of different pulses on system performance, and impacts of different antennas on system performance. The measurement results show that TR can effectively suppress the multi-path effect, remarkably increase signal amplitude, and recover the signal waveform to a certain extent. The transmission performance of the system has something to do not only with the richness degree of the multi-path, but also with the signal waveform and the characteristics of the antennas. The experiment system transmits well at the pulse rate of 1 Gpulses/s, indicating the great potential on transmission rate of TR-UWB.Chapter 5 summarizes the paper and points out the direction of the work in future. |
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