| Time Reversal(TR) is a signal processing technology, which can realize spatial and temporal focusing. This technology was proposed by M. Fink in 1990 s, and first used in underwater acoustic communications. In 2004, TR was introduced into the Electromagnetic area.It is found that TR can be used as a multiple access method in wireless communications. This multiple access method is based on the TR spatial-temporal focusing to distinguish different users, and could be considered as a special space division multiple access(SDMA). Different from the general SDMA, this method takes advantage of the TR spatial-temporal focusing rather than the beamforming.In this thesis, we have studied the wireless multiple access method based on the time reversal spatial-temporal focusing. Based on the statistic models of wireless channel, the impact of TR spatial-temporal focusing and wireless channel characters on the proposed multiple access method have been studied by the FDTD(Finite Difference Time Domain) simulation.The text is divided into four parts:Part I is the general introduction of the study of Time Reversal, as well as the multiple access methods.Part II introduces the basic theory of Time Reversal and its application in wireless communications.Part III is about the focusing characteristic of TR in space and time respectively. The spatial focusing is studied in terms of the Time Reversed electric field distribution, and also the wireless channel. The study of temporal focusing is mainly aimed at the TR reversed signal, a noise adding phenomenon is found.Part IV is focused on the TR multiple access method. A mathematical derivation of this multiple access method is given. Based on the researches in the former parts, a demonstration system of TR multiple access is shown. In addition, a noise suppression method is proposed and studied.In the last part, a summary is given and the potential work of further researches are prospected. |
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