On the Use of Uniform Circular Arrays for Characterizing UWB Time Reversal

Time reversal (TR) is a promising technique for the improvement of future telecommunication systems. A better understanding of this phenomenon requires deeper investigation of real propagation channels. This paper presents a new scheme to characterize the space-time focusing characteristics of time reversal. The originality of this technique relies on the use of a virtual uniform circular array, which allows to simply derive the space-time focusing characteristics of the channel. An extensive ultrawideband (UWB) propagation experiment is reported, and the method is applied to the experimental data. Different focusing parameters are computed in different configurations. In particular, the paper shows that the delay spread parameter is inappropriate to study time focusing, and a new parameter characterizing the maximum symbol rate is introduced. In a UWB single-input single-output (SISO) configuration, time reversal increases the power of the strongest path by up to 10 dB and the total received power by up to 5 dB. Our analysis shows that when the received signal is appropriately focused in time, the data rate can be increased by a factor of three. The received signal is also focused in space, and the average size of the focus area is approximately 3lambda , where lambda is the wavelength of the central frequency. We observed that the focusing spot is larger than the ideal case and is often directed inline with the transmitter direction. At 9 lambda away from the target, the received signal is attenuated by up to 10 dB in a non line-of-sight environment, which demonstrates the high focusing capabilities of the TR-UWB scheme.

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