Application of Time Reversal (TR) Technique to Ultra wideband (UWB) and multi antenna (MIMO) communication systems

Abstract : In ultra wideband (UWB) systems, extremely narrow RF pulses are employed to communicate between transmitters and receivers. Because of their extremely wide bandwidth, UWB signals result in large number of resolvable multi-paths and thus reducing the interference caused by the superposition of these multi-paths. However, it also results in a complex receiver system. Time reversal (TR) is a transmission approach which permits to detect the received signal with simple receivers by shifting the complexity to the transmitter. The received signal in the TR scheme is very focused in time and spatial domains. Temporal and spatial focusing permit to reduce inter symbol interference and multi-user interference respectively. In this Ph.D. thesis, we investigate the TR UWB scheme and its application to high data rate communications. A validation of the TR scheme in the laboratory is performed with simulation, semi-measurement and measurement approaches. A parametric analysis of the TR is carried out with multiple antenna configurations (SISO, SIMO, MISO and MIMO). The results show that MIMO-TR outperforms all other configurations The robustness of the TR scheme is also studied in non stationary environments. The results suggest that if the channel maintains some partial correlation with the previous channel, TR can give a robust performance even if the total correlation of the channels is very low. Although higher bandwidths generally give better performance than the lower bandwidths, but the degradation in the performance with the variations in the channel is of the same magnitude Furthermore, TR scheme is investigated from the communication point of view. Experimental validations of a new modulation scheme and high data rate communication for TR UWB are performed for dense multipath propagation channels. It is shown that the BER performance in the indoor channel is better than the reverberation chamber. Furthermore, with the sub-band TR transmission approach, a sort of equalization is achieved which significantly improves the BER performance Finally, multi-user TR communication has been examined with modifications in the TR pre-filter. The modified TR scheme outperforms simple TR and TR with circular shift scheme, especially at higher number of simultaneous users. The results presented in this thesis suggest that the TR UWB scheme, which can easily be combined with the MIMO systems, is a promising and attractive transmission approach for future wireless local and personal area networks (WLAN & WPAN) and wireless streaming applications.
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Submitted on : Friday, July 9, 2010 - 4:23:26 PM
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Ijaz Haider Naqvi. Application of Time Reversal (TR) Technique to Ultra wideband (UWB) and multi antenna (MIMO) communication systems. Signal and Image processing. INSA de Rennes, 2009. English. ⟨tel-00499469⟩

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