Analysis of Time-Reversal-Based Propagation for Spatial focusing and Multiplexing

4 pagesInternational audienceTime-Reversal (TR) technique is well-known for itsability of focusing waves. A common claim, based on this focusing ability, supports that TR technique may allow spatial multiplexing and secure transmissions. In the present paper, measurements campaigns were performed in a reverberation chamber and in a standard office to assess the viability of TR technique. It is shown that the results obtained do not support the common claim, especially in standard indoor environment where the focusing ability is strongly degraded

True Time Reversal via Dynamic Brillouin Gratings in Polarization Maintaining Fibers

A novel technique to realize true time reversal of an optical signal, using dynamic Brillouin gratings in high-birefringence fibers, is proposed. A data sequence of optical pulses with 2-ns duration was efficiently time-reversed

Performance of MISO Time Reversal Ultra-wideband over an 802.15.3a Channel Model

Abstract-This paper analyzes the performance of a baseband multiple-input single-output (MISO) time reversal ultrawideband system (TR-UWB) over the IEEE 802.15.3a channel model. Two scenarios are considered, CM1 based on LOS (0-4m) channel measurements and CM3 based on NLOS (4-10m) channel measurements. A semi-analytical performance expression is derived and compared with simulation results in terms of the number of antenna elements, number of users, and transmission rate. The results show that the system performance is improved with an increase in the number of transmit antenna elements and that additional equalization and multiple access enhancement schemes are necessary for high transmission rates

Intrinsic subspace convergence in TDD MIMO communication

In numerical linear algebra, students encounter early the iterative power method, which finds eigenvectors of a matrix from an arbitrary starting point through repeated normalization and multiplications by the matrix itself. In practice, more sophisticated methods are used nowadays, threatening to make the power method a historical and pedagogic footnote. However, in the context of communication over a time-division duplex (TDD) multipleinput multiple-output (MIMO) channel, the power method takes a special position. It can be viewed as an intrinsic part of the uplink and downlink communication switching, enabling estimation of the eigenmodes of the channel without extra overhead. Generalizing the method to vector subspaces, communication in the subspaces with the best receive and transmit signal-to-noise ratio (SNR) is made possible. In exploring this intrinsic subspace convergence (ISC), we show that several published and new schemes can be cast into a common framework where all members benefit from the ISC.Peer Reviewe

Code-Multiplexing-Based One-Way Detect-and-Forward Relaying Schemes for Multiuser UWB MIMO Systems

In this paper, we consider decode-and-forward (DF) one-way relaying schemes for multiuser impulse-radio ultrawideband (UWB) communications. We assume low-complexity terminals with limited processing capabilities and a central transceiver unit (i.e., the relay) with a higher computational capacity. All nodes have a single antenna differently from the relay in which multiple antennas may be installed. In order to keep the complexity as low as possible, we concentrate on noncoherent transceiver architectures based on multiuser code-multiplexing transmitted-reference schemes. We propose various relaying systems with different computational complexity and different levels of required channel knowledge. The proposed schemes largely outperform systems without relay in terms of both bit error rate (BER) performance and coverage

Spatial diversity in passive time reversal communications

A time reversal mirror exploits spatial diversity to achieve spatial and temporal focusing, a useful property for communications in an environment with significant multipath. Taking advantage of spatial diversity involves using a number of receivers distributed in space. This paper presents the impact of spatial diversity in passive time reversal communications between a probe source (PS) and a vertical receive array using at-sea experimental data, while the PS is either fixed or moving at about 4 knots. The performance of two different approaches is compared in terms of output signal-to-noise ratio versus the number of receiver elements: (1) time reversal alone and (2) time reversal combined with adaptive channel equalization. The time-varying channel response due to source motion requires an adaptive channel equalizer such that approach (2) outperforms approach (1) by up to 13 dB as compared to 5 dB for a fixed source case. Experimental results around 3 kHz with a 1 kHz bandwidth illustrate that as few as two or three receivers (i.e., 2 or 4 in array aperture) can provide reasonable performance at ranges of 4.2 and 10 km in 118 in deep water. (c) 2006 Acoustical Society of America