Channel Shortening for OFDM Systems: An Improved Algorithm in Noisy Environments

International audience—In this paper, we propose an efficient channel shortening algorithm, applied to OFDM systems, exploiting a particular decomposition of the Toeplitz convolution channel matrix and of the channel shortening filter (CSF). Unlike classical methods which optimize the CSF following one single criterion applied to the whole response of the filter, our decomposition allows for addition of complementary criteria. Similarly to classical CS techniques, the proposed method tries to concentrate most of the energy of the shortened channel impulse response (SCIR) within the tolerated delay-spread window. However, our second applied criterion aims at limiting the noise enhancement on each sub-carrier by minimizing the spectral distortions related to the filtering function. The performance of the algorithm in terms of computational complexity and bit error rate (BER) is studied by simulations and compared to the reference algorithm of the literature referred to as maximum shortening signal to noise ratio (MSSNR) algorithm

Capacity estimation of MIMO ionospheric channels

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Design and test of a HF MIMO system of transmission set up with compact antenna arrays

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Design of a high-frequency (3-30 MHz) multiple-input multiple-output system resorting to polarisation diversity

International audienceThis study presents a multiple-input multiple-output (MIMO) architecture utilising polarisation diversity to increase the capacity of high-frequency (HF) radio links through the ionospheric channel. A summary of physics focuses on the polarisation of radio waves propagated in the ionosphere. This preliminary step introduces the original idea of diversity in the transmitted polarisations to replace the classical space diversity for MIMO applications. This solution enables a reduction of the inter antenna spacing which is convenient in the context of decametric wavelengths. Simulations, referring to the theoretical expression of channel capacity and involving realistic models of ionospheric radio links, underline a significant increase in performances for this particular MIMO structure if compared to a single-input single-output system. Additionally, the trade-off between capacity gain and complexity appears balanced with the development of a 2 x N MIMO system transmitting two complementary circular polarisations. More specifically, the design of a 2 x 2 MIMO system is described in the context of a single carrier waveform and frequency-domain equalisation, resorting to classical solutions for the different signal processing modules. A global simulation, involving the entire transmission system, is carried out and gives an estimate of the maximal data transfer rate compatible with a requested quality of service

A MIMO solution based on polarization diversity for ionospheric radio links

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Performance Estimation of a Diversely Polarized MIMO Solution for HF (3-30 MHz) Applications

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Implementation of a MIMO solution for ionospheric HF (3-30 MHz) radio links

International audienceMIMO architectures are generally based on antenna arrays with spatial diversity. An implementation in the particular context of trans horizon transmission through the ionospheric channel copes with the problem of prohibitive array aperture, the wavelength being decametric in the corresponding HF frequency band (3-30 MHz). Therefore, this paper proposes an alternative resorting to the diversity in transmitted polarizations. The design of an original 2x2 MIMO system is detailed and the experimentations carried out on a 280km long transmission are presented. The first results underline a data transfer rate reaching a value of 24.09 kbps (in a 4.2 kHz bandwidth) which significantly exceeds the current standards for HF modems. Keyword

Development and test of a trans-horizon communication system based on a MIMO architecture

International audienceA multiple-input multiple-output (MIMO) system for trans-horizon radio communications within the high-frequency (HF) band (3 to 30 MHz) is presented. The diversity of transmitted polarizations is proposed as an alternative to spatial diversity in order to limit the aperture of antenna arrays at both ends of the radio link. In a theoretical step providing the estimation of capacity gain for different MIMO architectures, a 2 x 2 MIMO solution transmitting two complementary circular polarizations is identified as a balanced trade-off between performance increase and complexity. The design of the corresponding system is described with a focus on antenna arrays and the kind of signal processing that should be implemented. This novel communication system has been tested on a 280-km-long radio link. The first results underline a data transfer rate reaching a value of 24.09 kbps (in a 4.2-kHz bandwidth) that significantly exceeds the current standards for HF modems

辮狀河川生物棲地之水理與地形因素探討

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