Interference Suppression

Une méthode itérative d'estimation de symboles peu complexe, dans le cas de systèmes mono ou multi-porteuses avec préfixe cyclique est présentée. On profite de la structure particulière du canal convolutif inconnu ainsi que l'appartenance des symboles à un alphabet fini. La technique présentée est une technique de minimisation au sens des moindres carrés puis de projection. Elle s'avère peu coûteuse et efficace dans les problèmes de détection et d'estimation, même dans le cas de signaux bruités.

A novel quasi-MLD solution denoted Directional Lattice Descent (DLD in short) is proposed in this paper to the MIMO and ISI detection problems, which exhibits quadratic time complexity. We formulate the detection problem as that of finding the closest point in a lattice. This is solved by a proposed discrete space analogy to the continuous-space gradient descent method: an initial lattice point is selected and subsequent lattice points are iteratively calculated so that each resides at a smaller distance from the received point than its predecessor, till a termination point. The problem and its solution are formulated within a broader general framework. Implementation aspects and comparative simulation results are presented.

In this paper, two decision methods for the conventional and spread frequency shift keying (FSK and SFSK) are detailed and their extension to the coded FSK using the permutation coding are proposed. The performance results of the different methods are compared under the real indoor narrowband PLC (NB PLC) channel attenuation and impulse noise. The decision schemes are mainly the probability density function PDF-based system for the SFSK and the Non-PDF-based system (select largest) for the conventional FSK. The BER performances of the different techniques prove that the coded FSK using the Select Largest method achieves good performance results in the PLC constraints while having a low complexity, in comparison with SFSK system. The coded FSK Select Largest gives an error floor equal to 6×10 under impulse noise and channel effect compared to 2×10achieved by the coded SFSK. Index Terms FSK, SFSK, coded modulation, permutation codes, channel attenuation, impulse noise, BER.

Dans un contexte OFDM où le canal est sélectif en fréquence, on se propose d'optimiser la transmission de données scalables à la fois à l'issue de l'encodage source (nombre de classes à transmettre) et lors de l'encodage canal (protection inégale extrême contre les erreurs grâce aux rendements de code et aux modulations), sous une contrainte de qualité de service définie par l'utilisateur. Un algorithme répondant à ce problème d'optimisation, nomme FT-OFDM, est ici proposé et appliqué à la transmission de données de parole (MPEG-4). Les performances en terme de qualité perçue de la donnée reconstruite seront analysées et comparées à celles des schémas de protection inégale contre les erreurs actuels.

Hochfrequenztechnik of the German Aerospace Center (DLR) is operating the experimental airborne SAR E-SAR with a Pband radar front-end. The microstrip patch array antenna allows a signal bandwidth of slightly more than 10% of the 450 MHz carrier frequency. The radar is polarimetric on a pulse-to-pulse basis.

A linear receiver for direct-sequence spreadspectrum multiple-access communication systems under the aperiodic random sequence model is considered. The receiver consists of the conventional matched filter followed by a tapped delay line with the provision of incorporating the use of antenna arrays. It has the ability of suppressing multipleaccess interference (MAI) and narrowband interference in some weighted proportions, as well as combining multipath components without explicit estimation of any channel conditions. Under some specific simplified channel models, the receiver reduces to the minimum variance distortionless response beamformer, the RAKE receiver, a notch filter, or an MAI suppressor. The interference rejection capability is made possible through a suitable choice of weights in the tapped delay line. The optimal weights can be obtained by straightforward but computationally complex eigenanalysis. In order to reduce the computational complexity, a simple blind adaptive algorithm is also developed.

This paper presents design and practical implementation of the method for cross-channel interference suppression in polarimetric LFM-CW radar with dual-orthogonal sounding signals. Simultaneously transmitted and received signals have limited orthogonality, what results in the interfering signals in the processing channels of the radar receiver. The suppression of the interfering signals is implemented in real time, characterized by simplicity and low increase of computational resources. The efficiency of the cross-channel interference suppression is demonstrated experimentally.

The article describes the IRCTR PARSAX radar system, the S-band high-resolution Doppler polarimetric frequency modulated continuous wave (FM-CW) radar with dual-orthogonal sounding signals, which has the possibility to measure all elements of the radar target polarization scattering matrix simultaneously, in one sweep. The performance of such radar depends of the level of sounding signals orthogonality. In the main operational mode, the radar will be used for atmospheric remote sensing and polarimetric studies of ground-based targets. In such mode it will use a pair of synchronous linearly- frequency modulated (LFM) continuous signals with opposite frequency excursions of 50 MHz and duration of 1 ms. Such a combination of sounding signals has limited orthogonality even for huge BT-products, which produce cross-channel interferences. These interferences in case of radar scene with multiple pointed and distributed targets can completely degrade radar operational performance. In this a...

A new approach for matrix inversion is introduced. The approach is based on vector representation of multiple-input multiple-output (MIMO) channel matrix, in which the channel matrix is described by a linear combination of channel vectors weighted by their respective system inputs. The MIMO system output is then fed into a bank of adaptive filters, wherein the response of a given adaptive filter is iteratively minimized to match its output to the given system input. In doing so, adaptive filters equalize the impact of respective channel vectors on the MIMO channel output, while simultaneously orthogonalizing themselves from all other channel vectors, forming the channel matrix inverse. The method demonstrates satisfactory convergence and accuracy in Monte Carlo simulations conducted with varying signal-to-noise ratios (SNRs) and matrix conditioning scenarios. The suggested approach, by virtue of its adaptable characteristics, can also be employed for time-varying linear equation systems.

In this work, we propose an evolutionary-like approach to the problem of blind adaptive spatial filtering that is based on the decision-directed criterion and on the dopt-aiNet, an artificial immune network conceived to perform multimodal search in dynamic environments. The proposal was tested under static and time-varying undermodeled channel models, and, in all cases, its ability to find and track a solution close to the Wiener global optimum was attested. The obtained results reveal that the dopt-aiNet may decisively enhance the performance of adaptive arrays in scenarios built from elements that are representative of some aspects of real-world communication systems. N many real-world applications, it is of particular relevance to separate signals associated with multiple users of a given systemic resource or to restore an information signal corrupted by the presence of interferers and noise. The fulfillment of these objectives depends on the availability of a number of distinct measurements, the role of which is to engender some sort of diversity. In purely spatial problems, this diversity emerges from the placing of an adequate number of sensors in different positions, since the physical properties of the environment will be responsible, as a rule, for combining the signals in a manner that will tend to be different for each element. Therefore, it might be possible, by processing the sensor outputs in a rational way, either to model the medium through which the messages are sent or to extract the subjacent sources of information. In digital communications, problems of this kind are very common due to the pervasive requirement that several users This work was sponsored by grants from FAPESP and CNPq. C. Junqueira is with the General-Command of Aerospace Technology (CTA-IAE),

Co-channel interference cancellation is particularly challenging in the downlink of cellular radio systems, because usually only one receive antenna is available at the mobile terminal. The authors provide an overview of promising singleantenna co-channel interference cancellation techniques.

A family of detectors that exploit signal constraints is developed for maximum-likelihood detection for multiple-input-multiple-output (MIMO) systems. Real constrained detectors and decision-feedback detectors are proposed for real constellations by forcing the relaxed solution to be real. A generalized minimum mean square error (GMMSE) and constrained least squares MIMO detectors are also developed for unitary and nonunitary signal constellations. Using these constrained detectors, we propose a new ordering scheme to achieve a tradeoff between interference suppression and noise enhancement. Moreover, to mitigate the inherent error propagation, the decisionfeedback MIMO detectors are integrated with signal constraints. The simulation results show that our combined detector achieves a significant performance gain over vertical Bell Laboratories layered space-time (V-BLAST) detection.