Robin Gerzaguet • Associate Professor @ ENSSAT

I am an associate professor in "Ecole Nationale Supérieure des sciences appliquées et de technologies (ENSSAT)" and a researcher in Granit Team of IRISA laboratory since 2017.

I have received the degree in electrical engineering from Grenoble-INP, France, in 2011 and a Ph.D. degree in both the Gipsa-lab (involved in the CICS team) and ST-Microelectronics in 2015.

Between 2015 and 2017 I have been a research engineer at CEA-Leti.

My research interests are in signal processing techniques dedicated to digital communication, including multicarrier waveforms, channel estimation, synchronisation and digital RF impairments compensation.

Teaching

Lecture on Wireless Communications

Robin Gerzaguet

Lessons on Wireless communications. Recall on digital communications, introduction on deterministic multipath channel and Raygleigh channel. Presentation on Wideband Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiple (OFDM)

Digital Signal Processing Lab

Robin Gerzaguet, Daniel Menard

Study and implementation of a Infinite Impulse Response (IIR) filter on DSP from Texas Instrument. Float and fixed point analysis and real time implementation.

Work

5G Field Trials @3.5GHz (2017)

Multi-service transmissions are expected in the upcoming fifth-generation (5G) of cellular networks. These heterogeneous applications lead to many constraints that need to be addressed in a flexible way. We have investigated the division of the bandwidth into several subbands, each having a different service and numerology.

This work highlights and demonstrates the possible coexistence of Broadband (eMBB), Ultra-Reliable Low-Latency (uRLLC) and new IoT (eIoT) services within the same channel using a flexible waveform. Field test experiments have been done with an implementation of the BF-OFDM physical layer on prototype hardware boards. These field trials have been made in Minatec Campus in Grenoble and use the new 5G 3.5GHz band.

Field trials in Minatec Campus


5G new waveforms (2015 -- )

The future generations of wireless networks (a.k.a 5G) will have to cope with a high degree of heterogeneity in terms of services (Broadband, machine type communications (MTC), Internet of Things (IOT), Vehicular to vehicular (V2V) . . . ) and requirements (high data rates, low latency, high reliability, coexistence, . . . )

Even though Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) is the most prominent multi-carrier modulation technique in wireless standards for below 6GHz transmission (used in 4G, DVB-T, Wifi, . . . ), it also exhibits some intrinsic drawbacks. These limitations make CP-OFDM poorly appealing for 5G and have motivated the study and the comparison of alternative waveforms such as Universal-Filtered OFDM (UF-OFDM) or Filter Bank Multicarrier (FBMC).

We have introduced a new quasi-orthogonal waveform called Block-Filtered OFDM (BF-OFDM) that combines most of the advantages of the aforementioned waveforms at the price of slight complexity increase. Spectral localization and performance in multi-user scenario is enhanced w.r.t OFDM and simple equalization as well as all classical MIMO schemes can be straightforwardly considered. The proposed waveform is scalable and can be used in various configurations and services, which paves the way for future heterogeneous systems.

This waveform has been studied in the scope of mmMagic and Fantastic-5G H2020 projects and in the french ANR WONG-5. The initial proposal has won the 2017 International Conference on Communication (ICC-2017) best paper award.

Waveform comparison


Riesco Platform (2013 - 2015)

Riesco (for Radio Logicielle pour l'Evaluation des Systèmes complexes) is a platform of the Gipsa-Lab dedicated to digital communication applications. It is composed of software defined radios (SDRs) network and has been developed since 2013 (by Damien Roque) for teaching, proves of concept and real-time digital communication validation .

Channel Estimation versus time and versus OFDM carrier index, with USRP-B200

The platform is composed of 6 software defined radios, 4 USRP N210 and 2 USRP B200 from Ettus Research. The SDRs are mastered by an external Octoclock and controlled by a host PC under Xubuntu with GnuRadio project .



PhD Thesis (2012 - 2015)

Radio frequency transceivers are now massively multi-standards, which means that several communication standards can cohabit in the same environment. As a consequence, analog components have to face critical design constraints to match the different standards requirements and self-interferences that are directly introduced by the architecture itself are more and more present and detrimental.

My work exploits the dirty RF paradigm : we accept the signal to be polluted by self-interferences and we develop digital signal processing algorithms to mitigate those aforementioned pollutions and improve signal quality.

The main purpose is to study different self-interferences and propose baseband models and digital adaptive algorithms for which we derive closed form formulae of both transient and asymptotic performance. This approach is necessary to propose algorithms specifications than can cope with different standards or requirements. We also propose an original adaptive step-size overlay to improve transient performance of our method. The final step is to validate our approach on a system on chip dedicated to cellular communications and on a software defined radio.

Our work on Tx Leakage digital compensation has been granted by Crowncom 2016 Best paper award.

Publications

Articles in Journal

IEEE Access On the road to 5G: Comparative study of Physical layer in MTC context

Yahia Medjahdi, Sylvain Traverso, Robin Gerzaguet & al

During the past few years, we are witnessing the emergence of 5G and its high-level performance targets. Waveform (WF) design is one of the important aspects for 5G that received considerable attention from the research community in recent years. To find an alternative to the classical orthogonal frequency division multiplexing (OFDM), several multicarrier approaches addressing different 5G technical challenges, have been proposed. In this paper, we focus on critical machine-type communications (C-MTC), which is one of the key features of the foreseen 5G system. We provide a comparative performance study of the most promising multicarrier WFs. We consider several C-MTC key performance indicators: out-of-band radiations, spectral efficiency, end-to-end physical layer latency, robustness to time and frequency synchronization errors, power fluctuation, and transceiver complexity. The investigated multicarrier WFs are classified into three groups based on their ability to keep the orthogonality: in the complex domain, e.g., most of the OFDM-inspired WFs, in the real domain like offset-quadrature amp;litude modulation (QAM)-based techniques, and non-orthogonal WFs like generalized frequency division multiplexing and filter bank-based multicarrier-QAM. Finally, the performances of these WFs are thoroughly discussed in order to highlight their pros and cons and permit a better understanding of their capabilities in the context of C-MTC.

Eurasip Journal Performance of fractional delay estimation in joint estimation algorithm dedicated to digital Tx leakage compensation in FDD transceivers

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

This paper deals with the performance of the fractional delay estimator in the joint complex amp;litude/delay estimation algorithm dedicated to digital Tx leakage compensation in FDD transceivers. Such transceivers suffer from transmitter-receiver signal leakage. Combined with non linearity of components in the receiver path, the baseband received signal is impaired by a baseband polluting signal. This baseband polluting term depends on the equivalent Tx leakage channel which models leakages of the receiver path. In (Gerzaguet et al., Digit. Signal Proc 51:35–46, 2016), we have proposed a Tx leakage interference cancellation algorithm based on joint estimation of the complex gain and the fractional delay of the equivalent Tx leakage channel and we have derived the asymptotic performance of the complex gain estimator, that showed the necessity of the fractional delay estimation. In this paper, we propose a comprehensive study of the fractional delay estimation algorithm and its analytic performance. The study is based on the analysis of the S-curve and loop noise variance of the timing error detector, from which an approximation of the asymptotic performance of the joint estimation algorithm is derived.

Physical Communication Waveform contenders for 5G: Description, analysis and comparison

Jean-Baptiste Doré, Robin Gerzaguet, Nicolas Cassiau, DimitriKtenas

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, flexible and efficient use of all available non-contiguous spectra for different network deployment scenarios is one challenge for the future 5G. To maximize spectrum efficiency, a flexible 5G air interface technology capable of mapping various services to the best suitable combinations of frequency and radio resources will also be required. In this work, a fair comparison of several 5G waveform candidates (UFMC, FBMC-OQAM, and FBMC-QAM) is proposed under a common framework. Spectral efficiency, power spectral density, peak to average power ratio and performance in terms of bit error rate under various realistic channel conditions are assessed. The waveforms are then compared in an asynchronous multi-user uplink transmission. Based on these results, in order to increase the spectral efficiency, a bit loading algorithm is proposed to cope with the non-uniform distribution of the interference across the carriers. The benefits of these new waveforms for the foreseen 5G use cases are clearly highlighted. It is also stressed that some concepts still need to be improved to achieve the full range of expected benefits of 5G.

Eurasip Journal The 5G candidate waveform race: a comparison of complexity and performance

Robin Gerzaguet, Nikolaos Bartzoudis, Leonardo Gomes Baltar, Vincent Berg, Jean-Baptiste Doré, Dimitri Kténas, Oriol Font-Bach, Xavier Mestre, Miquel Payaró, Michael Färber, Kilian Roth

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, the flexible and efficient use of non-contiguous unused spectrum for different network deployment scenarios is considered a key challenge for 5G systems. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and radio resources. In this work, we propose a comparison of several 5G waveform candidates (OFDM, UFMC, FBMC and GFDM) under a common framework. We assess spectral efficiency, power spectral density, peak-to-average power ratio and robustness to asynchronous multi-user uplink transmission. Moreover, we evaluate and compare the complexity of the different waveforms. In addition to the complexity analysis, in this work, we also demonstrate the suitability of FBMC for specific 5G use cases via two experimental implementations. The benefits of these new waveforms for the foreseen 5G use cases are clearly highlighted on representative criteria and experiments.

Digital Signal Processing Performance of a digital transmitter leakage LMS-based cancellation algorithm for multi-standard radio-frequency transceivers

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

This paper deals with a joint estimation algorithm that is dedicated to digital compensation of transmitter leakage pollution in frequency division duplexing transceivers. These transceivers are affected by transmitter to receiver signal leakage. Combined with the nonlinearity of amp;lifying components in the receiver path, the baseband signal received can be severely polluted by a baseband polluting term. This term is based on the square modulus of the transmitted signal, and it depends on the equivalent transmitter leakage channel which models leakages and the receiver path. Here, we consider a nonconvolutive, time-varying channel that is modeled by a time-varying complex gain and the presence of a fractional delay, modeling the propagation effects into the receiver. The complex gain is a sum of two components, a constant term that models static effects, and a first-order autoregressive model that approximates the time variation of the transmitter leakage channel. We focus here on a fully digital approach, using digital signal processing techniques and knowledge of the transmitted samp;les to mitigate the pollution. We first express the asymptotic performance of a transmitter leakage gain estimator piloted by a reference-based least-mean-square (LMS) approach in the synchronized case, and then we derive the influence of the fractional delay. We show that, in practice, the fractional delay cannot be neglected, and we propose a joint estimation of the fractional delay and the transmitter leakage gain to perform digital compensation. The proposed method is adaptive, recursive and online, and it has low complexity. This algorithm, that is developed for a flat transmitter leakage channel case, is seen to be robust in a typical selective channel simulation case, and more suitable than a classic multi-tap LMS scheme proposed in the literature.

Digital Signal Processing On the Performance of Digital Adaptive Spur Cancellation for Multi-Standard Radio Frequency Transceivers

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

This study deals with the asymptotic performance of a multiple-spur cancellation scheme. Radio frequency transceivers are now multi-standard and specific impairment can occur. The clock harmonics, called spurs, can leak into the signal band of the reception stage, and thus degrade the performance. The performance of a fully digital approach is presented here. A one-spur cancellation scheme is first described, for which we exploit the a priori knowledge of the spur frequency to create a reference of the polluting tone with the same frequency. A least-mean-square (LMS) algorithm block that uses this reference to mitigate the polluter is designed. However, due to imperfections in the physical components, there is a shift between the a priori frequency and the actual frequency of the spur, and the spur is affected by Brownian phase noise. Under these circumstances, we study the asymptotic and transient performance of the algorithm. We next improve the transient performance by adding a previously proposed adaptive-step-size process. In a second part of this paper, we present a multiple-spur parallel approach that is based on the one-spur~cancellation scheme, for which we provide a closed-form expression of the asymptotic signal-plus-noise interference ratio in the presence of frequency shifts and phase noise.

Conference Proceedings & Patents

ISWCS Comparison of promising candidate waveforms for 5G: WOLA-OFDM versus BF-OFDM

Robin Gerzaguet, Yahia Medjahdi, David Demmer, Rafik Zayani, Jean-Baptiste Doré, Hmaied Shaiek, Daniel Roviras

One of the main issues, in the specification of the 5G radio access network (RAN) technology, is the design of a new waveform, overcoming the limitations of the CP-OFDM in terms of frequency localization, spectral efficiency and robustness to users asynchronism, while keeping low latency and reduced transceiver implementation complexity. In the last decade, many waveforms have been proposed in order to achieve the best compromise between the aforementioned constraints. This paper aims at comparing, as fair as possible, the performances of promising schemes namely WOLA-OFDM and BF-OFDM in terms of spectrum confinement, transmitter complexity and robustness in a typical multi-user asynchronous scenario.

EuCNC Filter design for 5G BF-OFDM waveform

David Demmer, Robin Gerzaguet, Jean-Baptiste Doré, Didier Le Ruyet, Dimitri Kténas

A flexible and efficient use of the frequency resource is a key challenge for future wireless technologies. The new requirements are not satisfied by the CP-OFDM which has motivated the research on alternative waveforms. Recently, Block-Filtered OFDM modulation scheme has been proposed. This waveform addresses most of the CP-OFDM's drawbacks at the price of a slight complexity increase of the transmitter. The scheme is based on a filter-bank, a precoding stage that ensures the Near Perfect Reconstruction property and a pre-compensation stage which avoids filtering at the receiver. In this paper, the filter specifications for BF-OFDM are derived and an optimization method based on self-interference rejection is proposed. Optimized filter shape can provide up to 70 dB of Signal-to-Interference Ratio which justifies the Near Perfect Reconstruction property with an enhanced spectral confinement and no channel performance degradation.

ICC Block-filtered OFDM: A novel waveform for future wireless technologies

David Demmer, Robin Gerzaguet Jean-Baptiste Doré & Dimitri Kténas

The forthcoming fifth generation of mobile technology (5G) will be designed to satisfy the demands of 2020 and beyond. 5G does not just promise a huge increase in terms of data rates and capacity but it also targets new kind of use cases like Internet of Things or vehicular communications. The currently deployed 4G technology does not provide enough network capabilities to support this wide diversity of applications which has motivated the research on alternative waveforms. In this article, a new promising modulation scheme is introduced: Block-Filtered OFDM (BF-OFDM). The proposed waveform demonstrates an excellent frequency localization and can straightforwardly be integrated with the OFDM know-how and LTE principles. Besides, the proposed waveform relies on a receiver similar to the one used in CP-OFDM. BF-OFDM systems are also scalable, which is an interesting feature in order to steer the network capabilities on demand.

ICC Block-Filtered OFDM: A new Promising Waveform for Multi-service Scenarios

Robin Gerzaguet, David Demmer, Jean-Baptiste Doré & Dimitri Kténas

Best Paper Award

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, flexible and efficient use of all available non-contiguous spectrums for different network deployment scenarios is one challenge for the future 5G. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and radio resources. Such requirements are not satisfied by legacy CP-OFDM and alternative multicarrier waveforms such as UFMC and FBMC partially meet them. In this article, we introduce a new quasi-orthogonal waveform called Block-Filtered OFDM (BF-OFDM) that combines most of the advantages of the aforementioned waveforms at the price of slight complexity increase. Spectral localization and performance in multi-user scenario will be enhanced w.r.t OFDM and simple equalization as well as all classical MIMO schemes can be straightforwardly considered. The proposed waveform offers the same performance in presence of multipath channel as CP-OFDM and is also scalable which paves the way for future multi-service scenarios.

Globecom Evaluation of Waveforms for Mobile Radio Communications Above 6 GHz

Ali A. Zaidi, Jian Luo, Robin Gerzaguet & al

This paper provides a high level comparison of several multi-carrier and single-carrier waveforms based on the evaluations performed in mmMAGIC project. The waveforms are assessed for the performance indicators that are relevant to mobile radio communication above 6 GHz, specially the millimeter wave frequencies. The evaluations are performed in mmMAGIC waveform simulators under common assumptions on carrier frequencies, waveform parameters, channel and impairment models. The evaluation results reveal that OFDM is suitable for above 6 GHz communication. For above ↑30 GHz communication, OFDM with PAPR reduction and DFTS-OFDM are both promising options. Moreover, some potential enhancements to OFDM (use of window/pulse shape, subband filters, unique word, zero tailing), parametrization of FBMC, and constrained envelop continuous phase modulation for above 6 GHz communication have been discussed.

ISWCS Performance of soft-decision linear receivers for spatial-multiplexing FBMC/OQAM

David Demmer, Robin Gerzaguet, Jean-Baptiste Doré & Didier Le Ruyet

With the increasing demand for mobile data traffic, enhanced frequency localized transmissions are considered for the generation of wireless networks to come. Filter Bank Multi-Carrier modulation, with the use of Offset-QAM, proves to be an interesting candidate to satisfy those spectrum constraints. Contrary to CP-OFDM, FBMC does not use any CP. Its spectral efficiency is improved but it also weakens the transmissions over highly frequency selective channels. Complex detection stage based on precoding or multi-tap equalization is thus necessary to prevent orthogonality losses. Another solution can be the use of the Frequency-Spreading scheme which improves the frequency resolution. In this paper, we propose to extend probabilistic decoding to linear FBMC receivers. The performances of the two common FBMC receiver structures, PolyPhase Network and Frequency-Spreading, are assessed over frequency-selective LTE channel models. The analytical formulae of the likelihood metrics are also derived.

Crowncom Performance of fractional delay estimation in joint estimation algorithm dedicated to digital Tx leakage compensation in FDD transceivers

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

Best paper award

This paper deals with the performance of the fractional delay estimator in the joint complex amp;litude / delay estimation algorithm dedicated to digital Tx leakage compensation in FDD transceivers. Such transceivers are affected from transmitter-receiver signal leakage. Combined with non linearity of components in the received path, it leads to a pollution in the baseband signal. The baseband polluting term depends on the equivalent Tx leakage channel, modeling leakages and the received path. We have proposed in [7, 8] a joint estimation of the complex gain and the fractional delay and derived asymptotic performance of the complex gain estimator, that showed the necessity of the fractional delay estimation. In this paper, we propose a comprehensive study of the fractional delay estimation algorithm and its analytic performance. The study is based on the analysis of the S-curve and loop noise variance of the timing error detector, from which an approximation of the asymptotic performance of the joint estimation algorithm is derived.

VTC Spring A Preliminary Study on Waveform Candidates for 5G Mobile Radio Communications Above 6 GHz

Ali A. Zaidi, Jian Luo, Robin Gerzaguet and al

This paper provides an overview and preliminary comparison of several multi-carrier and single-carrier waveforms that are potential candidates for future 5G mobile radio communications above 6 GHz. The waveforms are assessed primarily based on the established and known results as well as recent findings keeping in view the design requirements that are relevant to using frequencies above 6 GHz, especially the millimeter wave frequencies. The Key Performance Indicators and degrees of freedom in the design of different waveforms and their potential applications for mm-wave communications are discussed. Certain features that are particularly interesting for mm-wave communication and require further investigations are also highlighted. Furthermore, a common framework for synthesizing different waveform candidates has been developed. Finally, a preliminary qualitative comparison of different multi-carrier and single carrier waveforms has been derived.

VTC Spring 5G Cellular Networks with Relaxed Synchronization: Waveform Comparison and New Results

Jean-Baptiste Doré, Robin Gerzaguet & Dimitri Kténas

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Flexible and efficient use of all available spectrums for different network deployment scenarios is one challenge for the future 5G. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and time resources. In this work, we study and fairly compare the performance of different waveforms (UFMC, FBMC, and legacy LTE waveforms) in cellular networks with relaxed synchronization. First, a unified frame structure is discussed to introduce the context. Then we compare the robustness of the waveform contenders in the envisaged scenario. Based on these results, a bit loading algorithm is proposed to cope with the non-uniform distribution of the interference across the carriers in order to increase the spectral efficiency.

ETSI Workshop A Preliminary Study on Waveform Candidates for 5G Mobile Radio Communications Above 6 GHz

Robin Gerzaguet, Jean-Baptiste Doré, Nicolas Cassiau & Dimitri Kténas

5G will have to cope with a high degree of heterogeneity in terms of services and requirements. Among these latter, flexible and efficient use of all available non-contiguous spectrums for different network deployment scenarios is one challenge for the future 5G. To maximize spectrum efficiency, the 5G air interface technology will also need to be flexible and capable of mapping various services to the best suitable combinations of frequency and radio resources. In this work, a fair comparison of several 5G waveform candidates (UFMC, FBMC, and GFDM) has been proposed under a common framework. Spectral efficiency, power spectral density, peak to average power ratio and robustness to asynchronous multi-user uplink transmission are assessed. The benefits of these new waveforms for the foreseen 5G use cases are clearly highlighted and it is also underlined that some concepts still need to be improved to achieve the full range of expected benefits of 5G.

GRETSI Compensation numérique de spurs multiples avec estimation conjointe des décalages de fréquences dans le contexte OFDM

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

Les spurs sont des fuites issues des horloges internes d'un terminal Radio-Fréquence. Ces fuites se traduisent par des fréquences pures qui viennent polluer le signal de réception. On se propose ici de compléter l'analyse d'un algorithme numérique de suppression de spurs multiples, proposé dans [2], et basé sur la parallélisation de structures de compensation d'une spur par un algorithme LMS piloté par une référence construite à partir de la connaissance de la fréquence a priori de la spur. Dans cet article, on se focalise sur les performances de la structure lorsque le signal reçu suit une modulation OFDM. On montre que les performances de l'algorithme peuvent être fortement altérées lorsque le décalage entre les fréquences attendues et effectives des spurs polluantes est important, et on propose de remédier a ce problème par une structure d'estimation conjointe de l'amp;litude complexe de la spur et du décalage de fréquence. L'efficacité de notre méthode est démontrée a la fois par des simulations qui viennent valider nos résultats théoriques , ainsi que par une expérimentation sur une plateforme de radio logicielle.

ICECS Joint Estimation of Complex Gain and Fractional Delay for Tx Leakage Compensation in FDD Transceivers.

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

This paper deals with a joint estimation algorithm dedicated to the digital compensation of the Tx leakage in FDD transceivers. Such transceivers are affected from transmitter-receiver signal leakage. Combined with non linearity of components in the received path, it leads to a pollution in the baseband signal. The baseband polluting term depends on the equivalent Tx leakage channel, modeling leakages and the received path. In this paper we consider a first-order autoregressive model to approximate Tx-Leakage channel gain variations, and the presence of a fractional delay, modeling propagation effects. We first express asymptotic performance of a gain estimator based on a least-mean-square (LMS) approach in the synchronized case and then derive the influence of the fractional delay. We show that in practice, the fractional delay can not be neglected and we propose a joint estimation of the fractional delay and the cross-channel gain to perform the digital compensation. The proposed method is recursive, online and exhibits low complexity.

Gretsi Architectures numériques parallèles et successives pour la suppression de spurs multiples dans un terminal radio fréquence multi-standard et performances théoriques

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

Le thème de ce papier concerne la comparaison d'architectures numériques pour l'annulation de plusieurs spurs, pollutions internes qui surviennent dans les terminaux Radio fréquence (RF). Les spurs sont des fuites issues des horloges internes d'un terminal RF. Ce sont des brouilleurs harmoniques qui entraînent une pollution du signal de réception. Plusieurs spurs pouvant tomber dans une bande de signal d'intérêt, on se propose ici d'étudier deux architectures numériques actives pour la suppression de ces multiples spurs: une structure parallèle et une structure successive, basées sur des blocs dédiés à l'annulation d'une seule spur mis à jour par un algorithme du gradient stochastique (LMS) utilisant une référence. On montre dans cet article que ces deux architectures ont des performances asymptotiques très voisines, avec un léger avantage pour la structure parallèle en terme de complexité.

Gretsi Performances d'un suppresseur numérique adaptatif de spurs dans un terminal Radio-Fréquence multistandard en présence d'imperfections sur la référence

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

Les spurs sont des fuites issues des horloges internes d'un terminal Radio-Fréquence. Ces fuites se caractérisent par des fréquences pures, qui viennent polluer le signal d'émission ou de réception. On se propose ici d'étudier une méthode active d'annulation d'une spur basée sur un algorithme des moindres carrés (LMS), en utilisant une référence construite à partir de la connaissance de la pulsation a priori du pollueur. Toutefois, cette référence n'est pas une image parfaite de la spur, du fait d'une imprécision de la pulsation réelle ou de la présence de bruit de phase. On apporte une étude analytique complète (performances asymptotiques, pas optimal) des performances de l'algorithme en présence d'un décalage de pulsation (DP) ou d'un bruit de phase (BP). Par ailleurs, on propose une surcouche adaptative originale à l'algorithme LMS pour accélérer sa convergence en maintenant les mêmes performances asymptotiques.

DSP Self-Adaptive Stochastic Rayleigh Flat Fading Channel Estimation

Robin Gerzaguet, Laurent Ros, Fabrice Belvèze & Jean-Marc Brossier

This paper deals with channel estimation over flat fading Rayleigh channel with Jakes' Doppler Spectrum. Many estimation algorithms exploit the time-domain correlation of the channel by employing a Kalman filter based on a first-order (or sometimes second-order) approximation of the time-varying channel with a criterion based on correlation matching (CM), or on the Minimization of Asymptotic Variance (MAV). In this paper, we first consider a reduced complexity approach based on Least Mean Square (LMS) algorithm, for which we provide closed-form expressions of the optimal step-size coefficient versus the channel state statistic (additive noise power and Doppler frequency) and of corresponding asymptotic mean-squared-error (MSE). However, the optimal tuning of the step-size coefficient requires knowledge of the channel's statistic. This knowledge was also a requirement for the aforementioned Kalman-based methods. As a second contribution, we propose a self-adaptive estimation method based on a stochastic gradient which does not need a priori knowledge. We show that the asymptotic MSE of the self-adaptive algorithm is almost the same as the first order Kalman filter optimized with the MAV criterion and is better than the latter optimized with the conventional CM criterion. We finally improve the speed and reactivity of the algorithm by computing an adaptive speed process leading to a fast algorithm with very good asymptotic performance.

EU Patent IQ Mismatch Compensation

Fabrice Belvèze & Robin Gerzaguet

In telecommunication systems, modulation and demodulation steps are fundamental. The imperfection of demodulators leads to a gain and phase Imbalance between the I (in phase) and Q (in quadrature) branches called IQ mismatch. This mismatch, unavoidable in the analog front end causes interference, and must be compensated in the Digital front end. In accordance to the dirty RF field, digital signal processing tecnhniques can be implemented for the IQ Mismatch compensation, based on estimation of gain mismatch and phase mismatch. Here a new approach, based on blind source separation (BSS) from Valkama's work has been established. The good performance of the algorithm (speed, tracking capacity...) have been greatly increased thanks to the creation of an adaptative step BSS. The increase of mismatch compensation allows to consider using a less accurate frequency transposition realization, since the mismatch will be completely compensated.

Tools

Gnuradio PhyGRC source code

Florian Cotte & Robin Gerzaguet

GnuRadio source code for physical Layer model and implementation.

Gnuradio OFDM GRC file

Florian Cotte & Robin Gerzaguet

Simple Tx-Rx full Duplex OFDM chain (need phyGRC to be installed)

Vim vimrc

Robin Gerzaguet

Vim is a powerful tool. Try it, love it, adopt it. Here a tiny config file to have a minimal but swag working environment.

Vim ctags

Robin Gerzaguet

ctags file for vim-Latex. Display sections, files, and todo in ctags Environnement.