fr Tue, 14 May 2013 15:52:58 +0200 http://cedric.cnam.fr/index.php/publis/article/view?id=2745 http://cedric.cnam.fr/index.php/publis/article/view?id=2745 We investigate in this paper the resource allocation problem in an uplink OFDMA multiuser system. We focus on the Proportional Fairness approach which aims to maximize the system throughput and while ensuring fairness between users. In this paper, we propose a Weighted Proportional Fair algorithm for resource allocation that introduces priorities between users to better exploit good channel conditions in the cell center. We also perform a theoretical analysis to compare both standard and weighted proportional fair algorithms. Simulation results, compared to existing algorithms, show that the proposed algorithm approaches the max sum rate upper bound but still maintains sufficient fairness between users. Tue, 14 May 2013 15:52:58 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2744 http://cedric.cnam.fr/index.php/publis/article/view?id=2744 This paper proposes a resource allocation and decoding strategy at the secondary systems for underlay and interweave multi-carrier cooperative cognitive radio. The objective is to maximize the sum rate of both primary and secondary systems, taking into account the interference threshold constraint and the fact that the primary receiver always considers interference as noise. The decoding strategy at the secondary receivers is either Successive Interference Cancellation or treating interference as noise, depending on their channel gains. The sum rate and secondary rates are highly improved, compared with other resource allocation algorithms. The proposed algorithm benefits from multi-user diversity when the number of secondary cells increases. Tue, 14 May 2013 15:49:13 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2743 http://cedric.cnam.fr/index.php/publis/article/view?id=2743 This work proposes two new Resource Block (RB) allocation algorithms for the LTE uplink. They take into account the RB adjacency constraint and update the allocation metric. Two different heuristics are proposed: an Opportunistic and Efficient RB allocation Algorithm (OEA) and a Quality of Service based Opportunistic and Efficient RB allocation Algorithm (QoS based OEA). Both algorithms seek to maximize the aggregate throughput and avoid RB wastage unlike other algorithms in the literature. The complexity of the proposed algorithms are also computed analytically and compared to other well known heuristics. Tue, 14 May 2013 15:41:40 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2729 http://cedric.cnam.fr/index.php/publis/article/view?id=2729 We present a laser ranging system, under development, that uses a high frequency modulated beam to achieve sub-nm resolution by the combined use of interferometric and time-of-flight measurements. We first describe how the absolute distance is extracted from a two-mode interference signal. In particular we show that the signal, which presents both optical and synthetic wavelength scales, is essential to achieve nm-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. Then we present results obtained with the telemeter implemented on an optical table, for a distance of about four meters, implemented by folding the laser beam path to the target. The challenge here is to achieve a phase and amplitude measurement of two 20 GHz signals with a resolution well below 10-4 cycle and 10-4, respectively, despite the fact that the signal undergoes very strong (×3 ) amplitude changes. Thu, 18 Apr 2013 14:48:39 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2728 http://cedric.cnam.fr/index.php/publis/article/view?id=2728 . Thu, 18 Apr 2013 10:32:12 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2727 http://cedric.cnam.fr/index.php/publis/article/view?id=2727 This paper deals with interval state observer design for time-varying discrete-time systems. The problem of a similarity transformation computation which connects a (time-varying) matrix and its nonnegative representation is studied. Three solutions are proposed: for a generic time-varying system, a system with positive state, and for a particular class of periodical systems. Numerical simulations are provided to demonstrate advantages of the developed techniques. Wed, 10 Apr 2013 11:05:50 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2712 http://cedric.cnam.fr/index.php/publis/article/view?id=2712 . Wed, 27 Feb 2013 14:33:07 +0100 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2711 http://cedric.cnam.fr/index.php/publis/article/view?id=2711 . Wed, 27 Feb 2013 14:25:09 +0100 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2699 http://cedric.cnam.fr/index.php/publis/article/view?id=2699 We demonstrate a laser ranging scheme that uses a high-frequencymodulated beam to achieve subnanometer precision by the combined use of interferometric and time-of-flight measurements.We first describe how the absolute distance is extracted from a two-mode interference signal. In particular, we show that the signal, which presents both optical and synthetic wavelength scales, allows one to achieve nanometer-scale accuracy, despite the significant long-term phase drifts in the 20 GHz detection chains. We present results obtained with the telemeter implemented for a distance of about four meters, obtained by folding the laser beam path to the target. Thu, 17 Jan 2013 11:26:34 +0100 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2695 http://cedric.cnam.fr/index.php/publis/article/view?id=2695 This paper focuses on the performance analysis of a linear system solving based on Cholesky decomposition and QR factorization, implemented on 16bits fixed-point DSP-chip (TMS320C6474). The classical method of Cholesky decomposition has the advantage of low execution time. However, the modified Gram-Schmidt QR factorization performs better in term of robustness against the round-off error propagation. In this study, we have proposed a third method called Modified Gram-Schmidt Cholesky Decomposition. We have shown that it provides a compromise of the two performance criterias cited above. A joint theoretical and experimental analysis of global performance of the three methods has been presented and discussed. Mon, 07 Jan 2013 09:45:28 +0100 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2684 http://cedric.cnam.fr/index.php/publis/article/view?id=2684 Multicarrier (MC) Modulation attracts a lot of attention for high speed wireless transmissions because of its capability to cope with frequency selective fading channels turning the wideband transmission link into several narrowband subchannels whose equalization, in some situations, can be performed independently and in a simple manner. Nowadays, orthogonal frequency division multiplexing (OFDM) with the cyclic prefix (CP) insertion is the most widespread modulation among all MC modulations, and this thanks to its simplicity and its robustness against multipath fading using the cyclic prefix. Systems or standards such as ADSL or IEEE802.11a have already implemented the CP-OFDM modulation. Other standards like IEEE802.11n combine CP-OFDM and multiple-input multiple-output (MIMO) in order to increase the bit rate and to provide a better use of the channel spatial diversity. Nevertheless, CP-OFDM technique causes a loss of spectral efficiency due to the CP as it contains redundant information. Moreover, the rectangular prototype filter used in CP-OFDM has a poor frequency localization. This poor frequency localization makes it difficult for CP-OFDM systems to respect stringent specifications of spectrum masks. To overcome these drawbacks, filter-bank multicarrier (FBMC) was proposed as an alternative approach to CP-OFDM. Indeed, FBMC does not need any CP, and it furthermore offers the possibility to use different time-frequency well-localized prototype filters which allow much better control of the out-of-band emission. In the literature we find several FBMC systems based on different structures. In this thesis, we focus on the Saltzberg?s scheme called OFDM/OQAM (or FBMC/OQAM). The orthogonality constraint for FBMC/OQAM is relaxed being limited only to the real field while for OFDM it has to be satisfied in the complex field. Consequently, one of the characteristics of FBMC/OQAM is that the demodulated transmitted symbols are accompanied by interference terms caused by the neighboring transmitted data in time-frequency domain. The presence of this interference is an issue for some MIMO schemes and until today their combination with FBMC remains an open problem. The aim of this thesis is to study the combination between FBMC and MIMO techniques, namely spatial multiplexing with ML detection. In the first part, we propose to analyze different intersymbol interference (ISI) cancellation techniques that we adapt to the FBMC/OQAM with MIMO context. We show that, in some cases, we can cope with the presence of the inherent FBMC interference and overcome the difficulties of performing ML detection in spatial multiplexing with FBMC/OQAM. After that, we propose a modification in the conventional FBMC/OQAM modulation by transmitting complex QAM symbols instead of OQAM ones. This proposal allows to reduce considerably the inherent interference but at the expense of the orthogonality condition. Indeed, in the proposed FBMC/QAM, the data symbol and the inherent interference term are both complex. Finally, we introduce a novel FBMC scheme and a transmission strategy in order to avoid the inherent interference terms. This proposed scheme (that we call FFT-FBMC) transforms the FBMC system into an equivalent system formulated as OFDM regardless of some residual interference. Thus, any OFDM transmission technique can be performed straightforwardly to the proposed FBMC scheme with a corresponding complexity growth. We develop the FFT-FBMC in the case of single-input single-output (SISO) configuration. Then, we extend its application to SM-MIMO configuration with ML detection and Alamouti coding scheme. Mon, 26 Nov 2012 17:21:03 +0100 LAETITIA Paper http://cedric.cnam.fr/index.php/labo/membre/view?id=1739 http://cedric.cnam.fr/index.php/labo/membre/view?id=1739 a Fri, 16 Nov 2012 10:53:29 +0100 LAETITIA Job http://cedric.cnam.fr/index.php/labo/membre/view?id=1738 http://cedric.cnam.fr/index.php/labo/membre/view?id=1738 a Fri, 16 Nov 2012 10:52:29 +0100 LAETITIA Job http://cedric.cnam.fr/index.php/labo/membre/view?id=1737 http://cedric.cnam.fr/index.php/labo/membre/view?id=1737 a Fri, 16 Nov 2012 10:49:34 +0100 LAETITIA Job http://cedric.cnam.fr/index.php/publis/article/view?id=2668 http://cedric.cnam.fr/index.php/publis/article/view?id=2668 . Mon, 08 Oct 2012 18:12:23 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2664 http://cedric.cnam.fr/index.php/publis/article/view?id=2664 Spectral efficiency comparison between OFDM/OQAM and OFDM-based CR networks Sun, 30 Sep 2012 19:50:47 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2661 http://cedric.cnam.fr/index.php/publis/article/view?id=2661 CDMA transmission with complex OFDM/OQAM Wed, 26 Sep 2012 17:17:30 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2659 http://cedric.cnam.fr/index.php/publis/article/view?id=2659 This paper presents an implementation on the fixed-point DSP chip of an interference cancellation algorithm containing a linear system. Difficulty in matching the algorithms performance obtained in full precision (IEEE float-point) implementation to those given by a finite precision tends to increase when the algorithms contains one or several linear system to solve. Gauss and Cholesky methods are implemented. Their performance results are showed and compared. The global implementation margins are discussed. Tue, 25 Sep 2012 10:23:52 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2658 http://cedric.cnam.fr/index.php/publis/article/view?id=2658 This paper presents a self-adjustment of the length of the channel impulse response using a classical Cholesky Factorization. This is of special importance in the context of algorithms containing a matrix inversion and the rank of this matrix is strongly related to the length of the channel impulse, i.e. interferer cancellation algorithm. When the length of the channel impulse response is overestimated, the matrix inversion is carried out with a singular matrix. A self-adjustment is then required to avoid an increase in the noise level. Tue, 25 Sep 2012 10:12:14 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2643 http://cedric.cnam.fr/index.php/publis/article/view?id=2643 In the next generation of wireless communication, adaptive resource allocation techniques will play an important role to improve quality of service and spectral efficiency. In order to employ adaptive fairness scheduling for multiple-input single-output (MISO) orthogonal frequency-division multiple access (OFDMA), the channel state information belonging to all users is required at the base station. However, the amount of feedback increases with the number of users, transmit antennas and subchannels. Therefore, it is important to perform a user selection at the receiver side without cooperation among the users and to quantize the channel state information. In this paper, the reduced feedback channel designs are examined for MISO-OFDMA systems while providing fairness between the users. In order to reduce the feedback rate, we choose the users considering their norm and orthogonality properties as well as their location in the cell. In order to limit the feedback rate, channel direction information is quantized by designing a specific codebook thanks to the proposed criterion. We obtain an expression to determine the amount of required feedback information for MISO-OFDMA systems to support more than one beam per subchannel for a given number of users, subchannels and transmit antennas. The performance results of the reduced feedback channel designs are evaluated for fair scheduling in wireless channels. Fri, 14 Sep 2012 09:42:49 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2642 http://cedric.cnam.fr/index.php/publis/article/view?id=2642 Spectral correlation theory for cyclostationary time-series signals has been studied for decades. Explicit formulas of spectral correlation function for various types of analog-modulated and digital-modulated signals are already derived. In this paper, we investigate and exploit the cyclostationarity characteristics for two kinds of multicarrier modulated (MCM) signals: conventional OFDM and filter bank based multicarrier (FBMC) signals. The spectral correlation characterization of MCM signal can be described by a special linear periodic time-variant (LPTV) system. Using this LPTV description, we have derived the explicit theoretical formulas of nonconjugate and conjugate cyclic autocorrelation function (CAF) and spectral correlation function (SCF) for OFDM and FBMC signals. According to theoretical spectral analysis, Cyclostationary Signatures (CS) are artificially embedded into MCM signal and a low-complexity signature detector is, therefore, presented for detecting MCM signal. Theoretical analysis and simulation results demonstrate the efficiency and robustness of this CS detector compared to traditionary energy detector. Fri, 14 Sep 2012 09:36:22 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2640 http://cedric.cnam.fr/index.php/publis/article/view?id=2640 Universellement accessibles et permettant la mobilité, les systèmes sans fil connaissent un usage croissant. Cependant, le débit et la qualité de service ne sont pas encore au niveau des systèmes filaires. Par une approche macroscopique des systèmes sans fil, cet ouvrage répond aux questions de puissance, de débit, d'accès multiple, d'organisation cellulaire et d'organisation des réseaux d'accès. Ce livre met en application les principes fondamentaux des systèmes de télécommunications sans fil. Les grands concepts technologiques des systèmes radio (F/TDMA, GSM, CDMA, UMTS, OFDM, LTE, MIMO et UWB) et leurs principaux résultats théoriques sont présentés. Une série de problèmes résolus ayant pour objet d'établir des éléments du bilan de liaison global de différents systèmes de radiocommunications est proposée. Sun, 09 Sep 2012 19:18:23 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2620 http://cedric.cnam.fr/index.php/publis/article/view?id=2620 This paper is devoted to design of interval observers for Linear Time Varying (LTV) systems and a class of nonlinear time-varying systems in the output canonical form. An interval observer design is feasible if it is possible to calculate the observer gains making the estimation error dynamics cooperative and stable. It is shown that under some mild conditions the cooperativity of an LTV system can be ensured by a static linear transformation of coordinates. The efficiency of the proposed approach is demonstrated through numerical simulations. Sun, 22 Jul 2012 17:13:16 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2619 http://cedric.cnam.fr/index.php/publis/article/view?id=2619 This paper investigates the impact of the prototype filter on the sensitivity of the FBMC system to timing synchronization errors. A global evaluation of the average error rate has been made for OFDM and two FBMC systems using PHYDYAS and IOTA prototype filters. This evaluation has been performed taking into account different parameters: the timing error range, the guard band length and the load factor of the network. The validity of the simulation results will be verified by comparison with those obtained with the analytical expressions. Wed, 18 Jul 2012 22:38:43 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2618 http://cedric.cnam.fr/index.php/publis/article/view?id=2618 Multicarrier systems are widely used today due to their robustness to multipath effects and efficient implementation using FFT. Orthogonal Frequency Division Multiplexing (OFDM) system is a class of multicarrier modulation which consists of splitting up a wide-band signal at a high symbol rate into several lower rate signals, each one occupying a narrower band. System performance improves because subcarriers experience flat fading channels and are orthogonal to one another. Recently, a number of papers have focused on a new alternative called Filter bank based multicarrier system (FBMC) which can offer a number of advantages over CP-OFDM system such as the improved spectral efficiency by not using a redundant CP and by having much better control of the out-of-band emission due to the time-frequency localized shaping pulses. Furthermore, asynchronism inherently exists in several communication systems due to many factors e.g. the propagation delays and the spatial distribution of users. As one of the most challenging issue in design of communication systems, the asynchronism can harmfully affect the system performance by causing the so-called asynchronous interference. In this dissertation, we investigate the impact of asynchronism on the performance of OFDM FBMC systems. First, we present a unified framework for multicarrier interference characterization and analysis in asynchronous environments. We propose a new family of interference tables that model the correlation between a given interfering subcarrier and the victim one, not only as a function of the spectral distance separating both subcarriers but also with respect to the timing misalignment between the subcarriers holders. These tables are derived for CP-OFDM, PHYDYAS-FBMC and IOTA-FBMC systems. Furthermore, the impact of the asynchronous interference on the average error rate and the average spectral efficiency of OFDM and FBMC systems is addressed. Based on computing the moment generating functions of the asynchronous interference power, simple new expressions for the exact evaluation of the average error rate and the average spectral efficiency are derived considering the frequency correlation fading between adjacent interfering subcarriers. These expressions significantly reduce the computation complexity of the performance evaluation. For each technique two scenarios are examined: fully-loaded network and partially loaded ones. The accuracy of the obtained expressions has been validated through different simulation results. In contrast to OFDM, FBMC waveforms are demonstrated to be less sensitive to timing asynchronism, due to the better frequency localization of the used prototype filters. Wed, 18 Jul 2012 10:13:32 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2617 http://cedric.cnam.fr/index.php/publis/article/view?id=2617 . Tue, 17 Jul 2012 22:40:16 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2616 http://cedric.cnam.fr/index.php/publis/article/view?id=2616 The problem of output stabilization of a class of nonlinear systems subject to parametric and signal uncertainties is studied. First, an interval observer is designed estimating the set of admissible values for the state. Next, it is proposed to design a control algorithm for the interval observer providing convergence of interval variables to zero, that implies a similar convergence of the state for the original nonlinear system. An application of the proposed technique shows that a robust stabilization can be performed for linear time-varying and Linear-Parameter-Varying (LPV) systems without assumption that the vector of scheduling parameters is available for measurements. Efficiency of the proposed approach is demonstrated through two examples. Tue, 17 Jul 2012 22:29:20 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2598 http://cedric.cnam.fr/index.php/publis/article/view?id=2598 This paper investigates the impact of the prototype filter on the sensitivity of the FBMC system to timing synchronization errors. A global evaluation of the average error rate has been made for OFDM and two FBMC systems using PHYDYAS and IOTA prototype filters. This evaluation has been performed taking into account different parameters: the timing error range, the guard band length and the load factor of the network. The validity of the simulation results will be verified by comparison with those obtained with the analytical expressions. Fri, 22 Jun 2012 09:40:53 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2589 http://cedric.cnam.fr/index.php/publis/article/view?id=2589 Future broadband radio systems have ambitious objectives in terms of performance and quality of service. Moreover, new network topologies are likely to be introduced. Therefore, the physical layer has to evolve to meet the new requirements. With this in mind, the filter bank multicarrier (FBMC) technique is proposed as an enhancement to the present OFDM technique. After a brief presentation of the FBMC principle, the adaptation to the radio context is described. Then, the main features which impact radio networks are reviewed with emphasis on the potential benefits of the evolution. The paper provides an overview of the work carried out in the European research project EC-FP7-Phydyas (physical layer for dynamic access and cognitive radio). Wed, 20 Jun 2012 14:08:24 +0200 LAETITIA Paper http://cedric.cnam.fr/index.php/publis/article/view?id=2588 http://cedric.cnam.fr/index.php/publis/article/view?id=2588 OFDM and FBMC transmission techniques : a compatible high performance proposal for broadband power line communications Wed, 20 Jun 2012 13:56:59 +0200 LAETITIA Paper