http://hdl.handle.net/10230/5923 2013-05-19T07:35:15Z http://hdl.handle.net/10230/20518 Mutual information of IID complex Gaussian signals on block Rayleigh-faded channels Rusek, Fredrik; Lozano Solsona, Àngel; Jindal, Nihar We present a method to compute, quickly and efficiently, the mutual information achieved by an IID (independent identically distributed) complex Gaussian signal on a block Rayleigh-faded channel without side information at the receiver. The method accommodates both scalar and MIMO (multiple-input multiple-output) settings. Operationally, this mutual information represents the highest spectral efficiency that can be attained using Gaussian codebooks. Examples are provided that illustrate the loss in spectral efficiency caused by fast fading and how that loss is amplified when multiple transmit antennas are used. These examples are further enriched by comparisons with the channel capacity under perfect channel-state information at the receiver, and with the spectral efficiency attained by pilot-based transmission. 2012-01-01T00:00:00Z http://hdl.handle.net/10230/20517 Outage probability analysis for MRC in η-μ fading channels with co-channel interference Morales-Jiménez, David; Paris, José F.; Lozano Solsona, Àngel Exact closed-form expressions are obtained for the outage probability of maximal ratio combining in η-μ fading channels with antenna correlation and co-channel interference. The scenario considered in this work assumes the joint presence of background white Gaussian noise and independent Rayleigh-faded interferers with arbitrary powers. Outage probability results are obtained through an appropriate generalization of the moment-generating function of the η-μ fading distribution, for which new closed-form expressions are provided. 2012-01-01T00:00:00Z http://hdl.handle.net/10230/20436 Low-density parity-check codes for nonergodic block-fading channels Boutros, Joseph Jean; Guillén i Fàbregas, Albert; Biglieri, Ezio; Zémor, Gilles We design powerful low-density parity-check (LDPC) codes with iterative decoding for the block-fading channel. We first study the case of maximum-likelihood decoding, and show that the design criterion is rather straightforward. Since optimal constructions for maximum-likelihood decoding do not perform well under iterative decoding, we introduce a new family of full-diversity LDPC codes that exhibit near-outage-limit performance under iterative decoding for all block-lengths. This family competes favorably with multiplexed parallel turbo codes for nonergodic channels. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20435 Sequential estimation of multipath MIMO-OFDM channels Angelosante, Daniele; Biglieri, Ezio; Lops, Marco Wireless “MIMO” systems, employing multiple transmit and receive antennas, promise a significant increase of channel capacity, while orthogonal frequency-division multiplexing (OFDM) is attracting a good deal of attention due to its robustness to multipath fading. Thus, the combination of both techniques is an attractive proposition for radio transmission. The goal of this paper is the description and analysis of a new and novel pilot-aided estimator of multipath block-fading channels. Typical models leading to estimation algorithms assume the number of multipath components and delays to be constant (and often known), while their amplitudes are allowed to vary with time. Our estimator is focused instead on the more realistic assumption that the number of channel taps is also unknown and varies with time following a known probabilistic model. The estimation problem arising from these assumptions is solved using Random-Set Theory (RST), whereby one regards the multipath-channel response as a single set-valued random entity. Within this framework, Bayesian recursive equations determine the evolution with time of the channel estimator. Due to the lack of a closed form for the solution of Bayesian equations, a (Rao–Blackwellized) particle filter (RBPF) implementation of the channel estimator is advocated. Since the resulting estimator exhibits a complexity which grows exponentially with the number of multipath components, a simplified version is also introduced. Simulation results describing the performance of our channel estimator demonstrate its effectiveness. 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20434 Multiuser detection in a dynamic environment — Part II: Joint user identification and parameter estimation Angelosante, Daniele; Biglieri, Ezio; Lops, Marco The problem of jointly estimating the number, the identities, and the data of active users in a time-varying multiuser environment was examined in a companion paper (IEEE Trans. Information Theory, vol. 53, no. 9, September 2007), at whose core was the use of the theory of finite random sets on countable spaces. Here we extend that theory to encompass the more general problem of estimating unknown continuous parameters of the active-user signals. This problem is solved here by applying the theory of random finite sets constructed on hybrid spaces. We do so deriving Bayesian recursions that describe the evolution with time of a posteriori densities of the unknown parameters and data. Unlike in the above cited paper, wherein one could evaluate the exact multiuser set posterior density, here the continuous-parameter Bayesian recursions do not admit closed-form expressions. To circumvent this difficulty, we develop numerical approximations for the receivers that are based on Sequential Monte Carlo (SMC) methods (“particle filtering”). Simulation results, referring to a code-divisin multiple-access (CDMA) system, are presented to illustrate the theory. 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20433 On high-rate full-diversity 2x2 space-time codes with low-complexity optimum detection Sezginer, Serdar; Sari, Hikmet; Biglieri, Ezio The 2×2 MIMO profiles included in Mobile WiMAX specifications are Alamouti’s space-time code (STC) fortransmit diversity and spatial multiplexing (SM). The former has full diversity and the latter has full rate, but neither of them has both of these desired features. An alternative 2×2 STC, which is both full rate and full diversity, is the Golden code. It is the best known 2×2 STC, but it has a high decoding complexity. Recently, the attention was turned to the decoder complexity, this issue was included in the STC design criteria, and different STCs were proposed. In this paper, we first present a full-rate full-diversity 2×2 STC design leading to substantially lower complexity of the optimum detector compared to the Golden code with only a slight performance loss. We provide the general optimized form of this STC and show that this scheme achieves the diversitymultiplexing frontier for square QAM signal constellations. Then, we present a variant of the proposed STC, which provides a further decrease in the detection complexity with a rate reduction of 25% and show that this provides an interesting trade-off between the Alamouti scheme and SM. 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20432 3GPP LTE and LTE-Advanced Clerckx, Bruno; Lozano Solsona, Àngel; Sesia, Stefania; van Rensburg, Cornelius; Papadias, Constantinos B. Editorial introductòria del número de la revista, en la qual s'exposa el tema del nou estàndard de mòbil, anomenat Long-TermEvolution (LTE), també referenciat com Evolved UMTS Terrestrial Radio Access (E-UTRA), que s'està definint com el substitut del sistema UMTS de tercera generació. LTE-Advanced, al seu torn, es refereix a la versió més avançada de LTE. 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20431 On fast-decodable space-time block codes Biglieri, Ezio; Hong, Yi; Viterbo, Emanuele We focus on full-rate, fast-decodable space–time block codes (STBCs) for 2 x 2 and 4 x 2 multiple-input multiple-output (MIMO) transmission. We first derive conditions and design criteria for reduced-complexity maximum-likelihood (ML) decodable 2 x 2 STBCs, and we apply them to two families of codes that were recently discovered. Next, we derive a novel reduced-complexity 4 x 2 STBC, and show that it outperforms all previously known codes with certain constellations. 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20430 Distortion control for delay-sensitive sources Faridi, Azadeh; Ephremides, Anthony We investigate the problem of finding minimum-distortion policies for streaming delay-sensitive but distortion-tolerant data. We consider cross-layer approaches which exploit the coupling between presentation and transport layers. We make the natural assumption that the distortion function is convex and decreasing. We focus on a single source-destination pair and analytically find the optimum transmission policy when the transmission is done over an error-free channel. This optimum policy turns out to be independent of the exact form of the convex and decreasing distortion function. Then, for a packet-erasure channel, we analytically find the optimum open-loop transmission policy, which is also independent of the form of the convex distortion function. We then find computationally efficient closed-loop heuristic policies and show, through numerical evaluation, that they outperform the open-loop policy and have near optimal performance. 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20429 On codes, matroids, and secure multiparty computation from linear secret-sharing schemes Cramer, Ronald; Daza, Vanesa; Gracia, Ignacio; Jiménez Urroz, Jorge; Leander, Gregor; Martí-Farré, Jaume; Padró, Carles Error-correcting codes and matroids have been widely used in the study of ordinary secret sharing schemes. In this paper, the connections between codes, matroids, and a special class of secret sharing schemes, namely, multiplicative linear secret sharing schemes (LSSSs), are studied. Such schemes are known to enable multiparty computation protocols secure against general (nonthreshold) adversaries. Two open problems related to the complexity of multiplicative LSSSs are considered in this paper. The first one deals with strongly multiplicative LSSSs. As opposed to the case of multiplicative LSSSs, it is not known whether there is an efficient method to transform an LSSS into a strongly multiplicative LSSS for the same access structure with a polynomial increase of the complexity. A property of strongly multiplicative LSSSs that could be useful in solving this problem is proved. Namely, using a suitable generalization of the well-known Berlekamp–Welch decoder, it is shown that all strongly multiplicative LSSSs enable efficient reconstruction of a shared secret in the presence of malicious faults. The second one is to characterize the access structures of ideal multiplicative LSSSs. Specifically, the considered open problem is to determine whether all self-dual vector space access structures are in this situation. By the aforementioned connection, this in fact constitutes an open problem about matroid theory, since it can be restated in terms of representability of identically self-dual matroids by self-dual codes. A new concept is introduced, the flat-partition, that provides a useful classification of identically self-dual matroids. Uniform identically self-dual matroids, which are known to be representable by self-dual codes, form one of the classes. It is proved that this property also holds for the family of matroids that, in a natural way, is the next class in the above classification: the identically self-dual bipartite matroids. 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20428 On the computational security of a distributed key distribution scheme Daza, Vanesa; Herranz, Javier; Sáez, Germán In a distributed key distribution scheme, a set of servers helps a set of users in a group to securely obtain a common key. Security means that an adversary who corrupts some servers and some users has no information about the key of a noncorrupted group. In this work, we formalize the security analysis of one such scheme which was not considered in the original proposal. We prove the scheme is secure in the random oracle model, assuming that the Decisional Diffie-Hellman (DDH) problem is hard to solve. We also detail a possible modification of that scheme and the one in which allows us to prove the security of the schemes without assuming that a specific hash function behaves as a random oracle. As usual, this improvement in the security of the schemes is at the cost of an efficiency loss. 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20060 mGPT: a probabilistic planner based on heuristic search Bonet, Blai; Geffner, Hector We describe the version of the GPT planner to be used in the planning competition. This version, called mGPT, solves mdps specified in the ppddl language by extracting and using different classes of lower bounds, along with various heuristic-search algorithms. The lower bounds are extracted from deterministic relaxations of the mdp where alternative probabilistic effects of an action are mapped into different, independent, deterministic actions. The heuristic-search algorithms, on the other hand, use these lower bounds for focusing the updates and delivering a consistent value function over all states reachable from the initial state with the greedy policy. 2005-01-01T00:00:00Z http://hdl.handle.net/10230/20025 The Multiscenario Multienvironment BioSecure Multimodal Database (BMDB) Ortega-Garcia, Javier; Fierrez, Julian; Alonso-Fernández, Fernando; Galbally, Javier; Freire, Manuel R.; González-Rodríguez, Joaquín; García-Mateo, Carmen; Alba-Castro, José-Luís; González-Agulla, Elisardo; Otero-Muras, Enrique; García-Salicetti, Sonia; Allano, Lorene; Ly-Van, Bao; Dorizzi, Bernadette; Kittler, Josef; Bourlai, Thirimachos; Poh, Norman; Deravi, Farzin; Ng, Ming W.R.; Fairhurst, Michael; Hennebert, Jean; Humm, Andreas; Tistarelli, Massimo; Brodo, Linda; Richiardi, Jonas; Drygajlo, Andrzej; Ganster, Harald; Sukno, Federico M.; Pavani, Sri-Kaushik; Frangi Caregnato, Alejandro; Akarun, Lale; Savran, Arman A new multimodal biometric database designed and acquired within the framework of the European BioSecure Network of Excellence is presented. It is comprised of more than 600 individuals acquired simultaneously in three scenarios: 1) over the Internet, 2) in an office environment with desktop PC, and 3) in indoor/outdoor environments with mobile portable hardware. The three scenarios include a common part of audio/video data. Also, signature and fingerprint data have been acquired both with desktop PC and mobile portable hardware. Additionally, hand and iris data were acquired in the second scenario using desktop PC. Acquisition has been conducted by 11 European institutions. Additional features of the BioSecure Multimodal Database (BMDB) are: two acquisition sessions, several sensors in certain modalities, balanced gender and age distributions, multimodal realistic scenarios with simple and quick tasks per modality, cross-European diversity, availability of demographic data, and compatibility with other multimodal databases. The novel acquisition conditions of the BMDB allow us to perform new challenging research and evaluation of either monomodal or multimodal biometric systems, as in the recent BioSecure Multimodal Evaluation campaign. A description of this campaign including baseline results of individual modalities from the new database is also given. The database is expected to be available for research purposes through the BioSecure Association during 2008. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20024 @neurIST infrastructure for advanced disease management through integration of heterogeneous data, computing, and complex processing services Benkner, Siegfried; Arbona, Antonio; Berti, Guntram; Chiarini, Alessandro; Dunlop, Robert; Engelbrecht, Gerhard; Frangi Caregnato, Alejandro; Friedrich, Christoph M.; Hanser, Susanne; Hasselmeyer, Peer; Hose, D. Rodney; Iavindrasana, Jimison; Köhler, Martin; Lo Iacono, Luigi; Lonsdale, Guy; Meyer, Rodolphe; Moore, Bob; Rajasekaran, Hariharan; Summers, Paul E.; Wöhrer, Alexander; Wood, Steven The increasing volume of data describing human disease processes and the growing complexity of understanding, managing, and sharing such data presents a huge challenge for clinicians and medical researchers. This paper presents the @neurIST system, which provides an infrastructure for biomedical research while aiding clinical care, by bringing together heterogeneous data and complex processing and computing services. Although @neurIST targets the investigation and treatment of cerebral aneurysms, the system’s architecture is generic enough that it could be adapted to the treatment of other diseases. Innovations in @neurIST include confining the patient data pertaining to aneurysms inside a single environment that offers clinicians the tools to analyze and interpret patient data and make use of knowledge-based guidance in planning their treatment. Medical researchers gain access to a critical mass of aneurysm related data due to the system’s ability to federate distributed information sources. A semantically mediated grid infrastructure ensures that both clinicians and researchers are able to seamlessly access and work on data that is distributed across multiple sites in a secure way in addition to providing computing resources on demand for performing computationally intensive simulations for treatment planning and research. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20023 Morphodynamic analysis of cerebral aneurysm pulsation from time-resolved rotational angiography Zhang, Chong; Villa-Uriol, Maria-Cruz; De Craene, Mathieu; Pozo Soler, José Ma. (José María); Frangi Caregnato, Alejandro This paper presents a technique to estimate and model patient-specific pulsatility of cerebral aneurysms over one cardiac cycle, using 3D rotational X-ray angiography (3DRA) acquisitions. Aneurysm pulsation is modeled as a time varying -spline tensor field representing the deformation applied to a reference volume image, thus producing the instantaneous morphology at each time point in the cardiac cycle. The estimated deformation is obtained by matching multiple simulated projections of the deforming volume to their corresponding original projections. A weighting scheme is introduced to account for the relevance of each original projection for the selected time point. The wide coverage of the projections, together with the weighting scheme, ensures motion consistency in all directions. The technique has been tested on digital and physical phantoms that are realistic and clinically relevant in terms of geometry, pulsation and imaging conditions. Results from digital phantom experiments demonstrate that the proposed technique is able to recover subvoxel pulsation with an error lower than 10% of the maximum pulsation in most cases. The experiments with the physical phantom allowed demonstrating the feasibility of pulsation estimation as well as identifying different pulsation regions under clinical conditions. 2009-01-01T00:00:00Z http://hdl.handle.net/10230/19958 Cardiac motion estimation by joint alignment of tagged MRI sequences Oubel, E.; De Craene, Mathieu; Hero, A.O.; Pourmorteza, A.; Huguet, Marina; Avegliano, G.; Bijnens B.H.; Frangi Caregnato, Alejandro Image registration has been proposed as an automatic method for recovering cardiac displacement fields from Tagged Magnetic Resonance Imaging (tMRI) sequences. Initially performed as a set of pairwise registrations, these techniques have evolved to the use of 3D+t deformation models, requiring metrics of joint image alignment (JA). However, only linear combinations of cost functions defined with respect to the first frame have been used. In this paper, we have applied k-Nearest Neighbors Graphs (kNNG) estimators of the -entropy (H ) to measure the joint similarity between frames, and to combine the information provided by different cardiac views in an unified metric. Experiments performed on six subjects showed a significantly higher accuracy (p < 0.05) with respect to a standard pairwise alignment (PA) approach in terms of mean positional error and variance with respect to manually placed landmarks. The developed method was used to study strains in patients with myocardial infarction, showing a consistency between strain, infarction location, and coronary occlusion. This paper also presents an interesting clinical application of graph-based metric estimators, showing their value for solving practical problems found in medical imaging. 2011-01-01T00:00:00Z http://hdl.handle.net/10230/19957 Three-dimensional morphological analysis of intracranial aneurysms: a fully automated method for aneurysm sac isolation and quantification Larrabide, Ignacio; Villa-Uriol, Maria-Cruz; Cardenes R; Pozo Soler, José Ma. (José María); Macho, Juan M.; San Román, Luis; Blasco, Jordi; Vivas, Elio; Marzo, Alberto; Hose, D. Rodney; Frangi Caregnato, Alejandro Morphological descriptors are practical and essential biomarkers for diagnosis and treatment selection for intracranial aneurysm management according to the current guidelines in use. Nevertheless, relatively little work has been dedicated to improve the three-dimensional quanti cation of aneurysmal morphology, automate the analysis, and hence reduce the inherent intra- and inter-observer variability of manual analysis. In this paper we propose a methodology for the automated isolation and morphological quanti cation of saccular intracranial aneurysms based on a 3D representation of the vascular anatomy. 2011-01-01T00:00:00Z http://hdl.handle.net/10230/19956 Deployment of self-expandable stents in aneurysmatic cerebral vessels: comparison of different computational approaches for interventional planning Bernardini, A.; Larrabide, Ignacio; Petrini, L.; Pennati, G.; Flore, E.; Kim, Minsuok; Frangi Caregnato, Alejandro In the last few years, there has been a growing focus on faster computational methods to support clinicians in planning stenting procedures. This study investigates the possibility of introducing computational approximations in modelling stent deployment in aneurysmatic cerebral vessels to achieve simulations compatible with the constraints of real clinical workflows. The release of a self-expandable stent in a simplified aneurysmatic vessel was modelled in four different initial positions. Six progressively simplified modelling approaches (based on Finite Element method and Fast Virtual Stenting – FVS) have been used. Comparing accuracy of the results, the final configuration of the stent is more affected by neglecting mechanical properties of materials (FVS) than by adopting 1D instead of 3D stent models. Nevertheless, the differences showed are acceptable compared to those achieved by considering different stent initial positions. Regarding computational costs, simulations involving 1D stent features are the only ones feasible in clinical context. 2011-01-01T00:00:00Z http://hdl.handle.net/10230/19955 Characterization of myocardial deformation in patients with different etiologies of left ventricular hypertrophy by using strain distribution from Magnetic Resonance Imaging Piella Fenoy, Gemma; De Craene, Mathieu; Bijnens B.H.; Tobón Gómez, Catalina, 1981-; Huguet, Marina; Avegliano, G.; Frangi Caregnato, Alejandro Introducción y objetivos. Se ha señalado que, en la miocardiopatía hipertrófica (MCH), la desorganización de las fibras regionales da lugar a segmentos en los que la deformación es nula o está gravemente reducida, y que estos segmentos tienen una distribución no uniforme en el ventrículo izquierdo (VI). Esto contrasta con lo observado en otros tipos de hipertrofia como en el corazón de atleta o la hipertrofia ventricular izquierda hipertensiva (HVI-HT), en los que puede haber una deformación cardiaca anormal, pero nunca tan reducida como para que se observe ausencia de deformación. Así pues, proponemos el empleo de la distribución de los valores de strain para estudiar la deformación en la MCH. Métodos. Con el empleo de resonancia magnética marcada (tagged), reconstruimos la deformación sistólica del VI de 12 sujetos de control, 10 atletas, 12 pacientes con MCH y 10 pacientes con HVI-HT. La deformación se cuantificó con un algoritmo de registro no rígido y determinando los valores de strain sistólico máximo radial y circunferencial en 16 segmentos del VI. Resultados. Los pacientes con MCH presentaron unos valores medios de strain significativamente inferiores a los de los demás grupos. Sin embargo, aunque la deformación observada en los individuos sanos y en los pacientes con HVI-HT se concentraba alrededor del valor medio, en la MCH coexistían segmentos con contracción normal y segmentos con una deformación nula o significativamente reducida, con lo que se producía una mayor heterogeneidad de los valores de strain. Se observaron también algunos segmentos sin deformación incluso en ausencia de fibrosis o hipertrofia. Conclusiones. La distribución de strain caracteriza los patrones específicos de deformación miocárdica en pacientes con diferentes etiologías de la HVI. Los pacientes con MCH presentaron un valor medio de strain significativamente inferior, así como una mayor heterogeneidad de strain (en comparación con los controles, los atletas y los pacientes con HVI-HT), y tenían regiones sin deformación.; Introduction and objectives. It has been suggested that in hypertrophic cardiomyopathy (HCM) the regional fibre disarray results in segments of none or severely reduced deformation, distributed non-uniformly within the left ventricle (LV). This is in contrast with other types of hypertrophies such as athlete’s heart or hypertensive left ventricular hypertrophy (HT-LVH) which may have abnormal cardiac deformation but never as reduced as showing absence of deformation in certain segments. Hence, we propose to use the distribution of the strain values to study deformation in HCM. Methods. Using tagged magnetic resonance imaging, we reconstructed the LV systolic deformation from 12 controls, 10 athletes, 12 patients with HCM and 10 patients with HT-LVH. Deformation was quantified using a fast nonrigid registration algorithm and measuring radial and circumferential peak systolic strain values from 16 LV segments. Results. HCM patients showed significantly lower average strain values when compared to other groups. However, while the deformation in healthy subjects and HT-LVH was concentrated around the mean value, in HCM there was a coexistence of segments with normal contraction and segments with none or significantly reduced deformation, resulting in a larger heterogeneity of the strain values. Some non-deforming segments were also found in the absence of fibrosis or hypertrophy. Conclusions. Strain distribution characterizes specific patterns of myocardial deformation in patients with different etiologies of LVH. HCM patients had significantly lower average strain as well as 2larger strain heterogeneity (compared to controls, athletes and HT-LVH), and they presented non-deforming regions. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/19954 Wall motion estimation in intracranial aneurysms Oubel, E.; Cebral, J.R.; De Craene, Mathieu; Blanc, R.; Blasco, Jordi; Macho, Juan M.; Putman, C.M.; Frangi Caregnato, Alejandro The quantification of wall motion in cerebral aneurysms is becoming important owing to its potential connection to rupture, and as a way to incorporate the effects of vascular compliance in computational fluid dynamics (CFD) simulations. Most of papers report values obtained with experimental phantoms, simulated images, or animal models, but the information for real patients is limited. In this paper, we have combined non-rigid registration (IR) with signal processing techniques to measure pulsation in real patients from high frame rate digital subtraction angiography (DSA). We have obtained physiological meaningful waveforms with amplitudes in the range 0mm-0.3mm for a population of 18 patients including ruptured and unruptured aneurysms. Statistically significant differences in pulsation were found according to the rupture status, in agreement with differences in biomechanical properties reported in the literature. 2010-01-01T00:00:00Z