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Xu Q.,OPERA | Mabed H.,FEMTO ST Institute | Caminada A.,OPERA | Lassabe F.,OPERA
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC | Year: 2015

Multimedia Broadcast Multicast Service system supports efficient diffusion of multicast multimedia services in cellular networks. Our previous work shows that the radio resource management problem for MBMS can be modeled as a combinatorial optimization problem which tries to find optimal assignment of power and channel codes [1]. In this paper, we propose to solve such problem by using metaheuristic algorithm: Tabu Search (TS). In our work, we modify the general TS algorithm and map it onto our model. We also extend the classic TS procedure by proposing a tabu repair mechanism, which helps to explore new candidate solutions. The proposed algorithm is compared with two other metaheuristics: Greedy Local Search (GLS) and Simulated Annealing (SA). Simulations show that, within acceptable amount of time, TS can find better solution than GLS and SA. © 2014 IEEE.

Harmouche M.,OPERA | Laghrouche S.,OPERA | Chitour Y.,University Paris - Sud
International Journal of Robust and Nonlinear Control | Year: 2015

In this paper, we have studied the control problem of target point-based path following for car-type vehicles. This special path-following task arises from the needs of vision-based guidance systems, where a given target point located ahead of the vehicle, in the visual range of the camera, must follow a specified path. A solution to this problem is developed through a nonlinear transformation of the path-following problem into a reference trajectory tracking problem, by modeling the target point as a virtual vehicle. The use of target point complicates the control problem, as the development produces a first-order nonlinear nonglobally Lipschitz differential equation with finite escape time. This problem is solved by using small control signals. Bounded feedback laws are designed to control the real vehicle's angular acceleration and the virtual vehicle's velocity, to achieve stability. The resulting controller is globally asymptotically stable with respect to the origin, the proof of which is derived from Lyapunov-based arguments and a bootstrap argument. It is also shown that the use of exponentially convergent observers/differentiators does not affect the stability of the closed-loop system. The effectiveness of this controller has been illustrated through simulations. Copyright © 2014 John Wiley & Sons, Ltd.

Giboli M.,Total S.A. | Baina R.,OPERA | Douillard A.,Total S.A.
EAGE/SPE Subsalt Imaging Workshop 2014: Challenges of Subsalt Exploration and Imaging in the Middle East and North Africa Deep Water | Year: 2014

In this paper we briefly review different methods to produce CIGSs with WE migration techniques and we discuss potential interest to produce 3D surface offset gathers. Since we are interested in using modern migration techniques to handle the complex overburden for wave propagation and in using ray-based tomography to update the subsalt velocity, we demonstrate the application of RTM 3D surface offset gathers to subsalt TTI image enhancement and velocity updating. We use a bi-azimuth data set from offshore Angola to illustrate how the proposed method helps to improve subsalt model building and image quality.

Fomel S.,University of Texas at Austin | Landa E.,OPERA
Journal of Applied Geophysics | Year: 2014

Structural information in seismic images is uncertain. The main cause of this uncertainty is uncertainty in velocity estimation. We adopt the technique of velocity continuation for estimating velocity uncertainties and corresponding structural uncertainties in time-migrated images. Data experiments indicate that structural uncertainties can be significant even when both structure and velocity variations are mild. © 2013 The Authors.

Silvestrov I.,Russian Academy of Sciences | Baina R.,OPERA | Landa E.,Tel Aviv University
Geophysical Prospecting | Year: 2016

We propose a method for imaging small-scale diffraction objects in complex environments in which Kirchhoff-based approaches may fail. The proposed method is based on a separation between the specular reflection and diffraction components of the total wavefield in the migrated surface angle domain. Reverse-time migration was utilized to produce the common image gathers. This approach provides stable and robust results in cases of complex velocity models. The separation is based on the fact that, in surface angle common image gathers, reflection events are focused at positions that correspond to the apparent dip angle of the reflectors, whereas diffracted events are distributed over a wide range of angles. The high-resolution radon-based procedure is used to efficiently separate the reflection and diffraction wavefields. In this study, we consider poststack diffraction imaging. The advantages of working in the poststack domain are its numerical efficiency and the reduced computational time. The numerical results show that the proposed method is able to image diffraction objects in complex environments. The application of the method to a real seismic dataset illustrates the capability of the approach to extract diffractions. © 2015 European Association of Geoscientists & Engineers.

Cheverda V.,Russian Academy of Sciences | Landa E.,OPERA | Reshetova G.,ICM and MG
6th Saint Petersburg International Conference and Exhibition on Geosciences 2014: Investing in the Future | Year: 2014

Common Middle Point seismic sections and their successive time migration provide extremely important knowledge about the internal structure of the 3D heterogeneous geological media and are key elements for successive geological interpretation. Full scale numerical simulation, that is one which starts with single shot seismograms, provides a deep understanding how the features of the image are linked with its subsurface prototype. Unfortunately, this kind of simulations for realistic geological media and 3D seismic surveys needs huge computer resources, especially for simulation of seismic waves' propagation through multiscale media like cavernous fractured reservoirs. In order to significantly reduce the query of computer resources we propose to model these 3D seismic cubes directly rather than shot-by-shot simulation with subsequent CMP stacking. In order to do that the well known "exploding reflectors principle" is modified for 3D heterogeneous multiscale media. Its parallel implementation allows modeling of realistic 3D Common Middle Point stacks with reasonable computational costs. Numerical results for simulation of Common Middle Points sections and their time migration are presented and discussed. Copyright © 2014 by the European Association of Geoscientists & Engineers. All rights reserved.

Skoulis I.,Opera | Vassiliadis P.,University of Ioannina | Zarras A.V.,University of Ioannina
Information Systems | Year: 2015

Like all software systems, databases are subject to evolution as time passes. The impact of this evolution can be vast as a change to the schema of a database can affect the syntactic correctness and the semantic validity of all the surrounding applications. In this paper, we have performed a thorough, large-scale study on the evolution of databases that are part of larger open source projects, publicly available through open source repositories. Lehman's laws of software evolution, a well-established set of observations on how the typical software systems evolve (matured during the last forty years), has served as our guide towards providing insights on the mechanisms that govern schema evolution. Much like software systems, we found that schemata expand over time, under a stabilization mechanism that constraints uncontrolled expansion with perfective maintenance. At the same time, unlike typical software systems, the growth is typically low, with long periods of calmness interrupted by bursts of maintenance and a surprising lack of complexity increase. © 2015 Elsevier Ltd. All rights reserved.

Berkovitch A.,Geomage | Deev K.,Geomage | Landa E.,OPERA
First Break | Year: 2011

MultiFocusing technology can dramatically improve the quality of seismic imaging especially in cases of low fold data, poor signal-to-noise ratio and sparse 3D acquisition. MF technology, based on multiparameter analysis of the wavefield and summation along predicted time surfaces, has been applied to enhance time imaging sections by dramatically increasing the fold of coherent summation of seismic signals. One of the main limitations of the zero-offset MF method is a quasi-hyperbolic approximation for actual travel-time surfaces. COMF traveltime formulas provide an adequate representation of arrival times for arbitrary offset and source-receiver configuration. The COMF correction formula is remarkably accurate even for strong curved reflectors. The correlation procedure is repeated for each imaging point, for each offset and for each time sample. It is important to note that the described procedure can be applied locally within a small vicinity of each seismic trace and does not require global full offset approximation.

Landa E.,OPERA
Hart's E and P | Year: 2011

Multifocusing (MF) technology, based on multiparameter stacking, has been applied to enhance time imaging sections by dramatically increasing the fold of coherent summation of seismic signals. Implementation of the MF method is technically challenging because it requires defining three moveout parameters in the 2-D case and eight in the 3-D case, as opposed to a single parameter. MF technology was applied to low-fold and low-quality data from northwestern Russia. The MF method not only provides coherent stacking of seismic data with arbitrary source-receiver distribution to create high-quality time images, but it also has the potential to compute enhanced prestack seismic traces. The number and location of traces in the produced supergathers can be different from the input locations, and the resulting traces can be regular with increased signal-to-noise ratio due to partial coherent summation. The method is robust in the presence of non-coherent noise.

Landa E.,Opera
72nd European Association of Geoscientists and Engineers Conference and Exhibition 2010: A New Spring for Geoscience. Incorporating SPE EUROPEC 2010 | Year: 2010

Seismic diffractions are the response of important small scale elements in the subsurface such as faults, karsts, fractures. We distinguish between reflective and diffractive contributions to the wavefield and recognize the diffractive component as a key ingredient in establishing resolution. We present past, present and future of using the diffractions for seismic imaging and illustrate it with many interesting and exiting examples © 2010, European Association of Geoscientists and Engineers.

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