Albert Falqués Serra

System level evaluation of LTE networks with semidistributed intercell interference coordination

3GPP LTE is the evolution of UMTS which will make possible to deliver high quality multimedia services with an improved user experience. Since Radio Resource Management (RRM) has been recognized as a key point to successfully accomplish this target, the performance evaluation of a multi-cell resource allocation scheme applied to LTE downlink (DL) is presented in this paper. A semi-distributed RRM framework is discussed and evaluated from a system level viewpoint. Detailed link level simulations have also been carried out to properly back up the results.

Applying interposition techniques for performance analysis of OPENMP parallel applications

Tuning parallel applications requires the use of effective tools for detecting performance bottlenecks. Along a parallel program execution, many individual situations of performance degradation may arise. We believe that an exhaustive and time-aware tracing at a fine-grain level is essential to capture this kind of situations. This paper presents a tracing mechanism based on dynamic code interposition, and compares it with the usual compiler-directed code injection. Dynamic code interposition adds monitoring code at run-time to unmodified binaries and shared libraries, making it suitable for environments in which the compiler or the available tools do not offer instrumentation facilities. Static injection and dynamic interposition techniques are used to collect detailed traces that feed an analysis tool. Both environments meet the accuracy and performance goals required to profile and analyze parallel applications and runtime libraries.

A mechanism inhibiting rip channel formation for oblique waves

Previous numerical modelling studies based on 2DH morphodynamical model show that oblique waves tend to inhibit the formation of rip channel systems, but the mechanisms were not investigated. Field observations do not always agree with this model result, thus, understanding the mechanisms seems essential. To this end, the global analysis technique, originally developed to describe the long term behavior of bars (saturation of the bar growth), is also applied here to the initial stage of the bar evolution (formation of the bars). As a result, rip channels grow slower for larger wave angle because of the weakening of the instability mechanism -that only depends on the cross-shore current- rather than the increase of the damping due to the diffusive bedslope transport.

Porting multithreading libraries to an exokernel system

In this paper, we present an extension to allow multithreaded applications to run on an Intel-based exokernel system. For this purpose, we have ported a user-level threads package to such environment. Our goal is to evaluate the suitability of running multithreaded parallel applications on top of a multiprocessor system managed by an exokernel. We present the design of a prototype library, the lessons learned during its implementation and our proposals for this kind of systems.

A new instability mechanism related to high-angle waves

Waves with a large incidence angle in deep water can drive a morphodynamic instability on a sandy coast whereby shoreline sand waves, cuspate forelands, and spits can emerge. This instability is related to bathymetric perturbations extending offshore in the shoaling zone. Here, we explore a different mechanism where the large incidence angle is supposed to occur at breaking and the bathymetric perturbations occur only in the surf zone. For wave incidence angles at breaking above ≈ 45∘, the one-line approximation of coastal dynamics predicts an unstable shoreline. This instability (EHAWI) is scale-free and the growth rate increases without bound for decreasing wavelength. Here we use a 2DH morphodynamic model resolving surf zone instabilities to investigate whether EHAWI could approximate a real instability in nature with a characteristic length scale. Assuming very idealized conditions on the bathymetric profile and sediment transport, we find a 2DH instability mode consisting of shore-oblique up-current bars coupled to a meandering of the longshore current. This mode grows for high-angle waves, above about 30∘ (offshore) and the maximum growth rate occurs for the angle maximizing the angle at breaking, about 70∘ (offshore). The dominant wavelength is of the order of the surf zone width. Interestingly, for long sand waves, the growth rate never becomes negative and it matches very well the anti-diffusive behavior of EHAWI. This distinguishes the present instability mode from other modes found in previous studies for other bathymetric and sediment transport conditions. Thus, we conclude that EHAWI approximates a real morphodynamic instability only for quite particular conditions. In such case, a characteristic length scale of the instability emerges thanks to surf zone processes that damp short wavelengths.

Km-scale shoreline sand waves in the Western Mediterranean Sea

A number of morphodynamic models have been developed to simulate the dynamics of large-scale bedform patterns on the continental shelf. Most of the models are based on linear stability analysis and, therefore, only describe the characteristics of the bedforms at their formation. Apart from studying the principal formation mechanism, the models have take into account various processes (three dimensional flows, sediment sorting, wave stirring, different tidal constituents, etc) to describe the characteristics of the bedforms at specific locations. Exploration of the finite amplitude regime have also been made with simplified models. Future model developments are needed to explore long-term dynamics.Multibeam data processing is essential for bedform mapping because the resulting bathymetric map is the basis for the characterization of bedforms and for further analysis and interpretations. The existence of a large amount of spatial data in general and swath bathymetry data in particular requires the creation of metadata and spatial data services that should make it possible to find, view and download data in order to share them at various levels, meeting international standards following the INSPIRE Directive (2007).A number of morphodynamic models have been developed to simulate the dynamics of large-scale bedform patterns on the continental shelf. Most of the models are based on linear stability analysis and, therefore, only describe the characteristics of the bedforms at their formation. Apart from studying the principal formation mechanism, the models have take into account various processes (three dimensional flows, sediment sorting, wave stirring, different tidal constituents, etc) to describe the characteristics of the bedforms at specific locations. Exploration of the finite amplitude regime have also been made with simplified models. Future model developments are needed to explore long-term dynamics.

Km-scale shoreline sand waves

A number of morphodynamic models have been developed to simulate the dynamics of large-scale bedform patterns on the continental shelf. Most of the models are based on linear stability analysis and, therefore, only describe the characteristics of the bedforms at their formation. Apart from studying the principal formation mechanism, the models have take into account various processes (three dimensional flows, sediment sorting, wave stirring, different tidal constituents, etc) to describe the characteristics of the bedforms at specific locations. Exploration of the finite amplitude regime have also been made with simplified models. Future model developments are needed to explore long-term dynamics.Multibeam data processing is essential for bedform mapping because the resulting bathymetric map is the basis for the characterization of bedforms and for further analysis and interpretations. The existence of a large amount of spatial data in general and swath bathymetry data in particular requires the creation of metadata and spatial data services that should make it possible to find, view and download data in order to share them at various levels, meeting international standards following the INSPIRE Directive (2007).A number of morphodynamic models have been developed to simulate the dynamics of large-scale bedform patterns on the continental shelf. Most of the models are based on linear stability analysis and, therefore, only describe the characteristics of the bedforms at their formation. Apart from studying the principal formation mechanism, the models have take into account various processes (three dimensional flows, sediment sorting, wave stirring, different tidal constituents, etc) to describe the characteristics of the bedforms at specific locations. Exploration of the finite amplitude regime have also been made with simplified models. Future model developments are needed to explore long-term dynamics.