Ecualización y optimización de la codificación para la simulación de sistemas OFDM

Los sistemas basados en la técnica OFDM (Multiplexación por División de Frecuencias Ortogonales) son una evolución de los tradicionales sistemas FDM (Multiplexación por División de Frecuencia), gracias a la cual se consigue un mejor aprovechamiento del ancho de banda. En la actualidad los sistemas OFDM y sus variantes ocupan un lugar muy importante en las comunicaciones, estando implementados en diversos estándares como pueden ser: DVB-T (estándar de la TDT), ADSL, LTE, WIMAX, DAB (radio digital), etc. Debido a ello, en este proyecto se implementa un sistema OFDM en el que poder realizar diversas simulaciones para entender mejor su funcionamiento. Para ello nos vamos a valer de la herramienta Matlab. Los objetivos fundamentales dentro de la simulación del sistema es poner a prueba el empleo de turbo códigos (comparándolo con los códigos convolucionales tradicionales) y de un ecualizador. Todo ello con la intención de mejorar la calidad de nuestro sistema (recibir menos bits erróneos) en condiciones cada vez más adversas: relaciones señal a ruido bajas y multitrayectos. Para ello se han implementado las funciones necesarias en Matlab, así como una interfaz gráfica para que sea más sencillo de utilizar el programa y más didáctico. En los capítulos segundo y tercero de este proyecto se efectúa un estudio de las bases de los sistemas OFDM. En el segundo nos centramos más en un estudio teórico puro para después pasar en el tercero a centrarnos únicamente en la teoría de los bloques implementados en el sistema OFDM que se desarrolla en este proyecto. En el capítulo cuarto se explican las distintas opciones que se pueden llevar a cabo mediante la interfaz implementada, a la vez que se elabora un manual para el correcto uso de la misma. El quinto capítulo se divide en dos partes, en la primera se muestran las representaciones que puede realizar el programa, y en la segunda únicamente se realizan simulaciones para comprobar que tal responde nuestra sistema a distintas configuraciones de canal, y las a distintas configuraciones que hagamos nosotros de nuestro sistema (utilicemos una codificación u otra, utilicemos el ecualizador o el prefijo cíclico, etc…). Para finalizar, en el último capítulo se exponen las conclusiones obtenidas en este proyecto, así como posibles líneas de trabajo que seguir en próximas versiones del mismo. ABSTRACT. Systems based on OFDM (Orthogonal Frequency Division Multiplexing) technique are an evolution of traditional FDM (Frequency Division Multiplexing). Due to the use of OFDM systems are achieved by more efficient use of bandwidth. Nowadays, OFDM systems and variants of OFDM systems occupy a very important place in the world of communications, being implemented in standards such as DVB-T, ADSL, LTE, WiMAX, DAB (digital radio) and another more. For all these reasons, this project implements a OFDM system for performing various simulations for better understanding of OFDM system operation. The system has been simulated using Matlab. With system simulation we search to get two key objectives: to test the use of turbo codes (compared to traditional convolutional codes) and an equalizer. We do so with the intention of improving the quality of our system (receive fewer rates of bit error) in increasingly adverse conditions: lower signal-to-noise and multipath. For these reasons necessaries Matlab´s functions have been developed, and a GUI (User Graphical Interface) has been integrated so the program can be used in a easier and more didactic way. This project is divided into five chapters. In the second and third chapter of this project are developed the basis of OFDM systems. Being developed in the second one a pure theoretical study, while focusing only on block theory implemented in the OFDM system in the third one. The fourth chapter describes the options that can be carried out by the interface implemented. Furthermore the chapter is developed for the correct use of the interface. The fifth chapter is divided into two parts, the first part shows to us the representations that the program can perform, and the second one just makes simulations to check that our system responds to differents channel configurations (use of convolutional codes or turbo codes, the use of equalizer or cyclic prefix…). Finally, the last chapter presents the conclusions of this project and possible lines of work to follow in future versions

An architecture for integrating learning object repository resources into web videoconference services

Reusing Learning Objects saves time and reduce development costs. Hence, achieving their interoperability in multiple contexts is essential when creating a Learning Object Repository. On the other hand, novel web videoconference services are available due to technological advancements. Several benefits can be gained by integrating Learning Objects into these services. For instance, they can allow sharing, co-viewing and synchronized co-browsing of these resources at the same time that provide real time communication. However, several efforts need to be undertaken to achieve the interoperability with these systems. In this paper, we propose a model to integrate the resources of the Learning Object Repositories into web videoconference services. The experience of applying this model in a real e-Learning scenario achieving interoperability with two different web videoconference services is also described

Effect of the AlAs capping layer thickness on the structure of InAs/GaAs QD

Recently, very thin AlAs capping layers (CLs) have been proposed as a useful tool to increase the performance of InAs/GaAs quantum dot (QDs) devices. However, the structure of QDs after AlAs deposition remains poorly understood and the mechanisms to explain it are often contradictory. In this work, the structural and compositional changes of InAs QDs using different AlAs CL thicknesses have been studied by state-of-the-art STEM-related techniques. First, the heights and In contents of InAs QDs progressively increase with the CL thickness, demonstrating that the AlAs capping produces a strong shielding effect against the decomposition of QDs. However, QD populations for CL thicknesses above 5 ML split into a bimodal distribution in which smaller lenticular QDs cohabit with bigger truncated pyramids. Second, the actual Al contents around the QDs are well below the nominal design, but increasing for thicker CLs. Its distribution is initially non-uniform, tending to accumulate on the flanks of the QDs to the detriment of the apex. Only for thicknesses above 2 ML the Al contents around the QDs start to be similar to those in the regions between the QDs, behaving as a continuous film without irregularities from 5 ML onwards. © 2021 The Author(s)The work has been co-financed by the Spanish National Research Agency (AEI projects MAT2016-77491-C2-2-R and PID2019-106088RB-C33), Regional Government of Andalusia (project FEDER-UCA18-108319) and the European Regional Development Fund (ERDF)

Análisis de la distribución composicional en superredes de InAsBi/InAs sobre InAs para fotodetectores en el infrarrojo lejano

Resumen del proyecto de líneas prioritarias titulado "Análisis de la distribución composicional en superredes de InAsBi/InAs sobre InAs para fotodetectores en el infrarrojo lejano" del IMEYMAT

Growth interruption strategies for interface optimization in GaAsSb/GaAsN type-II superlattices

Recently, GaAsSb/GaAsN type II short-period superlattices (SLs) have been proposed as suitable structures to be implemented in the optimal design of monolithic multi-junction solar cells. However, due to strong surface Sb segregation, experimental Sb composition profiles differ greatly from the nominal square-wave design. In this work, the improvement of the interface quality of these SLs in terms of compositional abruptness and surface roughness has been evaluated by implementing different growth interruption times under Sb4/As4 (soaking) and As4 (desorption) overpressure conditions before and after the growth of GaAsSb layers, respectively. The com-bined effects of both processes enhance Sb distribution, achieving squarer compositional profiles with reduced surface roughness interfaces. It has been found that the improvement in compositional abruptness is quantita-tively much higher at the lower interface, during soaking, than at the upper interface during desorption. Conversely, a larger decrease in surface roughness is achieved at the upper interface than at the lower interface. Fitting of the Sb segregation profiles using the 3-layer kinetic fluid model has shown that the increase in Sb incorporation rate is due to the decrease in segregation energy, presumably to changes in the surface recon-struction of the floating layer at the surface

Suppressing the Effect of the Wetting Layer through AlAs Capping in InAs/GaAs QD Structures for Solar Cells Applications

Recently, thin AlAs capping layers (CLs) on InAs quantum dot solar cells (QDSCs) have been shown to yield better photovoltaic efficiency compared to traditional QDSCs. Although it has been proposed that this improvement is due to the suppression of the capture of photogenerated carriers through the wetting layer (WL) states by a de-wetting process, the mechanisms that operate during this process are not clear. In this work, a structural analysis of the WL characteristics in the AlAs/InAs QD system with different CL-thickness has been made by scanning transmission electron microscopy techniques. First, an exponential decline of the amount of InAs in the WL with the CL thickness increase has been found, far from a complete elimination of the WL. Instead, this reduction is linked to a higher shield effect against QD decomposition. Second, there is no compositional separation between the WL and CL, but rather single layer with a variable content of InAlGaAs. Both effects, the high intermixing and WL reduction cause a drastic change in electronic levels, with the CL making up of 1-2 monolayers being the most effective configuration to reduce the radiative-recombination and minimize the potential barriers for carrier transport.The work has been co-financed by the Spanish National Research Agency (AEI projects MAT2016-77491-C2-2-R and PID2019-106088RB-C33), Regional Government of Andalusia (project FEDER-UCA18-108319) and the European Regional Development Fund (ERDF)

Redes de nueva generación

Es un trabajo que involucra el diseño e implementación de una red de nueva generación, la cual soporta servicios como: IPTV, PBX, VLANs, soportados por protocolos tales como: MPLS, RTP, IPv4 e IPv6.This work involves the design and implementation of a new generation network, which supports services such as: IPTV, PBX, VLANs, supported by protocols such as: MPLS, RTP, IPv4 and IPv6

Histopatología y bioquímica clínica de ratas expuestas de forma subcrónica al extracto de migración de un material nanocompuesto

Junta de Andalucía AGR5969Ministerio de Ciencia e Innovación AGL2010-2121

Tailoring of AlAs/InAs/GaAs QDs Nanostructures via Capping Growth Rate

The use of thin AlA capping layers (CLs) on InAs quantum dots (QDs) has recently received considerable attention due to improved photovoltaic performance in QD solar cells. However, there is little data on the structural changes that occur during capping and their relation to different growth conditions. In this work, we studied the effect of AlA capping growth rate (CGR) on the structural features of InAs QDs in terms of shape, size, density, and average content. As will be shown, there are notable differences in the characteristics of the QDs upon changing CGR. The Al distribution analysis in the CL around the QDs was revealed to be the key. On the one hand, for the lowest CGR, Al has a homogeneous distribution over the entire surface, but there is a large thickening of the CL on the sides of the QD. As a result, the QDs are lower, lenticular in shape, but richer in In. On the other hand, for the higher CGRs, Al accumulates preferentially around the QD but with a more uniform thickness, resulting in taller QDs, which progressively adopt a truncated pyramidal shape. Surprisingly, intermediate CGRs do not improve either of these behaviors, resulting in less enriched QDs