21 research outputs found

    On Transmission System Design for Wireless Broadcasting

    Get PDF
    This thesis considers aspects related to the design and standardisation of transmission systems for wireless broadcasting, comprising terrestrial and mobile reception. The purpose is to identify which factors influence the technical decisions and what issues could be better considered in the design process in order to assess different use cases, service scenarios and end-user quality. Further, the necessity of cross-layer optimisation for efficient data transmission is emphasised and means to take this into consideration are suggested. The work is mainly related terrestrial and mobile digital video broadcasting systems but many of the findings can be generalised also to other transmission systems and design processes. The work has led to three main conclusions. First, it is discovered that there are no sufficiently accurate error criteria for measuring the subjective perceived audiovisual quality that could be utilised in transmission system design. Means for designing new error criteria for mobile TV (television) services are suggested and similar work related to other services is recommended. Second, it is suggested that in addition to commercial requirements there should be technical requirements setting the frame work for the design process of a new transmission system. The technical requirements should include the assessed reception conditions, technical quality of service and service functionalities. Reception conditions comprise radio channel models, receiver types and antenna types. Technical quality of service consists of bandwidth, timeliness and reliability. Of these, the thesis focuses on radio channel models and errorcriteria (reliability) as two of the most important design challenges and provides means to optimise transmission parameters based on these. Third, the thesis argues that the most favourable development for wireless broadcasting would be a single system suitable for all scenarios of wireless broadcasting. It is claimed that there are no major technical obstacles to achieve this and that the recently published second generation digital terrestrial television broadcasting system provides a good basis. The challenges and opportunities of a universal wireless broadcasting system are discussed mainly from technical but briefly also from commercial and regulatory aspectSiirretty Doriast

    DVB-H link layer

    Get PDF

    Combined Time, Frecuency and Space Diversity in Multimedia Mobile Broadcasting Systems

    Full text link
    El uso combinado de diversidad en el dominio temporal, frecuencial y espacial constituye una valiosa herramienta para mejorar la recepci贸n de servicios de difusi贸n m贸viles. Gracias a la mejora conseguida por las t茅cnicas de diversidad es posible extender la cobertura de los servicios m贸viles adem谩s de reducir la infraestructura de red. La presente tesis investiga el uso de t茅cnicas de diversidad para la provisi贸n de servicios m贸viles en la familia europea de sistemas de difusi贸n terrestres estandarizada por el prpoyecto DVB (Digital Video Broadcasting). Esto incluye la primera y segunda generaci贸n de sistemas DVB-T (Terrestrial), DVB-NGH (Handheld), y DVB-T2 (Terrestrial 2nd generation), as铆 como el sistema de siguiente generaci贸n DVB-NGH. No obstante, el estudio llevado a cabo en la tesis es gen茅rico y puede aplicarse a futuras evoluciones de est谩ndares como el japon茅s ISDB-T o el americano ATSC. Las investigaciones realizadas dentro del contexto de DVB-T, DVB-H y DVBT2 tienen como objetivo la transmisi贸n simult谩nea de servicios fijos y m贸viles en redes terrestres. Esta Convergencia puede facilitar la introducci贸n de servicios m贸viles de TB debido a la reutilizaci贸n de espectro, contenido e infraestructura. De acuerdo a los resultados, la incorporaci贸n de entrelazado temporal en la capa f铆sica para diversidad temporal, y de single-input multiple-output (SIMO) para diversidad espacial, son esenciales para el rendimiento de sistemas m贸viles de difusi贸n. A pesar de que las t茅cnicas upper later FEC (UL-FEC) pueden propocionar diversidad temporal en sistemas de primera generaci贸n como DVB-T y DVB-H, requieren la transmisi贸n de paridad adicional y no son 煤tiles para la recepci贸n est谩tica. El an谩lisis en t锟矫眅rminos de link budjget revela que las t茅cnicas de diversidad noson suficientes para facilitar la provision de servicios m贸viles en redes DVB-T y DVB-T2 planificadas para recepci贸n fija. Sin embargo, el uso de diversidad en redes planificadas para recepci贸n portableGoz谩lvez Serrano, D. (2012). Combined Time, Frecuency and Space Diversity in Multimedia Mobile Broadcasting Systems [Tesis doctoral no publicada]. Universitat Polit猫cnica de Val猫ncia. https://doi.org/10.4995/Thesis/10251/16273Palanci

    COST EFFICIENT PROVISIONING OF MASS MOBILE MULTIMEDIA SERVICES IN HYBRID CELLULAR AND BROADCASTING SYSTEMS

    Full text link
    Uno de los retos a los que se enfrenta la industria de las comunicaciones m贸viles e inal谩mbricas es proporcionar servicios multimedia masivos a bajo coste, haci茅ndolos asequibles para los usuarios y rentables a los operadores. El servicio m谩s representativo es el de TV m贸vil, el cual se espera que sea una aplicaci贸n clave en las futuras redes m贸viles. Actualmente las redes celulares no pueden soportar un consumo a gran escala de este tipo de servicios, y las nuevas redes de radiodifusi贸n m贸vil son muy costosas de desplegar debido a la gran inversi贸n en infraestructura de red necesaria para proporcionar niveles aceptables de cobertura. Esta tesis doctoral aborda el problema de la provisi贸n eficiente de servicios multimedia masivos a dispositivos m贸viles y portables utilizando la infraestructura de radiodifusi贸n y celular existente. La tesis contempla las tecnolog铆as comerciales de 煤ltima generaci贸n para la radiodifusi贸n m贸vil (DVB-H) y para las redes celulares (redes 3G+ con HSDPA y MBMS), aunque se centra principalmente en DVB-H. El principal paradigma propuesto para proporcionar servicios multimedia masivos a bajo coste es evitar el despliegue de una red DVB-H con alta capacidad y cobertura desde el inicio. En su lugar se propone realizar un despliegue progresivo de la infraestructura DVB-H siguiendo la demanda de los usuarios. Bajo este contexto, la red celular es fundamental para evitar sobre-dimensionar la red DVB-H en capacidad y tambi茅n en 谩reas con una baja densidad de usuarios hasta que el despliegue de un transmisor o un repetidor DVB-H sea necesario. Como principal soluci贸n tecnol贸gica la tesis propone realizar una codificaci贸n multi-burst en DVB-H utilizando c贸digos Raptor. El objetivo es explotar la diversidad temporal del canal m贸vil para aumentar la robustez de la se帽al y, por tanto, el nivel de cobertura, a costa de incrementar la latencia de la red.G贸mez Barquero, D. (2009). COST EFFICIENT PROVISIONING OF MASS MOBILE MULTIMEDIA SERVICES IN HYBRID CELLULAR AND BROADCASTING SYSTEMS [Tesis doctoral no publicada]. Universitat Polit猫cnica de Val猫ncia. https://doi.org/10.4995/Thesis/10251/6881Palanci

    The planning and optimisation of DVB-H radio network

    Get PDF
    In the DVB-H (Digital Video Broadcasting - Handheld) radio network planning, there are details that lack final consensus in the scientific field. The aim of this doctoral dissertation is to investigate advanced DVB-H radio network planning and optimisation. This dissertation presents the results of measurement techniques, network coverage and quality estimation, technological and economical optimisation, as well as error correction and single frequency network performance. The outcome includes proposed DVB-H radio network planning and optimisation methods that can be applied to the further investigation of detailed parameters in the radio link budget. There are also case studies that show the functionality of the presented methods with typical performance values. Based on comparative investigations, a process chart was created for DVB-H radio network planning and optimisation. The process blocks can be applied in a typical DVB-H network deployment, for the initial high-level phase as well as in the detailed network planning and optimisation phase. Using this process, the most relevant items were selected for in-depth studies. The investigations are presented in the annexed publications. The reminder was revised by comparative literature studies. The structure of the thesis follows the designed process charts. The main focus of this dissertation is the development of DVB-H radio network planning methodologies. One of the goals was to investigate the radio interface measurements, their post-processing and analysis. This can provide a guide to the selection of the appropriate values as a function of the radio channel type. An additional goal is the controlled management of over-sized single frequency network areas through the balancing of elevated SFN interference levels and related SFN gains. The development of a radio path loss simulator is the basis for these studies. The case results are presented as a function of the relevant radio parameter values, transmitter power levels and site antenna heights, both in theoretical and realistic network layouts. In addition to these topics, this document also investigates selected electro-magnetic compatibility, human exposure safety zones and radio coverage estimations. Also the balancing of technical radio parameters and network costs in order to complete the planning process steps is covered

    Architecture and algorithms for the implementation of digital wireless receivers in FPGA and ASIC: ISDB-T and DVB-S2 cases

    Full text link
    [EN] The first generation of Terrestrial Digital Television(DTV) has been in service for over a decade. In 2013, several countries have already completed the transition from Analog to Digital TV Broadcasting, most of which in Europe. In South America, after several studies and trials, Brazil adopted the Japanese standard with some innovations. Japan and Brazil started Digital Terrestrial Television Broadcasting (DTTB) services in December 2003 and December 2007 respectively, using Integrated Services Digital Broadcasting - Terrestrial (ISDB-T), also known as ARIB STD-B31. In June 2005 the Committee for the Information Technology Area (CATI) of Brazilian Ministry of Science and Technology and Innovation MCTI approved the incorporation of the IC-Brazil Program, in the National Program for Microelectronics (PNM) . The main goals of IC-Brazil are the formal qualification of IC designers, support to the creation of semiconductors companies focused on projects of ICs within Brazil, and the attraction of semiconductors companies focused on the design and development of ICs in Brazil. The work presented in this thesis originated from the unique momentum created by the combination of the birth of Digital Television in Brazil and the creation of the IC-Brazil Program by the Brazilian government. Without this combination it would not have been possible to make these kind of projects in Brazil. These projects have been a long and costly journey, albeit scientifically and technologically worthy, towards a Brazilian DTV state-of-the-art low complexity Integrated Circuit, with good economy scale perspectives, due to the fact that at the beginning of this project ISDB-T standard was not adopted by several countries like DVB-T. During the development of the ISDB-T receiver proposed in this thesis, it was realized that due to the continental dimensions of Brazil, the DTTB would not be enough to cover the entire country with open DTV signal, specially for the case of remote localizations far from the high urban density regions. Then, Eldorado Research Institute and Idea! Electronic Systems, foresaw that, in a near future, there would be an open distribution system for high definition DTV over satellite, in Brazil. Based on that, it was decided by Eldorado Research Institute, that would be necessary to create a new ASIC for broadcast satellite reception. At that time DVB-S2 standard was the strongest candidate for that, and this assumption still stands nowadays. Therefore, it was decided to apply to a new round of resources funding from the MCTI - that was granted - in order to start the new project. This thesis discusses in details the Architecture and Algorithms proposed for the implementation of a low complexity Intermediate Frequency(IF) ISDB-T Receiver on Application Specific Integrated Circuit (ASIC) CMOS. The Architecture proposed here is highly based on the COordinate Rotation Digital Computer (CORDIC) Algorithm, that is a simple and efficient algorithm suitable for VLSI implementations. The receiver copes with the impairments inherent to wireless channels transmission and the receiver crystals. The thesis also discusses the Methodology adopted and presents the implementation results. The receiver performance is presented and compared to those obtained by means of simulations. Furthermore, the thesis also presents the Architecture and Algorithms for a DVB-S2 receiver targeting its ASIC implementation. However, unlike the ISDB-T receiver, only preliminary ASIC implementation results are introduced. This was mainly done in order to have an early estimation of die area to prove that the project in ASIC is economically viable, as well as to verify possible bugs in early stage. As in the case of ISDB-T receiver, this receiver is highly based on CORDIC algorithm and it was prototyped in FPGA. The Methodology used for the second receiver is derived from that used for the ISDB-T receiver, with minor additions given the project characteristics.[ES] La primera generaci贸n de Televisi贸n Digital Terrestre(DTV) ha estado en servicio por m谩s de una d茅cada. En 2013, varios pa铆ses completaron la transici贸n de transmisi贸n anal贸gica a televisi贸n digital, la mayor铆a de ellas en Europa. En Am茅rica del Sur, despu茅s de varios estudios y ensayos, Brasil adopt贸 el est谩ndar japon茅s con algunas innovaciones. Jap贸n y Brasil comenzaron a prestar el servicio de Difusi贸n de Televisi贸n Digital Terrestre (DTTB) en diciembre de 2003 y diciembre de 2007 respectivamente, utilizando Radiodifusi贸n Digital de Servicios Integrados Terrestres (ISDB-T), tambi茅n conocida como ARIB STD-B31. En junio de 2005, el Comit茅 del 脕rea de Tecnolog铆a de la Informaci贸n (CATI) del Ministerio de Ciencia, Tecnolog铆a e Innovaci贸n de Brasil - MCTI aprob贸 la incorporaci贸n del Programa CI-Brasil, en el Programa Nacional de Microelectr贸nica (PNM). Los principales objetivos de la CI-Brasil son la formaci贸n de dise帽adores de CIs, apoyar la creaci贸n de empresas de semiconductores enfocadas en proyectos de circuitos integrados dentro de Brasil, y la atracci贸n de empresas de semiconductores interesadas en el dise帽o y desarrollo de circuitos integrados. El trabajo presentado en esta tesis se origin贸 en el impulso 煤nico creado por la combinaci贸n del nacimiento de la televisi贸n digital en Brasil y la creaci贸n del Programa de CI-Brasil por el gobierno brasile帽o. Sin esta combinaci贸n no hubiera sido posible realizar este tipo de proyectos en Brasil. Estos proyectos han sido un trayecto largo y costoso, aunque meritorio desde el punto de vista cient铆fico y tecnol贸gico, hacia un Circuito Integrado brasile帽o de punta y de baja complejidad para DTV, con buenas perspectivas de econom铆a de escala debido al hecho que al inicio de este proyecto, el est谩ndar ISDB-T no fue adoptado por varios pa铆ses como DVB-T. Durante el desarrollo del receptor ISDB-T propuesto en esta tesis, se observ贸 que debido a las dimensiones continentales de Brasil, la DTTB no ser铆a suficiente para cubrir todo el pa铆s con la se帽al de televisi贸n digital abierta, especialmente para el caso de localizaciones remotas, apartadas de las regiones de alta densidad urbana. En ese momento, el Instituto de Investigaci贸n Eldorado e Idea! Sistemas Electr贸nicos, previeron que en un futuro cercano habr铆a un sistema de distribuci贸n abierto para DTV de alta definici贸n por sat茅lite en Brasil. Con base en eso, el Instituto de Investigaci贸n Eldorado decidi贸 que ser铆a necesario crear un nuevo ASIC para la recepci贸n de radiodifusi贸n por sat茅lite, basada el est谩ndar DVB-S2. En esta tesis se analiza en detalle la Arquitectura y algoritmos propuestos para la implementaci贸n de un receptor ISDB-T de baja complejidad y frecuencia intermedia (IF) en un Circuito Integrado de Aplicaci贸n Espec铆fica (ASIC) CMOS. La arquitectura aqu铆 propuesta se basa fuertemente en el algoritmo Computadora Digital para Rotaci贸n de Coordenadas (CORDIC), el cual es un algoritmo simple, eficiente y adecuado para implementaciones VLSI. El receptor hace frente a las deficiencias inherentes a las transmisiones por canales inal谩mbricos y los cristales del receptor. La tesis tambi茅n analiza la metodolog铆a adoptada y presenta los resultados de la implementaci贸n. Por otro lado, la tesis tambi茅n presenta la arquitectura y los algoritmos para un receptor DVB-S2 dirigido a la implementaci贸n en ASIC. Sin embargo, a diferencia del receptor ISDB-T, se introducen s贸lo los resultados preliminares de implementaci贸n en ASIC. Esto se hizo principalmente con el fin de tener una estimaci贸n temprana del 谩rea del die para demostrar que el proyecto en ASIC es econ贸micamente viable, as铆 como para verificar posibles errores en etapa temprana. Como en el caso de receptor ISDB-T, este receptor se basa fuertemente en el algoritmo CORDIC y fue un prototipado en FPGA. La metodolog铆a utilizada para el segundo receptor se deriva de la utilizada para el re[CA] La primera generaci贸 de Televisi贸 Digital Terrestre (TDT) ha estat en servici durant m茅s d'una d猫cada. En 2013, diversos pa茂sos ja van completar la transici贸 de la radiodifusi贸 de televisi贸 anal貌gica a la digital, i la majoria van ser a Europa. A Am猫rica del Sud, despr茅s de diversos estudis i assajos, Brasil va adoptar l'est脿ndard japon茅s amb algunes innovacions. Jap贸 i Brasil van comen莽ar els servicis de Radiodifusi贸 de Televisi贸 Terrestre Digital (DTTB) al desembre de 2003 i al desembre de 2007, respectivament, utilitzant la Radiodifusi贸 Digital amb Servicis Integrats de (ISDB-T), coneguda com a ARIB STD-B31. Al juny de 2005, el Comit茅 de l'脌rea de Tecnologia de la Informaci贸 (CATI) del Ministeri de Ci猫ncia i Tecnologia i Innovaci贸 del Brasil (MCTI) va aprovar la incorporaci贸 del programa CI Brasil al Programa Nacional de Microelectr貌nica (PNM). Els principals objectius de CI Brasil s贸n la qualificaci贸 formal dels dissenyadors de circuits integrats, el suport a la creaci贸 d'empreses de semiconductors centrades en projectes de circuits integrats dins del Brasil i l'atracci贸 d'empreses de semiconductors centrades en el disseny i desenvolupament de circuits integrats. El treball presentat en esta tesi es va originar en l'impuls 煤nic creat per la combinaci贸 del naixement de la televisi贸 digital al Brasil i la creaci贸 del programa Brasil CI pel govern brasiler. Sense esta combinaci贸 no hauria estat possible realitzar este tipus de projectes a Brasil. Estos projectes han suposat un viatge llarg i cost贸s, tot i que digne cient铆ficament i tecnol貌gica, cap a un circuit integrat punter de baixa complexitat per a la TDT brasilera, amb bones perspectives d'economia d'escala perqu猫 a l'inici d'este projecte l'est脿ndard ISDB-T no va ser adoptat per diversos pa茂sos, com el DVB-T. Durant el desenvolupament del receptor de ISDB-T proposat en esta tesi, va resultar que, a causa de les dimensions continentals de Brasil, la DTTB no seria suficient per cobrir tot el pa铆s amb el senyal de TDT oberta, especialment pel que fa a les localitzacions remotes allunyades de les regions d'alta densitat urbana.. En este moment, l'Institut de Recerca Eldorado i Idea! Sistemes Electr貌nics van preveure que, en un futur pr貌xim, no hi hauria a Brasil un sistema de distribuci贸 oberta de TDT d'alta definici贸 a trav茅s de sat猫l驴lit. D'acord amb aix貌, l'Institut de Recerca Eldorado va decidir que seria necessari crear un nou ASIC per a la recepci贸 de radiodifusi贸 per sat猫l驴lit. basat en l'est脿ndard DVB-S2. En esta tesi s'analitza en detall l'arquitectura i els algorismes proposats per l'execuci贸 d'un receptor ISDB-T de Freq眉猫ncia Interm猫dia (FI) de baixa complexitat sobre CMOS de Circuit Integrat d'Aplicacions Espec铆fiques (ASIC). L'arquitectura ac铆 proposada es basa molt en l'algorisme de l'Ordinador Digital de Rotaci贸 de Coordenades (CORDIC), que 茅s un algorisme simple i eficient adequat per implementacions VLSI. El receptor fa front a les defici猫ncies inherents a la transmissi贸 de canals sense fil i els cristalls del receptor. Esta tesi tamb茅 analitza la metodologia adoptada i presenta els resultats de l'execuci贸. Es presenta el rendiment del receptor i es compara amb els obtinguts per mitj脿 de simulacions. D'altra banda, esta tesi tamb茅 presenta l'arquitectura i els algorismes d'un receptor de DVB-S2 de cara a la seua implementaci贸 en ASIC. No obstant aix貌, a difer猫ncia del receptor ISDB-T, nom茅s s'introdueixen resultats preliminars d'implementaci贸 en ASIC. Aix貌 es va fer principalment amb la finalitat de tenir una estimaci贸 primerenca de la zona de dau per demostrar que el projecte en ASIC 茅s econ貌micament viable, aix铆 com per verificar possibles errors en l'etapa primerenca. Com en el cas del receptor ISDB-T, este receptor es basa molt en l'algorisme CORDIC i va ser un prototip de FPGA. La metodologia utilitzada per al segon receptor es deriva de la utilitzada per al receptor IRodrigues De Lima, E. (2016). Architecture and algorithms for the implementation of digital wireless receivers in FPGA and ASIC: ISDB-T and DVB-S2 cases [Tesis doctoral no publicada]. Universitat Polit猫cnica de Val猫ncia. https://doi.org/10.4995/Thesis/10251/61967TESI

    Application of network coding in satellite broadcast and multiple access channels

    Get PDF
    Satellite broadcasting and relaying capabilities enable mobile broadcast systems over wide geographical areas, which opens large market possibilities for handheld, vehicular and fixed user terminals. The geostationary (GEO) satellite orbit is highly suited for such applications, as it spares the need for satellite terminals to track the movement of the spacecraft, with important savings in terms of complexity and cost. The large radius of the GEO orbit (more than 40000 km) has two main drawbacks. One is the large free space loss experienced by a signal traveling to or from the satellite, which limits the signal-to-noise ratio (SNR) margins in the link budget with respect to terrestrial systems. The second drawback of the GEO orbit is the large propagation delay (about 250 msec) that limits the use of feedback in both the forward (satellite to satellite terminal) and the reverse (satellite terminal to satellite) link. The limited margin protection causes loss of service availability in environments where there is no direct line of sight to the satellite, such as urban areas. The large propagation delay on its turn, together with the large terminal population size usually served by a GEO satellite, limit the use of feedback, which is at the basis of error-control. In the reverse link, especially in the case of fixed terminals, packet losses are mainly due to collisions, that severely limit the access to satellite services in case a random access scheme is adopted. The need for improvements and further understanding of these setups lead to the development of our work. In this dissertation we study the application of network coding to counteract the above mentioned channel impairments in satellite systems. The idea of using network coding stems from the fact that it allows to efficiently exploit the diversity, either temporal or spatial, present in the system. In the following we outline the original contributions included in each of the chapters of the dissertation. Chapter 3. This chapter deals with channel impairments in the forward link, and specifically with the problem of missing coverage in Urban environments for land mobile satellite (LMS) networks. By applying the Max-flow Min-cut theorem we derive a lower bound on the maximum coverage that can be achieved through cooperation. Inspired by this result, we propose a practical scheme, keeping in mind the compatibility with the DVB-SH standard. We developed a simulator in Matlab/C++ based on the physical layer abstraction and used it to test the performance gain of our scheme with a benchmark relaying scheme that does allow coding at packet level. Chapter 4. The second chapter of contributions is devoted to the information theoretical study of real-time streaming transmissions over fading channels with channel state information at the transmitter only. We introduce this new channel model and propose several transmission schemes, one of which is proved to be asymptotically optimal in terms of throughput. We also provide an upper bound on the achievable throughput for the proposed channel model and compare it numerically with the proposed schemes over a Rayleigh fading channel. Chapter 5. Chapter 5 is devoted to the study of throughput and delay in non-real-time streaming transmission over block fading channels. We derive bounds on the throughput and the delay for this channel and propose different coding techniques based on time-sharing. For each of them we carry out an analytical study of the performance. Finally, we compare numerically the performance of the proposed schemes over a Rayleigh fading channel. Chapter 6. In the last technical chapter we propose a collision resolution method for the return link based on physical layer network coding over extended Galois field (EGF). The proposed scheme extracts information from the colliding signals and achieves important gains with respect to Slotted ALOHA systems as well as with respect to other collision resolution schemes.Una de les caracter铆stiques mes importants de les plataformes de comunicacions per sat猫l.lit 茅s la seva capacitat de retransmetre senyals rebuts a un gran n煤mero de terminals. Aix貌 es fonamental en contextes com la difusi贸 a terminals m貌bils o la comunicaci贸 entre m脿quines. Al mateix temps, la disponibilitat d鈥檜n canal de retorn permet la creaci贸 de sistemes de comunicacions per sat猫l.lit interactius que, en principi, poden arribar a qualsevol punt del planeta. Els sat猫l.lits Geoestacionaris son particularment adequats per a complir amb aquesta tasca. Aquest tipus de sat猫l.lits mant茅 una posici贸 fixa respecte a la Terra, estalviant als terminals terrestres la necessitat de seguir el seu moviment en el cel. Per altra banda, la gran dist脿ncia que separa la Terra dels sat猫l.lits Geoestacionaris introdueix grans retrassos en les comunicacions que, afegit al gran n煤mero de terminals en servei, limita l鈥櫭簊 de t猫cniques de retransmissi贸 basades en acknowledgments en cas de p猫rdua de paquets. Per tal de sol.lucionar el problema de la p猫rdua de paquets, les t猫cniques m茅s utilitzades son el desplegament de repetidors terrestres, anomenats gap fillers, l鈥櫭簊 de codis de protecci贸 a nivell de paquet i mecanismes proactius de resoluci贸 de col.lisions en el canal de retorn. En aquesta tesi s鈥檃nalitzen i s鈥檈studien sol.lucions a problemes en la comunicaci贸 per sat猫l.lit tant en el canal de baixada com el de pujada. En concret, es consideren tres escenaris diferents. El primer escenari es la transmissi贸 a grans poblacions de terminals m貌bils en enorns urbans, que es veuen particularment afectats per la p猫rdua de paquets degut a l鈥檕bstrucci贸, per part dels edificis, de la l铆nia de visi贸 amb el sat猫l.lit. La sol.luci贸 que considerem consisteix en la utilitzaci贸 de la cooperaci贸 entre terminals. Una vegada obtinguda una mesura del guany que es pot assolir mitjan莽ant cooperaci贸 en un model b脿sic de xarxa, a trav茅s del teorema Max-flow Min-cut, proposem un esquema de cooperaci贸 compatible amb est脿ndards de comunicaci贸 existents. El segon escenari que considerem es la transmissi贸 de v铆deo, un tipus de tr脿fic particularment sensible a la p猫rdua de paquets i retards end貌gens als sistemes de comunicaci贸 per sat猫l.lit. Considerem els casos de transmissi贸 en temps real i en diferit, des de la perspectiva de teoria de la informaci贸, i estudiem diferents t猫cniques de codificaci贸 anal铆tica i num猫rica. Un dels resultats principals obtinguts es l鈥檈xtensi贸 del l铆mit assolible de la capacitat erg貌dica del canal en cas que el transmissor rebi les dades de manera gradual, enlloc de rebre-les totes a l鈥檌nici de la transmissi贸. El tercer escenari que considerem es l鈥檃cc茅s aleatori al sat猫l.lit. Desenvolupem un esquema de recuperaci贸 dels paquets perduts basat en la codificaci贸 de xarxa a nivell f铆sic i en extensions a camps de Galois, amb resultats molt prometedors en termes de rendiment. Tamb茅 estudiem aspectes relacionats amb la implementaci贸 pr脿ctica d鈥檃quest esquema
    corecore