Advanced Fade Countermeasures for DVB-S2 Systems in Railway Scenarios

This paper deals with the analysis of advanced fade countermeasures for supporting DVB-S2 reception by mobile terminals mounted on high-speed trains. Recent market studies indicate this as a potential profitable market for satellite communications, provided that integration with wireless terrestrial networks can be implemented to bridge the satellite connectivity inside railway tunnels and large train stations. In turn, the satellite can typically offer the coverage of around 80% of the railway path with existing space infrastructure. This piece of work, representing the first step of a wider study, is focusing on the modifications which may be required in the DVB-S2 standard (to be employed in the forward link) in order to achieve reliable reception in a challenging environment such as the railway one. Modifications have been devised trying to minimize the impact on the existing air interface, standardized for fixed terminals

Propagation Measurement on Earth-Sky Signal Effects for High Speed Train Satellite Channel in Tropical Region at Ku-Band

Recent advances in satellite communication technologies in the tropical regions have led to significant increase in the demand for services and applications that require high channel quality for mobile satellite terminals. Determination and quantification of these requirements are important to optimize service quality, particularly in the Malaysian region. Moreover, the tests on current satellite propagation models were carried out at temperate regions whose environmental characteristics are much different from those in Malaysia. This difference renders these propagation models inapplicable and irrelevant to tropical regions in general. This paper presents the link characteristics observations and performance analysis with propagation measurements done in tropical region to provide an accurate database regarding rain and power arches supply (PAs) attenuations in the tropics for mobile scenarios. Hence, an extension for improving the performance assessment and analysis of satellite/transmission has been achieved. The Malaysia propagation measurement for mobile scenario (Malaysia-PMMS) enables first-hand coarse estimation and attenuation analysis, because the attenuation resulting from rain and PAs becomes easily amenable for measurement. Parallel to that, the measured attenuation has been compared with that of the simulated output at noise floor level. The underlying analytical tool is validated by measurements specific at tropical region, for dynamic model of mobile satellite links operating at higher than 10 GHz

QoSatAr: a cross-layer architecture for E2E QoS provisioning over DVB-S2 broadband satellite systems

This article presents QoSatAr, a cross-layer architecture developed to provide end-to-end quality of service (QoS) guarantees for Internet protocol (IP) traffic over the Digital Video Broadcasting-Second generation (DVB-S2) satellite systems. The architecture design is based on a cross-layer optimization between the physical layer and the network layer to provide QoS provisioning based on the bandwidth availability present in the DVB-S2 satellite channel. Our design is developed at the satellite-independent layers, being in compliance with the ETSI-BSM-QoS standards. The architecture is set up inside the gateway, it includes a Re-Queuing Mechanism (RQM) to enhance the goodput of the EF and AF traffic classes and an adaptive IP scheduler to guarantee the high-priority traffic classes taking into account the channel conditions affected by rain events. One of the most important aspect of the architecture design is that QoSatAr is able to guarantee the QoS requirements for specific traffic flows considering a single parameter: the bandwidth availability which is set at the physical layer (considering adaptive code and modulation adaptation) and sent to the network layer by means of a cross-layer optimization. The architecture has been evaluated using the NS-2 simulator. In this article, we present evaluation metrics, extensive simulations results and conclusions about the performance of the proposed QoSatAr when it is evaluated over a DVB-S2 satellite scenario. The key results show that the implementation of this architecture enables to keep control of the satellite system load while guaranteeing the QoS levels for the high-priority traffic classes even when bandwidth variations due to rain events are experienced. Moreover, using the RQM mechanism the user’s quality of experience is improved while keeping lower delay and jitter values for the high-priority traffic classes. In particular, the AF goodput is enhanced around 33% over the drop tail scheme (on average)

Codificación a nivel de paquete para comunicaciones móviles por satélite

Una de les opcions que es contemplen per transmetre continguts multimèdia i proporcionar accés a Internet a grups de usuaris mòbils és fer servir satèl·lits. Les condiciones de propagació del canal mòbil impliquen que d'una manera o altra haurem de garantir la qualitat de servei. Això té fins i tot més importància si tenim en compte que, en el cas d'accés a Internet, no es té la capacitat d'assumir cert percentatge de pèrdua de dades que tenim, per exemple, en la transmissió de so o vídeo (rebaixant la qualitat). Entre les principals alternatives per a aquesta classe d'entorns es troba la inclusió de codificacions a nivell de paquet. El funcionament d'aquesta tècnica es basa en incloure a la transmissió paquets redundants, obtinguts mitjançant un determinat algoritme. El receptor podrà recuperar la informació original que es volia enviar, sempre que hagi rebut una certa quantitat de paquets, similar a la quantitat de paquets originals. A aquest mecanisme se'l coneix com Forward Error Correction (FEC) a nivell de paquet. En aquesta memòria es valoren breument les alternatives existents i s'expliquen algunes de les codificacions per a FEC més importants. A continuació es realitza un estudi compartiu d'algunes d'elles: les variants de LDPC (Low Density Parity Check) conegudes com LDGM (Low Density Generator Matrix), i la codificació RaptorUna de las opciones contempladas para transmitir contenidos multimedia y proporcionar acceso a Internet a grupos de usuarios móviles es el uso de satélites. Las condiciones de propagación del canal móvil implican que de alguna manera deberemos garantizar la calidad de servicio. Esto cobra incluso más importancia si tenemos en cuenta que, en el caso de acceso a Internet, no se tiene la capacidad de asumir cierto porcentaje de pérdida de datos que tenemos, por ejemplo, en la transmisión de sonido o vídeo (rebajando la calidad). Entre las principales alternativas estudiadas para esta clase de entornos está la inclusión de codificaciones a nivel paquete. El funcionamiento de esta técnica se basa en incluir en la transmisión paquetes redundantes, obtenidos mediante un determinado algoritmo. El receptor será capaz de recuperar la información original que se quería enviar, siempre y cuando haya recibido correctamente una cierta cantidad de paquetes, similar a la cantidad de paquetes originales. A este mecanismo se le conoce como Forward Error Correction (FEC) a nivel de paquete. En esta memoria se valora brevemente las alternativas existentes y se explican algunas de las codificaciones para FEC más importantes. A continuación se realiza un estudio comparativo de algunas de ellas: las variantes de LDPC (Low Density Parity Check) conocidas como LDGM (Low Density Generator Matrix), y la codificación Raptor.The use of satellites is one of the options considered to broadcast multimedia contents and to provide access to the Internet for groups of mobile users. The propagation conditions of mobile channel make necessary to guarantee the quality of service. This is even more important if we note that no data loss is allowed in the case of providing Internet access, while in sound or video transmissions it is (reducing the quality). One of the main alternatives which is being studied for this environments is the inclusion of packet level codifications. The basic idea of this technique is to include redundant packets in the transmission. These redundant packets can be obtained using a codification algorithm. The receiver will be able to recover all the original information provided it has received a certain amount of packets which will be similar to the amount of original packets. This technique is known as packet level Forward Error Correction (FEC). In this dissertation, the alternatives to FEC are briefly explained. Next, some of the most important packet level FEC codifications are explained. After that, a comparative study of some of them will be done, specifically the LDPC (Low Density Parity Check) variants known as LDGM (Low Density Generator Matrix) and the Raptor codification.Nota: Aquest document conté originàriament altre material i/o programari només consultable a la Biblioteca de Ciència i Tecnologia

Ubiquitous Computing

The aim of this book is to give a treatment of the actively developed domain of Ubiquitous computing. Originally proposed by Mark D. Weiser, the concept of Ubiquitous computing enables a real-time global sensing, context-aware informational retrieval, multi-modal interaction with the user and enhanced visualization capabilities. In effect, Ubiquitous computing environments give extremely new and futuristic abilities to look at and interact with our habitat at any time and from anywhere. In that domain, researchers are confronted with many foundational, technological and engineering issues which were not known before. Detailed cross-disciplinary coverage of these issues is really needed today for further progress and widening of application range. This book collects twelve original works of researchers from eleven countries, which are clustered into four sections: Foundations, Security and Privacy, Integration and Middleware, Practical Applications

Advanced Fade Countermeasures for DVB-S2 Systems in Railway Scenarios

This paper deals with the analysis of advanced fade countermeasures for supporting DVB-S2 reception by mobile terminals mounted on high-speed trains. Recent market studies indicate this as a potential profitable market for satellite communications, provided that integration with wireless terrestrial networks can be implemented to bridge the satellite connectivity inside railway tunnels and large train stations. In turn, the satellite can typically offer the coverage of around 80% of the railway path with existing space infrastructure. This piece of work, representing the first step of a wider study, is focusing on the modifications which may be required in the DVB-S2 standard (to be employed in the forward link) in order to achieve reliable reception in a challenging environment such as the railway one. Modifications have been devised trying to minimize the impact on the existing air interface, standardized for fixed terminals. </p