7 research outputs found

    Ka-Band HTS System User Uplink SNIR Probability Models

    Get PDF
    Ka-band High-throughput-satellite (HTS) systems reuse frequency bands in spot beams for much higher system capacity and better spectrum efficiency. They however are prone to intra-system co-color interference and so suffer from the channel signal-to-noise-plus-interference ratio (SNIR) degradation. This chapter presents the development of the uplink SNIR probability models for Ka-band spot beam HTS systems. The models are applicable to different Ka-band propagation channel conditions of statistical significance. Its use of collective representation to model traffic variation of co-color beams captures the statistics of traffic variation and allows feasibility and variety of use case representation. The analytical approach complements known studies and fills in the blank of the use cases of urban and mobile users. The models can be used for system design performance estimation and prediction. It features computation time and memory savings in numerical implementation

    High Performance Signal Processing-Based Collision Resolution for Random Access Schemes

    Get PDF
    Els darrers anys han experimentat un augment de la demanda de serveis interactius per satèl·lit per al gran consum, cobrint serveis fixes i mòbils, tal i com accés de banda ampla, comunicacions màquina-màquina (M2M), supervisió, control i adquisició de dades (SCADA), transaccions i aplicacions de seguretat crítiques. Aquestes xarxes de comunicacions es caracteritzen per tenir una gran població d’usuaris compartint l’amplada de banda amb unes condicions de tràfic molt dinàmiques. Concretament, en el canal de retorn (de l’usuari a la xarxa) de xarxes d’accés de banda ampla, els usuaris residencials generen grans ràfegues de tràfic amb períodes d’inactivitat freqüents. Una situació similar succeeix en xarxes de comunicacions mòbils per satèl·lit, on una gran població de terminals generen transmissions infreqüents de senyalització, serveis basats en la localització or altres aplicacions de missatgeria. Aquests serveis requereixen el desenvolupament de protocols d’accés múltiple eficients que puguin operar en les condicions descrites anteriorment. Els protocols d´accés aleatori són bons candidats per servir tràfic poc predictiu, amb transmissions infreqüents així com sensibles amb el retard. A més, els protocols d´accés aleatori suporten un gran nombre de terminals compartint el canal de comunicacions i requereixen poca complexitat en el terminals. El protocols d´accés aleatori han estat àmpliament estudiats i desplegats en xarxes terrestres, però les seves prestacions són pobres en el entorn satèl·lital, que està caracteritzat per retards de propagació molt grans. Avui en dia, el seu ús en les xarxes de comunicacions per satèl·lit està principalment limitat a la senyalització d’inici de sessió, transmissió de paquets de control i en alguns casos a la transmissió de petits volums de dades amb unes eficiència d’utilització del canal molt baixa. Aquesta tesi proposa tres noves tècniques d’accés aleatori, bens adaptades per proveir els serveis esmentats anteriorment en un entorn satèl·lital, amb altes prestacions i una complexitat en el terminal d’usuari reduïda. Les noves tècniques d’accés aleatori són Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) i Enhanced Spread Spectrum Aloha (E-SSA), adaptades per un tipus d’accés ranurat, asíncron i d’espectre eixamplat respectivament. Les tres tècniques utilitzen una codificació de canal (FEC) robusta, capaç d’operar en front de interferències elevades, que són típiques en l’accés aleatori, i d’un mecanisme de cancel·lació successiva d’interferència que s’implementa en el receptor sobre els paquets descodificats satisfactòriament. Els nous protocols obtenen un throughput normalitzat superior a 1 bit/s/Hz amb una tassa de pèrdua de paquets inferior a 10-3, el qual representa un factor de millora de 1000 respecte a protocols d’accés aleatori tradicionals com l’ALOHA ranurat. Les prestacions de les noves tècniques d’accés aleatori has estat analitzades per mitjà de simulacions, així com amb nou models analítics desenvolupats en aquesta tesi capaços de caracteritzar el tràfic, la distribució estadística de la potència dels paquets, les prestacions de la codificació de canal (FEC) i el procés de cancel·lació d’interferència successiva.Los últimos años han experimentado un crecimiento de la demanda de servicios interactivos por satélite para el gran consumo, cubriendo servicios fijos i móviles, como el acceso de banda ancha, comunicaciones máquina a máquina (M2M), supervisión, control y adquisición de datos (SCADA), transacciones i aplicaciones criticas de seguridad. Estas redes de comunicaciones se caracterizan por tener una gran población de usuarios compartiendo el ancho de banda en unas condiciones de tráfico muy dinámicas. Concretamente, en el canal de retorno (del usuario a la red) de redes de acceso de banda ancha, los usuarios residenciales generan grandes ráfagas de tráfico con periodos frecuentes de inactividad. Una situación similar ocurre en las redes de comunicaciones móviles por satélite, donde una gran población de terminales generan transmisiones infrecuentes de señalización, servicios basados en la localización u otras aplicaciones me mensajería. Estos servicios requieren el desarrollo de protocolos de acceso múltiple eficientes capaces de operar en las condiciones descritas anteriormente. Los protocolos de acceso aleatorio son buenos candidatos para servir el tráfico poco predictivo, con transmisiones infrecuentes así como sensibles al retardo. Además, los protocolos de acceso soportan un gran número de terminales compartiendo el canal de comunicaciones y requieren poca complejidad en los terminales. Los protocolos de acceso aleatorio han estado ampliamente estudiados i desplegados en las redes terrestres, pero sus prestaciones son pobres en el entorno satelital, que se caracteriza por retardos de comunicaciones muy elevados. Hoy en día, su uso en la redes de comunicaciones por satélite está principalmente limitado a la señalización de inicio de sesión, transmisión de pequeños volumenes de datos con eficiencia de utilización del canal muy baja. Esta tesis propone tres nuevas técnicas de acceso aleatorio bien adaptadas para proveer los servicios mencionados anteriormente en un entorno de comunicaciones por satélite, con altas prestaciones y una complejidad en el terminal de usuario reducida. Las nuevas técnicas de acceso aleatorio son Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) y Enhanced Spread Spectrum Aloha (E-SSA), adaptadas para un tipo de acceso ranurado, asíncrono y de espectro ensanchado respectivamente. Las tres técnicas utilizan una codificación de canal (FEC) robusta, capaz de operar en condiciones de interferencia elevadas, que son típicas en el acceso aleatorio, y de un mecanismo de cancelación sucesiva de interferencias que se implementa en el receptor sobre los paquetes que han sido decodificados satisfactoriamente. Los nuevos protocolos obtienen un throughput normalizado superior a 1 bit/s/Hz con una tasa de pérdida de paquetes inferior a 10-3, lo cual representa un factor de mejora de 1000 respecto a los protocolos de acceso aleatorio tradicionales como el ALOHA ranurado. Las prestaciones de las nuevas técnicas de acceso aleatorio han sido analizadas con simulaciones así como con nuevos modelos analíticos desarrollados en esta tesis, capaces de caracterizar el tráfico, la distribución estadística de la potencia de los paquetes, las prestaciones de la codificación de canal (FEC) y el proceso de cancelación sucesiva de interferencias.Over the past years there has been a fast growing demand for low-cost interactive satellite terminals supporting both fixed and mobile services, such as consumer broadband access, machine-to-machine communications (M2M), supervisory control and data acquisition (SCADA), transaction and safety of life applications. These networks, are generally characterized by a large population of terminals sharing the available resources under very dynamic traffic conditions. In particular, in the return link (user to network) of commercial satellite broadband access networks, residential users are likely to generate a large amount of low duty cycle bursty traffic with extended inactivity periods. A similar situation occurs in satellite mobile networks whereby a large number of terminals typically generate infrequent packets for signaling transmission as well for position reporting or other messaging applications. These services call for the development of efficient multiple access protocols able to cope with the above operating conditions. Random Access (RA) techniques are by nature, good candidates for the less predictive, low duty cycle as well as time sensitive return link traffic. Besides, RA techniques are capable of supporting large population of terminals sharing the same capacity and require low terminal complexity. RA schemes have been widely studied and deployed in terrestrial networks, but do not perform well in the satellite environment, which is characterized by very long propagation delays. Today, their use in satellite networks is mainly limited to initial network login, the transmission of control packets, and in some cases, for the transmission of very small volumes of data with very low channel utilization. This thesis proposes three novel RA schemes well suited for the provision of the above-mentioned services over a satellite environment with high performance and low terminal complexity. The new RA schemes are Contention Resolution Diversity Slotted Aloha (CRDSA), Asynchronous Contention Resolution Diversity Aloha (ACRDA) and Enhanced Spread Spectrum Aloha (E-SSA), suited for slotted, unslotted and spread spectrum-based systems respectively. They all use strong Forward Error Correction (FEC) codes, able to cope with heavy co-channel interference typically present in RA, and successive interference cancellation implemented over the successfully decoded packets. The new schemes achieve a normalized throughput above 1 bit/s/Hz for a packet loss ratio below 10-3, which represents a 1000-fold increase compared to Slotted ALOHA. The performance of the proposed RA schemes has been analyzed by means of detailed simulations as well as novel analytical frameworks that characterize traffic and packets power statistical distributions, the performance of the FEC coding as well as the iterative interference cancellation processing at the receiver

    Cognitive-Based Solutions to Spectrum Issues in Future Satellite Communication Systems

    Get PDF
    With particular attention to Satellite Communications (SatComs), cognitive-based solutions are investigated. With cognitive-based solutions we refer to all those techniques that aim at improving spectrum utilization of the available spectrum and rely on the knowledge of the environment in which the systems operate. As a matter of fact, an improved spectrum utilization enables higher throughput capacities that will satisfy the future markets and demands of an increasingly connected world. Throughout the thesis, several techniques are proposed, developed, and assessed with respect to specific scenarios of interest. Particular focus has been put on spectrum awareness techniques for system coexistence, and on spectrum exploitation techniques for an improved efficiency in terms of resource utilization

    Multibeam Joint Processing in Satellite Communications

    Get PDF
    Cooperative Satellite Communications (SatComs) involve multi-antenna satellites enabled for the joint transmission and reception of signals. This joint processing of baseband signals is realized amongst the distinct but interconnected antennas. Advanced signal processing techniques –namely precoding and Multiuser Detection (MUD)– are herein examined in the multibeam satellite context. The aim of this thesis is to establish the prominence of such methods in the next generation of broadband satellite networks. To this end, two approaches are followed. On one hand, the performance of the well established and theoretically concrete MUD is analysed over the satellite environments. On the other, optimal signal processing designs are developed and evaluated for the forward link. In more detail, the present dissertation begins by introducing the topic of multibeam joint processing. Thus, the most significant practical constraints that hinder the application of advanced interference mitigation techniques in satellite networks are identified and discussed. Prior to presenting the contributions of this work, the multi-antenna joint processing problem is formulated using the generic Multiuser (MU) Multiple InputMultiple Output (MIMO) baseband signal model. This model is also extended to apply in the SatComs context. A detailed presentation of the related work, starting from a generic signal processing perspective and then focusing on the SatComs field, is then given. With this review, the main open research topics are identified. Following the comprehensive literature review, the first contribution of this work, is presented. This involves the performance evaluation of MUD in the Return Link (RL) of multiuser multibeam SatComs systems. Novel, analytical expressions are derived to describe the information theoretic channel capacity as well as the performance of practical receivers over realistic satellite channels. Based on the derived formulas, significant insights for the design of the RL of next generation cooperative satellite systems are provided. In the remaining of this thesis, the focus is set on the Forward Link (FL) of multibeam SatComs, where precoding, combined with aggressive frequency reuse configurations, are proposed to enhance the offered throughput. In this context, the alleviation of practical constraints imposed by the satellite channel is the main research challenge. Focusing on the rigid framing structure of the legacy SatCom standards, the fundamental frame-based precoding problem is examined. Based on the necessity to serve multiple users by a single transmission, the connection of the frame-based precoding and the fundamental signal processing problem of physical layer multigroup multicasting is established. In this framework and to account for the power limitations imposed by a dedicated High Power Amplifier (HPA) per transmit element, a novel solution for multigroup multicasting under Per Anntenna Constraints (PACs) is derived. Therefore, the gains offered by multigroup multicasting in frame-based systems are quantified over an accurate simulation setting. Finally, advanced multicast and interference aware scheduling algorithms are proposed to glean significant gains in the rich multiuser satellite environment. The thesis concludes with the main research findings and the identification of new research challenges, which will pave the way for the deployment of cooperative multibeam satellite systems

    Enlace de retorno satelital DVB-RCS2 : modelagem de fila e otimização de alocação de recursos baseada em teoria dos jogos

    Get PDF
    Tese (doutorado) — Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2022.É esperado que satélites tenham um papel fundamental no futuro dos sistemas de comunicação, integrando-se às infraestruturas terrestres. Esta dissertação de mestrado propõe três contribuições principais: primeiramente, se apresenta um arcabouço de simulação capaz de prover detalhes da performance de redes de comunicação satelital em cenários realistas. Este arcabouço aplica uma metodologia orientada a eventos, modelando a rede de comunicação como um sistema baseado em eventos discretos (DES), focando no enlace de retorno do protocolo DVB-RCS2. Três diferentes cenários simulados demonstram os possíveis usos das saídas do simulador para entender o comportamento dinâmico da rede e alcançar um ponto ótimo de operação do sistema. Cada cenário explora uma característica diferente do simulador, enquanto cobre um grande território de usuários, que em nosso caso estudo o país de escolha foi o Brasil. Em um segundo tópico, este trabalho introduz um novo algoritmo modificado do método de alocação de timeslots baseado em teoria dos jogos, aplicando-se no protocolo DVB-RCS2. Este procedimento considera a eficiência espectral do terminal como um parâmetro de peso para o problema de otimização convexa resultante da solução da barganha de Nash. Este novo método garante o cumprimento dos requisitos de Qualidade de Serviço (QoS) enquanto provê uma medida de justiça maior; os resultados mostram uma melhoria de 5% na medida de justiça, com uma diminuição de 75% no desvio padrão de justiça entre os quadros, também alcançando um aumento de 12% na satisfação individual média pela alocação de capacidade aos terminais. Por final, apresentamos uma modelagem alternativa para o enlace de retorno do DVB-RCS2 usando cadeias de Markov, predizendo parâmetros tradicionais de fila como a intensidade de tráfego, tempo médio de espera, dentre outros. Utilizamos dados coletados de uma série de simulações usando o arcabouço orientado a eventos para validar o modelo de filas como uma aproximação numérica útil para o cenário real de aplicação. Nós apresentamos o algoritmo de alocação de controle do parâmetro alfa (GTAC) que consegue controlar o tempo médio de espera de um RCST na fila, respeitando um limiar de tempo enquanto otimiza a taxa média média de transmissão de dados dos terminais.Satellite networks are expected to play a vital role in future communication systems, with complex features and seamless integration with ground-based infrastructure. This dissertation proposes three main contributions: firstly, it presents a novel simulation framework capable of providing a detailed assessment of a satellite communication’s network performance in realistic scenarios, employing an event-driven methodology and modeling the communications network as a DES (discrete event system). This work focuses on the return link of the Digital Video Broadcast Return Channel via Satellite (DVB-RCS2) standard. Three different scenarios demonstrate possible uses of the simulator’s output to understand the network’s dynamic behavior and achievable optimal system operation. Each scenario explores a different feature of the simulator. The simulated range covers a large territory with thousands of users, which in our case study was the country of Brazil. In the second theme, this work introduces a novel algorithm modification for the conventional game theory-based time slot assignment method, applying it to the DVB-RCS system. This procedure considers the spectral efficiency as a weighting parameter. We use it as an input for the resulting convex optimization problem of the Nash Bargaining Solution. This approach guarantees the fulfillment of Quality of Service (QoS) constraints while maintaining a higher fairness measure; results show a 5% improvement in fairness, with a 73% decrease in the standard deviation of fairness between frames, while also managing to reach a 12.5% increase in average normalized terminal BTU allocation satisfaction. Lastly, we present an alternative queuing model analysis for the DVB-RCS2 return link using Markov chains, developed to predict traditional queue parameters such as traffic intensity, average queue size, average waiting time, among others. We used data gathered from a series of simulations using the DES framework to validate this queuing model as a useful numerical approximation to the real application scenario, and, by the end of the scope, we present the alpha allocation algorithm (GTAC) that can maintain the average waiting time of a terminal in the queue to a threshold while optimizing the average terminal throughput

    Earth resources technology satellite spacecraft system design studies. Volume 2, book 1 - Subsystems studies Final report

    Get PDF
    Developing structure, payload, communication and data handling subsystems for ERT

    Abstracts on Radio Direction Finding (1899 - 1995)

    Get PDF
    The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion
    corecore