Dissertations / Theses on the topic 'Satellite communications'

Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: A low earth orbit satellite system can be useful in numerous communication applications where physical connections are not possible. Communication time available from any point on earth to the satellite is less than one hour per day. This one hour is fragmented into smaller time slots due to the satellite orbiting. This is not much time to transfer data and there is even less time available to transfer data when there are other external factors affecting the system. It is thus crucial to optimise the satellite communications link so that more data can be transferred per orbit. The goal of this thesis is to improve the performance of a low earth orbit satellite communication channel by varying certain parameters of the system, such as the protocol used, modulation scheme, packet size, transmission power etc. and then to observe how these parameters influence the system. The protocols that were chosen to be implemented are CSMA-CA, CSMA-CA with DSSS technology and Round-Robin Polling. A simulator for each protocol was designed with the Opnet platform, so that specific parameters could be changed and the results observed, in order to optimise the communications link between the satellite and ground stations. The results showed that there is no particular configuration of modulation scheme, packet size, transmission power etc. presenting the best overall solution for LEO satellite communications. It must be considered what the specific LEO satellite application would be used for and the characteristics required by that specific application. A suitable configuration must subsequently be chosen from the set of configurations available to satisfy most of the application requirements.
AFRIKAANSE OPSOMMING: ’n Satelliet met ’n lae wentelbaan kan gebruik word in verskeie kommunikasie toepassings waar fisiese verbindinge nie noodwendig moontlik is nie. Die kommunikasietyd van enige punt van aarde af na die satelliet, is minder as een uur per dag. Hierdie tyd word nog verder verklein omdat die satelliet besig is om, om die aarde te wentel. ’n Uur is glad nie baie tyd om data oor te dra nie en in realiteit is daar nog minder tyd beskikbaar as daar eksterne faktore op die sisteem inwerk. Dus is dit baie belangrik om die satelliet kommunikasiekanaal te optimiseer sodat soveel moontlik data as moontlik oorgedra kan word per omwenteling. Die doel van hierdie tesis is om die deurset van die kommunikasiekanaal van n lae wentelbaan satelliet te optimiseer, deur verskeie parameters te verander soos, protokol wat gebruik word, modulasie skema, pakkie grootte, transmissiekrag ens. en dan waar te neem hoe dit die sisteem beïnvloed. Die protokolle wat geïmplementeer is, is CSMA-CA, CSMA-CA met DSSS tegnologie en Round-Robin Polling. ’n Simulator vir elke protokol was ontwerp in die Opnet simulasie platform, sodat die spesifieke parameters verander kon word om die resultate te bestudeer met die doel om die kommunikasiekanaal tussen die satelliet en grond stasies optimaal te benut. Die resultate het bewys dat daar geen spesifieke konfigurasie van modulasie skema, pakkie grootte, transmissiekrag ens. is wat die algehele beste oplossing is nie. Die spesifieke applikasie waarvoor die lae wentelbaan satelliet gaan gebruik word moet geanaliseer word sowel as die spesifieke karakteristieke van daai applikasie. Daarvolgens moet n unieke konfigurasie opgestel word wat meeste van die applikasie se behoeftes bevredig.

Yes
We are delighted to bring to you this special issue on satellite communications, which we have prepared as part of the spreading of excellence remit of the satellite communications network of excellence (SatNEx). The SatNEx project, which began in 2004, is funded for five years under the European Union¿s Sixth Framework Programme (FP6) Information Society Technologies (IST) Thematic Area. Led by the German Aerospace Center, SatNEx brings together a network of 24 partners, distributed throughout Europe, with membership drawn from ten countries. The philosophy underlying the SatNEx approach revolves around the selection of focused actions under Joint Programmes of Activities, which are carried out collectively by the partners and include research, integration, and dissemination activities. Training represents an important part of the SatNEx remit and is supported through a number of initiatives including the hosting of internship projects and an annual summer school. The call for papers resulted in a high number of submissions, from which we have been able to select 12 excellent papers dealing with the different aspects of satellite communications and navigation.
European Union

This report outlines the steps taken to design and develop a 1.2 GHz and 2.4 GHz LEO satellite communication facility at the QUT satellite ground station to allow experimentation and communication links with low earth orbiting (LEO) satellites. The design, setup, construction, testing and installation of the antenna system required by the QUT satellite ground station to operate in the 1.2 GHz and 2.4 GHz frequency bands are described. Existing ground station capabilities and limitations were studied and a complete operational satellite station is suggested for the future to further perform telemetry, tracking and command control. Upgrading the ground station to 1.2 and 2.4 GHz will enable QUT to proceed with investigations and trials on other space related projects.

This project deals the performances of precoding technique in satellite communications. Satellite system use multi-beam coverage to increase its throughput and capacity through the geometrical deployment of contiguos beam. In order to mitigate the interference between adjacent beams, the Minimum Mean Square Error has been implemented to evaluate its performances in terms of achievable rate. The scenario is made up an antenna pattern array placed on geostationary satellite in clear sky condition and with full frequency reuse. The document contain a simulation of real scenario in which mathematical model of satellite architecture is implemented through the design of an antenna pattern array and its relative coverage. Later, the Minimum Mean Square Error estimation channel has been applied to the system to study its behavior. The reported results shown a link between the antenna parameters and the rate suggesting a solution for the optimization of precoding.

Thesis (M.S. in Operations Research) Naval Postgraduate School, September 1997.
"Deptember 1997." Thesis advisor(s): Samuel H. Parry. Includes bibliographical references (p. 119). Also available online.

The high amount of scientific and communications data produced by low earth orbiting satellites necessitates economical methods of communication with these satellites. A volumetric phased array for demonstrating horizon-to-horizon electronic tracking of the NASA satellite EO-1 was developed and demonstrated. As a part of this research, methods of optimizing the elemental antenna as well as the antenna on-board the satellite were investigated. Using these optimized antennas removes the variations in received signal strength that are due to the angularly dependent propagation loss exhibited by the communications link. An exhaustive study using genetic algorithms characterized two antenna architectures, and included optimizations for radiation pattern, bandwidth, impedance, and polarization. Eleven antennas were constructed and their measured characteristics were compared to those of the simulated antennas. Additional studies were conducted regarding the optimization of aperiodic arrays. A pattern-space representation of volumetric arrays was developed and used with a novel tracking algorithm for these arrays. This algorithm allows high-resolution direction finding using a small number of antennas while mitigating aliasing ambiguities. Finally, a method of efficiently applying multiple beam synthesis using the Fast Fourier Transform to aperiodic arrays was developed. This algorithm enables the operation of phased arrays combining the benefits of aperiodic element position with the efficiency of FFT multiple beam synthesis. Results of this research are presented along with the characteristics of the volumetric array used to track EO-1. Experimental data and the interpretations of that data are presented, and possible areas of future research are discussed.

The thesis is concerned with the design of a phase-shift keying system for a digital modem, operating over a satellite link. Computer simulation tests and theoretical analyses are used to assess the proposed design. The optimum design of both transmitter and receiver filters for the system to be used in the modem are discussed. Sinusoidal roll-off spectrum with different roll-off factor and optimum truncation lengths of the sample impulse response are designed for the proposed scheme to approximate to the theoretical ideal. It has used an EF bandpass filter to band limit the modulated signal, which forms part of the satellite channel modelling. The high power amplifier (HPA) at the earth station has been used in the satellite channel modelling due to its effect in introducing nonlinear AMAM and AM-PM conversion effects and distortion on the transmitted signal from the earth station. The satellite transponder is assumed to be operating in a linear mode. Different phase-shift keying signals such as differentially encoded quaternary phase-shift keying (DEQPSK), offset quaternary phase-shift keying (OQPSK) and convolutionally encoded 8PSK (CE8PSK) signals are analysed and discussed in the thesis, when the high power amplifier (HPA) at the earth station is operating in a nonlinear mode. Convolutional encoding is discussed when applied to the system used in the modem, and a Viterbi -algorithm decoder at the receiver has been used, for CE8PSK signals for a nonlinear satellite channel. A method of feed-forward synchronisation scheme is designed for carrier recovery in CE8PSK receiver. The thesis describes a method of baseband linearizing the baseband signal in order to reduce the nonlinear effects caused by the HPA at the earth station. The scheme which compensates for the nonlinear effects of the HPA by predistorting the baseband signal prior to modulation as opposed to correcting the distortion after modulation, thus reducing the effects of nonlinear distortion introduced by the HPA. The results of the improvement are presented. The advanced technology of digital signal processors (DSPs) has been used in the implementation of the demodulation and digital filtering parts of the modem replacing large parts of conventional circuits. The Viterbi-algorithm decoder for CE8PSK signals has been implemented using a digital signal processor chip, giving excellent performance and is a cost effective and easy way for future developments and any modifications, The results showed that, by using the various studied techniques, as well as the implementation of digital signal processor chip in parts of the modem, a potentially more cost effective modem can be obtained.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada
Employment of the retro-directive technique described in Reference 1 describes a totally Autonomous Ground Station providing hemispheric coverage and continuous tracking. This System establishes communications between the satellite and ground station without human intervention or moving parts. When a satellite is in view, the ground station beacon antenna, using CDMA, enables the desired satellite transmitter and directs its beam to the ground station. The ground station, using the satellite’s transmitted signal, directs it’s receive and transmit arrays to point the ground station beams to the satellite, establishing two-way communications. The process is automatic and provides continuous horizon to horizon tracking.

Les nombreux avantages introduits par l’utilisation des satellites tels que la couverture à grande échelle, notamment dans les zones difficilement accessibles ou pauvres en infrastructure terrestres, a incité différentes communautés à développer des communications efficaces pour l’accès à Internet, la télévision et la téléphonie. Pendant longtemps, les techniques d’accès multiple basées sur la réservation de ressources (DAMA) ont largement été déployées sur la liaison retour, occupant ainsi une grande partie de la bande passante. Cependant, outre le temps aller-retour (RTT) additionnel dû à la demande d’allocation, qui est à la base important lors d’une communications par satellite, les ressources peuvent être sous-exploitées ou insuffisantes face à des applications entraînant un grand nombre d’utilisateurs telles que l’Internet des objets et les communications de machine à machine. Par conséquent, les techniques d’accès basées sur le protocole ALOHA ont largement pris place dans les études de recherche sur l’accès aléatoire (RA), et ont considérablement évolué ces derniers temps. La méthode CRDSA a particulièrement marqué ce domaine; elle a inspiré de nombreuses techniques d’accès aléatoire. Dans ce contexte, une méthode complémentaire, appelée MARSALA, permet de débloquer CRDSA lorsque celle-ci n’est plus en mesure de décoder de nouveaux paquets. Par contre, cela entraîne une complexité de corrélation liée à la localisation des paquets, qui est nécessaire pour combiner des répliques afin d’avoir une puissance de signal potentiellement plus élevée. C’est pourquoi, l’objectif principal de cette thèse est de proposer des alternatives efficientes et moins complexes. Nous nous intéressons plus précisément à la manière de gérer les transmissions multi-utilisateurs et de résoudre les interférences à la réception, avec la plus petite complexité. De plus, le phénomène de boucle qui se produit lorsque plusieurs utilisateurs transmettent leurs paquets dans les mêmes positions est traité, sachant qu’un plancher d’erreur au niveau des performances en taux de perte de paquets est par conséquent créé. Nous proposons donc des solutions synchrones et asynchrones, principalement basées sur un partage de données, au préalable, entre l’émetteur et le récepteur, dans le but de réduire la complexité de localisation, atténuer le phénomène de boucle et améliorer les performances du système. Ces techniques sont décrites et analysées en détails au cours de ce manuscrit
The effective coverage of satellites and the technology behind have motivated many actors to develop efficient communications for Internet access, television and telephony. For a long time, reservation resources of Demand Assignment Multiple Access (DAMA) techniques have been largely deployed in the return link of satellite communications, occupying most of the frequency bandwidth. However, these resources cannot follow the technological growth with big users communities in applications like the Internet of Things and Machine to Machine communications. Especially because the Round Trip Time is significant in addition to a potential underuse of the resources. Thus, access protocols based on ALOHA took over a big part of the Random Access (RA) research area and have considerably evolved lately. CRDSA have particularly put its fingerprint in this domain, which inspired many different techniques. In this context, a complementary method, called MARSALA comes to unlock CRDSA when packets can no longer be retrieved. This actually involves a correlation complexity related to packet localization which is necessary for replicas combinations that results in a potentially higher signal power. Accordingly, the main goal of this PhD research is to seek for effective and less complex alternatives. More precisely, the core challenge focuses on the way to manage multi-user transmissions and solve interference at reception, with the smallest complexity. In addition, the loop phenomenon which occur when multiple users transmit their packets at the same positions is tackled as it creates an error floor at the packet loss ratio performance. Synchronous and asynchronous solutions are proposed in this thesis, mainly based on providing the transmitter and the receiver with a shared prior information that could help reduce the complexity, mitigate the loop phenomenon and enhance the system performance. An in-depth description and analysis of the proposed techniques are presented in this dissertation

Mestrado em Engenharia Electrónica e Telecomunicações
The satellite communications have become a valid alternative to conventional communications, through fiber or copper, in situations of catastrophe or even as complement to improve the quality of the services provided at a worldwide scale. Recently, radio frequency engineers have worked towards a reliable solution to replace the travelling wave tube amplifiers on board of the satellite communications. Despite the travelling wave tube amplifiers reveal a good performance, its weight, size and cost are a serious technical problem to the main satellite manufacturers. However, this scenario tends to change due to the exploitation of the Gallium Nitride technology in high power, efficiency and frequency applications. The objective of this work involves an implementation of two power amplifiers in class B, resorting to a Gallium Nitride transistors and using different types of planar transmission lines, for a 5.8GHz frequency which is often used in uplink transmissions for C-band or even in recent applications of wireless power transmission. The best results were obtained for the microstrip lines power amplifier, achieving 34.1dBm of output power, 62.35% of drain efficiency at saturation and a small-gain of 17dB.
As comunicações via satélite têm-se tornado uma alternativa válida às vias de comunicações convencionais, como a fibra e o cobre, em situações de catástrofe ou até como complemento para melhorar a qualidade de serviços disponibilizados à escala global. Recentemente, os engenheiros de rádio frequência têm trabalhado para encontrar uma solução definitiva e fiável para a substituição dos amplificadores a válvulas nos satélites de comunicações. Apesar destes amplificadores apresentarem uma performance de destaque, o seu tamanho, peso, consumo e custo são sérios problemas para as empresas especializadas na sua construção. Contudo, o panorama tende a mudar devido à exploração da tecnologia de Nitreto de Gálio em aplicações de alta potência, frequência e eficiência. O objetivo desta trabalho passa pela implementação de dois amplificadores de potência em classe B, recorrendo a transístores de Nitreto de Gálio e usando diferentes linhas de transmissão planares, para a frequência de 5.8GHz que é frequentemente usada em transmissões uplink na banda C, ou mesmo nas recentes aplicações de transferência de energia sem fios. Os melhores resultados foram obtidos pela implementação em linhas microstrip, atingindo os 34.1dBm de potência de saída, 62.35% de eficiência na saturação e um ganho máximo de 17dB.

Network coding (NC) is an important technology that allows the network services to be optimal. The main advantage of NC is to reduce the necessity for re-transmissions of packets. Satellite Communications (SatComs) are one of the potential applications that can leverage on the benefits of NC due to their challenging fading environments and high round trip times. The motivation is to take the physical layer-awareness into consideration for adapting and hence extend the NC gains. Different rate and energy efficient adaptive NC schemes for time variant channels are proposed. We compare our proposed physical layer adaptive schemes to physical layer non-adaptive NC schemes for time variant channels. The adaptation of packet transmissions is on the basis of the corresponding time-dependent erasures, and allows proposed schemes to achieve significant gains in terms of throughput, delay and energy efficiency. The proposed schemes are robust for large and small size of packets. Although, the energy per bit is affected, a similar rate and energy gains can be arise. However, the performance gains are not motivated by the packet size, but through duty cycle silence of transfer packets. In this thesis, virtual schemes are also proposed to solve an open literature problem in the NC. The objective is to find a quasi-optimal number of coded packets to multicast to a group of independent wireless receivers suffer from a different channel conditions. In particular, we propose two virtual network that allows for the representation of a group of receivers as a multicast group to be visible as one receiver and single channel. Most of the schemes are applied to LEO/MEO/GEO satellite scenarios. They demonstrate remarkable gains compared to that strategy in which the adaptation depends only on one receiver point-to-point.

La projection favorable vers le segment des satellites pourrait se maintenir, surtout aujourd'hui, puisque la demande de nouveaux services a considérablement augmentée. Cela se justifie par les caractéristiques uniques du satellite, telles que les capacités de multidiffusion et de radiodiffusion, les aspects de mobilité et la couverture mondiale. À titre d'exemple, nous soulignons l'utilisation du satellite pour soutenir les futures communications de machine à machine (M2M). Dans ce contexte, l'un des principaux défis consiste à développer des techniques permettant une meilleure coordination entre les services existants et futurs. C'est dans ce cadre que les techniques de radio cognitive (RC) sont devenues intéressantes pour les applications spatiales. Cette thèse étudie la faisabilité d'une transmission d'un utilisateur cognitif (UC) sur une infrastructure existante d'utilisateurs primaires en utilisant les techniques de RC de type overlay. Dans cette optique, la première contribution présente une méthodologie de design pour ce paradigme dans le domaine des communications par satellite. Ensuite, nous discutons d'une approche pour contrôler la puissance de sortie de l’UC en abordant la technique de mise en forme du treillis et d'une nouvelle méthode pour récupérer la perte modulo. Ces techniques montrent un compromis entre l'efficacité de puissance, (réduction de la perte modulo), et la complexité, (réduction des opérations de l’encodeur). Enfin, nous examinons les solutions proposées à la lumière d'un scénario satellite réaliste en utilisant des exemples de pièces commerciales (COTS) et en supposant des valeurs pratiques pour le bilan de liaison
The favorable projection towards the satellite segment could be sustained especially today, since the demand for the rising new services has increased considerably. This is justified by the unique satellite characteristics such as multicast and broadcasting capabilities, mobility aspects and global reach, besides the ability to cover and connect remote areas and hostile environments. As a typical example, we point out the use of satellite to support the Machine-to-Machine (M2M) communications. In this context, a main challenge is to develop techniques that enable a better coordination among legacy and future services. It is within this framework that the Cognitive Radio (CR) techniques have also become attractive for space applications. This doctoral thesis studies the feasibility of a Cognitive User (CU) transmission over the primary user infrastructure by using the CR techniques in the overlay paradigm applied to the satellite context. In this perspective, the first thesis contribution present a framework for overlay paradigms towards satellite communications. In this sense, a low complexity solution is proposed related to the Trellis Shaping based DPC encoder for the CU. Subsequently, we discuss an approach to control the CU output power by addressing the trellis shaping (TS) technique. Moreover, by using auxiliary bits as well as the proper mapping selection, further constellation expansion is performed in order to increase the number of shaping regions. The relation among these implemented techniques provides a trade-off between power efficiency,by the reduction of the modulo loss, and complexity, by the reduction of the encoder operations. Finally, we examine the proposed solutions at the light of a realistic satellite scenario. In this general contribution, by using examples of commercial off-the-shelf (COTS) parts and assuming practical link budget parameters

Les systèmes de communication par satellite d’aujourd’hui reposent principalement sur le multiplexage temporel pour optimiser leurs performances. Chaque utilisateur utilise le canal pendant une fraction de temps connu. Pendant cette période, la modulation et le taux de codage sont choisis de manière à transmettre le plus d’information possible. En pratique, ce schéma est facile à mettre en œuvre ce qui justifie sa popularité. Cependant, il est désormais bien connu que la répartition temporelle n’est pas optimale en termes d’efficacité spectrale offerte aux récepteurs. En effet, la stratégie qui consiste à superposer des données offre de meilleures performances que le multiplexage temporel. C’est dans ce contexte que s’inscrit la problématique de cette thèse. Le travail réalisé propose des applications du codage par superposition dans le domaine des communications par satellite. Tout d’abord, nous étudions la modulation hiérarchique qui est une implémentation du codage par superposition au niveau de la modulation. Les performances de ce type de modulation sont évaluées d’un point de vue théorique et pratique. Dans un deuxième temps, nous quantifions l’amélioration en termes d’efficacité spectrale que peut apporter la modulation hiérarchique pour les systèmes de communication par satellite. Les standards de diffusion par satellite DVB-SH et DVB-S2 fournissent un cadre pratique. Nous montrons que des gains non négligeables sont envisageables selon la configuration du système. Le dernier point abordé concerne un système où des utilisateurs communiquent entre eux à l’aide d’un satellite qui sert de relais. Nous proposons un schéma de communication où plusieurs utilisateurs émettent en même temps en coordonnant leur puissance de transmission. Ainsi, les signaux vont naturellement se superposer. Les récepteurs utilisent deux mécanismes pour le décodage des signaux : le codage réseau couche physique et la démodulation de constellations superposées. Finalement, les gains de performance obtenus dans les différents domaines par le codage par superposition ouvrent des perspectives pour des travaux futurs
Modern satellite communication systems mainly rely on time sharing to optimize the throughput. Each receiver uses the channel during a given fraction of time. During this period, the transmission parameters (i.e., the modulation and the coding rate) are chosen in order totransmit as much information as possible. The scheme is easy to implement which explains its popularity. However, it is today well established that time sharing is not optimal in terms of spectrum efficiency offered to the receivers. Indeed, the scheme that consists in sending superposed data offers better performance than the time sharing. This thesis investigates the application of superposition coding in satellite communication systems. First of all, we study the performance of hierarchical modulation which is an implementation of superposition coding at the modulation level. We propose a performance evaluation method for such modulations. We also compare the performance of hierarchical and non hierarchical modulations in terms of spectrum efficiency and link unavailability. These two criteria are very important for broadcast system and we show that hierarchical modulations often offer better performance than non hierarchical modulations.Then, we study the performance improvement in terms of spectrum efficiency when using hierarchical modulation in satellite communication systems. Two issues are addressed. The first one is how to group the receivers in pairs in order to transmit data with a hierarchical modulation. The second issue is the computation of the spectrum efficiency. We show that significant gains are possible depending on the system configuration. The last part considers a system where multiple users communicate through a satellite. The satellite acts as a relay in our scenario. We propose a communication scheme where several users emit at the same time with appropriate transmitting power. Thus the signals naturally superpose and generate interference. The receivers use two mechanisms for decoding the signals: physical layer network coding and demodulation of superposed constellations. Finally, we explain how the performance improvements obtained by superposition coding in several scenarios open perspectives for future work

The space is experiencing a revolution due to the em ergence of satellite services to satisfy environmental, socio-econom ic, and geo-political demands. Earth Observation satellite systems have become dependable resources for climate monitoring, modern agriculture, and other applications. The 5G incursion in the aerospace domain has promoted the satellites as promising platforms to achieve global coverage, and cope the limitations of ground facilities. These demands can be summarized in two system requirements: (1) increase of data transfer capacity, and (2) decrease of end-to-end com m unications latency. Distributed Satellite Systems have emerged as an effective solution of m ultiple satellites operating simultaneouslyto satisfycommon requirements. Federated Satellite Systems are serious candidates to exploit the potential of distributed architectures by establishing opportunistic collaborations among satellites to share unallocated resources. These collaborations, called federations, allows to conceive the space as a cloud in which satellites leverage from other resources to improve their performance. The successive investigations have been centered on developing novel federation technologies. However, multiple design aspects are still open fields of study, such as the development of communications capabilities to establish these federations. This dissertation contributes to fill this gap bydefining mechanisms to deploy a network infrastructure for this purpose. A networked environment in which satellites are able to establish sporadically, and opportunisticallyfederations has been discussed. This context is called the Internet of Satellites paradigm, and prometes the temporal deployment of inter-satellite networks, composed of heterogeneous satellites. This feature---with satellite motion--­poses a challenge on the definition of end-to-end communications routes composed of intermediate satellites. Areview of current routing protocols from other satellite networks is conducted to identify the ideal protocol for these dynam ic networks. The outcome remarks the need to combine capabilities from different domains to achieve the desired performance. Among them, the capabilityto predict future inter-satellite links becomes crucial to mitigate the fragmentation of the network. With this prem ise in mind, this dissertation presents a predictive protocol that perform s the estimation of these inter-satellite contacts in a distributed manner. This new satellite capability may support the routing protocol by allowing the estimation of future routes as a sequence of satellite contacts over time. The research presented in this dissertation also tackles other questions that remained unanswered: How can satellites be aware of the available resources offered by other satellites? What are the necessary mechanisms to deploy a federation? A software stack with two protocols to deal with this technology gap has been developed. The Opportunistic Service Availability Dissem ination Protocol allows notifying the services that are available in a satellite, while the Federation Deploym ent Control Protocol form alizes the rules to establish and m anage a federation. The application of these protocols considerably enhancded the capabilityof the satellite system to download data, becom ing thus enablers of future satellite m issions. The achieved perform anee has motivated the developm ent of a dedicated system. 11 has been named Federated Satellite Systems Experiment payload, and includes a communications device to create inter-satellite links. This system has been verified in a stratospheric balloon campaign, and integrated in a CubeSat miss ion. This dissertation discusses the results of the campaign, which emphasize the benefits and viabilityof this implementation. We expect that the contributions of this dissertation mayencourage to keep investigating on this inter-satellite communications for satellite federations.
L'espai esta experimentant! una revolució degut a l'aparició de serveis per satèl·lit que satisfan les noves demandes ambientals, socials i geo-polítiques. Els sistemes de satèl·lits per observar la Terra han esdevingut recursos essencials per el control del clima, !'agricultura moderna, i altres aplicacions. L'entrada del 5G en el sector aeroespacial ha promogut els satèl·lits com plataformes per aconseguir una cobertura global. Aquestes necessitats poden ser classificades en dos requeriments de sistema: (1) L'augment de la capacitat per transferir dades, i (2) la reducció de la latència en les comunicacions d'extrem-a-extrem. Els sistemes distribuïts de satèl·lits han esdevingut una solució efectiva amb múltiples satèl·lits essent operats simultàniament per satisfer uns requeriments comuns. Els sistemes federats de satèl·lits són candidats prometedors per explotar el potencial de les arquitectures distribuïdes mitjançant col·laboracions oportunistiques entre satèl·lits per compartir recursos. Aquestes col·laboracions, anomenades federacions, permeten concebre l'espai com un entorn on els satèl·lits poden beneficiar-se dels recursos d'altres per millorar el seu funcionament. Les investigacions s'han central en desenvolupar noves tecnologies per aquestes federacions. No obstant, molts aspectes de disseny encara són punts oberts de recerca, com ara el desenvolupament de protocols de comunicació per establir aquestes federacions. Aquesta tesina contribueix definint mecanismes que permeten desplegar una infraestructura en xarxa per establir federacions. A més a més, es discuteix sobre aquest context interconnectat on els satèl·lits poden establir esporàdicament i oportunísticament les federacions. Aquest escenari s'ha anomenat la Internet dels Satèl·lits, i promou els desplegament temporal de xarxes entre satèl·lits heterogenis. Aquesta característica, amb el moviment dels satèl·lits, suposa un repte en la definició de rutes entre extrems formades per satèl·lits intermitjos. Una revisió de protocols d'enrutament actuals d'altres xarxes de satèl·lits s'ha realitzat per identificar el protocol ideal per aquest tipus de xarxa dinàmica. El resultat remarca la necessitat de combinar capacitats de diferents dom in is per aconseguir el funcionament desitjat. Entre aquestes, la capacitat de preveure futurs enllaços entre satèl·lits esdevé crucial per mitigar la fragmentació de la xarxa. Amb aquesta premissa, aquesta tesina presenta un protocol predictiu que estima aquests contactes entre satèl·lits de forma distribuïda. Aquesta nova capacitat pot complementar el protocol d'enrutament mitjançant l'estimació de futures rutes com seqüències of contactes de satèl·lits a través del temps. La recerca presentada en aquesta tesina també respon altres preguntes que no s'havien res post encara: Com els satèl·lits poden descobrir els recursos disponibles en la xarxa? Quins són els mecanismes necessaris per establir i mantenir una federació? Una pila de protocols per cobrir aquesta necessitat tecnològica ha sigut desenvolupat. El protocol de dispersió de la disponibilitat de serveis oportunístics permet notificar els serveis disponibles en un satèl·lit, mentre que el protocol desplegament i control de federacions s'encarrega d'establir i gestionar les federacions. L'aplicació d'aquests protocols considerablement van realçar la capacita! del sistema de satèl·lit per descarregar dades, esdevenint així potenciadors de futures missions. Aquests resultats han motivat el desenvolupament d'un sistema dedica!, que inclou un dispositiu de comunicacions per crear enllaços entre satèl·lit. Aquest sistema ha estat verifica! en una campanya de globus estratosfèrics, i ha sigut integral en una missió de CubeSats. Aquesta dissertació presenta els resultats de la campanya, els quals emfasitzen els profits i viabilitat d'aquesta implementació.

L’objectif de la thèse est l’étude des codes correcteurs d’erreurs au niveau applicatif (Application Layer – Forward Error Correction, ou AL-FEC) pour les communications par satellite. Dans ce contexte, pendant les deux première années de thèse, nous avons proposé de nouvelles méthodes d’analyse, de construction et d’optimisation des codes à effacements définis par des matrices de parité à faible densité (code LDPC, pour « Low Density Parity Check » en anglais). La troisième année de la thèse a été consacrée à : (1) La suite des études portant sur de nouvelles méthodes de construction des codes LDPC non-binaires. D’une part, nous avons développé un nouvel algorithme (Scheduled-PEG) qui permet d’optimiser la construction des codes LDPC non-binaires pas rapport aux métriques de performance spécifiques à la couche application, notamment dans le cadre des systèmes de diffusion de contenu (broadcasting). D’autre part, nous avons proposé une nouvelle méthode de construction de codes à faible rendement, qui utilise l’image binaire étendue d’un code LDPC non-binaire. Ces études ont fait l’objet de deux publications dans deux conférences internationales : (a) “Scheduled-PEG construction of LDPC codes for Upper-Layer FEC”, International Workshop on Coding and Cryptography, April 2011, Paris, France. (b) “Extended Non-Binary Low-Density Parity-Check Codes over Erase Channels”, IEEE International Symposium on Wireless Communication Systems, November 2011, Aachen, Germany. (2) Une étude portant sur l’analyse asymptotique de codes cluster-LDPC non-binaires. Cette nouvelle classe de codes – introduite récemment (ISIT’2011) – se distingue par ses excellentes propriétés en termes de distance minimale. Notre étude a permis de déterminer de manière analytique la capacité de correction des codes cluster-LDPC non-binaires, aussi bien pour le décodage itératif par propagation de croyances (BP, pour « Belief Propagation ») que pour le décodage par maximum de vraisemblance (ML, pour « Maximum Likelihood »). Ces résultats seront intégrés à une publication scientifique sur les codes cluster-LDPC, en cours de rédaction, qui sera soumise à « IEEE Transactions on Information Theory », avant la fin de l’année 2011. (3) Une étude portant sur une méthode de construction des codes LDPC qui permet de réduire de manière significative le plancher d’erreur (« error floor ») du code, sans dégrader ses performances dans la région de « waterfall ». Ainsi, nous avons proposé la structuration de la matrice de parité du code, de manière à intégrer une partie irrégulière, optimisée pour la partie « waterfall », et une partie régulière, qui permet de réduire le plancher d’erreur du code. Cette étude fera l’objet d’une publication dans une conférence internationale (à déterminer), à soumettre début 2012
The advent of content distribution, IPTV, video-on-demand and other similar services accelerate the demand for reliable data transmission over highly heterogeneous networks and toward terminals potentially heterogeneous too. In this context, Forward Error Correction (FEC) codes that operate at the transport or the Application Layer (AL-FEC) are used in conjunction with the FEC codes implemented at the physical layer, in order to improve the overall performance of the communication system. AL-FEC codes are aimed at recovering erased data packets and they are essential in many multicast/broadcast environments, no matter the way the information is transported, for instance using a wired or wireless link, and a terrestrial, satellite-based or hybrid infrastructure.This thesis addresses the design of Low Density Parity Check (LDPC) codes for AL-FEC applications. One the one hand, we provide an asymptotical analysis of non-binary LDPC codes over erasure channels, as well as waterfall and error-floor optimization techniques for finite-length codes. On the other hand, new concepts and coding techniques are developed in order to fully exploit the potential of non-binary LDPC codes.The first contribution of this thesis consists of the analysis and optimization of two new ensembles of LDPC codes. First, we have derived the density evolution equations for a very general ensemble of non-binary LDPC codes with rank-deficient coefficients. This allows improving the code performance, as well as designing ensembles of LDPC codes that can be punctured in an effective manner. The second approach allows the asymptotical optimization of a particular ensemble of LDPC codes, while ensuring low error-floors at finite lengths.The second contribution is the construction of finite length LDPC codes with good waterfall and error floor performance. Two approaches were investigated, according to the metric used to evaluate the code. The “Scheduled” Progressive Edge Growth (SPEG) algorithm is proposed, in order to optimize the waterfall performance of the code. Another method is proposed which consists in optimizing a specific structure of the parity check matrix. This approach gives low error-floors.The third contribution investigates a new technique of rate adaptability for non-binary LDPC codes. We propose a new method to generate “on-the-fly” incremental redundancy, which allows designing codes with flexible coding rates, in order to cope with severe channel conditions or to enable Fountain-like distribution applications.The fourth contribution focuses on a new class of LDPC codes, called non-binary cluster-LDPC codes. We derive exact equations of the density evolution for the iterative decoding and an upper bound for the maximum-likelihood decoding.Finally, we propose a practical solution to the problem of reliable communication via satellite to high-speed trains. Here, the challenge is that obstacles present along the track regularly interrupt the communication. Our solution offers optimal performance with a minimum amount of redundancy

The use of mobile Internet has reached the transport industry. Internet will be used to transport important and security-critical information from and to vehicles. Using Internet in this context raises a severe problem. Only 6% of the world is covered by GSM, the primary Internet bearer for mobile usage. The subject of this thesis is to explore suitable backups in order to provide the user with global coverage for important information exchange. The messages to send and receive are small in size, often less than 100 bytes. The time factor of the transmission is important, an alert message often has to be passed within minutes to be of any use. These factors together with the global coverage leave us with only one suitable solution, a satellite data communication system. The first part of this thesis contains an investigation of the satellite communication market. Two different systems, Inmarsat-C and ORBCOMM, are chosen for further study and evaluation. One Inmarsat-C unit and two ORBCOMM units are found suitable for the application. The last part of the thesis contains the evaluation, testing and system integration of these units. The conclusion is that ORBCOMM, although not yet fully developed, has the capabilities and performance necessary for use in a mobile environment such as a truck. The two different ORBCOMM units tested, Panasonic and Stellar, were found to have comparable qualities.

This thesis covers the history of satellite communications from its beginning in 1957 until recent years, describes the space subsystem and explains the major components of satellite communications. It defines the practical problems of satellite communications such as radiation and frequency dependence attenuation. It also examines certain aspects of satellite communications in the Hellas environment including reliability and survivability in a hostile environment. The last chapter outlines the major decisions and evaluation required for a tactical satellite system for the Hellenic Navy. Keywords: Frequency division multiple access, Time division multiple access, Spread spectrum multiple access, Ultrahigh frequency communications, Active passive satellite, Uplink downlink calculations. (rh)

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The Coast Guard has developed a C4ISR infrastructure ashore to aid personnel in decision making, job performance, and information exchange, but in doing so they have neglected their most important asset; the afloat community. In an effort to explore and find a wireless connectivity solution for CG cutters, the authors examined the requirements for solutions in the area of commercial satellite connectivity. This connection is necessary for USCG afloat assets to access vital maritime, law enforcement, and Fisheries databases maintained ashore, as well as to keep those ashore informed of mission status. This connection also allows cutters to connect to CGDN+ and the Internet, improving both morale and personnel administration issues (leave, medical records, training, assignment process, etc.) With the technologies now available, the USCG must identify which solutions can best be utilized with respect to bandwidth, security, cost, equipment installation requirements, durability, and range. Primarily our research dissects Qualcomm's Globalstar satellite options, INMARSAT and capacity expander (ICE) technology, and current Navy INMARSAT technology solutions. The authors have identified technological limitations and proper requirement analysis techniques that will aid in future Coast Guard evaluations of these extremely high cost wireless networks. Finally, the authors make recommendations for near and long-term solutions to the Coast Guard's connectivity requirements.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada
The NMSUSat is part of the AFRL/NASA University Nanosatellite program. The constellation will consist of a main microsatellite that will have a command link from ground and a telemetry link to ground while a picosatellite will act as a sensor reporting data to the microsatellite. Innovative command and data handling will be incorporated at low cost and greater accessibility. In this paper we present the necessary communications and control architecture for the space segment and the ground segment of the nanosatellite.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada
Satellite transmission systems have proven themselves very effective in a variety of applications. One such application is the transmission of telemetry (TM) data and associated information in a near real-time environment. This paper describes the satellite data relay system currently utilized by the Telemetry Data Center at Patuxent River, Maryland and the corresponding remote receiving site, and discusses the performance of this system.

International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, Nevada
As the volume of linkages in the satellite communications systems increases, the parallel bus between the various processors of the satellite becomes a bottle neck to transfer the commands and data. The remedies to this problem are trivial in the ground stations; however, this problem imposes severe restrictions in parallel bus implementation of the satellite communications systems. The most severe restriction is the minimization of wire connections in the physical layer to minimize the weight, size and power consumption, and also to maximize the reliability. Another restriction is the flexibility in the link layer to adapt the different characteristics of the command and data messages. In this paper, the implementation to overcome the imposed restrictions in both physical and link layer of the parallel bus will be discussed.

The trend in the construction of the latest array antennas is such, that electronic beam scanning can be conducted for a significantly large angular sector. Indeed, as far as circular array antennas are concerned, the quality of the radiation pattern will not be impaired when scanned in the full azimuthal axis. Compared to planar and several different shapes of conformal antenna arrays, spherical array antennas have the unique property of scanning their beam with no deterioration in full spherical coverage (i.e. azimuth and elevation axes). Furthermore, multi-beam functioning and direction finding techniques can be applied to spherical array antennas. In contrast to antennas that use mechanical motors for steering, they exhibit higher speed and stability. Low Earth Orbit (LEO) satellite communications can utilize the aforementioned properties of spherical array antennas. Spherical harmonic (phase mode) theory constitutes the base on which the signal processing of the spherical array antenna is developed. In this analysis, spherical harmonics are employed, which take advantage of the sphere’s symmetry and regenerate themselves in the far-field. The spherical phase mode approach is able to provide considerable improvements and computational simplification in several array processing levels. Specifically, research efforts are concentrated toward the choice of an optimal uniform spherical distribution and the minimum number of array elements that are necessary in the process. Various antenna element distributions are investigated and compared to each other placing special emphasis on the design and fabrication efficiency. Additionally, the direction finding potential of a spherical array antenna is explored by applying one of the main DOA estimation algorithms used with spherical arrays, the spherical ESPRIT algorithm. A spherical array, called LISA, has been designed and a prototype demonstrator has been manufactured. The spherical array has a radius of 40 cm, and operates at 3 GHz, employing circular polarization. A multi-planar approach, with 240 triangular planar tiles approximating the spherical surface, is adopted. Special attention is given to the RF front end of the array, and especially to the development of the microstrip antenna design that is accommodated on each tile (three elements) and a bespoke feed network. Valuable simulation and measurement results are also provided, demonstrating satisfactory performance of the tested tiles and offering essential conclusions for discussion and further investigation.

The Land Mobile Satellite System (LMSS) to be available in the 1990 time frame will provide connection between mobile vehicles and the conventional terrestrial communication network. The design is dependent on the propagation characteristics of the land mobile satellite signal. Unlike fixed satellite links, there is blockage in the line of sight path, mainly in the form of vegetative shadowing. The focus of this study is to develop models for the fading of the received satellite signal. A brief review of the physics and statistics associated with mobile propagation is presented. This is followed by a review of current literature and experiments. The modeling of the cumulative distribution function for a totally vegetatively shadowed mobile (VS distribution) is presented. The VS distribution is then used in a model for the cumulative distribution function of a partially shadowed mobile. The complete model for partially shadowed routes permits calculations for arbitrary combinations of open and forested terrain. Comparisons are made to data reported for partially shadowed routes. The deterministic path model (DPM) developed in an earlier effort is a geometrically based tool for determining the signal path length through a stand of trees. It is expanded to give approximate expressions for the statistical parameters describing the fading of the line-of-sight component of the received signal. New expressions for the secondary statistics of a totally vegetatively shadowed mobile are derived. These new expressions are then used in models for the level crossing rate and average fade duration of a partially shadowed mobile. Comparisons are made to data reported for partially shadowed routes.
M.S.

Satellite systems are being planned for two-way communication with mobile vehicles using UHF and L-band frequencies. Of special concern in the system design are the characteristics of propagation in suburban and rural areas where fading occurs due to multipath effects and vegetative shadowing. A review of the literature was performed to study these propagation impairments. Available experimental data are examined, compared, and summarized. Propagation through vegetation is studied in order to compare reported modeling efforts and to determine the parameter dependences of path loss. A simple deterministic path model is then presented to estimate vegetative path loss. An overall statistical model is also proposed to describe the signal level fading statistics. The statistical model is compared to data, and the deterministic path model is used to determine the mean of signal level distribution functions in the presence of shadowing.
Master of Science

In this thesis, Advanced Random Access techniques for Satellite Communications are studied. In the last years, new advances in multi-access communication protocols together with the increasing need for bidirectional communications in consumer type of interactive satellite terminals have revived the interest for a set of schemes able to guarantee high-speed and low latency communications in bursty traffic conditions. In this work, starting from the latest findings on Aloha-based Random Access schemes, the optimization of such techniques and their use in closed-loop scenarios is investigated with particular regard to the Return Channel over Satellite of Digital Video Broadcasting. The thesis starts with a summary on the state of the art of Demand Assigned and Random Access techniques as well as on the recent evolution from the first to the second version of the Return Channel over Satellite of the Digital Video Broadcasting specification. In chapter 2 a stability and packet delay model for channel analysis and design are presented, showing that proper design through this tools can ensure high performance of the new access scheme. The use of control limit policies is also introduced and its use is thoroughly discussed both for finite and infinite users population showing that, differently from Slotted Aloha, in some cases static design over dynamic policies might be preferable if long propagation delay is present. In chapter 3 the same models and tools introduced for CRDSA are extended to the case of asynchronous Random Access schemes and a comparison of the two families of schemes is put in place demonstrating that asynchronous techniques are convenient only when the signal-to-noise ratio is high enough to ensure decodability of partially colliding packets. In chapter 4 a new access scheme currently patent pending is presented. In this scheme terminals access the channel in an unframed manner. It is shown that such a change brings improvements that further diminish latency due to immediate transmission of the first replica and further boost throughput because the number of loops on the corresponding bipartite graph representation is mitigated. The thesis concludes with a call for a new discussion of resource allocation in multi-access satellite communication scenarios such as DVB-RCS2 in light of the obtained results and of the new requirements in interactive satellite networks.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California
An operational concept for how a Demand Access Multiple Assignment (DAMA) system could be configured for the NASA Space network is examined. Unique aspects of this concept definition are the use of the Multiple Access system within the Space Network to define an order wire channel that continuously scans the Low Earth Orbit space for potential users and the use of advanced digital signal processing technology to look for the Doppler-shifted carrier signal from the requesting satellite. After the reception of the signal, validation and processing of the request is completed. This paper outlines the concept and the ways in which the system could work.

La thèse concerne les techniques de prédistorsion appliquées aux communications par satellite de type DVB-S2X dans la perspective de la montée en débit de ces systèmes. Pour atteindre cet objectif, de faibles facteurs de retombée (inférieurs à 5%) et desordres de modulation plus élevés sont préconisés, augmentant la vulnérabilitévis-à-vis des non-linéarités introduites lors du passage par le satellite. Dans la littérature, deux classes de méthodes se distinguent par leur performance de linéarisation. La première est constituée des architectures d’apprentissage direct (Direct Learning Architecture) et indirect(Indirect Learning Architecture) et la seconde regroupe les méthodes itératives basées sur le théorème du point fixe. Le principal défaut de la première classe est la nécessité de choisir une structure de prédistortion a priori tandis que pour la deuxième classe, les conditions d'application du théorème du point fixe sont difficiles à vérifier dans la majorité des cas et nécessitent l'addition d'un gain empirique. Nous avons donc proposé 1) un schéma de prédistorsion itérative basé sur le théorème du point fixe, appliqué sur le signal mais optimisé en minimisant une erreur quadratique entre les symboles de modulation et la sortie de l'échantillonneur, 2) un schéma de prédistorsion itérative incluant une adaptation automatique des paramètres et adapté à tout type de canal
The thesis focuses on predistortion techniques applied to DVB-S2X satellite communications in order to increasing the throughput of these systems. To achieve this objective, sharp roll-off factors (less than 5%) and higher modulation orders are recommended, increasing sensibility with regard to the non-linearities introduced during the passage by the satellite. In the literature, two classes of methods are distinguished by their linearization performance. The first consists of direct (Direct Learning Architecture) and indirect (Indirect Learning Architecture) learning architectures and the latter includes iterative methods based on the fixed point theorem. The main defect of the first class is the need to choose a predistortion structure a priori, while for the second class, the conditions for applying the fixed point theorem are difficult to verify in most cases and require the addition of an empirical gain. We therefore proposed 1) an iterative predistortion scheme based on the fixed point theorem, applied to the signal but optimized by minimizing a quadratic error between the modulation symbols and the sampler output, 2) an iterative predistortion scheme including an automatic adaptation of the parameters and suitable for all types of channels

Future mobile broadband communication systems aim to provide a wide range of multimedia services (telephony, video conferencing, audio and video broadcasting, etc.) to a large number of users. In order to achieve a global coverage and reach remote users, satellite is foreseen to be a key component in the development of such networks. When compared to first-generation mobile satellite communication systems, these future satellite networks will need to provide significantly higher data rates whilst achieving very low bit error probability values. In order to keep the mobile user terminal as well as on-board processing complexity as low as possible, it is important to reach the required quality of service with very low values of the signal-to-noise ratio. Hence, particular attention must be paid to the design of the air interface of these future satellite systems. The use of CDMA presents a number of advantages for mobile communication systems, and hence CDMA technology has recently received a lot of attention for both second generation and future terrestrial multimedia systems. However, less effort has been put into the design of CDMA solutions for satellite communications. Moreover, good air interface designs for terrestrial systems do not necessarily translate into efficient solutions for the satellite environment. Hence, different techniques aimed at improving the performance of CDMA satellite systems are proposed in this thesis. First, the performance of S-CDMA, which reduces the level of MAI by co-ordinating the transmission of the different users, is analysed in satellite fading channels. Comparisons with the more conventional A-CDMA are provided and the impact on the transmission quality of imperfect power control, synchronisation errors and pulse shaping is assessed. In order to meet the very tight requirements set for multimedia services, FEC coding is required. Hence, the performance of S-CDMA in fading channels is presented for different channel coding techniques. The performance of the different schemes is characterised with both power and spectral efficiency and comparisons are made. In order to reduce the performance degradation due to the MAI, it is also possible to use multiuser detection algorithms at the receiver. In this thesis, the performance of MUD algorithms using an ANN architecture is analysed in satellite fading channels. Different training strategies and algorithms are considered and the performance of the ANN receivers is compared to that of the conventional correlator as well as other MUD algorithms. Finally, a number of different multi-rate spreading techniques are proposed and their respective complexity is discussed and compared. The power fluctuations caused by these different multi-rate spreading techniques are analysed in order to evaluate their performance in the satellite non-linear channel.

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Communications satellite system architecture trades traditionally consider only the cost per unit of capacity provided. This selection method ignores the other requirements with which the system architectures were designed and which are critical to providing a capability to the warfighter. A survey of communications satellite systems identified five common attributes that are incorporated in the design process: communications capacity; access; interoperability; commandability; and information assurance and protection. A mathematical model was implemented to enable the analysis of communications satellite system architectures based on multiple system attributes. Utilization of the model in a hypothetical case indicates system selection can differ from the traditional solution when additional key performance attributes are considered.

The performance of a mobile satellite communications link can be determined by the propagation path between a satellite and mobile users. Some of the most important factors are multipath propagation and vegetative shadowing. System designers should have the most reliable information about the statistics of fade duration in order to determine fade margin or to compensate for the fades using modulation and coding scheme.

This report describes a simulator, PROSIM, developed at Virginia Tech for simulating a propagation model in land mobile satellite communications. The simulator is based on a random number generator that generates data sets to compute statistics of the propagation channel. Performance of the simulator was evaluated by comparing statistics from an analytical model and experimental data provided by W. Vogel of Univ. of Texas at Austin and J. Goldhirsh of the Applied Physics Laboratory. New expressions for phasor plot and its mathematical expression for lognormal channel were derived and were simulated. Finally, the advantages of the simulator using random number generator in simulating the propagation model are described.
Master of Science

Thesis (M.S. in Information Systems Technology)--Naval Postgraduate School, September 2001.
Thesis advisor(s): Tri T. Ha, Nancy Roberts. Includes bibliographical references (p. 85-87). Also available online.

The main areas of research of this thesis are Interference Management and Link-Level Power Efficiency for Satellite Communications. The thesis is divided in two parts. Part I tackles the problem of interference environments in satellite communications, and interference mitigation strategies, not just in terms of avoidance of the interferers, but also in terms of actually exploiting the interference present in the system as a useful signal. The analysis follows a top-down approach across different levels of investigation, starting from system level consideration on interference management, down to link-level aspects and to intra-receiver design. Interference Management techniques are proposed at all the levels of investigation, with interesting results. Part II is related to efficiency in the power domain, for instance in terms of required Input Back-off at the power amplifiers, which can be an issue for waveform based on linear modulations, due to their varying envelope. To cope with such aspects, an analysis is carried out to compare linear modulation with waveforms based on constant envelope modulations. It is shown that in some scenarios, constant envelope waveforms, even if at lower spectral efficiency, outperform linear modulation waveform in terms of energy efficiency.

The main areas of research of this thesis are Interference Management and Link-Level Power Efficiency for Satellite Communications. The thesis is divided in two parts. Part I tackles the problem of interference environments in satellite communications, and interference mitigation strategies, not just in terms of avoidance of the interferers, but also in terms of actually exploiting the interference present in the system as a useful signal. The analysis follows a top-down approach across different levels of investigation, starting from system level consideration on interference management, down to link-level aspects and to intra-receiver design. Interference Management techniques are proposed at all the levels of investigation, with interesting results. Part II is related to efficiency in the power domain, for instance in terms of required Input Back-off at the power amplifiers, which can be an issue for waveform based on linear modulations, due to their varying envelope. To cope with such aspects, an analysis is carried out to compare linear modulation with waveforms based on constant envelope modulations. It is shown that in some scenarios, constant envelope waveforms, even if at lower spectral efficiency, outperform linear modulation waveform in terms of energy efficiency.

This research activity develops in the rapidly and constantly growing field of avionics for small satellites. The relatively widespread availability of low-cost piggyback launch opportunities recently made feasible for a heterogeneous set of entities the access to orbit. Universities, industries, local governments and even amateurs, all became interested in space and the rather unique opportunities offered by its environment. This led to the development of a large number of nano and pico satellite missions, respectively with spacecrafts of mass lower than 10 kg and 1 kg. Such tiny satellites are usually built with commercially available electronic components not specifically qualified for the space environment, allowing for savings along the whole development cycle in recurring and non recurring costs. Design re use extends this approach to the system level, with an aggressive exploitation of existing technologies and, possibly, of space-flown architectures. Communication subsystems, a small but critical set of elements common to every mission, are not exempt from such a philosophy. On board networks, on-board transceivers and antennas, ground stations, and the protocols in between are primary requirements for a spacecraft mission, some of the most specialized and complex ones. Design re-use is then sought at every level, to the point of favoring “old and trusted” technologies in spite of lower performances and reduced flexibility. While this was acceptable for pioneer pico satellite missions, with the growth of scientific goals the traditional trade-offs are not appropriate anymore. Even further, the stream of innovations coming from the ground mobile market is not being adequately exploited and today outdated architectures set, rather than match, mission capabilities and achievable goals. The research aims at finding new solutions to common problems becoming prevalent in this field. Better trade-offs are needed in the ground and flight communication segments and in the elements linking them. Better performances are achievable with an increase in system complexity, always taking into account energy, mass and cost constraints.

The development and growth of the Internet during the past thirty years has led to demand for and development of Internet services everywhere and over every possible communications medium. This includes the medium of satellite communications. During those same three decades, the growth in use of satellite communications to provide a widely-available wireless communications infrastructure has led to the development of broadband satellite communications using satellite constellation networks. These two technological trends have intersected. Here, we examine networking and internetworking issues affecting satellite networking in complex satellite constellation networks, and determine what is needed in order to support services based on the TCP/IP suite well in satellite constellations. We analyse constellation network topology. Its movement and effects on end-to-end delays experienced by network traffic travelling across the constellation are examined in detail. Analysis of the impact of cross-seam links upon delays experienced by traffic across star constellations shows that the use of cross-seam links is worthwhile. We examine the effects of multi-path routing within the constellation upon TCP communication, and demonstrate the performance advantages of an intelligent flowbased approach to routing in the constellation network. The desirability of implementing IP routing functionality in the space segment of the constellation is shown. The use of IP routing, to enable good support for IP QoS and IP multicast, is shown to be possible. We present an approach to implementing IP multicast within the constellation, evaluating use of a core-based tree algorithm, and outline an architecture permitting IP routing of IP traffic in an ATM-based satellite constellation network, using MPLS. Finally, we present and demonstrate the advantages of a novel method of managing path delay between ground terminals across a rosette constellation with intersatellite links, by using controlled handover to manage surface diversity to provide classes of service to network traffic.

The emerging trend in distributed spacecraft systems of using multiple spacecraft which share functions as opposed to independent spacecraft has given opportunities for missions previously infeasible. Inter-satellite link (ISL) communications provide a direct link within the space segment without need of an intermediate ground segment to relay the data. As the distributed spacecraft systems (DSS) have become less exotic and more complex, the need and demand for inter-satellite antenna systems has increased and the requirements for the antenna systems more diverse and become more demanding. This document is a research of the antennas currently used for ISL, already flown or will be launched in the near future. While the emphasis is strongly in the antennas, the other parts of the ISL communications sub-systems are observed. To limit the scope of the work, optical cross links are not observed in this document. ISL used only for very close proximity, such as several kilometres, are given only limited scope as the main challenges on those do not involve antennas. Furthermore, the major emphasis is given to systems which can be seen as commercially important. This document is divided in five main sections and the conclusions. In the first section the features and the challenges of ISLs are described. In the second section a parametrisation system for antennas is defined and this system is used in following sections to describe the ISL sub-systems and antenna used in them. The third part is a survey of recently flown space missions with ISLs. The fourth section is a survey on the missions which are scheduled to fly in near future and a brief survey of the solutions offered by satellite service providers and manufacturers. Due to the limited technical data available, the fourth section contains far more reverse engineering and assumptions than the survey on legacy missions. The fifth section describes the several families of ISL suitable antennas under development and discusses about several topics which relate to the ISL antenna development. In this part also are defined several example antenna specifications and the applications of those. The study concludes that antennas suitable for inter-satellite links are not inherently different from ground segment communication antennas of the S/C. The major difference is the need for greater coverage, which can be attained by multiple antenna elements, beam steering or antenna pointing. Specific considerations are needed to be taken into account and often the use of ISLs will increase the technical challenges, but it can provide solutions for problems which cannot be solved otherwise.
çDie sich abzeichnende Entwicklung von Einzelsatellitensysteme hin zu Systemen mit einer Vielzahl an Plattformen gleicher Funktionalität, eröffnet Möglichkeiten für die Durchführung von Missionen die bisher als nicht praktikabel/undurchführbar bewertet wurden. Inter-satellite Link (ISL) Kommunikation stellt eine direkte Verbindung zwischen den einzelnen Komponenten eines Raumsegments zur Verfügung ohne auf ein zwischengeschaltetes Bodensegment zur Datenübertragung angewiesen zu sein. Die gestiegene Anwendungshäufigkeit und Komplexität von Distributed Spacecraft Systemen (DSS) bringen eine Erhöhung der Nachfrage bezüglich Antennen für die inter-satelliten Kommunikation mit sich, wobei die Anforderungen an diese vielfältiger und anspruchsvoller geworden sind. Diese Abschlussarbeit stellt eine Untersuchung bezüglich Antennensystemen dar, welche in der Vergangenheit, der Gegenwart sowie der nahen Zukunft ihre Verwendung in der ISL fanden und finden werden. Während auch die anderen Bestandteile eines ISL Kommunikation Subsystems betrachtet werden, liegt der Schwerpunkt der Studie maßgeblich auf den Antennen selbst. Um den Rahmen der Arbeit zu wahren wird auf die Betrachtung optischer Kommunikationssysteme verzichtet. Bei inter-satellite Link Systemen die zur Datenübertragung über kurze Distanzen von nur einigen Kilometern benutzt werden liegen die Herausforderungen nicht bei den Antennen, weswegen diese nur bedingt untersucht werden. Weiter werden besonders die Systeme betrachtet welche als wichtig für die kommerzielle Anwendung erachtet werden können. Diese Arbeit ist in insgesamt sechs Abschnitte unterteilt. Im ersten Kapitel werden zunächst die Eigenschaften und die Herausforderungen bezüglich ISLs erläutert. Ein System zur Parametrisierung von Antennen wird im zweiten Kapitel definiert um es in den folgenden Abschnitten zur Beschreibung der ISL Subsysteme anzuwenden. Eine Analyse der Instrumentierung vergangener Weltraummission mit ISL Systemen wird im dritten Kapitel durchgeführt, die Betrachtung zukünftiger Missionen erfolgt in Kapitel 4. Da für Letztere nur begrenzt technische Daten zur Verfügung stehen, beinhaltet das vierte Kapitel weitaus mehr Reverse Engineering und Annahmen als die Untersuchung abgeschlossener Missionen. Im fünften Kapitel werden verschiedenen, für die inter-satellite Kommunikation geeigneten Antennentypen beschrieben und unterschiedliche Themen bezüglich der ISL Antennenentwicklung diskutiert. Weiter werden in diesem Abschnitt verschiedene Antennenspezifikationen definiert und entsprechende Anwendungsbeispiele beschrieben. Im letzten Teil werden die gefundenen Erkenntnisse abschließend diskutiert. Die Untersuchung zeigt dass Antennen welche für die inter-satelliten Kommunikation geeignet sind, sich grundsätzlich nicht von gängigen Antennen zur Bodensegmentkommunikation des S/C unterscheiden. Der Hauptunterschied liegt in der Notwendigkeit einer größeren Abdeckung. Dies kann durch eine größere Anzahl von Antennenelementen, Strahlsteuerung oder Antennenausrichtung erreicht werden. Systemspezifische Erwägungen müssen in Betracht gezogen werden wobei die Anwendung von ISL Systemen die technischen Herausforderungen/Anforderungen erhöht. Im Gegenzug ermöglicht sie Lösungen für Probleme die auf andere Weise nicht behandelt werden können.
Une nouvelle tendance est apparue dans les systèmes décentralisés des satellites, consistant à utiliser plusieurs satellites qui partagent des fonctionnalités, plutôt que des satellites indépendants. Cela a rendu possible des missions qui étaient précédemment irréalisables. Le lien inter-satellite (ISL) permet en effet de communiquer directement dans l’espace, sans devoir utiliser le segment sol pour transmettre les données. Alors que les systèmes décentralisés des satellites (DSS) sont devenus moins exotiques et plus complexes, la nécessité et la demande de systèmes d’antennes inter-satellite se sont développées et les exigences pour les systèmes d’antennes se sont diversifiés et sont devenus plus contraignants. Ce document réalise une étude des différentes antennes actuellement utilisées pour le ISL, dont certaines sont déjà opérationnelles et d’autres seront lancées prochainement. Tandis qu’il met fortement l’accent sur les antennes en ellesmêmes, il étudie aussi les autres parties des sous-systèmes de communication ISL. Néanmoins, pour limiter la portée du document, les réticulations optiques ne sont pas abordées. De même, les ISLs utilisés pour les communications à faible portée, de l’ordre de quelques kilomètres, ne sont que brièvement évoquées, étant donné que les défis majeurs concernant ceux-ci n’impliquent pas les antennes. Au delà de ça, ce document met surtout l’accent sur les systèmes qui peuvent être vu comme commercialement importants. Ce document est divisé en cinq sections, en plus de la conclusion. Dans la première section sont décrit les caractéristiques et les challenges des ISLs. Dans la seconde section, un système de paramétrage pour les antennes est défini et ce système est utilisé dans les sections suivantes pour décrire les sous-systèmes ISLs ainsi que les antennes associées. La troisième partie donne un aperçu des récentes missions spatiales lancées avec ISLs. La quatrième section étudie quant à elle les missions prochainement programmées et donne un bref aperçu des solutions offertes par les fournisseurs et fabricants des services satellitaires. Dû à la limitation des donéees techniques disponibles, cette section est principalement basée sur l’ingénierie inverse et des hypothèses, comparé aux missions déjà lancées et discutées en section 3. Finalement, la cinquième section décrit les différentes familles d’antennes ISL sous développement et discute de plusieurs sujets liés à leur développement. Elle définit aussi plusieurs exemples de spécifications d’antennes, et les applications associées. L’étude conclut que les antennes adaptées pour les liens inter-satellite ne sont pas très différentes des antennes de communication au sol du satellite, la plus grande différence étant la nécessité d’une plus grande couverture réseau. Celle-ci peut être atteinte via l’utilisation de plusieurs antennes, l’orientation du faisceau ou le pointage de l’antenne. Des considérations particulières doivent être prises en compte et souvent, l’utilisation des ISLs augmente les défis techniques. Néanmoins, cela constitue une solution à des problèmes qui ne peuvent pas être résolus autrement.

Dans le cadre des communications par satellite, les caractéristiques du lien rendent difficile la mis en œuvre des systèmes de télécommunications. Pour certaines applications, le problème principal est le délai de propagation. Un autre problème est la perte des données due aux caractéristiques du canal. Le but de cette thèse est de proposer un mécanisme qui assure la fiabilité de la communication tout en maximisant l’efficacité d’utilisation de la bande passante. Le protocole HARQ est reconnu pour sa capacité à atteindre le meilleur compromis fiabilité/débit. Cependant, ce mécanisme doit être optimisé pour pouvoir être utilisé sur un lien satellite. Dans un premier temps, nous proposons une méthode de fiabilisation basée sur l’HARQ statique, où le nombre de bits à envoyer à chaque transmission est fixé à l’avance. Cette méthode s’adresse aux services qui tolèrent un certain délai avant la réception du message. À partir de la distribution statistique du canal, elle définit la probabilité de décodage optimale à chaque transmission. Le nombre de bits à envoyer est calculé en fonction de ces probabilités et de la distribution d’information mutuelle du canal. Dans un deuxième temps, nous introduisons une version adaptative de la méthode précédente. Le récepteur calcule le nombre de bits à envoyer en fonction de l’état du canal pendant la transmission actuelle. Le nombre de bits calculé est renvoyé dans un acquittement vers l’émetteur. Finalement, nous présentons une structure de trame couche physique dans le cadre des mécanismes HARQ proposés et nous évaluons ses performances en faisant varier les paramètres du système. L’objectif est de trouver l’ordre de grandeur optimal des tailles de trames et des codes correcteurs d'erreurs à utiliser
As part of a satellite communications system, the characteristics of the communication links make it difficult to set up telecommunications systems. For certain applications, the main problem is the propagation delay. Another problem is the loss of data due to the characteristics of the channel. The aim of this thesis is to propose a mechanism that ensures the reliability of communication and maximize the utilization efficiency of the available bandwidth. HARQ protocol is known for its ability to achieve the best compromise reliability/ throughput.However, this mechanism must be optimized to be used on a satellite link. First, we propose a reliability method based on static HARQ, where the number to be sent is fixed previously. This method is specifically for services that tolerate some delay before the reception of the message. It consists in defining the probability of decoding at each transmission, using an optimization algorithm that we propose. The number of bits to be sent is calculated based on these probabilities and the distribution of the mutual information, assuming knowledge of the statistical distribution of the channel attenuation. Secondly, we introduce an adaptive version of the proposed method. This new approach calculates the number of bits to be sent by taking into account variations of the channel state during the communication. The receiver calculates the number of bits to be sent depending on the channel state during the current transmission. This calculated number is sent in an acknowledgement to the transmitter. Finally, we propose a frame structure for a physical layer that implements the proposed mechanisms and evaluate their performance by varying the system parameters. The aim is to find the optimal order of frame sizes and codes to be used