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Διερεύνηση των τεχνικών παραμέτρων και μηχανισμών της ηλεκτρομαγνητικής διάδοσης ασύρματου καναλιού δορυφορικής κινητής τηλεφωνίαςΑϊάς, Νάσερ 19 January 2011 (has links)
Η παρούσα εργασία περιλαμβάνει την μελέτη και τον χαρακτηρισμό του καναλιού ενός δορυφορικού καναλιού καθώς και την επίγεια διάδοση
Αρχικά γίνεται μια εισαγωγή στα ασύρματα συστήματα τηλεπικοινωνιών . Ειδικά παρουσιάζεται το δορυφορικό σύστημα και αναλύονται τα μέρη αυτού. Γίνεται παρουσίαση των δορυφορικών ζεύξεων και μελετάται το περιβάλλον μέσα στο οποίο λαμβάνει χώρα μια σύνδεση. Αρχικά αναλύονται οι μέθοδοι διάδοσης της ηλεκτρομαγνητικής ακτινοβολίας και οι διάφορες εξασθενήσεις που υφίσταται το σήμα λόγω φαινομένων της ατμόσφαιρας καθώς και άλλων επιδράσεων.
Γίνεται έπειτα μια εκτενής αναφορά στις διαλείψεις και στην ταξινόμησή τους. Στη συνέχεια γίνεται μια κατηγοριοποίηση των διαλείψεων αυτών με βάση τα χαρακτηριστικά τους. Ακολουθεί η στατιστική αναπαράσταση των καναλιών με διαλείψεις χρησιμοποιώντας τις βασικότερες κατανομές που συναντώνται στα τηλεπικοινωνιακά συστήματα. / This work includes the study and channel characterization for a satellite signal and also its terrestrial propagation.
First we introduce the wireless telecommunications systems. We focus on the satellite system and its components are analyzed. A presentation of the satellite links follows and the propagation environment is studied. We analyze the propagation methods of electromagnetic radiation and the various losses that the signal endures due to atmospheric phenomena and other effects.
There is then a reference to the fading channel and and its analysis. Then there is categorization of the fading according to its characteristics. The statistical representation of the fading channel follows, with the use of the key distributions found in telecommunication systems.
Lastly, the satellite transmission is simulated for various orbit heights and conditions
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Inter-Satellite Link Design for Nanosatellites in New SpaceFredmer, Andreas January 2020 (has links)
New Space is a phrase used to describe the expanding commercialization into the areas of space, for instance the Low Earth Orbit at approximately 500 km altitude. This is due to the decrease in cost as the satellites are becoming smaller and the transport vehicles cheaper. This reduction of cost provide the opportunity for industry and researchers tosend up customized equipment to orbit with standardized smaller satellites, such as the nanosatellites. Many parts of the nanosatellites system are commercially available but some subsystems are dependent on the situation. One of which is the satellite to satellite communication, referred to as Inter-Satellite Link (ISL). This thesis aims To evaluate the feasibility of asystem that allow for ISL capability and the basic operations of a satellite. Two hypothetical mission designs, Earth Observation and Global Coverage, were used to simulate the restrictions and requirements of the subsystems together with Commercial Of the Shelf (COTS) equipment to consider the satellite system as a whole. The major principles of the Radio Frequency (RF) communication system and their low level components are investigated and discussed. The scope of this thesis were to present and evaluate the high system level of the satellite. Thus the results and discussion describe a theoretical system performance that could be achieved with suggestions of low level components and system configuration. Besides from the communication subsystem this thesis also includes theory of mission design, the satellite subsystems and external interactions to describe how it all affects the design work of the communication system. Conclusion of this work offers a versatile preliminary system design that is theoretically capable of limited ISL communications. Furthermore this thesis include the fundamental principles of the satellite system that can be used for further work or alternative mission designs.
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Nätverksoptimering med öppen källkod : En studie om nätverksoptimering för sjöfartenDeshayes, Dan, Sedvallsson, Simon January 1900 (has links)
Detta examensarbete handlar om hur datatrafik över en satellitlänk kan optimeras för att minska laddningstider och överförd datamängd. Syftet med studien är att undersöka i vilken omfattning datatrafik mellan fartyg och land via satellitlänk kan styras så att trafiken blir effektivare. Genom att använda DNS-mellanlagring, mellanlagring av webbsidor samt annonsblockering med pfSense som plattform har examensarbetet utfört experiment emot olika hemsidor och mätt laddningstid samt överförd datamängd. Resultatet visade att det fanns stora möjligheter att optimera nätverkstrafiken och de uppmätta resultaten visade på en minskning av datamängden med 94% och laddningstiderna med 67%. / The thesis describes how network traffic transmitted via a satellite link can be optimized in order to reduce loading times and transmitted data. The purpose with this study has been to determine what methods are available to control and reduce the amount of data transmitted through a network and how this data is affected. By applying the practice of DNS caching, web caching and ad blocking with the use of pfSense as a platform the study has performed experiments targeting different web sites and measured the loading times and amount of transmitted data. The results showed good possibilities to optimize the network traffic and the measured values indicated a reduction of the network traffic of up to 94% and loading times with 67%.
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Inter-Satellite Links for an Earth-Observation Constellation (AlertSat) / Inter-Satellitlänkar för en Jordobservationkonstellation (AlertSat)Söderman, Emil January 2024 (has links)
Satellite constellations are becoming more common as the prices for satellite launches drops. These constellations have different purposes such as communications, navigation or Earth-observation. Earth-observation constellations can be used to detect natural disasters such as wildfires, floods and landslides. Many of these events occur in remote areas that are hard to reach. This means that detecting that they have occurred can take a long time and the delayed response can have serious consequences for the area. Forest wildfires for example spread quickly and a delayed response can lead to the fire growing out of control. These events can be detected using satellite imagery from Earth-Observation satellites. One issue is that even if it’s detected, satellites orbit Earth approximately once every 90 minutes in low Earth orbit, which for fast spreading disasters might not be fast enough. Another issue is that downlinking large amounts of data in the form of images often requires large, powerful and expensive satellites. The processing on the ground also takes time. This means that by the time the event has been detected it can already be to late. Combining the satellite sensors with software that can detect the critical events in-orbit, eliminates the need to downlink all images and only send the needed information. Instead it can be processed on-board the satellites, enabling smaller, less expensive satellites. When a satellite detect an event there is no certainty that it is above a ground station. The information can’t be sent to until it has line of sight of one. Having many ground stations spread across the world would increase cost and is limited by the availability of antennas. The information can instead be shared with the other satellites in the constellation via Inter-Satellite Links to reduce the latency of the information. The AlertSat constellation from the Swedish company PandionAI aims to do this. With it’s twin concept constellation design it will be able to do autonomous tasking, change detection and decision control using small, specialized satellites. When for example a wildfire is detected an Alert will be generated and quickly be sent through the constellation to a satellite within line of sight of a ground station so that it reaches the end user who can respond. This thesis aims to answer the question of how Inter-Satellite Links can be used ii | to reduce latency for the AlertSat constellation. It will identify the parameters, limits and trade offs that the communication has. Inter-Satellite Links have limits due to the distance that the satellites in orbit have to each other. The satellites are also limited in size and power which needs to be quantified for us to be able to see how much data that can be sent, while the link can still be closed. / Satellitkonstellationer blir ett mer vanligt fenomen då priset för satellit uppskjutningar sjunker. Dessa konstellationer har olika syften så som kommunikation, navigation och jordobservation. Jordobservationkonstellationer kan användas för att upptäcka naturkatastrofer så som skogsbränder, översvämmningar och jordskred. Många av dessa naturkatastrofer händer i avlägsna områden som är svåråtkomliga. Det betyder att upptäckten av de kan ta lång tid och den försenade responsen kan få allvarliga konsekvenser för området. Skogsbränder till exempel sprider sig snabbt och en sen respons kan leda till att branden sprider sig utom kontroll. Dessa händelser kan upptäckas genom att använda satellitbilder från jordobservationssatelliter. Ett problem är dock att även när en händelse observaras så är tiden för en satellit i låg omloppsbana runt jorden ungefär 90 minuter, vilket för vissa naturkatastrofer inte är snabbt nog. Ett annat problem är att nedlänka stora mängder data i formen av bilder vilket ofta kräver stora, kraftfulla och dyra satelliter. Att processera den här mängden data på jorden tar också tid. Det betyder att när en händelse blir upptäckt är det redan försent. Genom att kombinera satellitsensorer med mjukvara för att upptäcka dessa kritiska händelser i omloppsbanan kan man ta bort behövet att nedlänka alla bilder utan bara skicka den allra nödvändigaste informationen. Bilderna analyseras istället ombord själva satelliterna vilket möjliggör mindre, billigare satelliter. När en satellit upptäcker en händelse finns det ingen garanti för att den befinner sig ovanför en markstation. Informationen kan därför inte skickas förrens markstationen och satelliten har siktlinje av varandra. Att ha flera markstationer spridda över världen skulle öka kostnaden och är dessutom begränsad av antennernas tillgänglighet. Informationen kan istället delas med de andra satelliterna i konstellationen via inter-satellit länkar för att reducera latenstiden för informationen. AlertSat konstellationen från det svenska bolaget PandionAI har som mål att göra detta. Med sitt tvillingkoncept på konstellationen kommer den kunna utföra autonoma uppgifter, förändringsdetektering och beslutskontroll med hjälp av små, specialiserade satelliter. När till exempel en skogsbrand upptäcks kommer en varning bli genererad och snabbt skickas genom konstellationen till en satellit ovanför en markstation så att den kan nå den slutgiltiga användaren som kan agera. Den här uppsatsen har som mål att svara på hur inter-satellitlänkar kan användas för att reducera latensetiden för AlertSat konstellationen. Den ska också identifiera vilka parametrar, begränsningar och avvägningar som den här kommunikationen har. Eftersom satelliterna är begränsade i storlek och kraft behöver dessa kvantifieras så att det går att se hur mycket data som kan skickas medans länken fortfarande kan stängas.
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