Study and simulation of communication links in a LEO satellite constellation based on Link Budget calculations

Currently, about 40% of the world’s population has limited or no access to high-speed Internet. Especially in rural, hard-to-reach areas, there is a challenge in terms of infrastructure to guarantee a quality connection.The need for global coverage has led telecommunications service providers to explore new alternatives to traditional communication. This search has led to the development of a multitude of projects related to satellite constellations in LEO orbits, where a more economical business model has been found, capable of providing global coverage and high-speed connection. The growing interest in LEO communications has motivated this project. The objective of this thesis is to study communication links in a LEO constellation through link budget calculations. Both inter-satellite links and ground-satellite links will be evaluated in order to study the characteristics of each one. For this purpose, an orbit simulator has been used, where the necessary calculations have been introduced to evaluate the links according to parameters such as received power and SNR, among others. The results of this project are expected to determine the viability of communications in a constellation and the effect of the link budget parameters on the communications performance

Dtn and non-dtn routing protocols for inter-cubesat communications: A comprehensive survey

CubeSats, which are limited by size and mass, have limited functionality. These miniaturised satellites suffer from a low power budget, short radio range, low transmission speeds, and limited data storage capacity. Regardless of these limitations, CubeSats have been deployed to carry out many research missions, such as gravity mapping and the tracking of forest fires. One method of increasing their functionality and reducing their limitations is to form CubeSat networks, or swarms, where many CubeSats work together to carry out a mission. Nevertheless, the network might have intermittent connectivity and, accordingly, data communication becomes challenging in such a disjointed network where there is no contemporaneous path between source and destination due to satellites’ mobility pattern and given the limitations of range. In this survey, various inter-satellite routing protocols that are Delay Tolerant (DTN) and Non Delay Tolerant (Non-DTN) are considered. DTN routing protocols are considered for the scenarios where the network is disjointed with no contemporaneous path between a source and a destination. We qualitatively compare all of the above routing protocols to highlight the positive and negative points under different network constraints. We conclude that the performance of routing protocols used in aerospace communications is highly dependent on the evolving topology of the network over time. Additionally, the Non-DTN routing protocols will work efficiently if the network is dense enough to establish reliable links between CubeSats. Emphasis is also given to network capacity in terms of how buffer, energy, bandwidth, and contact duration influence the performance of DTN routing protocols, where, for example, flooding-based DTN protocols can provide superior performance in terms of maximizing delivery ratio and minimizing a delivery delay. However, such protocols are not suitable for CubeSat networks, as they harvest the limited resources of these tiny satellites and they are contrasted with forwarding-based DTN routing protocols, which are resource-friendly and produce minimum overheads on the cost of degraded delivery probability. From the literature, we found that quota-based DTN routing protocols can provide the necessary balance between delivery delay and overhead costs in many CubeSat missions

Analysis of OSPFv3 in LEO satellite networks

Communication via satellite networks is under continuous research and development as it offers many advances over traditional terrestrial networks such as global coverage, but has a major drawback to be solved, the problem of point-to-point routing. In this work we have developed a satellite network emulator using Linux containers, which has allowed us to analyze the behavior of the IP routing protocol OSPFv3 in this type of networks. Specifically, its behavior has been analyzed in the Iridium constellation, which is widely known and used in this type of studies. For this purpose, we have used files of the topology of these networks over time generated with the HypatiaSeam orbital propagator, a modification of Hypatia made by the SeamSAT research group of the UPC. This project is part of a more global project whose objective is to be able to use a network of LEO satellites for communication between aircraft and airspace control centers. This would make it possible to centralize the different control centers, since it would not be necessary for aircraft to be in direct range to communicate with these centers, but thanks to the global coverage provided by these networks, they could communicate from anywhere in the world. Specifically, in this project we have developed an emulation platform that has allowed us to analyze the behavior of the OSPFv3 protocol to find optimal routes, i.e., shortest distance in terms of the cost function of the protocol. We will present the design and implementation of the emulation platform as well as the analysis of OSPFv3 performance in terms of protocol convergence time to topology changes, number of hops between a satellite and a ground station, delay and loss rate