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Proyecto Fin De Grado ESCUELA TÉCNICA SUPERIOR DE INGENIERÍA Y SISTEMAS DE TELECOMUNICACIÓN PROYECTO FIN DE GRADO TÍTULO: Development of a simulator of low Earth orbit satellite communication networks to analyze interference problems. AUTOR: Ainoa García Martí TITULACIÓN: Sistemas de Telecomunicación TUTOR Taneli Riihonen UNIVERSIDAD: Tampere University of Technology (TUT) CENTRO: Tampere PAÍS: Finlandia Fecha de lectura: Calificación: El Coordinador de Movilidad, I ABSTRACT Tampere University of Technology Bachelor’s Degree Programme in Telecommunication Systems Examiner: D.Sc. Taneli Riihonen Keywords: Small satellites, LEO, polar constellation, SINR Low Earth orbit (LEO) communication networks are the near future of the communi- cation services. What started off as something merely for scientists and students has become an attractive solution for commercial communication. The massive market competition and the huge cost of developing, building and launching conventional satellites, as well as the need of global coverage, have forced the communication industry to look for alternatives and, thanks to the developments in nanotechnology and microtechnology, LEO communication networks are a promising one, since LEO are the closest orbits to the Earth, allowing the setting up of polar orbits and the use of smaller satellites, known as small satellites or SmallSats. The increasing interest in LEO communication systems is the main reason to write this thesis. Previous work has mainly been limited to analyzing and solving the interference of LEO networks with the geostationary ones. However, LEO are not stationary orbits, which means that satellites are not fixed. This fact, together with the small coverage area due to the low altitude, forces us to set up large satellite constellations. The big amount of satellites also causes interference to occur within the system itself, since the number of visible satellites at a point on Earth is often greater than one. The parameter intended to analyze this issue is the signal-to- interference-plus-noise ratio (SINR). This thesis offers an overview of satellite communication, focusing on low orbit com- munication networks further on. Then, a simulator is developed to analyze the SINR of a polar satellite constellation. The results show a significant decrease of SINR at polar regions. In order to improve SINR value, we decrease the inclination but it does not solve the problem as the low SINR values move to different Earth lati- tudes. Finally, we simulate the polar constellation using dipoles as ground antennas, obtained a light but promising increase of SINR at the conflict regions. II RESUMEN Las comunicaciones en órbita baja (LEO) son el futuro de los servicios de comuni- cación. Lo que empezó como algo destinado a científicos y estudiantes, se ha con- vertido en una atractiva solución para las comunicaciones comerciales. La masiva competencia del mercado y el elevado coste de desarrollo, construcción y lanzamiento de los satélites convencionales, así como la necesidad de cobertura global, ha forzado a la industria de las telecomunicaciones a buscar otras alternativas y, gracias a los avances en nano y microtecnología, las comunicaciones LEO es una de ellas. El creciente interés en las comunicaciones LEO es la principal razón por la cual se ha escrito esta tesis. Los trabajos previos se han limitado principalmente a analizar y resolver los problemas de interferencia de las redes LEO con las geoestacionarias (GEO). Los satélites en orbitas LEO no son geoestacionarias. Además, su área de cobertura es menor debido a la baja altitud. Estos dos hechos, obligan a establecer grandes constelaciones de satélites para garantizar una cobertura global y continua. Por ello, los problemas de interferencia no solo ocurren con los satélites GEO, sino que también se dan en las estaciones terrenas, ya que el número de satélites visibles es normalmente mayor que uno. Esta tesis comienza con un resumen del funcionamiento de las comunicaciones por satélite: las variables interfieren en un enlace satelital, las fórmulas que se emplean para conocer la posición y el movimiento de los satélites y los tipos de órbitas. Más tarde, se focaliza en las comunicaciones por satélite en órbita baja, ofreciendo in- formación sobre los satélites empleados en ellas, los pequeños satélites o también conocidos como SmallSats; y sobre el diseño de constelaciones satelitales, concreta- mente los parámetros que las definen y el método empleado para diseñarlas. Una vez definido el funcionamiento de una comunicación satelital y el diseño de una con- stelación de satélites de órbita baja, se presentan los resultados obtenidos a partir del simulador. La parte práctica de esta tesis está destinada a analizar la relación señal a ruido interferencia de las constelaciones polares, ya que son aquellas que garantizan una cobertura global. El parámetro que se analiza es la relación señal a ruido interferencia (SINR). Los resultados muestran que la SINR adquiere valores muy bajos en las regiones polares debido a la gran concentración de satélites encima de los polos. Con el fin de solucionar este problema, en un primer momento, se opta por disminuir la inclinación orbital, solución que es descartarda puesto que traslada los bajos valores de SINR a otras latitudes terrestres. La segunda solución propuesta es el uso de antenas terrenas directivas. Aplicando esta modificación en el simulador, III se obtiene un ligero aumento de la SINR. Por ello, se llega a la conclusión de que el uso de antenas terrenas muy directivas podría aumentar el valor de la SINR en las regiones polares para constelaciones polares en órbitas LEO. IV PREFACE This thesis, written during the four months I spent at Tampere University of Tech- nology, is made as a completion of the bachelor’s degree in Telecommunication Systems Engineering. Although this project has been a fairly challenge, it has been rewarded at the end. I would like to thank the following people for their support, without whose help this work would never have been possible. First, thanks to Universidad Politécnica de Madrid and Spanish government for the opportunity to benefit from an Erasmus scholarship. I gratefully acknowledge the help provided by D.Sc. Taneli Riihonen, as the supervisor of this thesis, who has been always available and prepared to give support and guidance. Thanks are also due to Adrian Garcia Baños, who gave me much valuable advice in the early stages of this work. My gratitude is also for all the people I have met at Tampere University of Tecn- hology, who have given me their unconditional support during all the stages of this project. Without them, I would have surrendered before finalizing it. Last but not least, I am thankful to my family and friends, who, from the distance, have given me all their love, specially mention to my boyfriend Diego to support me through this stage of my life. Tampere, May 21, 2018 V CONTENTS 1. Introduction . 1 1.1 Motivation and Scope . 2 1.2 Objective . 2 1.3 Organization of the Thesis . 3 2. Satellite Communications . 4 2.1 Satellite Link Design . 4 2.2 Orbit Mechanics . 6 2.3 Types of orbits . 7 3. LEO satellite communication networks . 9 3.1 Definition and Classification of Small Satellites . 10 3.2 Features of Small Satellites Networks . 10 3.3 Satellite Constellation Design . 12 3.3.1 Parameters of Satellite Constellation Design . 12 3.3.2 Walker Constellations . 15 4. Development of the simulator . 17 4.1 Representation of the constellations . 17 4.2 Elevation and Distance of a Satellite . 17 4.3 Signal-to-Interference Noise Ratio Calculation . 19 4.4 Antennas Directivity . 20 4.5 Main Function . 21 5. Analysis and solutions . 23 5.1 Parameters Used and Results . 23 5.1.1 Analysis of Polar Constellations . 28 5.1.2 Analysis of Inclined Constellations . 29 5.1.3 Ground Antennas Directivity . 30 6. Conclusions . 34 Bibliography . 35 VI LIST OF FIGURES 2.1 Uplink and Downlink . 5 2.2 Semi-major axis a ............................. 6 2.3 Types of Orbits . 8 3.1 Minimal Orbit Inclination . 13 3.2 Walker Delta Method . 16 4.1 Elevation and Distance from a Satellite to a Point on Earth . 19 5.1 Polar and 72◦ Inclined Constellations . 25 5.2 SINR and SNR of a Polar and 72◦ Inclined Constellations . 26 5.3 Parameters that Define SINR . 26 5.4 CDF Polar and 72◦ Inclined Constellations . 27 5.5 SINR Omnidirectional and Directional Ground Antennas . 31 5.6 CDF Directional Ground Antennas Polar Constellation . 32 5.7 SNR Omnidirectional and Directional Ground Antennas Polar Con- stellation . 33 VII LIST OF TABLES 2.1 Types of Orbits . 7 3.1 Small Satellites Classification . 10 5.1 Parameters of the Simulation . 24 VIII LIST OF ABBREVIATIONS AND SYMBOLS CDF Cumulative distribution function dB Decibel dBi Gain decibel GEO Geostationary orbit LEO Low Earth orbit SmallSat Small satellite SNR Signal-to-noise ratio SINR Signal-to-interference-plus-noise ratio dk Distance to Earth surface from satellite k LatE Earth latitude LonE Earth longitude LFS(d) Free space loss at distance d f Frequency GTX Gain of the transmitter antenna GRX Gain of the receiver antenna G Gravitational constant σ Incidence angle of the satellite k re Main radius of Earth α Nadir angle k∗ Nearest satellite to a point on Earth h Orbit altitude i Orbit inclination T Orbit period LRX Receiver loss PRX (d) Received power at distance d LatSk Satellite k latitude LonSk Satellite k longitude φk Satellite k elevation a Semi-major axis of the orbit µ Standard gravitational parameter LTX Transmitter loss PTX Transmitted power 1 1. INTRODUCTION Since the first human beings until now, we have had the necessity to communi- cate amongst ourselves. The media or communication channels have changed and evolved over time, beginning with the voice, passing through the paper and ending in space. In the field of wireless communications, the objective of space technology is to put two very far-away points in contact.
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