Search

Communications-integrated satellite-terrestrial networks used for global broadband services have gained a high degree of interest from scientists and industries worldwide. The most convenient structures for such use are low Earth orbit satellites, since they fly closer to the Earth compared to the other orbits, and consequently provide significantly lower latency, which is essential for reliable and safe communications. Among these efforts is the Starlink satellites constellation, developed and partly deployed by the United States Company SpaceX. The constellation is planned to be organized in three spatial shells, each of them made up of several hundreds of small-dimensioned and light-weighted low Earth orbit specially designed satellites to provide broadband services, intending to offer global Earth coverage through their interoperability, combined also with the ground stations as a part of the satellite-terrestrial integrated network. By October 24, 2020, 893 satellites are situated in orbit of altitudes of 550 km under different inclinations, determining the first Starlink orbital shell. Two next generations are planned to be situated at altitudes of 1,110 and 340 km, to complete the appropriate infrastructure of three Starlink satellite shells, toward a global presence of broadband internet services. These three orbital shells offer different space views seen from the ground station (user) because of their different altitudes, thus in this paper a few parameters which describe the satellite’s behavior considered from the ground station’s (user’s) point of view are compared. These parameters in fact stem from the space orbital parameters and are defined as: horizon plane wideness, slant range, latency, and coverage area. A comparison is given for the three Starlink orbit layers, with identification of appropriate drawbacks and advantages as performance indicators. By the end, these parameters are applied to geometrically interpret and confirm the handover process among satellites. This paper may serve to highlight the new challenges of the satellite-terrestrial integrated network, providing some theoretical analysis and performance comparisons for the satellites in different orbit layers seen from the ground station (user) perspective.

LEOSAR (Low Earth Orbit Search and Rescue) is an international satellite system which operates continuously, detecting transmissions from emergency beacons carried by ships, aircrafts and individuals, providing location information related to worldwide distress events. LEOSAR based on Low Earth Orbits it is still limited on instantaneous alert and coverage. To improve the performance, this system is migrating towards MEOSAR (Medium Earth Orbit Search and Rescue), restructuring the capability to Medium Earth Orbit satellites. By real time 24-h satellite tracking and the simulation of the Almanac YUMA file using Trimble’s Planning Software, a methodology of comparison is provided. For the MEOSAR system advantages in global coverage and instantaneous alert are evidenced. From the obtained results it is shown the limitation of the LEOSAR capability, but also the efficiency improvement of the search and rescue operations provided by MEOSAR.

The use of GPS is becoming increasingly popular for real-time navigation systems. To ensure that satellite failures are detected and excluded at the receiver is of high importance for the integrity of the satellite navigation system. The focus of this paper is to implement a fault detection and exclusion algorithm in a software GPS receiver in order to provide timely warnings to the user when it is not advisable to use the GPS system for navigation. The GPS system currently provides some basic integrity information to users via the navigation message, but it is not timely enough for safety-critical applications. RAIM is a means of providing integrity with the capability of detecting when a satellite failure or a measurement error has occurred. It is the simplest and most cost effective technique for integrity monitoring. After applying the iterative fault detection and the exclusion algorithm, a significant improvement in positioning accuracy is achieved.

Aims: NOAAs (National Oceanic and Atmospheric Administration) -LEO environmental satellites provide continuous coverage of Earth, supplying high -resolution global meteorological, oceanic and space observation data. These satellites are part of the international Search and Rescue Satellite Aided Tracking (SARSAT) system. SARSAT is designed to provide distress alert and location data in order to assist on search and rescue operation. SARSAT system detects and locates distress beacons (406MHz) activated at distress location. System calculates the distress event location using Doppler processing techniques. Each satellite pass transmits information about distress location. Passes with too short communication duration, are considered as m

NOAA's (National Oceanic and Atmospheric Administration) - LEO (Low Earth Orbit) environmental satellites provide continuous coverage of Earth, supplying high-resolution global meteorological, oceanic and space observation data what are too important in aerospace and maritime. In addition, these satellites are part of the international Search and Rescue Satellite Aided Tracking (SARSAT) system. SARSAT is a satellite system designed to provide distress alert and location data in order to assist on search and rescue operation. The position of the satellite within its orbit considered from the ground station point of view is defined by Azimuth and Elevation angles. There is a direct relationship between communication duration and maximal elevation. Higher maximal elevation provides longer communication between the satellite and a Local User Terminal (LUT). Longer communication provides more Doppler events providing higher accuracy on location determination. Passes with too short communication duration, consequently with no data provided are considered as missed passes. Under assumption that the LUT is implemented in Kosovo, it is simulated the variation of elevation for different orbits for a period of one month. Simulation about elevation variations, among SARSAT satellites and local user terminal dedicated for search and rescue services is provided through this paper.

Low Earth Orbit (LEO) satellites are used for public networking and for scientific purposes. Communication via satellite begins when the satellite is positioned in its orbital position. Ground stations can communicate with LEO satellites only when the satellite is in their visibility region, since LEO satellites move too fast relative to a fixed point (ground station) on the Earth. The major loss in communication between the LEO satellite and the ground station is the free space loss. Free space loss varies since the distance from the ground station to the satellite varies over time. Free space loss is usually compensated through variable satellite transmit power on the downlink. This paper tries another approach on free space loss compensation, through receiver bandwidth adjustability at the ground station, in order to obtain the constant margin at the receiver. For analytical and simulation purposes, the altitudes from 600km to 1200km are considered.

Communication via satellite begins when the satellite is positioned in the desired orbital position. Ground stations can communicate with LEO (Low Earth Orbiting) satellites only when the satellite is in their visibility region. The ground station’s ideal horizon plane is in fact the visibility region under 0˚ of elevation angle. Because of natural barriers or too high buildings in urban areas, practical (visible) horizon plane differs from the ideal one. The duration of the visibility and so the communication duration varies for each LEO satellite pass at the ground station, since LEO satellites move too fast over the Earth. The range between the ground station and the LEO satellite depends on maximal elevation of satellite’s path above the ground station. The dimension of the horizon plane depends on satellite’s orbital attitude. The range variations between the ground station and the satellite, and then ground station horizon plane simulation for low Earth orbiting satellites as a function of orbital attitude is presented. The range impact and horizon plane variations on communication duration between the ground station and LEO satellites are given.

NOAA (National Oceanic and Atmospheric Administration) - LEO environmental satellites provide continuous coverage of Earth, supplying high-resolution global meteorological, oceanic and space observation data. In addition, these satellites are part of the international COSPAS – SARSAT program, which aides search and rescue teams worldwide. The USA segment, referred to as SARSAT (Search and Rescue Satellite Aided Tracking) system, is designed to provide distress alert and location data to assist on search and rescue operations. SARSAT locates distress beacons (406MHz) activated at distress locations. The system calculates a location of the distress event using Doppler processing techniques. Processed data is continuously retransmitted through the SARSAT downlink to Local User Terminals (LUT) when satellites are in view. The downlink adjacent interference is expected when two satellites operate in close proximity and share the same frequency. The downlinks of all SARSAT LEO satellites use the same 1544.5 MHz frequency. In cases where the satellites are within the main lobe of the local user terminal antenna, transmissions from adjacent satellites act as interference to one-another, effectively decreasing the signal-to-noise ratio of the desired downlink. This can result in missed distress beacon bursts or no stored solutions received at the LUT, consequently no data is provided about a distress location. Analysis on interference prediction, impacts on system operation and recommendations for mitigating interference periods where the duration may be significant, are presented in this paper.

Low Earth Orbits (LEO) satellites are used for public communication and for scientific purposes. These satellites provide opportunities for investigations for which alternative techniques are either difficult or impossible to apply. Ground stations have to be established in order to communicate with such satellites. Usually these satellites communicate with ground stations at S-band. The communication quality depends on the performance of the satellite ground station, in addition to that of satellite. The performance of the satellite ground stations is expressed through Figure of Merit. The aim of this paper is to analyze the rain attenuation impact on the performance of the respective ground station. Rain attenuation depends on geographical location where the satellite ground station is implemented. In order to compare this effect on satellite ground station performance, some cities of Europe are considered. Finally, the rain attenuation impact on the satellite ground station Figure of Merit for the hypothetical satellite ground station installed in Prishtina is analyzed.

Since two decades the microsatellites in Low Earth Orbits (LEO) are in use. Low Earth Orbit satellites are used for public and massive communication and for scientific purposes, also. Low Earth Orbits vary with the type of satellites and their primarily purposes. Low Earth Orbit scientific satellites have very wide application, including Earth’ s surveillance and astronomy applications. These satellites provide opportunity for investigations for which existing techniques are either difficult or impossible to be applied. Thus, it is to be expected that such missions in the near future will be more developed especially in the fields where similar experiments can not be done by means on the Earth. So, also the ground stations have to be established in order to communicate with such satellites. The quality of communication depends on the performance of the satellite ground station, also. Before the implementation of the ground station the analyses related to environmental factors have to be considered, especially in urban areas. Rain effects, intermodulation products disturbance, contact time duration at low elevation, are few aspects which are considered in this work related to final decision on design of the ground station. The performance measurement of the ground station based on Sun flux density is described as an experimental method which provides opportunity to check the performance of the ground station.

This paper evaluates the positioning performance of a single-frequency software GPS receiver using Ionospheric and Tropospheric corrections. While a dual-frequency user has the ability to eliminate the ionosphere error by taking a linear combination of observables, a single-frequency user must remove or calibrate this error by other means. To remove the ionosphere error we take advantage of the Klobuchar correction model, while for troposphere error mitigation the Hopfield correction model is used. Real GPS measurements were gathered using a single frequency receiver and post-processed by our proposed adaptive positioning algorithm. The integrated Klobuchar and Hopfield error correction models yeild a considerable reduction of the vertical error. The positioning algorithm automatically combines all available GPS pseudorange measurements when more than four satellites are in use. Experimental results show that improved standard positioning is achieved after error mitigation.

By nodal regression and apsidal precession, the Earth flattering at satellite low Earth orbits (LEO) is manifested. Nodal regression refers to the shift of the orbit’s line of nodes over time as Earth revolves around the Sun. Nodal regression is orbit feature utilized for circular orbits to be Sun synchronized. A sun¬-synchronized orbit lies in a plane that maintains a fixed angle with respect to the Earth-Sun direction. In the low Earth Sun synchronized circular orbits are suited the satellites that accomplish their photo imagery missions. Nodal regression depends on orbital altitude and orbital inclination angle. For the respective orbital altitudes the inclination window for the Sun synchronization to be attained is determined. The apsidal precession represents major axis shift, respectively the argument of perigee deviation. The apsidal precession simulation, for inclination window of sun synchronized orbital altitudes, is provided through this paper.

Low Earth Orbit (LEO) satellites are used for public networking and for scientific purposes. Communication via satellite begins when the satellite is positioned in its orbital position. Ground stations can communicate with LEO satellites only when the satellite is in their visibility region. The duration of the visibility and the communication vary for each LEO satellite pass over the station, since LEO satellites move too fast over the Earth. The satellite coverage area is defined as a region of the Earth where the satellite is seen at a minimum predefined elevation angle. The satellite's coverage area on the Earth depends on orbital parameters. The communication under low elevation angles can be hindered by natural barriers. For safe communication and for savings within a link budget, the coverage under too low elevation is not always provided. LEO satellites organized in constellations act as a convenient network solution for real time global coverage. Global coverage model is in fact the complementary networking process of individual satellite's coverage. Satellite coverage strongly depends on elevation angle. To conclude about the coverage variation for low orbiting satellites at low elevation up to 10o, the simulation for attitudes from 600km to 1200km is presented through this paper. Keywords—LEO; satellite; coverage

Global Positioning Systems (GPS) refers to satellite-based radio-positioning systems and time-transfer systems that provide three-dimensional course, position, and time information to suitably equipped users. At present, GPS system is world-wide used for positioning and navigation, attracting great attention from the scientific, professional and social community.GPS satellites are orbiting Earth at altitudes of 20.200 km and the GPS signal is mostly affected by the atmospheric effects. The scope of this paper is to investigate the performance impact of the atmospheric correction models in the overall positioning accuracy. Real GPS measurements were gathered using a single frequency receiver and post–processed by our proposed innovative adaptive LMS algorithm. We integrated Klobuchar and Hopfield correction models enabling a considerable reduction of the vertical error.

LEO (Low Earth Orbit) environmental satellites provide continuous coverage of Earth, supplying meteorological and oceanic observation data which are important in aerospace and maritime. The missions of such satellites are mainly based on photo imagery. For photo imagery, it is also important that the area observed from the satellite is treated under the same lighting conditions. This can be achieved by keeping the orbital plane position constant relative to the Sun due to the Earth’s motion around the Sun, defined as orbital Sun synchronization. The line of nodes defines the orientation of the satellite’s orbital plane in space. Nodal regression is defined as the shift of the orbit’s line of nodes over time, as Earth revolves around the Sun. Nodal regression is caused by the Earth’s oblateness. Nodal regression is a very useful feature, especially used to synchronize low Earth circular orbits with the Sun. Nodal regression depends on orbital attitude and orbital inclination angle. This paper provides an inclination window calculation for different attitudes in order to maintain orbital Sun synchronization.

LEO environmental satellites provide continuous coverage of Earth, supplying high-resolution global meteorological and oceanic observation. In addition these satellites are equipped with devices dedicated for search and rescue services. These satellites accomplish their missions mainly based on photo imagery. For photo imagery, it is too important the observed area from the satellite to be treated under the same lighting (illumination) conditions. This could be achieved by keeping a constant Sun position related to the orbital plane due to the Earth’s motion around the Sun, defined as orbital Sun synchronization. Line of nodes defines the orientation of the satellite’s orbital plane in space. Nodal regression refers to the shift of the orbit’s line of nodes over time as Earth revolves around the Sun. The nodal regression is caused because of the Earth’s oblateness. Nodal regression is very useful feature which is especially utilized for low circular orbits providing to them the Sun synchronization. Nodal regression depends on orbital attitude and orbital inclination angle. The nodal regression simulation for different orbital attitudes and then the inclination window calculation for sun synchronization are provided through this paper.

Adjacent downlink satellite interference usually occurs because of the presence of side lobes in addition to the desired main lobe in the radiation pattern of the satellite ground station antenna. If the angular separation between two adjacent satellites is not sufficiently large, it is quiet possible that the power radiated through the antenna's radiation pattern, whose main lobe is directed towards the intended satellite, interferes with the received signal from the adjacent satellite. This problem becomes more difficult if both satellites transmit at the same frequency. The SARSAT (Search and Rescue Satellite Aided Tracking) system is designed to provide distress alert and location data in order to assist in search and rescue operation. SARSAT uplink detects and locates distress beacons (406MHz) activated at distress location. The system calculates the location of distress event using Doppler processing techniques. Processed data is repeatedly retransmitted through SARSAT downlink to Local User Terminals (LUT) when satellites are in view and also stored in on-board memory. The downlink of all SARSAT LEO (Low Earth Orbit) satellites uses the same 1544.5 MHz frequency. In case those satellites are within the main lobe of the local user terminal antenna, transmissions from adjacent satellites act as interference to each other. This can result in missed bursts or no solutions received at LUT, consequently no data provided about the distress location∗. Modulation index application for adjacent satellite downlink interference identification, for periods where the interference duration may be significant, is presented in this paper. Measurement results recorded at SARSAT terminals are provided.

NOAA (National Oceanic and Atmospheric Administration) - LEO environmental satellites provide continuous coverage of Earth, supplying high-resolution global meteorological, oceanic and space observation data. In addition, these satellites are part of the international COSPAS – SARSAT program, which aides search and rescue teams worldwide. The USA segment is referred to as SARSAT (Search and Rescue Satellite Aided Tracking) system, designed to provide distress alert and location data in order to assist on search and rescue operation. SARSAT system detects and locates distress beacons (406MHz) activated at distress location. System calculates the location of distress event using Doppler processing techniques. Processed data is repeatedly retransmitted to Local User Terminals (LUT) when satellites are in view and also stored in on-board memory. A simulation of implementing a Local User Terminal (LUT) in Kosovo and respective communication reliability analyses are provided through this paper. The methodology applied for LUTKOS simulation is applicable for other sites.

Microsatellites in Low Earth Orbits (LEO) have been in use for the past two decades. Low Earth Orbit satellites are used for public communication and also for scientific purposes. Thus, it may be expected that such missions will be further developed in the near future especially in fields where similar experiments by purely Earth-based means are impracticable. Ground stations have to be established in order to communicate with such satellites, and the quality of communication depends on the performance of the satellite ground station, in addition to that of the satellite. Usually these scientific satellites communicate with ground stations at S-band. Within these papers the comparison of downlink performance of hypothetical satellite ground station implemented in different cities of Central Europe is given.

Microsatellites in Low Earth Orbits (LEO) have been in use for the past two decades. Low Earth Orbit satellites are used for public communication and also for scientific purposes. Thus, it may be expected that such missions will be further developed in the near future especially in fields where similar experiments by purely Earth-based means are impracticable. Ground stations have to be established in order to communicate with such satellites, and the quality of communication depends on the performance of the satellite ground station, in addition to that of the satellite. Usually these scientific satellites communicate with ground stations at S-band. The performance of the ground station could be disturbed by intermodulation interference because of permanent presence of uplink signal. Intermodulation products caused by GSM signals and uplink satellite signal are potential to disturb, especially in urban areas. Thus, within these papers the interference of intermodulation products caused by uplink signal and any other radiofrequency signal present in the front end of the ground station’ s receiving system is analyzed and then modelled. Based on the modelling concept, the intermodulation interference calculator is introduced as a main application point of these papers.

International efforts are oriented on global mobile communication satellite system that is fully integrated with the terrestrial mobile system. Space observation and other scientific missions are developing especially in the fields where similar researches can not be done by means on the Earth. Thus, satellite ground stations applications in the future will further develop, related to both, massive communication and scientific purposes. The performance of the ground station is of high importance related to operation of the satellite communication system. Analyses on parameters which impact the performance of the ground station in urban areas are given. Aspects which are considered are: rain attenuation, intermodulation interference and communication duration under low elevation angle. Solar radio flux density is applied for experimental check of the ground station performance. By this dissertation it is confirmed mathematically and with a few experimental results that the ground station situated in an urban area, performs satisfactorily when receiving signals from a LEO satellite system when parameters with influence on performance are well technically considered. The satellite ground station can be built in urban area by applying sophisticated analytical methods during the implementation. Međunarodna težnja je orijentirana ka globalnim satelitskim mobilnim komunikacijama koje će biti u potpunosti usklađene sa postojećim zemaljskim mobilnim sustavima. Svemirska istraživanja i ostale znanstvene misije se razvijaju posebno u oblastima u kojima se takva istraživanja se ne mogu obaviti sa postojećim sredstvima na Zemlji. Tako da primjena satelitski zemaljski postaja će se u budućnosti razviti bilo za masivne komunikacije isto tako i za znanstvena istraživanja. Izvedba zemaljske postaje je od visokog značaja u smislu cjelokupnog funkcioniranja satelitskog komunikacijskog sustava. Analiza utjecaja parametara na izvedbu zemaljske postaje za znanstvene satelite u niskim putanjama u urbanim sredinama je ovdje data. Obuhvaćeni aspekti se odnose na: slabljenje zbog kiše, interferencija zbog intermodulacije i komunikacija pod niskim kutom elevacije. Gustoća solarnog radio fluksa je primjenjena radi kontrole izvedbe zemaljske postaje eksperimentalnim putem. Ovom disertacijom je potvrđeno matematički i sa nekoliko eksperimentalni rezultata da zemaljska postaja u urbanim sredinama zadovoljava svojom izvedbom prilikom prijema signala od satelite u niskim putanjama ako su parametri na utjecaj te izvedbe tehnički dobro smatrani. Satelitske zemaljske postaje se mogu graditi i u urbanim sredinama primjenom dobrih analitičkih metoda prilikom implementacije.

The project “ MOST” (Microvariability and Oscillations of Stars) is a Canadian micro satellite space telescope mission. The micro satellite carries a Rumak-Maksutov telescope with an aperture of 15cm. The size of the satellite is 65cm x 65cm x 30cm and the mass is about 65kg. The goals of the mission are to analyze the inner structure of stars, to set a lower limit to the age of the universe and to search for Exoplanets. The project MOST consists of a Low Earth Orbiting (LEO) Satellite and three Ground Stations, one of them in Vienna [1]. The Vienna ground station was set up at the Institute for Astronomy of the University of Vienna in cooperation with the Institute of Communications and Radio-Frequency Engineering of the Vienna University of Technology. The satellite link operates full duplex at the 2GHz band. This paper presents the methodology and the experiment for checking an eventual desensibilization of the receiving system caused by the presence of the permanent uplink signal.

Since two decades the microsatellites in Low Earth Orbits (LEO) are in use. Low Earth Orbit satellites are used for public and massive communication and for scientific purposes, also. Low Earth Orbits vary with the type of satellites and their primarily purposes. Low Earth Orbit scientific satellites have very wide application, including Earth’ s surveillance and astronomy applications. These satellites provide opportunity for investigations for which existing techniques are either difficult or impossible to be applied. Thus, it is to be expected that such missions in the near future will be more developed especially in the fields where similar experiments can not be done by means on the Earth. So, also the ground stations have to be established in order to communicate with such satellites. The quality of communication depends on the performance of the satellite ground station, also. Before the implementation of the ground station the analyses related to environmental factors have to be considered, especially in urban areas. Rain effects, intermodulation products disturbance, contact time duration at low elevation, are few aspects which are considered in this work related to final decision on design of the ground station. The performance measurement of the ground station based on Sun flux density is described as an experimental method which provides opportunity to check the performance of the ground station.

Low Earth Orbit (LEO) satellites are used for public communication and for scientific purposes. Low Earth Orbit scientific satellites have very wide applications, including Earth’ s surveillance, also. Usually these scientific satellites communicate with ground stations at S - band. During the link budget calculations atmospheric attenuation has to be considered. On this band the ionosphere effects are negligible. Thus, on these papers is presented the methodology applied for rain attenuation as the most important atmospheric factor on determining system reliability. It is presented the modelling method for calculations accompanied with results of some cities in Europe. S - band frequencies are considered.

The project "MOST" (micro variability and oscillations of stars) is a Canadian micro satellite space telescope mission. The micro satellite carries a Rumak-Maksutov telescope with an aperture of 15 cm. The size of the satellite is 65 cm times 65 cm times 30 cm and the mass is about 65 kg. The goals of the mission are to analyze the inner structure of stars, set a lower limit to the age of the universe and to search for exoplanets. The project MOST consists of a low earth orbiting (LEO) Satellite and three ground stations, one of them in Vienna. The satellite link operates on 2 GHz band. The separate antennas are used for uplink and downlink in order to achieve better downlink margin. The isolation measurement between uplink and downlink antennas is presented.

The project “ MOST” (Micro variability and Oscillations of Stars) is a Canadian micro satellite space telescope mission. The micro satellite carries a Rumak-Maksutov telescope with an aperture of 15cm. The size of the satellite is 65cm x 65cm x 30cm and the mass is about 65kg. The goals of the mission are to analyze the inner structure of stars, set a lower limit to the age of the universe and to search for Exoplanets. The project MOST consists of a Low Earth Orbiting (LEO) Satellite and three Ground Stations, one of them in Vienna. The satellite link operates on 2GHz band. The separate antennas are used for uplink and downlink in order to achieve better downlink margin.The isolation measurement between uplink and downlink antennas is presented.

Communication via satellite begins when the satellite is positioned in the desired orbital position. The satellite’ s coverage area on the Earth depends on orbital parameters. Ground stations can communicate with LEO (Low Earth Orbiting) satellites only when the satellite is in their visibility region. The duration of the visibility and so the communication duration varies for each satellite pass at the ground station. For low cost LEO satellite ground stations in urban environment it will be a big challenge to ensure communication down to the horizon. The communication at low elevation angles can be hindered through natural barriers or will be interfered by man made noise. This paper discusses the variations of the communication duration between the ground station and LEO satellites and investigates if it is useful to support low elevation passes. For this paper data recorded at the Vienna satellite ground station within the Canadian space observation project “ MOST” (Micro variability and Oscillations of Stars) are applied.

Noise introduces a fundamental limit on the performance of any communication system. Satellite communication systems are particularly susceptible to noise because of their inherent low received power. During the link budget calculations, noises of the equipment and line loss have to be considered. An alternative, but equivalent way of expressing the noisiness of the equipment and line loss is through noise temperature. The noise temperature which represents noise of all components in satellite receiving system chain is called composite noise temperature. Thus, on this paper the methodology applied for composite noise temperature caculations for satellite links is presented. In order to illustrate these calculations, data of Vienna ground station within MOST project are applied. The project MOST (Microvariability and Oscillations of Stars) is a Canadian micro satellite space telescope mission. The project MOST consists of a Low Earth Orbiting (LEO) Satellite and three ground stations, one of them in Vienna. The Vienna ground station system was set up at the Institute for Astronomy of the University of Vienna in cooperation with the Institute of Communications and Radio-Frequency Engineering of the Vienna University of Technology. The satellite link operates on 2GHz band [1].

The project "MOST" (Microvariability and Oscillations of Stars) is a Canadian micro satellite space telescope mission. The micro satellite carries a Rumak-Maksutov telescope with an aperture of 15 cm. The size of the satellite is 65 cm times 65 cm times 30 cm and the mass is about 65 kg. The goals of the mission are to analyze the inner structure of stars, set a lower limit to the age of the universe and to search for Exoplanets. The project MOST consists of a low Earth orbiting (LEO) Satellite and three ground stations, one of them in Vienna (W. Weiss and W. Keim, 2003). The Vienna ground station system was set up at the Institute for Astronomy of the University of Vienna in cooperation with the Institute of Communications and Radio-Frequency Engineering of the Vienna University of Technology. The ground satellite station in Vienna is installed in urban area with high penetration of GSM 1800 mobile systems. This paper presents the investigations related to the possibility of disturbances by the intermodulation factors generated by uplink signal and GSM 1800 mobile signals

The project "MOST" (microvariability and oscillations of stars) is a Canadian micro satellite space telescope mission. The micro satellite carries a Rumak-Maksutov telescope with an aperture of 15 cm. The size of the satellite is 65 cm times 65 cm times 30 cm and the mass is about 65 kg. The goals of the mission are to analyze the inner structure of stars, set a lower limit to the age of the universe and to search for Exoplanets. The project MOST consists of a low earth orbiting (LEO) satellite and three ground stations, one of them in Vienna [W. Weiss et al., 2003]. The Vienna ground station system was set up at the Institute for Astronomy of the University of Vienna in cooperation with the Institute of Communications and Radio-Frequency Engineering of the Vienna University of Technology. The downlink budget calculations are done for the worst propagation conditions. Among measurements related to the performance it is finally measured the figure of merit (G/Ts ) of the receiving system based on the sun flux density method