Search

Low Earth Orbit (LEO) satellites are used for public networking and for scientific purposes. Established satellite 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 ground station on the Earth. Each ground station is characterized by its own ideal horizon plane. Because of natural barriers that plane is modified to the designed one, defined by minimal elevation, in order to avoid natural obstacles. Designed horizon plane implementation implies also the power saving from the satellite to be transmitted. 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 toward the downlink. In order to obtain the constant downlink margin at the receiver, all over the time, for analytical and simulation purposes, the altitudes from 600km to 1200km are considered. For each altitude it is calculated the power saving by designed horizon plane implementation compared the ideal horizon plane, for different altitudes.

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.

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.

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.

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.

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.

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