Abstract
Satellite communications were originally developed for military and scientific researches in 1960s. However, with more and more commercial and private demands in recent years, satellite communications are currently experiencing a surge of applications. Since GEO satellite systems have fixed position relative to ground station and are much simpler to operate than LEO satellite systems, the former were first commonly used in satellite communications. On account of the saturation of geostationary earth orbits and great progresses on the technologies of LEO satellite systems in 1990s, low earth orbits become new lands that many countries desire to grain over. Due to the rapid growth of wireless communications, the present frequency bands, such as C-band, K-band, Ku-band, etc., are crowded, so developing new frequency band, Ka-band, is necessary. In order to develop these emerging technologies, the first scientific satellite of Taiwain, ROCSAT-1, which incorporates ECP payload using Ka-band, has been launched on January 27th 1999. Though Ka-band has the advantages, such as wide bandwidth and smaller antenna compared with present frequency bands, the atmospheric propagation impairments seriously impact the performance of systems using Ka-band. To understand the propagation characteristics and make a reliable broadcasting experiment plan for ROCSAT-1, the characteristics of Ka-band are studied and a simulation channel model is established. For LEO satellites, systems at low elevation angle suffer not only large free space loss but also great tropospheric losses, especially in Ka-band channel, therefore a good FEC system is needed to alleviate the impacts on system performance. To find out which FEC system can meet our needs, different FEC systems are compared and another structure of concatenated system is also proposed to provide different error correcting levels. By the analysis of LEO satellites, Ka-band channel and FEC systems, we will have more understandings on the characteristics of ROCSAT-1 ECP system and both simulation results and broadcasting experiment plan will be presented.