Evaluation of Frequency Sharing Scheme between Satellite and Terrestrial Links

Research and development activities have been implemented for the Satellite/Terrestrial Integrated Mobile Communication System (STICS) that enables mobile phones to seamlessly switch terrestrial communication links/satellite communication links. In STICS, through taking advantage of a large-antenna multi-beam satellite communication system, the satellite/terrestrial communications links are supposed to share frequency bandwidth. Such frequency sharing is accomplished in the following way: dividing the frequency bandwidth allocated to the system into sub-bands, allocating the sub-bands to the satellite cell, and also allowing the terrestrial links to use the same sub-bands in the circumference of the satellite cell. However, because the satellite antenna has sensitivities to areas outside the satellite cell, interference will occur between satellite links and terrestrial links. Furthermore, even inside the satellite cell, the terminals using the satellite communications links will receive interference from the terminals or base stations located outside the satellite cell. So, it is necessary to evaluate such interference and clarify the conditions for the frequency sharing. Therefore, National Institute of Information and Communications Technology (NICT), for the purpose of proving the feasibility of STICS’s frequency sharing method, conducted evaluations as follows: first, by applying a simple interference model, estimating the interference-levels along each of the interference paths to clarify the interference characteristics of each interference path and confirm the feasibility of the frequency sharing method; second, for the purpose of quantitatively ascertaining the upper-limit number of links that the system can accommodate under the satellite/terrestrial co-channel interference environment, making estimations on the number of simultaneously accommodated links for which the system can establish both its satellite communications link and a terrestrial communications link. For the estimation of such simultaneously accommodated links, NICT, newly developed a detailed interference model that can simulate the number and transmission power of terminals and ground stations as precisely as possible through accepting as the model parameters actual country-wide traffic distributions, and for the purpose of improving accuracy, applied statistical data that NICT had collected through cellular phone terminal transmission power observations in a variety of situations. Furthermore, as for base-station-to-satellite terminal interference, which is caused by a different mechanism from that of terrestrial-to-satellite interference, we made estimations on the base-station-to-satellite terminal separation distance that ensures the establishment of a link. In the following sections, we will introduce, in Section 2, the generalities of the satellite/terrestrial frequency sharing method and interference; in Section 3, the interference evaluations of each interference path using the simple interference model; in Section 4, the estimations of the number of simultaneously accommodated stations under co-channel interference environment; in Section 5, the evaluations of satellite terminal-to-base-station separation Evaluation of Frequency Sharing Scheme between Satellite and Terrestrial Links