The growing interest in High-Density Fixed Service Satellite systems (HDFSS) has led to studies at the International Telecommunication Union (ITU) aiming the development of a recommendation for guidance on its implementation in order to minimize interference affecting other telecommunications services. Such systems are of interest due to their flexibility in the ubiquitous deployment of small terminals, Without the need for coordination. In order to regulate the implementation of such systems, the Study Group 4 of the ITU Radiocommunication Sector, responsible for the fixed-satellite service, has developed and suggested studies aimed at creating a recommendation containing methodologies for frequency sharing involving earth stations (terminals) ubiquitously distributed. Thus, in 2003, at the World Radiocommunication Conference of the ITU, specific frequency bands for HDFSS systems operation have been addressed, and most of the frequency bands identified are shared, on a primary basis, With the terrestrial fixed service systems (FS) and, for this reason, such studies for regulation and control of this share has become important. The ITU main motivation for these studies is the analysis of the interference caused by the HDFSS systems deployed in a country, into the communication sevices of neighboring countries. In this scenario, this paper proposes a methodology for evaluating interference produced by a ubiquitously distributed terminals into FS systems. This method aims at determining a coordination region, thus enabling terminals to be freely deployed outside this region, without producing unacceptable levels of interference into the FS receivers.