The increasing demand of various wireless and satellite services invokes lack of the orbit and frequency resources, and thus most of the cases, satellite systems have to share the same frequency bands with other radio systems, at the expense of severe interference problem. International Telecommunication Union (ITU), the United Nations specialized agency for information and communication technologies, decided for ITU members to conduct studies for additional frequency allocation to the fixed and mobile satellite services under agenda items of the World Radiocommunication Conference 2015.
Under the current spectrum usage situation, the additional frequency allocation for the satellite system should be always accompanied by frequency sharing with existing radio services. Therefore, suitable frequency sharing criteria should be developed for compatibility between new allocation and existing services by means of assessing the radio interference in the frequency sharing situation.
Most of the previous studies on interference analysis on the satellite communication system with other radio stations have conducted by assessing the interference levels in point-to-point paths. Those research results can be used to estimate the impact of the interference from an interferer station to an interfered station, but they can hardly provide any suitable way to overcome the problems caused by interference. In addition, the study results did not properly reflect the ITU Radiocommunication Sector (ITU-R) Radio Regulations which need to be considered most importantly as an international law, so there are some differences between current studies and practical deployment of the satellite system.
This thesis presents two efficient means for frequency sharing between the satellite and other radio services. The first method is using suitable separation distance. In this research, the optimum separation distance is estimated by considering interference scenarios for a number of practical system implementation cases. In the interference assessment process, all the necessary regulations as well as technical requirements are properly considered, and thus they can provide high reliability. Through the simulation for assessing the interference scenario between Fixed Satellite Services (FSS) and Fixed Services (FS) in the Ka band, the study results reveal that a separation distance of 20 km would be required for frequency sharing for two radio services.
As a second method for efficient frequency sharing, a sub-band allocation method for multi-beam satellite system is proposed. In the case that there are multiple terrestrial radio stations in the service coverage of a multi-beam satellite system, it is presented that the radio interference would be mitigated by proper allocation of sub-sectionalized frequency bands to the radio stations depending on the locations. The simulation results show that the radio interference from the Earth stations to the terrestrial system would be decreased by dozens of dBW by utilizing the proposed mitigation technique. Considering that most of the satellite systems will be implemented with multi-beam antennas in the future, the proposed interference mitigation technique will play an important role to increase satellite spectrum efficiency.