Position location for access policing of satellite systems for mobile communications

Interference and unauthorised use of satellite communications channels are becoming of increasing importance. Interference can arise from a variety of sources varying from local interference to downlinks to more widespread interference on satellite uplinks. The potential for damage from a single malfunctioning ground terminal interacting with other users of a satellite transponder is very large. Furthermore the transparent nature of most satellite channels renders them susceptible to unauthorised use. The paper assesses the applicability of a location technique based on multiple satellite time and frequency difference of arrival measurements as an access policing tool on satellite systems supporting mobile terminals. Particular attention is paid to shipborne terminals accessing the current INMARSAT system. Some attention is also paid to the future medium Earth orbit systems typified by ICO.