The effect of open-loop power control margin on the pole capacity of WCDMA geosynchronous satellite systems

WCDMA geosynchronous satellite systems have been proposed for both military and commercial applications. In particular, the US Government is developing the Mobile User Objective System (MUOS) and plans to begin operations toward the end of the decade. As a WCDMA system, MUOS must employ user transmit power control. User power control begins in an open-loop state prior to the receipt of any feedback from the base station that improves the power control estimates. Power control attempts to minimize transmitted power while achieving the required QoS. Due to the longer path delays associated with a geosynchronous satellite, users will spend a longer time in an open-loop state. During this period, users must estimate the minimum power required to meet their QoS at the base station and add fixed margin to this estimate to overcome any uncertainties. This margin translates into added user transmit power and added interference (called mutual access interference or MAI) to other users. Added MAI reduces system capacity. This paper estimates the capacity reduction associated with increases in open-loop margin.