Capacity analysis of CDMA multibeam mobile satellite systems with imperfect power control

The capacity of a multibeam satellite mobile communications system employing code division multiple access (CDMA) communications is presented. An important problem in applying the CDMA scheme is unequal received power levels at the receiver. In a CDMA system, capacity is maximized when all transmitted user signals are received at the minimum power necessary to attain the specified signal power to interference and noise power ratio (SINR). Due to inherent long propagation delay, power control techniques cannot perfectly compensate the power fluctuations in mobile satellite channels. Consequently, the capacity of the system is reduced relative to system with perfect power control (PPC). This paper examines the performance of a multibeam satellite CDMA system using imperfect power control. Statistical characteristics (e.g. probability distribution function and cumulative distribution function) of mobile user bit energy to total interference ratios are obtained as a function of power control error and used for capacity calculations. The system capacity is calculated with a given outage probability and power control error (PCE).