Design issues and performance analysis of CDMA multi-beam satellites

The paper investigates the design issues of a multi-beam mobile satellite system employing CDMA and quantifies the system capacity in the presence of power control error and multiple access interference. In multi-beam mobile satellite CDMA systems, the interference characteristic is quite different from terrestrial systems and it is mainly characterized by a spotbeam antenna pattern. The other-cell (or beam) interference factor, which is defined as the interference power produced by users belonging to other beams divided by the interference power produced by interfering users in the considered beam, is much more critical for satellite systems. By taking this interference feature into account, we study the system capacity for different multi-beam system designs. Another important issue in applying the CDMA scheme is the problem of unequal received mobile user power levels at a satellite. The capacity of a CDMA system is maximized in the uplink channel when all user signals are received at equal power levels to obtain the specified signal-to-noise-plus-interference power ratio. Since power control techniques cannot perfectly compensate for power fluctuations in mobile satellite channels, the capacity of the system is reduced. We show that power control error with a standard deviation in the range of 1-2 dB would cause a dramatic capacity loss in comparison to perfectly power controlled systems.