I. INTRODUCTION
The commercial application of Mobile Satellite Systems iscontinuously growing for different type of services.
Typical applications include digital audio broadcast, mobile office, goods tracking and M2M communications.
In different regions of the world portions of the S-band spectrum have been allocated for MSS and in particular for hybrid systems combining a concurrent use of a space segment and Complementary Ground Components (CGC) to guarantee at
the same time wide area coverage and the continuity of service also in urban and shadowed areas.