Cross-layer packet scheduler design of a multibeam broadband satellite system with adaptive coding and modulation

This paper focuses on the broadcast channel of an interactive Multibeam Broadband Satellite (MBS) system with a transparent architecture. In particular, a cross-layer design is proposed for the packet scheduling on a forward link that implements Adaptive Coding and Modulation (ACM). A crosslayer approach is considered whereby the physical and Medium Access Control (MAC) layers share knowledge of the channel dynamics in presence of ACM. Transmission power and symbol rate are assumed to be constant, and hence the bit rate is time and space dependant according to the channel conditions. An architecture is proposed which relies on the physical characteristics of the Ka-band satellite propagation channel and the definition of "correlated areas". The stable throughput region has been derived assuming full-queue traffic conditions. Moreover, the proposed architecture is simple but flexible enough to allow the implementation of different scheduling policies like the proportionally fair or opportunistic ones. Finally, a new time-fair policy appropriate for wet seasons is proposed. It has the property of isolating users in clear-sky conditions from the effects of the reduced transmission rate experienced by users under a rain fade.