Hybrid HAP-Satellite Architecture for Reliable Multicast Transmissions

In this paper we propose the use of high altitude platforms (HAPs) in conjunction with a geostationary (GEO) satellite system in order to enable a reliable provision of multicast services to fixed (or semi-fixed) users on the earth. An immediate advantage derives from the possibility to split the GEO-to-subscriber terminal link into two parts, i.e. link from the satellite to the HAP with prevalent free-space propagation path loss, and link from the HAP to the subscriber terminals with prevalent atmospheric losses. This solution entails both a shorter link that permits to implement easily the return channel from handheld (or in general single-user) terminals and local retransmissions (from HAP to subscriber terminals, thus avoiding the need to propagate the request up to the satellite ground station, i.e. the multicast source on the earth). In this framework the main focus of this paper is to compare some possible system configurations and to evaluate the resulting performance by means of simulations.