Design alternatives for a reliable multicast service in a hybrid HAP-satellite network architecture

One interesting application for future broadband wireless telecommunication systems is represented by multicast and broadcast services that have unique characteristics with respect to point-to-point transmissions. The focus of this paper is on a multicast protocol for the reliable delivery of huge amount of data to a wide multitude of users on the earth. In particular, we propose a novel architecture characterized by the introduction of an intermediate communication segment between a geostationary satellite and user terminals. Such a segment is based on High Altitude Platforms (HAPs), which can have different roles for what concerns transport level functionalities. In particular, we will consider HAPs with or without multicast protocol support. Moreover, in order to assure reliability, we will use transport level coding to protect the transmitted files, and local retransmissions performed by HAPs, thus entailing a shorter delay. Three different scenarios are compared, where HAPs have an increasing role in managing multicast traffic. A simulator has been developed in the ns-2 environment, and the obtained results have proven that the combined effect of data coding applied at the transport layer, together with local retransmissions performed by HAPs, permits to achieve both high efficiency in utilizing air interface resources and low delays in transferring data, in a reliable way.