Multicast in Terrestrial-HAP Systems: “User Number” vs. “User Distribution” oriented RRM Policies

The focus of this paper is on the integration of High Altitude Platforms (HAPS) into a terrestrial UMTS system to effectively support MBMS applications. Its main objective is the efficient allocation of transmission resources to multicast traffic streams (by suitably selecting terrestrial and/or HAP channels) while still preserving the desired Grade of Service of background unicast traffic. Specifically, we compare two different approaches to the Radio Resource Management (RRM) in the depicted scenario: the first one takes into account the Number of users in each multicast group to drive the RRM policies; while the second one bases the RRM behavior on the Distribution of users belonging to each multicast group. By conducting a thorough investigation, the performance trade-off between "User Number oriented" vs. "User Distribution oriented" solutions is evaluated. The different conditions under which one approach outperforms the other are investigated and the degree of performance augmentation is always highlighted.