The Role of HAPs in Supporting Multimedia Broadcast and Multicast Services in Terrestrial-Satellite Integrated Systems

New-generation telecommunications systems are expected to meet the rising user exigencies of mobility and ubiquitous access to multimedia services. As a consequence, 3GPP consortium has introduced the Multimedia Broadcast and Multicast Service (MBMS) concept into 3G/beyond-3G networks. Supporting MBMS in next generation hybrid wireless platforms becomes a challenging issue due to high traffic load deriving from both signaling message exchange and data transmission between multicast sources (BM-SC) and end users. Therefore, in this context, key research issues are surely: effective exploitation of the limited radio spectrums available, coordination of users accessing radio resources, as well as provisioning of desired QoS guarantees. Given the high mobility profiles typical of UMTS users, it clearly appears that the cited target performance can only be achieved through networking solutions based on an overlapped terrestrial-HAP-satellite coverage. An inter-working scenario where HAPs operate in synergy with the UMTS terrestrial and satellite segments seems to be the most promising solution to provide mobile users with MBMS services. Our work, dealing with architectural design options, takes into account many metrics relevant to aspects, such as: frequency allocation, costs in terms of resource utilization, signaling traffic load, number and location of customers, reliability, possible retransmission paths, user mobility, and QoS.