Efficient multicast in hybrid wireless networks

The increasing popularity of smartphones and other similar multi-modal wireless devices has created an opportunity for the realization of large-scale hybrid (or heterogeneous) networks. Typically, modern mobile devices are likely to support a short range communication interface (e.g. IEEE 802.11/WiFi) and/or a longer range communication interface (e.g. cellular data link wireless technology). Multi-hop wireless networking over WiFi can help to extend the range of cellular networks in low SINR regions as well as to alleviate network congestion. Conversely, equipping a few nodes in a mobile ad hoc network (MANET) with cellular radios can help to heal wireless network partitions and, thus, to improve the overall network connectivity. One can envision large scale group communication (or multicast) applications including real-time video conferencing (e.g., iPhone FaceTime), P2P video and file sharing, and voice call groups in disaster relief and military hybrid networks. In this paper, the problem of resource-efficient multicast in hybrid wireless networks which include both point-to-point (cellular) and broadcast (MANET) links is considered. The underlying optimization problem is a hybrid of two well-known NP-hard graph optimization problems-the Minimum Steiner Tree problem (for point-to-point links) and the Minimum Steiner Connected Dominating Set problem (for broadcast links). We consider both edge- and node-weighted versions of this problem and use distinctly different methodologies to give three algorithms with guaranteed approximation factors. We further demonstrate by means of simulation modeling of standard deployment scenarios that while one algorithm outperforms another in terms of the tree cost, the latter outperforms the former in terms of complexity and other practical considerations.