Optimal relay deployment for multihop multicast scheduling in cellular wireless networks

Efficient multicasting of critical messages is of essential importance in public safety and commercial multimedia cellular networks. We study the effectiveness of using relay station nodes to enhance the spectral efficiency of multicast distribution under full coverage in a mobile wireless networks. Coloring oriented adaptive rate scheduling algorithms are considered, including such that temporally employ TDMA schedules with reuse levels of 1, 3, 4 and 7 over a cellular arrangement. These schemes are used to regulate multicast transmissions executed by base station and (when employed) relay station nodes. We examine the utility of using, in each cell, a single layer of placed three and six relay station (RS) nodes. We examine the optimal locations at which such RS nodes should be placed under symmetric deployment in each cell. Base stations coordinate the scheduling of base station (BS) and RS nodal transmissions by employing two-phase reuse schemes. We show that when the inter-site distance (ISD), identifying the range between BSs, is lower than certain threshold levels, it is most effective to employ a reuse-3 scheduling scheme that is based on direct (1-hop) multicast transmissions by base station (BS) nodes to associated mobile station (MS) clients. In turn, under longer ISD ranges (e.g., as employed in less dense cellular layouts), the spectral efficiency of the system can be significantly enhanced by using a joint scheduling and routing scheme that makes use of a relay aided two-hop coverage operation. We also show that it is then more effective to deploy in each cell 3 rather than 6 RS nodes.