MARS: Link-layer rate selection for multicast transmissions in wireless mesh networks

IEEE 802.11 devices dynamically choose among different modulation schemes and bit-rates for frame transmissions. This rate adaptation, however, is restricted only to unicast frames. Multicast (and broadcast) frames are constrained to use a fixed low bit-rate modulation, resulting in low throughput for multicast streams. Availability of high bandwidth and efficient use of the medium is crucial to support multimedia multicast streaming applications such as IPTV, especially in multihop mesh networks. To address this problem, we propose a rate adaptation algorithm for multicast transmissions in these networks. The proposed algorithm, MARS, is distributed in nature, and relies on local network measurements to select a transmission bit-rate for a given multicast group. The algorithm also facilitates the joint use of bit-rate selection and link-layer mechanisms such as acknowledgements and retransmissions to improve reliability of high throughput multicast streams. Based on implementation and evaluation on a testbed, the algorithm provides up to 600% gain in throughput compared to traditional 802.11 networks in some scenarios. Additionally, the algorithm can support multicast streams while consuming a small fraction (20%) of the resources compared to the basic 802.11 operation.