RAMCAST: Reliable and Adaptive Multicast Over IEEE 802.11n WLANs

Abstract

Wireless multicast over IEEE 802.11 WLANs suffers from two well-known problems: poor reliability and low spectral efficiency. To overcome these problems, we propose a novel PHY/MAC cross-layer wireless multicast scheme called reliable and adaptive multicast (RAMCAST). By considering the frame aggregation of IEEE 802.11n, RAMCAST enables an access point (AP) to selectively retransmit erroneous multicast frames and to dynamically adjust modulation and coding scheme under varying channel conditions. In particular, empowered by the orthogonality of subcarriers in the OFDM symbol, RAMCAST enables multiple multicast clients to transmit feedback to the AP simultaneously without collision, resulting in very low feedback overhead. We verified the feasibility of RAMCAST through USRP/GNU radio-based experiments and conducted an extensive simulation study using ns-2, and we found that RAMCAST outperforms the state-of-the-art wireless multicast scheme.