Exploiting Rate Diversity for Multicasting in Multi-Radio Wireless Mesh Networks

A multi-rate capable IEEE 802.11a/b/g node can utilize different link-layer transmission rates. Interestingly, multi-rate capability is defined by IEEE802.11 standards only for unicast transmissions. In this paper, we consider a novel type of multi-radio multi-channel wireless mesh network (WMN) where a radio can multicast at different link-layer transmission rates to its neighbors. Such link-layer multi-rate multicast capability will enable low-latency network-layer broadcast/multicast for multimedia. In our previous work, we assumed a "fully multi-rate multicast" (EMM) framework in which nodes can adjust link-layer multicast transmission rate for each link-layer frame. We propose a new framework called "single best-rate multicast" (SBM) that exploits the link-layer rate diversity by enabling each WMN to decide, depending on its topological properties, a single transmission rate for all its link-layer data multicasts. Although, EMM improves performance significantly, employing SBM is attractive since it can eliminate some undesirable features of practical multi-rate media access control (MAC) protocols. We propose methods to determine the "best" link-layer transmission rate for the SBM framework. We also propose two heuristic broadcast solutions, using SBM framework that can realize low-latency broadcast by exploiting inherent rate and interface diversity in multi-radio multi-channel WMN. Simulation results indicate that SBM broadcast heuristics give comparable performance to EMM broadcast heuristics, especially in dense networks