Cross-layer Link Rate Adaptation for High Performance Multimedia Broadcast over WLANs

In an IEEE 802.11 wireless LAN, the access point transmits broadcast packets once at a fixed rate, often the lowest rate of the basic rate set, which results in low bandwidth efficiency and no reliability. This problem can be addressed by proper-designed cross application and MAC layer broadcast mechanisms, in which reliability is provided by application layer forward error corrections, and broadcast bandwidth efficiency is solved by broadcast link rate adaptations. In this work the broadcast link rate adaptation problem is formulated to a quadratic programming (QP) problem that aims at high bandwidth efficiency while trying to maintain relative service time fairness when different stations has different optimal broadcast receiving link rates. Accordingly, a cross-layer link adaptation protocol is proposed. In the proposed protocol, broadcast link rate is decided at the application layer by solving the QP problem and is adjusted by the MAC layer following the instruction from the application layer. Both analytical and simulation results show the proposed algorithm achieves significantly higher bandwidth efficiency while maintaining better relative service time fairness among stations, compared to fixed rate broadcasting.