A cross-layer approach to multi-user diversity in heterogeneous wireless systems

Research on multi-user diversity (MUD) is traditionally carried out from an information-theoretic point of view. Such information-theoretic approaches are feasible in homogeneous systems where all terminals use the same modulation, channel coding, transmission rate, and packet length. In homogeneous systems, the selection of the terminal with highest SNR leads to the highest system goodput. Unfortunately, in heterogeneous systems, choosing the user with highest SNR does not lead to highest system goodput in general. In this paper, we propose a crosslayer approach to the MUD scheduling problem in heterogeneous systems. More specifically, we propose using a maximum expected goodput criterion for MUD scheduling. Furthermore, contrary to the traditional approach where link adaptation is not considered in MUD scheduling studies, we combine MUD scheduling with a link adaptation strategy based on the same maximum expected goodput criterion. Such techniques are analyzed and simulated in a IEEE802.11e environment.