Distributed Opportunistic Scheduling in IEEE 802.11 WLANs

摘要

Opportunistic scheduling monitors the receivers' channel states and schedules packets to the receivers in relatively good channel conditions. Opportunistic scheduling can be easily implemented in cellular networks such as the lxEVDO system because the channel state report function is embedded in the system. To apply opportunistic scheduling to WLANs, deficient of channel report functions, we first devise efficient channel probing mechanisms. Several opportunistic scheduling methods for WLANs have been proposed recently. These previous methods limit the candidate receivers and may not fully realize the potential multiuser diversity gains. In this paper, we develop new opportunistic scheduling called WDOS (Wireless LAN Distributed Opportunistic Scheduling). That is based on a modified RTS/CTS exchange scheme. In WDOS, a sender broadcasts a BRTS (Broadcast RTS) to all receivers. A receiver responds with a CTS after a backoff delay. The value of the backoff delay is determined such that the receivers in relatively better channel conditions acquire channel accesses. We evaluate the performance of WDOS both via an analytic method and via computer simulations. Our performance study shows that WDOS achieves the performance near optimal.