Two-stage DCF-based access scheme for throughput enhancement of OFDMA WLAN systems

In distributed coordination function-based (DCF-based) OFDMA WLANs, different sets of sub-channels are dynamically allocated to active stations and the transmission rate at physical layer is enhanced due to multi-user diversity gain. However, optimally allocating sub-channels to the stations requires excessive feedback of channel state information (CSI). With the increase of the number of stations, the signaling overhead severely degrades the throughput of OFDMA WLANs. To improve the throughput of OFDMA WLANs by reducing the signaling overhead while obtaining the multi-user diversity gain, this paper proposes a novel channel access scheme which enables two-stage DCF-based access. The key idea of the proposed scheme is to introduce an additional prioritized DCF-based access along with the traditional DCF-based random access. In the additional prioritized DCF-based access, by dynamically adjusting the contention window according to the CSI, the station having good channel state is prioritized to acquire the transmission opportunity. Since only the stations which have good channel state feedback their CSI in a fully distributed manner, the signaling overhead can be reduced. Numerical results confirm that the proposed scheme enhances the throughput of OFDMA WLANs.