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An Efficient Group-Based OFDMA MAC Protocol for Multiuser Access in Dense WLAN Systems

Existing medium access control (MAC) schemes for wireless local area network (WLAN) have been shown inefficient in dense user environment. Orthogonal frequency division multiple access (OFDMA) which enables multiuser simultaneously transmission is considered as one of the promising technologies to improve MAC efficiency for next generation WLAN. In this paper, an efficient group-based OFDMA (G- OFDMA) MAC protocol for multiuser access is proposed. In the proposed scheme, stations contend for channel resources by transmitting request-to- send (RTS) packets over a randomly selected sub- channel at one of the pre-defined RTS update intervals. Then, an algorithm jointing grouping and sub-channel allocation is proposed to group the stations that transmit RTS successfully and assign them to their favorable sub-channels. Simulation results show that for heavy user loaded WLANs, the proposed G-OFDMA achieves higher throughput than IEEE 802.11 distributed coordination function (DCF) and concurrent OFDMA- based CSMA/CA (C-OFDMA) MAC protocols.