Efficient Frame Construction for Multi-User Transmission in IEEE 802.11 WLANs

The latest standard of IEEE 802.11 WLANs embraces multi-user (MU) transmission via orthogonal frequency-division multiple access (OFDMA), multi-user multiple-input and multiple-output (MU-MIMO), or a mixture of both. However, due to the frame-basis transmission of WLANs, all concurrent user frames must have an identical transmission duration so as to fit in a common MU frame, which requires shorter frames padded with dummy bits, thus reducing transmission efficiency. Since stations are likely to have heterogeneous traffic demands and transmission bit rates in real networks, such inefficiency arises as a practical problem. To address this challenge, first we analyze how different overhead components impact the efficiency of MU transmission. Then, we propose a scheme to construct an MU frame with an optimal length maximizing its transmission efficiency, which provides a unified framework for OFDMA and MU-MIMO in both downlink and uplink. Through simulation, we demonstrate that the proposed scheme integrated with various scheduling algorithms reduces transmission delay and enhances traffic delivery ratio considerably compared to basic approaches.