Hybrid OFDMA and CSMA/CA-Based Transmission Strategy for Providing High Throughput and Low Delay in IEEE 802.11ax Wireless LANs

抄録

Currently, the number of wireless stations (STAs) connected to a wireless local area network (WLAN) is constantly increasing, and the quality of service (QoS) requirements of the transferred data are diverse. Even in such congested WLAN environments, it is necessary to assign sufficient frame transmission opportunities to each STA and base station (BS) according to the QoS requirements of the transferred data. IEEE 802.11ax introduces simultaneous transmission of multiple frames by orthogonal frequency division multiple access (OFDMA) for efficiently accommodating more STAs in a WLAN. For backward compatibility, OFDMA transmission in IEEE 802.11ax is used in cooperation with carrier sense multiple access with collision avoidance (CSMA/CA). However, when to trigger OFDMA transmission and which frames to transmit simultaneously are not specified in the standard. In this paper, we propose a frame transmission method that selectively uses OFDMA transmission and CSMA/CA-based transmission, taking into account both the characteristics of the two types of transmissions and the QoS requirements of the transferred data. In this method, to take full advantage of simultaneous transmission of multiple frames, OFDMA transmission is performed after more OFDMA-transmittable frames are buffered at the BS or STAs by applying transmission waiting processes to frames of data that requires minimizing the time for transferring the entire data. By contrast, frames of data that requires minimizing the transfer delay on a frame-by-frame basis are transmitted based on CSMA/CA without applying the transmission waiting process. Our extensive simulations show that the proposed method enhances data transfer throughput by effectively transmitting more frames by OFDMA and suppresses the increase of data frame transfer delay until more data transfer load.