Performance evaluation of OFDMA and MU-MIMO in 802.11ax networks

Daldoul, Yousri; Meddour, Djamal-Eddine; Ksentini, Adlen
Computer Networks, Volume 182, 9 December 2020

IEEE 802.11ax defines a new access method called Orthogonal Frequency Division Multiple Access (OFDMA) which can be used in both downlink (DL) and uplink (UL) directions. OFDMA divides the bandwidth into several Resource Units (RUs) and allows multiple stations to transmit or to receive simultaneously. UL OFDMA supports Scheduled Access (SA) RUs and Random Access (RA) RUs. Only scheduled stations are allowed to send on SA RUs, while the other stations should contend for the RA RUs. Moreover, 802.11ax defines UL MU-MIMO and enhances DL  MU-MIMO. In  this  paper, we  introduce and  evaluate the  efficiency of  DL  and  UL  multi-user transmissions using OFDMA and MIMO. Our results show that UL OFDMA is particularly useful when multi-ple stations regularly need to transmit few MPDUs. In this case, UL OFDMA may outperform full bandwidth access with up to 400%. Moreover, we find that increasing the number of RA RUs does not effectively reduce the collision rate but significantly decreases the throughput. Furthermore, we show that UL MU-MIMO significantly improves the network throughput and that the performance of DL MU-MIMO is clearly enhanced thanks to the decreased duration of the channel sounding procedure.  

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