IEEE 802.11ax: Effects of IQ Mismatching on the Performance of Uplink Multi-User MIMO

The exponential increase of data and video uplink (UL) traffic from small form devices has driven intensive research activities on both UL multi-user multiple-input multiple-output (UL MU-MIMO) and UL orthogonal frequency division multiple access (UL OFDMA) techniques in the IEEE Task Group (TG) 802.11ax, which is developing the sixth generation of wireless local area networks (WLANs). The effects of IQ imbalance on the performance of IEEE 802.11ax UL MU-MIMO physical layer (PHY) are investigated in this paper. Preliminary results that have been presented in TG 802.11ax meetings show that chip sets with single-side band suppression of -40 dBc allow that the UL MU-MIMO PHY can operate with power unbalancing among the clients as high as 18 dB and 6 dB for BPSK and 64-QAM signaling schemes, respectively, if perfect channel state information (CSI) is assumed. In this paper, we show that this statement can change dramatically if realistic CSI is assumed and, therefore, additional mitigation techniques are demanded to reduce substantially the non-linear effects of IQ imbalance on the IEEE 802.11ax UL MU-MIMO PHY.