On the impact of residual CFO in UL MU-MIMO

Uplink multiuser MIMO (UL MU-MIMO) is a new feature introduced in 802.11ax (currently under development). This paper investigates the residual carrier frequency offset (CFO) impact on the performance of UL MU-MIMO OFDM systems. We show that if a station (STA) has zero residual CFO, then its packet error rate (PER) will not suffer from other STAs that have residual CFO when a zero-forcing (ZF) or linear minimum mean squared error (LMMSE) MIMO receiver is used at the access point (AP). To reduce the impacts of residual CFO on system PER performance, two CFO correction methods are designed to compensate for the phase shift and cancel the inter-user interference caused by the residual CFO. Several simulation examples are provided to verify the results.