Massive multi-user multiple-input multiple-output (MU-MIMO), in which access points (APs) with a lot of antennas transmit to a lot of stations (STAs) with a few antennas, is attractive for wireless LAN systems due to its potential to greatly increase throughput. However, the throughput improvement at media access control - service access point (MAC-SAP) in massive antenna systems is limited by the overhead imposed by channel state information (CSI) feedback. In this letter, we clarify the problem of CSI feedback and evaluate two frame sequences with implicit CSI feedback (ICF) for downlink (DL-) MU-MIMO systems. The use of ICF eliminates the overhead of CSI feedback because MU-MIMO precoding weight is generated from the uplink CSI using a calibation matrix that compensates the channel responce differences between the transmitter and the receiver. This letter validates the effectiveness of DL-MU-MIMO with ICF by a performance evaluation at MAS-SAP in a comparson with the conventional approach which needs CSI feedback.