One of the most important features in 5G cellular communications is the super high bandwidth efficiency (BWE bps/Hz). The talk first presents how BWE increases from SU SISO (1-2G), to MIMO (3-4G) and to MU MIMO (4-5G). Then it explains how MU MIMO allows multiple users to communicate at the same time and in the same bandwidth using the subspace method. The DL transmits in the null space (NS) of its interference space and UL receives in the left NS of its interference space, so that there are no MU interference for both DL and UL. Since the dim of the NS for transmitting and receiving, which determines the number of the allowable data streams for each user, is determined by the number of transmit antennas at the BS, this method is practical. Then the talk presents simulation results on the performance and capacity of this subspace MU MIMO. The talk also compares this subspace MU MIMO with the massive antenna MU MIMO (proposed into 5G cellular standard) in terms of the performance and complexity. Finally the talk gives an example on how to upgrade the data rate of 300Mbps for the LTE system to 5G data rate of 10Gbps using the presented MU MIMO method without changing the LTE cellular infrastructure.