he corresponding user links. This would benefit the users with better channel conditions, while there is no near-far problem in SU-MIMO systems. The near-far problem in MU-MIMO systems may be alleviated via appropriate grouping of the users with similar channel conditions. The use of cooperative collocated transmit antennas in SU-MIMO schemes can facilitate encoding at the transmitter and decoding at the receiver. In contract, the users in a MU-MIMO scheme can cooperate in encoding at the BS in the downlink and decoding in the uplink; however, the users cannot cooperate in decoding in the downlink or encoding in the uplink directions. The capacity of the downlink and uplink are theoretically identical in the downlink and uplink for SU-MIMO systems (given the same transmit power and perfect channel knowledge in the transmitter and the receiver); however, the capacity of the MU-MIMO broadcast channel and multiple access channel are not identical. The capacity of SU-MIMO schemes is less impacted by lack of channel state information at the transmitter, whereas the capacity of the MU-MIMO broadcast channel suffers significantly from lack of channel state information at the transmitter. An important metric for measuring the performance of any communication channel is the infor- mation theoretic capacity. In a single-user MIMO channel, the capacity is the maximum amount of information that can be transmitted as a function of available bandwidth given a constraint on transmitted power. In single-user MIMO channels, it is common to assume that the total power distributed among all transmit antennas is limited. For the multi-user MIMO channel, the problem is somewhat more complex. Given a constraint on the total transmit power, it is possible to allocate varying fractions of that power to different users in the network, thus for any value of total power, different information rates are obtained. The result is a capacity region shown in Figure 10-33 for a two-user MU-MIMO channel. The maximum capacity for user 1 is achieved