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For broadcast channels (BC) in multiuser multiple-input multiple-output (MU-MIMO) systems, the overall achievable performance depends on the efficient use of the resources at the base station (BS). When channel state information (CSI) is known at the transmitter the gain is twofold: full spatial degrees of freedom can be attained [1] and the system can be optimized over a new degree of freedom given by the users. In the literature of MU-MIMO systems two dimensions of optimization are studied: multiplexing diversity and multiuser diversity (MUD). The former is a consequence of the independent fading across all MIMO links, which yields a set of parallel spatial channels where different data streams can be transmitted increasing the system capacity [2]. The latter is given when users that are geographically far apart have channels that fade independently at any point in time. For the system sum rate maximization, such independent fading process is exploited so that the user with the largest channel magnitude will be selected for transmission. In MU-MIMO systems spatial and temporal communication can be performed in two ways: 1) orthogonal multiple access (time, frequency, or code) and 2) spatial-division multiple access (SDMA). To achieve orthogonality in time, all the spatial resources at the BS (N t antennas) are used to communicate with one user (Nr antennas) at a time, which is known also as time-division multiple access (TDMA). This technique avoids inter-user interference, achieves power gains that scale with N t , enhances data rates for a single user specially at low signal-to-noise ratio (SNR) regime, and is robust to CSI uncertainty [1], [3]. SDMA exploits CSI at the BS allowing K >1 users to be scheduled at the same time achieving multiplexing gains of min(N t , K Nr) at high SNR regime, where the system is limited by the degrees of freedom and not by power. Since the BS has knowledge of the data symbols and CSI, the multiuser transmission can be optimized using coding techniques. The achievable rate region in BC is based on dirty paper coding (DPC) [4].

User Selection and Precoding Techniques for Rate Maximization in Broadcast MISO Systems