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The authors consider a MIMO fading broadcast channel where the fading channel coefficients are constant over time-frequency blocks that span a coherent time ? a coherence bandwidth. In closed-loop systems, Channel State Information at Transmitter (CSIT) is acquired by the downlink training sent by the base station and an explicit feedback from each user terminal. In open-loop systems, CSIT is obtained by exploiting uplink training and channel reciprocity. They use a tight closed-form lower bound on the ergodic achievable rate in the presence of CSIT errors in order to optimize the overall system throughput, by taking explicitly into account the overhead due to channel estimation and channel state feedback.
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