Training and feedback optimization for multiuser MIMO downlink

Mari Kobayashi, Nihar Jindal, Giuseppe Caire

Research output: Contribution to journalArticlepeer-review

117 Scopus citations


We 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. We use closed-form lower bounds and tight approximations of 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. Based on three time-frequency block models inspired by actual systems, we provide useful guidelines for the overall system optimization. In particular, digital (quantized) feedback is found to offer a substantial advantage over analog (unquantized) feedback.

Original languageEnglish
Article number5773636
Pages (from-to)2228-2240
Number of pages13
JournalIEEE Transactions on Communications
Issue number8
StatePublished - Aug 2011
Externally publishedYes


  • Channel estimation
  • MIMO broadcast channel
  • channel etate information feedback
  • multiuser MIMO downlink


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