MISO broadcast channel with hybrid CSIT: Beyond two users

Sina Lashgari, Ravi Tandon, Salman Avestimehr

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We study the impact of heterogeneity of channel-state-information available at the transmitters (CSIT) on the capacity of broadcast channels with a multiple-antenna transmitter and k single-antenna receivers (MISO BC). In particular, we consider the k -user MISO BC, where the CSIT with respect to each receiver can be either instantaneous/perfect, delayed, or not available; and we study the impact of this heterogeneity of CSIT on the degrees-of-freedom (DoFs) of such network. We first focus on the three-user MISO BC, and we completely characterize the DoF region for all possible heterogeneous CSIT configurations, assuming linear encoding strategies at the transmitters. The result shows that the state-of-the-art achievable schemes in the literature are indeed sum-DoF optimal, when restricted to linear encoding schemes. To prove the result, we develop a novel bound, called interference decomposition bound, which provides a lower bound on the interference dimension at a receiver which supplies delayed CSIT based on the average dimension of constituents of that interference, thereby decomposing the interference into its individual components. Furthermore, we extend our outer bound on the DoF region to the general k -user MISO BC, and demonstrate that it leads to an approximate characterization of linear sum-DoF to within an additive gap of 0.5 for a broad range of CSIT configurations. Moreover, for the special case where only one receiver supplies delayed CSIT, we completely characterize the linear sum-DoF.

Original languageEnglish (US)
Article number7587353
Pages (from-to)7056-7077
Number of pages22
JournalIEEE Transactions on Information Theory
Issue number12
StatePublished - Dec 2016


  • Broadcast channel
  • Gaussian channels
  • channel state information
  • interference networks
  • linear degrees of freedom
  • time varying channels

ASJC Scopus subject areas

  • Information Systems
  • Computer Science Applications
  • Library and Information Sciences


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