Two-user MISO broadcast channel: Synergistic benefits of alternating CSIT

The degrees of freedom (DoF) of the two-user multiple-input single-output (MISO) broadcast channel (BC) are studied under the assumption that the form, I_i, i = 1, 2, of the channel state information at the transmitter (CSIT) for each user´s channel can be either perfect (P), delayed (D) or not available (N), i.e., I₁, I₂ ϵ {P, N, D}, and therefore the overall CSIT can alternate between the 9 resulting states I₁I₂. The fraction of time associated with CSIT state I₁I₂ is denoted by the parameter λI₁I₂ and it is assumed throughout that λI₁I₂ = λI₂I₁, i.e., λ_PN = λ_NP, λ_PD = λ_DP, λ_DN = λ_ND. Under this assumption of symmetry, the main contribution of this paper is a complete characterization of the DoF region of the two user MISO BC with alternating CSIT. The results highlight the synergistic benefits of alternating CSIT and the tradeoffs between various forms of CSIT for any given DoF value.