This work 1  derives the optimal Degrees-of-Freedom (DoF) of the K-User MISO Broadcast Channel (BC) with delayed Channel-State Information at the Transmitter (CSIT) and with additional current noisy CSIT where the channel estimation error scales in P −α  for α ∈ [0, 1]. The optimal sum DoF takes the simple form (1 − α)K/H K  + αK where H K ≜ Σ k=1  K 1/k. This optimal performance is the result of a novel scheme which deviates from existing efforts as it digitally combines interference, decodes symbols of any order in the MAT alignment [1], and utilizes a hierarchical quantizer whose output is distributed across rounds in a way that minimizes unwanted interference. These jointly deliver, for the first time, the elusive DoF-optimal combining of MAT and ZF.
['Paul de Kerret', 'David Gesbert', 'Jingjing Zhang', 'Petros Elia']
Optimally bridging the gap from delayed to perfect CSIT in the K-user MISO BC