DoF analysis of the K-user MISO broadcast channel with hybrid CSIT
/ Authors
/ Abstract
We consider a K-user multiple-input single-output (MISO) broadcast channel (BC) where the channel state information (CSI) of user i(i = 1, 2, ..., K) may be either instantaneously perfect (P), delayed (D) or not known (N) at the transmitter with probabilities λ<sub>P</sub><sup>i</sup>, λ<sub>D</sub><sup>i</sup> and λ<sub>N</sub><sup>i</sup>, respectively. In this setting, according to the three possible CSIT for each user, knowledge of the joint CSIT of the K users could have at most 3<sup>K</sup> states. Although the results by Tandon et al. show that for the symmetric two user MISO BC (i.e., λ<sub>Q</sub><sup>i</sup> = λ<sub>Q</sub>, ∀<sub>i</sub> ∈ {1, 2}, Q ∈ {P, D, N}), the Degrees of Freedom (DoF) region depends only on the marginal probabilities, we show that this interesting result does not hold in general when K ≥ 3. In other words, the DoF region is a function of all the joint probabilities. In this paper, given the marginal probabilities of CSIT, we derive an outer bound for the DoF region of the K-user MISO BC. Subsequently, we investigate the achievability of the outer bound in some scenarios. Finally, we show the dependence of the DoF region on the joint probabilities.
Journal: 2015 IEEE International Conference on Communications (ICC)