Optimal DoF Region of the $K$ -User MISO BC With Partial CSIT

Abstract

We consider the $K$ -user multiple-input-single-output broadcast channel, where the transmitter, equipped with $M$ antennas, serves $K$ users, with $K \leq M$ . The transmitter has access to a partial channel state information of the users. This is modeled by letting the variance of the channel state information at the transmitter error of user $i$ scale as $O(P^{-\alpha _{i}}$ ) for the signal-to-noise ratio $P$ and some constant $\alpha _{i} \geq 0$ . In this letter, we derive the optimal degrees-of-freedom region in such setting, and we show that rate-splitting is the key scheme to achieve such a region.