Degrees of freedom in the MISO BC with delayed-CSIT and finite coherence time: a simple optimal scheme

We consider the multi-input single-output (MISO) Broadcast Channel (BC), the multi-user (MU) downlink in a cell with a multi-antenna base station and mobile terminals equipped with a single antenna. Most techniques designed for this channel require accurate current channel state information at the transmitter (CSIT). However, a radically different approach has been proposed by Maddah-Ali and Tse (MAT), in which significant gain can be obtained by solely relying on perfect but outdated CSIT. This approach is proven to yield the optimal multiplexing gain when the channel current state is completely independent of the fed back channel state. A recent work focused on an intermediate case, channels exhibiting some temporal correlation, proposed a complex scheme shown to be optimal in terms of multiplexing gain for the 2-user case. Using a different but equivalent channel model, we propose a simple transmission scheme for the general case K ∈ N that reaches the optimal number of degrees of freedom.