A unified approach to the analytical assessment of multi‐user diversity with imperfect channel state information: ergodic capacity and robustness analysis

In this paper, we explore the combined use of spatial and multi‐user diversity (MUD) in a cellular system where the channel state information (CSI) available at the base station (BS) is subjected to imperfections. To do that, we consider a general statistical approach to describe the degree of CSI imperfection. By doing so, performance assessment is conducted for the generalised case in terms of ergodic system capacity, for which closed‐form expressions are derived. In order to gain some insight, practical examples are presented and spatial versus MUD trade‐offs are analytically assessed. Next, we analyse several design trade‐offs in terms of increased ergodic (long term) system capacity versus robustness to short‐term SNR fluctuations for the transmission schemes under consideration.