Comparing Downlink Coordinated Multi-Point Schemes with Imperfect Channel Knowledge

Several linear transmit precoding and receive combining strategies with and without base station cooperation are compared to each other. The impact on sum-rate performance is shown with varying number of transmit and receive antennas, with different amounts of training and with varying receive power levels of the cooperating set. This is done by simulations in a two-user two-cell scenario. The limited scenario size helps to carve out the crucial parameters and show their interrelation with imperfect channel knowledge (CSI). These CSI imperfections are emulated based on a novel model, introduced in this paper. We show that imperfect CSI drastically reduces the relative coordinated multi-point (CoMP) gains over non-coordinated systems. The non-coordinated systems can already perform quite well, when multi-antenna terminals apply interference suppression strategies. Our results motivate that CoMP systems need to be studied under critical system assumptions, taking into account non-idealities, as they have a severe impact on the observed gains.