Performance evaluation of downlink beamforming over non-stationary channels with interference

Interference is one of the major bottlenecks in current cellular networks. A realistic evaluation of the achievable performance in interference-limited systems based on measured channels is thus necessary; however, only few results are known from literature. We evaluate the achievable performance in a cellular network with inter-cell interference based on measured channels in an urban macrocell scenario at 2.53 GHz. To this end, the mutual information is introduced as an appropriate performance measure over fast and slow fading channels that are non-stationary but doubly underspread. We discuss appropriate channel normalizations and the limitations of an evaluation based on sequential measurements. Moreover, we analyze the accuracy of an approximate but commonly used evaluation of the mutual information. A second-order multivariate Taylor series expansion reveals the signal and interference contributions to the approximation error. We find that the approximation is accurate in realistic ICI scenarios.