Analysis of mismatched downlink beamforming over non-stationary channels with interference

Inter-cell interference is the limiting factor in next generation cellular networks with frequency reuse factor 1. A promising approach to mitigate the effects of downlink interference is the use of transmit beamforming; however, only few measurement-based performance evaluations are currently available to assess realistic gains and limitations. We study the achievable performance of inter-cell interference-limited networks with single-user detection for slow and fast fading channels that are non-stationary but doubly underspread. The evaluation is based on channel measurements at 2.53 GHz in an urban macrocell scenario. Different beamforming techniques, a non-cooperative and two cooperative ones, are used and their robustness to the non-stationarity of the channel is evaluated. The cooperative techniques are found to be much less robust to the non-stationarity of the channel. Furthermore, an approximation of the mutual information is evaluated; it is more accurate for the cooperative techniques.