Dependence of adaptive beamforming performance on directional channel modelled micro-cell scenarios

A beamforming algorithm, the conjugate gradient, is applied to a base station array, in the uplink, for UTRA-TDD. Street-type, micro-cell propagation scenarios are considered, using a wideband directional channel model. Groups of mobile users are placed at different distances from the base station, along the street axis. The average beamforming gain is analysed, varying the number of array elements, the distance of users from the base station, their number and grouping. The desired signal and interference-plus-noise powers evolve differently towards optimisation, due to the composition of the correlation matrix and the algorithm´s cost function. Allied to the high number of arriving correlated signals, this implies that a solution other than the MMSE one can lead to better interference suppression, for the tested scenarios. Among the tested scenarios, their influence highly depends on the number of users and their distances to the base station, the time-of-arrival spread overruling the importance of angle-of-arrival spread for larger numbers of users, closer to the base station, e.g., from 4 to 16 mobile users at 50 m or 1000 m from the base station, the beamforming gain can be degraded by nearly 4 dB or 2.3 dB, respectively, for 12 array elements.