Fundamental wideband and directional channel parameters ruling adaptive beamforming performance in micro- and macro-cells

Propagation channels for micro- and macro-cells are analysed and compared, the channel richness parameter being defined, based on the angular and temporal densities of arriving signals. These quantities and the background reasoning are also shown to consistently relate to the respective array spatial correlation coefficients, all reflecting the available channel multipath richness, the consequent beamforming freedom and final performance. Conclusions are then drawn on the channel constraints that physically condition the placement of lobes and nulls, finally rendering most general fundamental conclusions. Channel richness results agree with the previously reported performance dependencies, generally being more than an order of magnitude larger in micro- than in macro-cells. Such difference has strong implications, e.g., in the case of terminal grouping, beamforming gains being limited to close to 0 dB, in macro-cells, whereas in micro-cells these reach up to 11.6 dB for 4 users, or 9.6 dB for 16. The spatial correlation is in agreement with such conclusions, apart from its narrow-band definition limitation, being significantly lower in micro-cells.