Adaptive beamforming dependencies on wideband and directional propagation characteristics in micro- and macro-cell UMTS scenarios

It is important to study the fundamental wideband and directional factors in order to establish how the channel properties affect adaptive beamforming, regarding intra-cell interference reduction. With such aim, a comparative set of micro- and macro-cell propagation scenarios is generated, allowing for the systematic analysis of the involved factors. A non-blind adaptive beamforming algorithm is applied, the conjugate gradient at the base station in the up-link makes use of the mobile terminal identifying the UMTS codes. Performance is measured through the gain in SINR relative to that obtained with a single omnidirectional antenna. The scenarios involve the variation of the grouping and angular displacement of mobile terminals, their distances to the base station, their number, and the number of array elements. It is found that the angular and temporal densities of incoming signals are the fundamental roots behind the differences in performances between macro- and micro-cells. For macro-cells, involving much larger angular densities, the effect of having common angles-of-arrival among links is much more critical than for micro-cells; in the case that terminals are grouped, beamforming gains are close to 0 dB. In such case, for micro-cells, values range from 0.9 to 9.6 dB, for 16 users, with a monotonous dependency on distance and on the number of array elements. Micro-cell environments not only allow for the application of simpler beamforming adaptive implementations, but also render larger performance increases by improving such implementations.