Joint downlink beamforming and power control for 3G WCDMA

We consider the downlink of a WCDMA system, which is limited by co-channel interference due to imperfect correlation properties of the spreading sequences in the presence of multipath propagation. If channel knowledge is available at the base station, the instantaneous carrier-to-interference ratios (CINR) measured at the input of each Rake receivers can be controlled by using a combination of fast power control and transmit beamforming. By carrying out numerical simulations, we demonstrate that joint optimization of beamforming and power control produces a significant performance improvement over conventional techniques. We also propose a new performance measure, which takes into account the joint effect of multipath propagation, beamforming and power control. Multiuser diversity is exploited by scheduling at any one time only the users with the best conjoint channel.