Impact of the Pilot Signal per Beam on the Ideal Number of Beams and Capacity Gain of Switched Beam Forming for WCDMA

This study devises a simple mathematical model that predicts the number of beams that maximizes system capacity for different WCDMA network configurations. The ideal number of beams to be synthesized within a cell by an antenna array (AA) with a fixed number of elements at the base station (BS) is primarily influenced by the average antenna gain and the relative power allocated to the secondary common pilot channel (S-CPICH) transmitted on each directional beam. It is shown that for a fixed maximum Node-B transmit power the overall system capacity gain in the downlink (DL) provided by switched beam forming (SBF) decreases with the cell size, that is, as more power is needed by the pilot channels to assure coverage. Predictions from our model are compared with simulation results obtained from a detailed dynamic system level simulator in order to be validated. A remarkably good match is observed