Simulated and measured performance of 4-branch uplink reception in WCDMA

In the initial deployment phase of the WCDMA networks the coverage is important to be able to provide 3G services to as many customers as possible, and to reduce the required number of base station sites and the related costs. It is shown by Holma and Toskala (see WCDMA for UMTS, John Wiley & Sons, p.344, 2000) that the WCDMA macro cell coverage is uplink limited. In this paper a base station four-branch receiver antenna solution is studied using simulations and field measurements as an approach to increase the coverage area of the WCDMA cell. The effect of the four-branch reception to the uplink capacity is also studied. The simulations show that the four-branch reception gives an average coverage gain of 3 dB compared to the traditional two-branch receiver diversity in ITU Vehicular A channel. When the amount of multipath diversity is lower, like in ITU Pedestrian A channel, the gain is higher - up to 4 dB. The four-branch reception can be implemented with two polarisation diversity antennas. When the correlation of those antennas is 1.0, i.e. the antennas are very close to each other, the gain reduces by 0.5 dB to 2.5 dB in ITU Vehicular A channel. The field measurements indicate an average reduction of 3 dB in the mobile transmission power, which is well in line with the simulation results. When the antennas are close to each other, the gain is reduced 0.3-0.4 dB which is also close to the corresponding simulation result.