Comparison of beamforming techniques for W-CDMA communication systems

Different beamforming techniques are employed in a wideband code-division multiple-access base station, and their uplink and downlink signal-to-interference-plus-noise ratio (SINR) performances are compared. It is found that the direction of arrival (DOA) method and the complex conjugate method have almost the same uplink SINR performance, but the complex conjugate method shifts the downlink main beam direction slightly due to the difference between the uplink and downlink carrier frequency. However, the degradation in the downlink mean SINR performance is less than 1 dB compared with that obtained by the DOA method. In the downlink, the SINR performances obtained by the single-beam method and multiple-beam beamforming technique are compared. It is found that the single-beam method has a poorer SINR performance in the low SINR region because it is more likely to suffer from deep fading. In the moderate or high SINR regions, the single-beam method has a much better SINR performance because it has a higher gain in the main path direction and a smaller angular coverage of the mainlobe, which results in a stronger signal level and smaller multiple-access interference at the mobile receiver.