Spatial- and Time-Domain Signal Processing for W-CDMA Communication System

• Main Authors: Ta-Yung Liu, 劉大勇
• Other Authors: Hsueh-Jyh Li
• Format: Others
• Language: en_US
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/93482372673228536542

博士 === 國立臺灣大學 === 電機工程學研究所 === 89 === In this thesis we briefly review the time-varying radio fading channel characteristics and the specification of the physical layer of the W-CDMA communication system. We propose channel parameters estimation algorithms and beamforming algorithms for the 3G W-CDMA basestation transceiver employing antenna array. To accurately estimate the channel parameters, including the Time of arrival (TOA), Direction of arrival (DOA), and complex amplitude of the desired user's signal in the presence of multiple-access interference (MAI), we propose a method to increase the SINR of the resultant delay profile, which is obtained by coherently integrating the matched filter output over different pilot bits and incoherently integrating all matched filter outputs of antenna array elements. With these two stages of integration, the desired signals are greatly enhanced. We exploit the estimated channel parameters to the data-branch for 2D-RAKE combining and find that the SINR performance after RAKE receiver can approach the theoretical values. We compare the uplink and downlink SINR performance obtained by different beamforming methods. In the uplink, we found that the DOA method and the complex conjugate method almost have the same SINR performance. However, the complex conjugate method doesn't need any computational loading. The DMI (Direct Matrix inversion) method can have much better performance than the DOA method when few users are present in the channel. When the number of users is much greater than the number of antenna element, however, we found that these two methods almost have the same performance. Nevertheless, the DMI method requires much higher computation loading. We have derived an analytical form of the SINR after 2D-RAKE receiver for the DMI method and the simulation results are very close to the analytic value. In the downlink, we compare the single-beam and multiple-beam beamforming techniques considering the independent fading of the uplink and downlink. We found that the multiple-beam method has a better SINR performance in the low SINR region because the single-beam method is more likely to suffer from deep fading. While in the moderate or high SINR region, the single-beam method has a much better SINR performance because it has a higher antenna gain in the main path direction, a smaller angular coverage of the mainlobe and the orthogonality between different code sequences. We employ the channel data measured by a newly purchased vector channel sounder to simulate the W-CDMA system and compare the uplink and downlink SINR performance using different beamforming techniques. In the uplink we found that the SINR performance obtained by measurement data has the same trend as that obtained by the simulation data. However, the SINR performance is very location dependent in the downlink. The SINR performance obtained by the DMI method is worse than the obtained by the DOA method. Explanations of the reasons are given in the content.