Use of smart antenna system in universal mobile communications systems (UMTS)

Smart antenna technology is gaining more and more interest in the wireless community. The smart antenna, compared to conventional antenna, significantly improves channel capacity, spectral efficiency, and coverage area. In a direct sequence-code division multiple access (DS-CDMA) system, since all users share the same frequency, the interference reduction is a major criterion to improve capacity and performance. In this study, we focus on adaptive beamforming algorithms with smart antenna at the CDMA base station for interference reduction and multipath suppression in the up (reverse) link. Two algorithms, least squares de-spread re-spread multitarget array (LS-DRMTA) and least squares de-spread re-spread multitarget constant modulus algorithm (LS-DRMTCMA) are examined and compared. Results show that a smart antenna using these algorithms provides nulls in all directions of the interferers even under extremely low signal-to-interference (SIR) ratio. The LS-DRMTA has several advantages over the LS-DRMTCMA. The LS-DRMTCMA can offer a much better bit error rate performance compared to the LS-DRMTA, but at the expense of additional complexity.