Application of Smart Antenna in Universal Mobile Communications Systems (UMTS)

摘要

The wireless communications market, particularly, the cellular telephone segment, has grown exponentially in recent years. This growth has placed a high demand on wireless communications networks to offer comparable quality and availability like the wireline networks. Smart antenna technology is gaining more and more interest in wireless community. Smart antenna compared to the conventional antenna, significantly increases channel capacity and spectral efficiency as well as coverage area. It improves system performance by providing a substantial gain on the target user's signal while significantly suppressing interference, reducing multipath fading, and improving bit error rate (BER) performance. In DS-CDMA system, all users share the same frequency. The interference cancellation is a major objective for improving capacity and performance of CDMA systems. Smart antennas, in general, can be applied to a broad range of wireless technologies, including FDMA, TDMA, and CDMA systems. Some advanced algorithms are useful, and can only be applied to CDMA systems because of the special feature of CDMA systems. In this study, we focus on adaptive beam-forming algorithms with smart antenna at the CDMA base station for interference cancellation and multipath suppression on the reverse link. Three algorithms, MT-LSCMA, LS-DRMTA and LS-DRMTCMA are examined and compared. Results shows smart antenna using these algorithms provides nulls in all directions of the interferers even under extremely low SIR condition. The LS-DRMTA has several advantages over the MT-LSCMA. The LS-DRMTCMA can offer a much better BER performance compared to the LS-DRMTA but at the expense of additional complexity.