Time domain downlink transmit diversity techniques in DS W-CDMA systems

Abstract

This dissertation is concerned with performance analysis of downlink transmit diversity techniques in DS W-CDMA systems from a time domain perspective and CPICH generation methods for four antennas. First, we introduce a Time Switched Transmit Diversity (TSTD) for FDD and TDD in high chip rate (HCR,3.84 Mcps) option and analyze the performance of the TSTD scheme with no diversity scheme in various operating conditions and power control. Depending on the modeling environments, the gain of TSTD over a non-diversity mode is between -0.2 to 7 dB. The effect of TSTD is the most significant in low mobile speeds and a single path environment which prevails in microcell or pico cell environments. The TSTD scheme is a simple, effective transmit diversity method from the viewpoint that it can increase down-link capacity in CDMA systems. It requires no additional components in MS because channel estimation and modulation for each slot is performed independently. However, due to a limitation in BS power amplifier maximum capacity requirement, it is not accepted as a scheme for dedicated physical channels. Hence, TSTD is finally adopted as a transmit diversity scheme for synchronization channel (SCH) both for W-CDMA FDD and HCR -TDD mode. Second, A TSTD scheme is also proposed for the downlink physical channels of the Low Chip Rate (LCR,1.28 Mcps) TDD system. The proposed scheme uses the sub-frame structure of LCR-TDD and yields a transmit diversity gain of up to 5dB with only one RF switch and one additional antenna in a base station. In order to utilize the TSTD efficiently, a new power control algorithm for generation of power control commands is required in UEs. From the viewpoint of both complexity and performance, the TSTD scheme is a simple and effective transmit diversity method that can increase downlink capacity in W-CDMA LCR-TDD systems. Hence, the TSTD scheme is adopted in W-CDMA LCR-TDD. Finally, a Common Pilot Channel (CPICH) generation method for four ante...