Performance analysis of downlink time switched transmit diversity in the WCDMA LCR-TDD system

Abstract

A downlink transmit diversity scheme is proposed [1] for WCDMA low chip rate (1.28 Mcps) Time Division Duplex (LCR-TDD) systems. In the proposed Time Switched Transmit Diversity (TSTD) scheme, two spatially separated antennas are alternately used at a base station in order to transmit consecutive sub-frames on the downlink physical channels. The proposed TSTD scheme takes advantage of the frame structure of the WCDMA LCR-TDD, where TSTD transmission is possible with a single power amplifier. Simply adding switching components in front of the transmit antennas yields a considerable gain compared with a non-diversity mode system. A new power control algorithm is also proposed for generating power control command for efficient use of TSTD. A performance gain of up to 5 dB, compared with a non-diversity scheme, is achieved in terms of the frame error rate for varying Eb/No and mobile speeds. 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 the WCDMA LCR-TDD systems.