Transmit diversity schemes for high speed downlink packet access in 3.5G cellular systems

HSDPA is the already standardized evolution of UMTS to significantly increase the data rate achieving peak values over 10 Mbit/s. This paper addresses the performance improvement of the HSDPA in multipath fading channels when using several transmitting antennas at the BS. 3GPP specifications define several transmit diversity schemes for two antennas, namely the standardized closed loop modes 1 and 2 and the open loop space time transmit diversity (STTD). This paper studies these techniques but also other transmitting schemes such as open loop modes using space time block codes (STBC) for 4 and 8 transmitting antennas, selective transmit diversity (STD) and hybrid modes combining space time block codes and STD. The performance impact of all these techniques is compared and evaluated using a HSDPA link level simulator.