Simulation of Third Generation CDMA Systems - Virginia Tech

2.9.2 Transmit Diversity SchemesTransmit diversity schemes at the downlink employ multiple transmit antennas at thebase station. They provide performance enhancement similar to that with multiple antennasat the mobile station receivers. These schemes are attractive since they transfer theprocessing burden to the base station. The transmit diversity schemes proposed for theWCDMA systems fall broadly into two different categories:• Open Loop• Closed LoopIn the open loop transmit diversity the techniques are Time Switched Transmit Diversity(TSTD), [6] and Space-Time TD (STTD). A space- time transmit diversity scheme similar tothe one proposed by Alamouti [13] has been evaluated in [14]. The closed loop techniqueincludes the feedback mode Transmit Diversity and Selection Transmit Diversity (STD) [15].2.9.3 Advanced Receiver StructureWCDMA systems are designed to provide reasonable service quality without usingcomplex receivers that use joint detection of multiple user signals. However if required, shortscrambling codes can be used at the uplink to implement multiuser receivers at moderatecomplexity.27