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This paper analyses the performance of the downlink transmit diversity techniques specified in the standard of the UTRA FDD mode. The Downlink DPCH can use either closed loop or open loop transmit diversity (space time block coding based transmit diversity) or closed loop transmit diversity to improve performance. In order to evaluate how these techniques work, a simulator of the physical layer of UMTS has been implemented in the C language. Simulation results show that the closed loop methods are the best way of getting diversity gain in radio environments with a low Doppler frequency, especially mode 2. Nevertheless, when a correct channel knowledge (high Doppler frequency) does not exist, the open loop transmit diversity mode is the best option.