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This paper analyses the effect of the propagation environment on the theoretical performance of the downlink transmit diversity techniques specified in the standard of the UTRA FDD mode. These techniques are classified as open loop and closed loop modes. Simulation results, obtained via a C simulator of the physical layer of UMTS, show the negative effect of mobility. The diversity gain obtained with the closed loop techniques, which are the best ones, drops drastically when the Doppler frequency rises. In that case, the open loop mode of diversity performs well. Nevertheless, it is highly dependent on the correlation of the antennas, which reduces the theoretical improvement.