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Space-time trellis codes (STTCs) have been designed for quasi-static Rayleigh channels. When these codes are directly used for additive white Gaussian noise (AWGN) channels or Ricean channels with a high factor, their frame error-rate (FER) performance is no longer optimal. We propose open-loop (no feedback) preprocessing methods for improving the error-rate performance of these codes when used in channels with a high . For (Rayleigh channels), these open-loop schemes generally do not alter the FER performance of the STTCs. The preprocessing operation at the transmitter is either to rotate the constellation points in one of the transmit antennas relative to the other by some angle, or suitably divide (unequally) the total power between the two transmit antennas. The angle of rotation and power division is optimized by maximizing the of the STTCs. Simulation results show that for AWGN or Ricean fading channels with a large , the FER performance can be significantly improved by doing either rotation or power division at the transmitter. While the FER performance is nearly unchanged for quasi-static Rayleigh channels, the improvement in performance is between 1 to 3 dB for Ricean or AWGN channels.