A constant-rate space-time code selection technique for transmit antenna diversity systems is proposed. The proposed technique selects both the space-time code and the number of transmitter antennas through a comparison of equivalent SISO channels with a set of predetermined threshold levels, using only four bits for feedback. The constant-rate transmission is based in the inclusion of a complementary transmission mode, which is used whenever no equivalent SISO channel's envelope is found to be

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... over the threshold levels. Simulation results show that the proposed technique outperforms other adaptive transmission techniques, while in comparison with its variable-rate counterpart, there is an increase in spectral efficiency with a slight penalty performance. Additionally to a constant-rate transmission, the new techniques makes BER performance almost independent of the relative velocity between the transmitter and the receiver. 12 .