Space–time code selection for OFDM–MISO systems

In this paper, a space–time code selection technique for multiple transmit antenna OFDM systems is proposed, and a constant-rate transmission mode for the space–time code selection technique is introduced. Subcarriers are divided into subcarrier groups and a comparison of the equivalent SISO channel envelopes with a set of predetermined threshold levels for a central subcarrier of each group is performed at the receiver, which decides on the subcarriers to be used at each antenna and sends this information to the transmitter. The transmitter adjusts the space–time code to the number of selected antennas at each subcarriers group using four bits for feedback information per group. Simulation results show that the system performs well for a range of Doppler frequencies for correlated and uncorrelated channels, outperforming transmit antenna selection techniques and adaptive transmit antenna diversity systems for both variable-rate and constant-rate transmission modes.