Link adaptation with adaptive transmit diversity for MISO-OFDM transmission systems

Link adaptation combined with adaptive transmit diversity can achieve further performance improvement in conventional OFDM systems. We propose adaptive modulation and frequency-domain power allocation based link adaptation algorithms with adaptive transmit diversity for broadband MISO/OFDM transmission systems. By employing adaptive modulation and power allocation on each subcarrier, the maximal SNR on each subcarrier obtained by adaptive transmit diversity is further enhanced under the constraint of power and overall bit rate. It is shown that the proposed link adaptation approaches can achieve better performance than the conventional adaptive transmit diversity based OFDM system over frequency-selective fading channels. Simulation results also show that the adaptive modulation based approach is more sensitive to the channel estimation errors than the adaptive power allocation based approach and that its performance is worse than the adaptive power allocation based link adaptation at BER lower than 10^-5.