Comparison of adaptive beamforming and adaptive OSTBC with outdated channel feedback

For high speed wireless systems adopting adaptive modulation, we compare the achievable performance of adaptive beamforming (A-BF) and adaptive orthogonal space time block coding (A-OSTBC) with outdated channel feedback. In the presence of feedback delay, we optimize the switching thresholds to maximize the average throughput subject to an average BER constraint and illustrate the effects of feedback delay on the performance of A-BF and A-OSTBC. We observe that while the A-BF scheme outperforms the A-OSTBC scheme with a small feedback delay, the A-OSTBC scheme achieves higher average throughput due to the reduced diversity advantage of A-BF when the feedback delay is large.