On Performance of Adaptive Modulation in MIMO Systems Using Orthogonal Space–Time Block Codes

We provide a systematic study of adaptive modulation schemes in multiple-input-multiple-output (MIMO) orthogonal space-time block code (OSTBC) systems. Closed-form expressions of system performance, such as average spectral efficiency, bit error ratio (BER), and outage probability, are obtained and confirmed by Monte Carlo simulations. Provided the closed-form expressions, the optimal signal-to-noise ratio (SNR) thresholds that yield the maximal average spectral efficiency can be solved. To reduce complexity of the optimal algorithm, an original method that can achieve approximately the same performance as the optimal method is proposed. Furthermore, we apply these methods in a more practical situation, where channel estimation is imperfect, and examine how the performance is affected due to channel estimation errors.