Variable-power discrete-rate adaptive modulation with orthogonal space-time block coding for Nakagami-m fading channels

The performance analysis of a space-time coded multiple-input and multiple-output system with variable-power adaptive modulation over Nakagami-m fading channels is presented. The optimum switching thresholds for attaining maximum spectrum efficiency (SE) subject to a target bit error rate (BER) and an average power constraint are derived. The existence and uniqueness of the Lagrange multiplier used in the constrained optimization are discussed. The probability density functions of instantaneous signal-to-noise ratio for both perfect and imperfect channel state information are derived, which lead to deriving closed-form SE and BER expressions. Simulation results show that the theoretical analysis and simulation are in good agreement. The variable-power adaptive modulation with space-time coding provides SE better than the constant power counterpart, and it has performance degradation in SE and BER for imperfect channel state information. Copyright © 2011 John Wiley & Sons, Ltd.