On the achievable spectral efficiency of adaptive transmission with transmit-beamforming

In this paper, we capitalize on some recently derived results yielding the probability density function (PDF) of the largest eigenvalue of complex central Wishart matrices with independent and identically distributed entries, to derive a closed-form expression for the capacity of adaptive transmission with the so-called multiple-input multiple-output (MIMO) maximal ratio combining systems, also known as transmit-beamforming (TB) systems, under Rayleigh fading. The achievable spectral efficiency by this type of MIMO systems is derived for two power and rate allocation policies, namely, the optimal power and rate adaptation policy (opra) and the channel inversion with fixed rate policy (cifr). The spectral efficiency of these adaptive transmission policies when used along with TB is evaluated and compared for different MIMO antenna configurations.