Average efficiency of power amplifiers in power-controlled systems with multi-antenna diversity

We present a study of average efficiency of power amplifiers (PAs) in power-controlled systems with multi-antenna diversity. The efficiencies are analytically calculated using the transmitted power distributions. Several well-known multiple-input multiple-output (MIMO) diversity techniques, power control rules, PA classes, and channel models are considered. The considered diversity techniques are maximum ratio combining, selection combining, transmitting antenna selection, and maximum ratio transmission. Also the probability of an OFDM symbol clipping caused by PA saturation is calculated for the system under study. The analytical results are verified using Monte Carlo simulations. The study shows that the input signal distribution, diversity techniques, and the power control cutoff value have a significant effect on the average PA efficiency. The highest average PA efficiency is achieved when input signal has constant amplitude and selection combining is used. The presented results can be applied for an arbitrary PA e.g. when comparing the efficiency of different PAs.