An Analysis of Band-limited Communication Systems from Amplifier Efficiency and Distortion Perspective

Considering growing concerns toward green communications, not only their bandwidth efficiency but also their power consumption is expected to gain increasing importance for future communication systems. A power amplifier (PA) is one of the most power consuming analog devices at the transmitter in communication systems and a precise estimation of the power consumption at the transmitter circuit requires the knowledge of its efficiency that depends on the distribution of input signal envelope and the amount of input back-off. In this paper, we develop a simple analytical model that can be used for estimating achievable efficiency of a linear PA as well as the amount of resulting nonlinear distortion for a given modulated signal exclusively from its envelope distribution. Based on this model, the trade-off relationships between the efficiency and signal-to-distortion power ratio for several spectrally efficient linear modulations are examined. It is also shown that in some special cases of Gaussian input and memoryless nonlinearity PA models, the results can be represented in simple closed-form expressions.