Fu Li

Date of Award

Spring 5-15-2013

Document Type


Degree Name

Doctor of Philosophy (Ph.D.) in Electrical and Computer Engineering


Electrical and Computer Engineering

Physical Description

1 online resource (ix, 94 pages)


Power amplifiers -- Design and construction, Nonlinear systems, Wireless communication systems -- Technological innovations




The nonlinearity of RF power amplifiers (PA) is one of critical concerns for RF designers because it causes spectral regrowth related to in-band and out-of-band spurious emissions control in communication standards. Traditionally, RF power amplifiers must be backed off considerably from the peak of their power level in order to prevent spectral regrowth. The digital predistortion (DPD) technique is being widely used for compensation of the nonlinearity of RF power amplifiers, as the high power efficiency becomes increasely important in wireless communication systems.

However, the latest generations of communication systems, such as Wi-Fi, WiMAX, and LTE, using wider bandwidth have some additional memory distortion, other than the traditional memoryless distortion. The distortion caused by memory effect makes the traditional predistorter not precise any more for the PA linearization.

In this dissertation, the traditional prediction of 3rd order memoryless spectrum regrowth is applied to 4G communication signals in terms of the 3rd intercept point of PAs, based on the previous researches in Portland State University led by Professor Fu Li. Then, the spectrum regrowth prediction is extended to an arbitrarily high order with intercept points of an RF power amplifier. A simple predistortion method which enables direct calculation of the predistorter coefficients from the intercept points is also proposed.

Furthermore, the memory effect is taken into account for both PA modeling and predistortion. A simplified Hammerstein structure based method is proposed to analyze the nonlinear characteristic of PAs more precisely and completely. By applying the inverse structures of the PA model, the proposed predistorter corrects both the traditional memoryless nonlinear distortions and the memory effect that may exist in RF power amplifiers. The order of nonlinearity and depth of memory of a predistorter can be chosen from 0 to any arbitrarily high number. This increases the flexibility for designers to decide how to linearize power amplifier effectively and efficiently.

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