Optimum table spacing in predistorting amplifier linearizers

Abstract

Abstract-Radio frequency (RF) power amplifiers require linearization to reduce the intermodulation (IM) power if the signal does not have a constant envelope. Digital predistortion (PD) is one of the more successful methods. However, implementations usually employ uniform spacing of the PD lookup table entries, since the question of optimum nonuniform spacing has been unresolved. This paper provides the solution: a way to compute the IM for different spacing methods, a comparison of several table spacing schemes, a derivation of the optimum table spacing method, and a demonstration that the IM of optimum spacing is only a few decibels lower than that of equal spacing by amplitude when variations in operating point are considered.

Multi-Lookup Table FPGA Implementation of an Adaptive Digital Predistorter for Linearizing RF Power Amplifiers With Memory Effects

“…The best linearity performance recognized in the literature is achieved with Cavers optimum companding function [29]. However, its computational complexity and its dependence on signal's probability density function make it less suitable in our generic approach.…”

Baseband Predistortion Lineariser Using Direct Spline Computation

“…A 16-QAM constellation has been used and the resulting system has been simulated by [5]. The pulse shaping filter box applies two independents square root raised cosine FIR filter to the data with a 8X oversampling rate [6].…”

Green Communications: Digital Predistortion for Wideband RF Power Amplifiers

“…For high-power, wideband applications such as UMTS and LTE, those PAs do still suffer from nonlinear distortion, so we still need some kind of linearization. In the second trick, for a given PA operating near saturation, the linearity can be improved by signal processing techniques, PA linearization [11], using techniques such as a) feedback distortion compensation [12], [13], [14], [15], [16], using closed-loop regulators to reduce the nonlinear distortion, b) feedforward distortion compensation [17], [18], [19], [20], [21], which utilizes an additional error amplifier in the forward loop to compensate for the nonlinear distortion introduced by the main PA, and c) predistortion linearization [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], which uses a stand-alone module to pre-distort the input signal to the PA, improving the linearity at PA output. Due to its high flexibility and excellent linearization performance, digital predistortion (DPD) has become one of the most preferred choice for linearizing RF PAs, and tends to be an fundamental component in current and next-generation wireless communication systems.…”