Baseband Equivalent Volterra Series for Behavioral Modeling and Digital Predistortion of Power Amplifiers Driven With Wideband Carrier Aggregated Signals

Abstract

This paper presents a new baseband equivalent (BBE) Volterra-series model suitable for the behavioral modeling and linearization of wideband RF power amplifiers (PAs). Starting with passband Volterra series, and following a number of signal transformations, a discrete expression relating the envelopes of the output and input signals to the carrier frequency was derived. The new BBE Volterra series reduces the number of kernels, and hence, avoids resorting to the pruning approaches commonly applied in the literature to the classical low-pass equivalent (LPE) Volterra formulation. The proposed baseband Volterra series has similar modeling and linearization performance to the full classical LPE Volterra series. It also outperforms the pruned LPE Volterra models, which use a dynamic deviation reduction approach, in terms of both linearization performance and complexity. The proposed BBE Volterra series was successfully used to linearize different PAs (200-W LDMOS Doherty and 45-W broadband GaN PA) driven with wideband and intra-band carrier aggregated signals (mixed LTE and WCDMA signals).

A low complexity pre‐distortion scheme for power amplifier linearization in wideband applications

“…where the coefficients c k0 , c k1 , …, c kk can be recursively determined from the coefficients of NARX DPD in (2). With the input of the NARX DPD as a generalized input with spectrum V( jω), then the output spectrum of the NARX DPD, U( jω) is bounded by…”

“…This is due to its several advantages over feedforward linearization techniques [1] such as high flexibility, low cost, and high performance. Popular techniques which have been presented in the past include Volterra series techniques [2], Hammerstein [3], memory polynomial (MP) pre-distortion [4], and generalized memory polynomial (GMP) pre-distortion [5]. A nonlinear autoregressive exogenous (NARX) model behaves like an infinite impulse response (IIR) filter [6].…”

Nonlinear distortion analysis of multi-band carrier aggregated OFDM signals

“…Thus models such as Volterra series [12], were conventionally used to model HPA with memory. However, Volterra series is computationally complex (with complexity increasing exponentially with the number of coefficients), hence truncated form of Volterra series known as the MPM is usually preferred in modelling HPA with memory.…”

Analysis on LUT based digital predistortion using direct learning architecture for linearizing power amplifiers

“…In order to improve the linearization performance with limited LUT dimension, some interpolated techniques are introduced in LUT-based DPDs. Polynomial [7,8,17] model-based DPD is also widely studied in the literature. They include the well-known Volterra series (VS) [18], memory polynomial (MP) [7,8,13], generalized memory polynomial (GMP) [19], other simplified VS variants [20] and so on.…”