Adjacent Channel Power Ratio Research Articles

A Crest Factor Reduction Technique for LTE Signals with Target Relaxation in Power Amplifier Linearization.

The signal conditioning treatment to achieve good relation of power with radio-frequency (RF) conversion in conventional transceiver systems require precise baseband models. A developed framework is built to provide a demonstration of the modeling figures of merit with orthogonal frequency division multiplexing (OFDM) support under signal conditioning and transmission restrictions to waveforms with high peak to average power ratio (PAPR) in practical applications. Therefore, peak and average power levels have to be limited to correct high PAPR for a better suited correction power from the amplifier that can lead to compression or clipping in the signal of interest. This work presents an alternative joint crest factor reduction (CFR) algorithm to correct the performance of PAPR. A real-time field-programmable gate array (FPGA) testbed is developed to characterize and measure the behavior of an amplifier using a single-carrier 64–QAM OFDM based on long-term evolution (LTE) downlink at GHz as stimulus, across wide modulation bandwidths. The results demonstrate that the CFR accuracy capabilities for the signal conditioning show a reliable clipping reduction to give a smooth version of the clipping signal and provide a factor of correction for the unwanted out-of-band emission validated according to the adjacent channel power ratio (ACPR), PAPR, peak power, complementary cumulative distribution function (CCDF), and error vector magnitude (EVM) figures of merit.

Enhancing5Gmulti‐bandlong haul optical fronthaul links performance by magnitude‐selective affine digital predistortion method

AbstractThis paper presents a novel magnitude‐selective affine (MSA) based digital predistortion (DPD) method for the performance investigation of multiband 5G new radio (NR) based analog radio over fiber link. The proposed MSA‐DPD method is derived from the canonical piecewise linear (CPWL) based model by employing MSA functions, which can result in reduction of the number of multiplication operations and the model complexity. The 5G NR standard at 20 GHz with 50 MHz bandwidth and flexible‐waveform signal at 3 GHz with 20 MHz bandwidth is used. A dual drive Mach Zehnder modulator having two distinct RF signals modulates a 1310 nm optical carrier using distributed feedback laser for 22 km of standard single mode fiber. The proposed MSA‐DPD method is compared with the CPWL and generalized memory polynomial method. The experimental results are presented in terms of adjacent channel power ratio, error vector magnitude, number of estimated coefficients and multiplications suggesting that MSA‐DPD method achieves a better performance as compared to CPWL and GMP models with much lesser complexity meeting the 3GPP Release 17 requirements.

The Impact of Long-Term Memory Effects on the Linearizability of GaN HEMT-Based Power Amplifiers

This article presents how the emission time constant of deep-level traps is responsible for the achievable linearity (linearizability) degradation of gallium nitride high electron mobility transistor (GaN HEMT)-based power amplifiers. It is shown that the worst case scenario happens when the emission rate is on the order of the signal bandwidth, with substantial improvement when they begin to differ. Moreover, because of the strong temperature dependence of the emission time constant, self-heating is shown to play a major role in that linearizability degradation. To demonstrate the importance of the coupling of these two effects (electrothermal and trapping), two GaN HEMT dies with the same structure but different trap activation energies (which dictate the impact of temperature on trapping) were used. Digital predistortion tests using long-term evolution-like signals showed that these devices present different adjacent channel power ratios and normalized mean squared errors, after linearization with the same procedure, which varied with the signal bandwidth as theoretically predicted.

A Highly Linear GaN MMIC Doherty Power Amplifier Based on Phase Mismatch Induced AM–PM Compensation

This article presents a highly linear Doherty power amplifier (DPA) based on phase mismatch. When output phase mismatch (OPM) is introduced, i.e., the phase shift of the output impedance transformer deviates from 90°, the power-combining network (PCN) will exhibit a certain amplitude-to-phase (AM–PM) characteristic. When input phase mismatch (IPM) is introduced, i.e., the main and auxiliary branches are not phase-aligned, the AM–PM of the PCN can be further finely tuned. By choosing proper OPM and IPM, the AM–PM of the overall DPA can be compensated by that of the PCN while maintaining reasonable back-off and saturated performances. Moreover, the PCN with phase mismatch shows gain expansion, and thus the amplitude-to-amplitude (AM–AM) distortion of the DPA can also be improved to some extent. A fully integrated DPA is implemented in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.25~\mu \text{m}$ </tex-math></inline-formula> gallium nitride (GaN)-HEMT process to validate the proposed method. The fabricated DPA realizes an AM–PM of 2° and an AM–AM of 0.3 dB at 6.3 GHz, with a saturated power of 41.1 dBm and a 6 dB back-off drain efficiency (DE) of 45%. Applying a 200 MHz signal with a 7.8 dB peak-to-average power ratio (PAPR), a raw adjacent channel power ratio (ACPR) of −42 dBc and an average DE of 37.4% are measured at the output power of 33.1 dBm. When the carrier frequency is swept from 6.1 to 6.5 GHz, a raw ACPR below −39 dBc and an average DE better than 37% are maintained.

A linearized optical single-sideband modulation RoF link with tunable optical carrier-to-sideband ratio

In this paper, an optical single-sideband (OSSB) modulation radio over fiber (RoF) link with tunable optical carrier-to-side-band ratio (OCSR) and simultaneous third-order intermodulation distortion (IMD3) and power fading suppression is proposed. In the proposed link, a phase-modulated signal and an optical carrier are polarization multiplexed using a Sagnac loop. The periodic power fading caused by chromatic dispersion is avoided by filtering the lower sideband. By adjusting the polarization state, the IMD3 is suppressed and a tunable OCSR can be achieved. Compared with the traditional Mach–Zehnder modulator (MZM) based link, the spurious free dynamic range (SFDR) of the proposed link is improved by more than 18 dB with different RF frequencies. In the broadband characteristic test, the proposed link exhibits lower error vector amplitude (EVM) and higher adjacent channel power ratio (ACPR) in a larger input RF power range.

A Fully Integrated 3.5-/4.9-GHz Dual-Band GaN MMIC Doherty Power Amplifier Based on Multi-Resonant Circuits

In this article, a fully integrated dual-band gallium nitride (GaN) Doherty power amplifier (DPA) based on multi-resonant circuits (MRCs) is presented. A lumped T-type network in combination with the output capacitances of the main and auxiliary transistors is able to realize the quarter-wavelength transformer (QWT) in DPA, and its component values are totally decided by the operating frequency, given a certain characteristic impedance. MRCs are proposed to exhibit the required component values at two different frequencies. By replacing each component in the T-type network with an MRC, a dual-band QWT can be achieved. An integrated dual-band DPA is implemented in a commercial 0.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> GaN-HEMT process to validate the proposed method. The fabricated DPA shows a saturated output power of 43.8–44.7/44.4–44.8 dBm, a 6-dB back-off drain efficiency (DE) of 41%–46%/41.5%–47%, and a saturated DE of 49%–52%/56%–59% in 3.35–3.6/4.8–5.2 GHz, with a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.8\times3.5$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Applying a 100-MHz OFDM signal with a 7.8-dB peak-to-average power ratio (PAPR), an average efficiency of 37%/40% and an average power of 37/37 dBm are measured at 3.5/5.0 GHz, and the adjacent channel power ratio (ACPR) is better than −49 dBc after digital predistortion (DPD). To the best of our knowledge, the proposed DPA is the first demonstration of fully integrated dual-band GaN DPAs.

Sparse Flexible Reduced-Volterra Model for Power Amplifier Digital Pre-Distortion

The Volterra framework plays an important role in digital pre-distortion (DPD) for power amplifier (PA) linearization. In practice, the full-Volterra (FV) model is avoided due to the so-called curse of dimensionality, which has motivated several Volterra pruning techniques in the literature. However, choosing the pruned-Volterra structure with a given complexity that most accurately describes a PA or DPD with unknown characteristics often requires trial and error. The motivation of this article is to propose a reduced-Volterra model that extends traditional memory polynomials, e.g., the generalized memory polynomial (GMP), by including higher-dimensional terms in a flexible and controlled way, avoiding the curse of dimensionality of the Volterra model and resulting in a model that can apply to a wide range of PA and DPD. Furthermore, the article investigates the parsimonious sizing of the proposed model using least absolute shrinkage and selection operator (LASSO) and sparse-group LASSO (SGL) convex optimization, significantly reducing the model’s running cost, while preserving its performance. In our experimental validation, the sparse versions of the proposed model achieved 3 dB better adjacent channel power ratio (ACPR) than the conventional GMP model for the same or lower DPD running cost, at the expense of a more costly estimation, which is performed off-line.

Comparison of Over-the-Air Efficiency Enhancement Techniques in Linear Phased Arrays

This article reviews the recent advancements in the utilization of over-the-air combining techniques to enhance the efficiency of phased-array transmitters for signals with a high peak-to-average-power ratio. A methodological comparison between three spatial over-the-air combining techniques--Doherty, outphasing, and quadrature combining--is proposed, along with analysis of their spatial properties, such as a beamwidth angle for a given error vector magnitude (EVM) value, directivity, out-of-band emission, and sensitivity to amplitude and phase mismatches between the different streams. The analysis suggests that the Doherty technique has the widest spatial angle range with EVM under -30 dB and the lowest sensitivity to mismatches, while quadrature combining exhibits the lowest adjacent channel power ratio (ACPR). Also, the Doherty technique enables the largest efficiency enhancement and allows to trade off efficiency enhancement for out-of-band emission. The different methods were tested over-the-air at 28 GHz with a four-element integrated phased array fabricated in 65 nm to validate the analysis.

Investigation of Input-Output Waveform Engineered High-Efficiency Broadband Class B/J Power Amplifier

This work introduces a new broadband Class B/J power amplifier (PA) design methodology by considering the input-output waveform shaping due to nonlinear CGS-VGS profile in gallium nitride (GaN) radio frequency (RF) devices. A comprehensive time domain modeling of drain voltage and drain current as a function of input nonlinearity is presented to predict continuous Class B/J PA performance. The proposed theory shows that continuous-mode operation can no longer maintain constant PA performance with varying fundamental and second harmonic impedances as predicted by the ideal class-J theory. This paper demonstrates that continuous-mode class B/J operation with input-output waveform shaping yields a new design space with two distinct regions: one advantageous region with capacitive second harmonic load terminations in which PA performance can be enhanced significantly; and another within an inductive second harmonic load area where the performance is degraded compared to that of a classical class B/J PA. For practical validation, source pull measurements and load pull analyses are presented and a broadband Class B/J PA is designed with the proposed second harmonic load and source termination. Source/Load-pull measurements/simulations confirm the theoretical predictions in terms of performance variation across the design space. A high efficiency design space is then identified for broadband PA design. The PA protype demonstrates drain efficiency of (60-73) % with output power above 40 dBm and corrected adjacent channel power ratio (ACPR) better than -55 dBc with digital predistortion (DPD) using 10 MHz LTE signal across (2.2-3.4) GHz.

A Low-Complexity Joint PAPR Reduction and Predistortion Based on Generalized Memory Polynomial Model

Digital predistortion (DPD) technique is an effective means to alleviate the nonlinearity of power amplifiers (PAs) and improve transmitter efficiency. However, for orthogonal frequency division multiplexing (OFDM) systems with a high peak-to-average power ratio (PAPR), the PAPR reduction needs to be deployed in combination with DPD, to maximize transmitter efficiency. The extra complexity caused by the introduction of PAPR reduction on the main road has become a non-negligible defect. To address this issue, this letter proposes a joint PAPR reduction and DPD model based on the generalized memory polynomial (GMP). To train the joint GMP model, this letter improves the ping-pong joint optimization (P2JO) approach under the offline case, to obtain accurate training data. The comparative experimental results based on 100-MHz Doherty PA show that the proposed joint model significantly reduces the model complexity on the main road, while ensuring adjacent channel power ratio (ACPR) and bit error rate (BER).

Under-Sampling Digital Predistortion of Power Amplifier Using Multi-Tone Mixing Feedback Technique

An under-sampling digital predistortion based on a multi-tone mixing feedback technique (MTM-DPD) is presented in this article. In contrast to the under-sampling digital predistortion (DPD) based on conventional receivers, the proposed method could simultaneously reduce the sampling rate and acquisition bandwidth using a multi-tone mixing (MTM)-based feedback channel. The MTM-DPD is implemented with an evolved direct learning architecture, where the coefficients of a predistorter are estimated based on the aliased feedback signal, preprocessed input signal, and preprocessed kernels of the DPD model. To preprocess the input signal and kernels, the behavioral model of the MTM-based feedback channel and its corresponding identification algorithm are analyzed in detailed. Experimental results show that for a gallium nitride (GaN)-based power amplifier (PA) with 40-MHz input, under the excitation of a 17 tone LO signal with frequency interval 7.68 MHz, the MTM-DPD with sampling rate 15.36 MSPS and acquisition bandwidth 15.36 MHz could improve the adjacent channel power ratio (ACPR) from −30.1 to −46.5 dBc and the error vector magnitude (EVM) from 9.13% to 1.76%. Compared with the conventional full sampling DPD (FS-DPD), the MTM-DPD could reduce the cost of analog-to-digital converters (ADCs) in feedback channel significantly while maintaining satisfactory linearization performance.

A Frequency-Selective Digital Predistortion Method Based on a Generalized Indirect Learning Architecture

Frequency-selective (FS) digital predistortion (DPD), which focuses on suppressing the nonlinear distortion at a specific band, has gained increased interest in recent years. However, there is a lack of a general FS DPD approach that is applicable to most scenarios and is suitable for practical implementation. This paper proposes an FS DPD method based on a generalized indirect learning architecture (GILA). Our work on this GILA-based FS DPD method is composed of two contributions. First, an FS Volterra series model structure, which consists of a basic linear part and a partial-band pre-compensation part, is proposed to construct an FS predistorter. Second, a GILA-based identification method is proposed to extract coefficients of the FS predistorter with the FS Volterra series model structure. The proposed GILA-based FS DPD is a general method with low complexity for implementation. Both simulations and experiments verify that the target band of the DPD linearization is arbitrary for the proposed GILA-based FS DPD method. As a special case, when using the proposed method to focus on suppressing the out-of-band distortion, the adjacent channel power ratio performance of the proposed method can be 7.1 dB better than that of the conventional full-band DPD.

Experimental Demonstration and Performance Enhancement of 5G NR Multiband Radio over Fiber System Using Optimized Digital Predistortion

This paper presents an experimental realization of multiband 5G new radio (NR) optical front haul (OFH) based radio over fiber (RoF) system using digital predistortion (DPD). A novel magnitude-selective affine (MSA) based DPD method is proposed for the complexity reduction and performance enhancement of RoF link followed by its comparison with the canonical piece wise linearization (CPWL), decomposed vector rotation method (DVR) and generalized memory polynomial (GMP) methods. Similarly, a detailed study is shown followed by the implementation proposal of novel neural network (NN) for DPD followed by its comparison with MSA, CPWL, DVR and GMP methods. In the experimental testbed, 5G NR standard at 20 GHz with 50 MHz bandwidth and flexible-waveform signal at 3 GHz with 20 MHz bandwidth is used to cover enhanced mobile broad band and small cells scenarios. A dual drive Mach Zehnder Modulator having two distinct radio frequency signals modulates a 1310 nm optical carrier using distributed feedback laser for 22 km of standard single mode fiber. The experimental results are presented in terms of adjacent channel power ratio (ACPR), error vector magnitude (EVM), number of estimated coefficients and multiplications. The study aims to identify those novel methods such as MSA DPD are a good candidate to deploy in real time scenarios for DPD in comparison to NN based DPD which have a slightly better performance as compared to the proposed MSA method but has a higher complexity levels. Both, proposed methods, MSA and NN are meeting the 3GPP Release 17 requirements.

A Low-Loss Load Correction Technique for Self-Healing Power Amplifiers Using a Modified Two-Tap Six-Port Network

This article presents a low-loss correction technique for a self-healing load-insensitive power amplifier (PA) using a modified two-tap six-port network, wherein the varying (complex) load is first compensated for its unwanted susceptance part, followed by adjustment of the transistor output stage to the ohmic load variation, by modifying its supply voltage and drive level. This two-step approach avoids the high-Q conditions that occur in tunable matching network solutions, which aims to correct for both the real and imaginary load deviations, such as providing lower insertion loss and voltage stress. Next, to facilitate a fully automated load mismatch correction without the need for calibration, a modified two-tap six-port network for impedance detection and control loop approach is proposed. As proof of principle, a prototype 900-MHz class-AB PA featuring the proposed correction technique, as well as, the six-port reflectometer and the control loop, has been implemented as a PCB demonstrator. Measurement results show that the self-healing load-insensitive PA in the events of load mismatch significantly improves the performance and approaches the 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> performance. On a 2:1 VSWR 360° mismatch trajectory and driven by a 64-QAM 3.86-MHz signal, the PA achieves a linear output power of 22 dBm with only ±0.1-dB variation and better than −45-dBc adjacent channel power ratio (ACPR).

Nonlinear Dynamic RF System Characterization: Envelope Intermodulation Distortion Profiles—A Noise Power Ratio-Based Approach

As radio frequency (RF) applications occupy larger bandwidths, nonlinear dynamics become nonnegligible. This work presents a theoretical framework capable of quantifying the impacts of nonlinear dynamic effects on RF systems through the observation of intermodulation distortion (IMD) profiles produced under multitone excitation. This framework defines static reference profiles and quantifies inband nonlinear dynamic effects as the error between the measured and reference profiles. This analysis demonstrates that classic linearity metrics, such as noise power ratio (NPR), adjacent-channel power ratio, and cochannel power ratio, do not have sufficient frequency resolution to reliably evaluate the impacts of nonlinear dynamics manifested in the IMD profiles produced by broadband RF systems. These observations result in a list of general characterization guidelines to overcome the limitations of classical linearity metrics in the assessment of nonlinear dynamics and the proposal and experimental validation of a novel method, swept-tone NPR, for the characterization of IMD profiles affected by nonlinear dynamic effects. Beyond this, the classic nonlinear dynamic mechanism, responsible for IMD asymmetry, is analyzed under multitone excitation at the system level for the first time, and the limitations of mechanism-based IMD analysis in the presence of nonlinear dynamic effects are evidenced with theoretical examples.

Combined Sidelobe Reduction and Omnidirectional Linearization of Phased Array by Using Tapered Power Amplifier Biasing and Digital Predistortion

Power amplifier (PA) efficiency and linearity are among the key drivers to reduce energy consumption while enabling high data rates in the fifth-generation (5G) millimeter-wave phased array transmitters. Analog per-branch phase and amplitude control is used to steer the beam, suppress the sidelobes, and form zeros to the desired spatial directions. The amplitude control of individual PA inputs makes nonlinearity vary from antenna to antenna, which challenges the common digital predistortion (DPD) used to linearize the array. In this article, we implement an amplitude control for beamforming by tuning the PA gate bias. Varying the output powers via PA biasing makes the nonlinear characteristics observed at the individual PA outputs similar that helps the array DPD to linearize also individual PAs. The technique is validated by both simulations and measurements. As a measurement platform, we use a 28-GHz phased array transceiver equipped with 64 antenna elements and 16 radio frequency chains. The desired beam shape is synthesized by controlling the per-antenna over-the-air-power with PA gate bias. Then, the system is linearized by training DPD with a reference antenna. The DPD is demonstrated with 100-MHz-wide 5G new radio modulated waveform. The best example case showed −23.5-dB maximum sidelobe level (SLL) with 4.9% error vector magnitude and −40.8-dB total radiated adjacent channel power ratio with DPD. The proposed approach enables simultaneous reduction of beam pattern SLL, achieves good linearity in all directions, and maintains the PA efficiency.

Design of dual‐mode high efficiency tri‐band power amplifier using input and output harmonic control technology

In this article, a design method for a tri-band power amplifier (PA) with dynamic drain bias voltage is presented. Continuous operation modes are used to expand the impedance design space. In the input and output matching networks, harmonic control circuits are set up to improve efficiency. The load harmonic impedances are obtained by continuous theory. Bias network and harmonic short circuit are used in the input matching network to control harmonics and obtain stop-band. Dynamic drain bias enables the PA to adapt to different emission environments. With input and output harmonic control technology, a 0.9, 1.5, and 2.1 GHz GaN PA is designed to achieve high efficiency in different modes. The measured efficiencies of the fabricated PA at all three bands are more than 58.6%. At 1.5 GHz, when driven with a 20 MHz LTE signal with a 7 dB peak-to-average power ratio, by applying digital pre-distortion, the PA prototype maintains an adjacent channel power ratio of better than −48.7 dBc.

Multi-Stream Spatial Digital Predistortion for Fully-Connected Hybrid Beamforming Massive MIMO Transmitters

In this paper, a novel multi-stream spatial digital predistortion (DPD) technique is proposed to model and linearize the fully-connected (FC) hybrid beamforming (HBF) transmitters. The proposed scheme solves the DPD implementation issue in the FC HBF array by estimating and linearizing the beam signals instead of the individual PAs. In FC HBF systems, significant intermodulation (IMD) between different transmit signals will be generated due to the analog beamforming and combining network upstream of the power amplifiers (PAs). The IMD beams will end up being radiated in different directions and some of them might fall in the linear beam directions. Therefore, multi-input DPD blocks using a practical multi-variable model are constructed for each RF chain to eliminate the complicated inner- and cross-channel IMDs of the beam signals. Simulations on a 4-stream 64-element FC HBF array and experimental tests on a 2-stream 4-element system are carried out to benchmark the proposed DPD technique against the conventional techniques. Better than 13 dB adjacent channel power ratio (ACPR) improvement and 12 dB normalized mean square error (NMSE) improvement have been achieved by the proposed DPD technique.

2.6-GHz Integrated LDMOS Doherty Power Amplifier for 5G Basestation Applications

This letter presents a compact output combining network for a packaged integrated asymmetric Doherty power amplifier (DPA) by taking advantage of device drain source capacitance, Cds and package parasitic components. A new method is introduced to/of/for absorbing part of the peaking amplifier's C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> ds</sub> into the impedance transformer, thus extending the C- L- C-based “ C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> ds</sub> -absorption” technique to two-way asymmetric DPAs. Based on the proposed combining network, a two-stage laterally-diffused metal-oxide semiconductor (LDMOS) integrated asymmetric DPA was designed and fabricated at 2.6 GHz. The fabricated RF integrated circuit (RFIC) is mounted in a quad flat no-lead (QFN) package. Under a single-tone continuous-wave (CW) signal at 2.6 GHz, the DPA achieves a peak power of 46 dBm, a linear gain of 31.7 dB, and a 48% power-added efficiency (PAE) at 8-dB output power back-off (OBO). The DPA also demonstrates good linearizability by meeting the 5G spectrum mask and achieving a digital predistortion (DPD) corrected adjacent channel power ratio (ACPR) better than -51.5 dBc for 160-MHz long-term evolution (LTE).

Uniformly Distributed Near-Field Probing Array for Enhancing the Performance of 5G Millimeter-Wave Beamforming Transmitters

This letter proposes a uniformly distributed near-field (NF) probing array (NFPA) capable of generating feedback signals suitable for monitoring and improving the performance of a 5G millimeter-wave (mm-wave) beamforming transmitter. The proposed NFPA configuration is carefully designed to ensure comparable coupling ratios between the individual RF chain outputs and the closest NF probes, across a wide frequency range. This maximizes the quality of the feedback signal available to perform array calibration and digital predistortion (DPD) when using realistic 5G modulated signals. A 16-element 27-30-GHz beamforming transmitter is designed and serves as the proof-of-concept prototype. Using a four-element NFPA, the 16 RF chains are calibrated using a 400-MHz modulated signal - achieving less than 0.27 dB and 2.8° root-mean-square (RMS) magnitude and phase calibration errors, respectively. Furthermore, a DPD engine trained using the NFPA-based feedback signal improves the over-the-air transmitted signal's adjacent channel power ratio (ACPR) and error vector magnitude (EVM) from 30 dB and 8.8% to 39 dB and 2.5%, respectively. The DPD also allowed for an increase of the effective isotropic radiated power (EIRP) from 27.5 to 33 dBm while staying below the maximum EVM of 3.5%.