Search Results (32)

This paper proposes an optimized digital predistortion (DPD) framework. Firstly, a peak-detection-based loop-delay estimation is developed by leveraging the unique peak distribution of Orthogonal Frequency Division Multiplexing (OFDM) signals. It reduces the required number of samples to as small as two without compromising estimation accuracy. Then, a Biased Memory Polynomial (BMP) model is proposed for power amplifier modeling. It addresses low-power inaccuracies caused by circuit imperfections (e.g., DC offsets) by adding a bias term to conventional memory polynomials, improving linearization accuracy in low-power regime. Last, to improve the accuracy of coefficient derivation, Memory-Clustering Biased Memory Polynomial (MBMP) is proposed by grouping signals into clusters based on memory-attenuated input vectors and processing them with dedicated sub-models. It improves linearization accuracy in high-power regime. Experimental results demonstrate that the MBMP model reduces normalized mean square error (NMSE) by 16.12 dB, and reduces adjacent channel power ratio (ACPR) by about 12 dBm compared to conventional MP. Full article

Complex distortion cancellation methods are often used at the radio frequency (RF) front end of multiantenna full-duplex transceivers to mitigate signal distortion; however, these methods have high computational complexity and limited practicality. To address these problems, the present study explored the complexities associated with such transceivers to develop a practical multistep approach for suppressing distortions arising from in-phase and quadrature (I/Q) imbalance, nonlinear power amplifier (PA) responses, and multipath self-interference caused by simultaneous transmissions on the same frequency. In this approach, the I/Q imbalance is estimated and then compensated for, following which nonlinear PA distortion is estimated and pre-compensated for. Subsequently, an auxiliary RF transmitter is combined with linearly regenerating self-interference signals to achieve full-duplex self-interference cancellation. The proposed method was implemented on a software-defined radio platform, with the distortion factor calibration specifically optimized for multiantenna full-duplex transceivers. The experimental results indicate that the image signal caused by I/Q imbalance can be suppressed by up to 60 dB through iterative computation. By combining IQI and DPD preprocessing, the nonlinear distortion spectrum can be reduced by 25 dB. Furthermore, integrating IQI, DPD, and self-interference preprocessing achieves up to 180 dB suppression of self-interference signals. Experimental results also demonstrate that the proposed method achieves approximately 20 dB suppression of self-interference. Thus, the method has high potential for enhancing the performance of multiantenna RF full-duplex systems. Full article

Piecewise modeling of power amplifiers (PAs) typically involves assembling different polynomials to capture nonlinear behavior across different operating regions. However, recombining these sub-models can introduce discontinuities at segment boundaries, degrading prediction accuracy and potentially impacting digital predistortion (DPD) performance. This work addresses this issue by introducing a statistical framework to detect discontinuities through localized variations in the conditional mean and variance of amplitude and phase responses. Using the Vector-Switched Generalized Memory Polynomial (VS-GMP) as a case study, we propose a low-complexity post-processing smoothing technique based on a raised cosine weighting function applied at model transition regions. Unlike structural approaches, the method requires no retraining and integrates seamlessly into existing workflows as a post-processing tool. Experimental validation across two PA architectures (Doherty and Single-Stage) and multiple 5G/LTE signals (20–200 MHz bandwidth, up to 11 dB PAPR, including carrier aggregation) demonstrates consistent improvements: up to a 3 dB NMSE reduction and notable spectral error suppression. Full article

The demand for higher data rates and energy efficiency in wireless communication systems drives power amplifiers (PAs) into nonlinear operation, causing signal distortions that hinder performance. Digital Pre-Distortion (DPD) addresses these distortions, but existing systems face challenges with complexity, adaptability, and resource limitations. This paper introduces DRL-DPD, a Deep Reinforcement Learning-based solution for DPD that aims to reduce computational burden, improve adaptation to dynamic environments, and minimize resource consumption. To ensure safety and regulatory compliance, we integrate an ad-hoc Safe Reinforcement Learning algorithm, CRE-DDPG (Cautious-Recoverable-Exploration Deep Deterministic Policy Gradient), which prevents ACLR measurements from falling below safety thresholds. Simulations and hardware experiments demonstrate the potential of DRL-DPD with CRE-DDPG to surpass current DPD limitations in both local and remote configurations, paving the way for more efficient communication systems, especially in the context of 5G and beyond. Full article

The increasing need for high-data-rate wireless applications in 5G and IoT networks requires sophisticated power amplifier (PA) designs in the sub-6 GHz spectrum. This work introduces a high-efficiency Gallium Nitride (GaN)-based power amplifier optimized for the 2.3–2.5 GHz frequency band, using digital pre-distortion (DPD) to improve spectral fidelity and reduce distortion. The design employs load modulation and dynamic biasing to optimize power-added efficiency (PAE) and linearity. Simulation findings indicate a gain of 13 dB, a 3 dB compression point at 29.7 dBm input power, and 40 dBm output power, with a power-added efficiency of 60% and a drain efficiency of 65%. The power amplifier achieves a return loss of more than 15 dB throughout the frequency spectrum, ensuring robust impedance matching and consistent performance. Electromagnetic co-simulations confirm its stability under high-frequency settings, rendering it appropriate for next-generation high-efficiency wireless communication systems. Full article

With the continuous expansion of communication bandwidth, accurately modeling the non-linear characteristics of power amplifiers has become increasingly challenging, directly affecting the performance of digital pre-distortion (DPD) technology. The high peak-to-average power ratio and complex modulation schemes of wideband signals further exacerbate the difficulty of DPD implementation, necessitating more efficient algorithms. To address these challenges, this paper proposes a wideband DPD algorithm based on edge signal correction. By acquiring signals near the center frequency and comparing them with equally band-limited feedback signals, the algorithm effectively reduces the required processing bandwidth. The incorporation of cross-terms for model calibration enhances the model fitting accuracy, leading to significant improvement in pre-distortion performance. Simulation results demonstrate that compared with traditional DPD algorithms, the proposed method reduces the error vector magnitude (EVM) from 1.112% to 0.512%. Experimental validation shows an average improvement of 11.75 dBm in adjacent channel power at a 2 MHz frequency offset compared to conventional memory polynomial DPD. These improvements provide a novel solution for power amplifier linearization in wideband communication systems. Full article

This paper presents a comprehensive review of GaAs HBT-based Doherty power amplifiers (DPAs) targeting 5G New Radio (NR) handset applications. Focusing on the critical challenges of linearity enhancement, back-off efficiency improvement, bandwidth extension under low-voltage (3.4 V) operation, and chip thermal management, the authors analyze state-of-the-art DPAs published in recent years. Key innovations including dynamic power division technique, third order intermodulation (IM3) cancellation technology, and compact output combiners are comparatively studied. Using 5G NR signals, the critical performance of the latest reported PA such as maximum linear power, back-off efficiency, bandwidth, and operating voltage are quantitatively investigated. The measurement results demonstrated that the best performance in recent DPAs achieved high linear power of 31 dBm with 34% PAE and 30 dBm with 31% PAE at the N78 and N77 bands, respectively. The corresponding adjacent channel leakage ratios (ACLRs) were lower than −36.5 dBc without digital pre-distortion (DPD). This review provides a comprehensive understanding of the latest advancements and future directions in highly efficient and linear DPA designs for 5G handset front-end modules. Full article

Digital predistortion (DPD) is essential for improving the efficiency and linearity of power amplifiers (PAs), particularly in radio frequency communication systems. We propose a wavelet decomposition prediction (WDP) framework that better adapts to the highly nonlinear characteristics of PAs. In this framework, the input data are first decomposed using wavelet transformation, allowing for a more effective representation of nonlinear features. Next, a nonlinear modeling process is conducted on the PA to capture its distortion characteristics. Once the nonlinear model is trained, it is frozen to preserve its learned features. Based on this frozen nonlinear model, DPD is then applied to the PA to compensate for nonlinear distortions. Experimental results demonstrate the effectiveness of our proposed method, achieving the best ACPR and EVM performance on the OpenDPD dataset. Full article

The design of conventional digital predistortion (DPD) requires an analogue-to-digital converter (ADC) with a sampling frequency that is multiple times the signal bandwidth, which is extremely challenging for sub-Nyquist sampling systems with undersampled signals. To address this, this paper proposes a neural network (NN)-assisted wideband power amplifier (PA) DPD method for sub-Nyquist sampling systems, wherein a dual-stage architecture is designed to handle the ambiguity caused by subsampled communications signals. In the first stage, the time-delayed polynomial reconstruction method is employed to estimate the wideband DPD nonlinearity coarsely with the undersampled signals with limited pilots. In the second stage, an NN-based DPD method is proposed for the virtual training of the DPD, which learns the up-sampled DPD behavior by taking advantage of the pre-estimated DPD model and the input data signals, which reduces the length of the training sequence significantly and refines the DPD behavior efficiently. Simulation results demonstrate the efficacy of the proposed method in tackling the wideband PA nonlinearity and its ability to outperform the conventional method in terms of power spectrum, error vector magnitude, and bit error rate. Full article

In this work, we implemented a short-reach real-time optical communication system using MLP for pre-distortion. Lookup table (LUT) algorithms are commonly employed for pre-distortion in intensity modulation and direct detection (IM/DD) systems. However, storage limitations typically restrict the LUT pattern length to 9, limiting its effectiveness in compensating for nonlinear effects. A multilayer perceptron (MLP) can overcome this limitation by predicting errors and generating pre-distorted signals, thus replacing the extensive storage requirements of LUTs with minimal computational resources. The MLP-based digital pre-distortion (MLP-DPD) technique enables the creation of long-pattern LUTs for improved nonlinear compensation. In this work, an MLP-DPD scheme was implemented on a field-programmable gate array (FPGA). The FPGA was used to generate a 14.7456 GBaud pre-distorted pulse amplitude modulation 4-level (PAM4) signal. This signal was then transmitted over 20 km of standard single-mode fiber (SSMF). At the receiver, the parallel constant modulus algorithm (PCMA) was applied for signal processing. The bit error rate (BER) achieved met the 2.4 × 10⁻² threshold for soft-decision forward error correction (SD-FEC), enabling a net transmission bit rate of 24.576 Gbit/s. This approach demonstrates the feasibility of using MLP-DPD for effective nonlinear compensation in high-speed optical communication systems with limited resources. Full article

This paper presents the theory, design, and application of a dual-branch series-diode analog pre-distortion (APD) linearizer to improve the linearity and efficiency of a K-band high-power amplifier (HPA). A first-of-its-kind, frequency-dependent large-signal APD model is presented. This model is used to evaluate different phase relationships between the linear and nonlinear branches, suggesting independent gain and phase expansion characteristics with this topology. This model is used to assess the impact of diode resistance, capacitance, and ideality factors on the APD characteristics. This feature is showcased with two similar GaAs diodes to find the best fit for the considered HPA. The selected diode is characterized and modeled between 1 and 26.5 GHz. A comprehensive APD design and simulation workflow is reported. Before fabrication, the simulated APD is evaluated with the measured HPA to verify linearity improvements. The APD prototype achieves a large-signal bandwidth of 6 GHz with 3 dB gain expansion and 8° phase rotation. This linearizer is demonstrated with a 17–21 GHz GaN HPA with 41 dBm output power and 35% efficiency. Using a wideband 750 MHz signal, this APD improves the noise–power ratio (NPR) by 6.5–8.2 dB over the whole HPA bandwidth. Next, the HPA output power is swept to compare APD vs. power backoff for the same NPR. APD improves the HPA output power by 1–2 W and efficiency by approximately 5–9% at 19 GHz. This efficiency improvement decreases by only 1–2% when including the APD post-amplifier consumption, thus suggesting overall efficiency and output power improvements with APD at K-band frequencies. Full article

This paper proposes the ultra−generalized continuous class F (UCCF) mode, which combines the influences of the drain current conduction angle and overdriven transistor on the drain current waveform to achieve a broader finite third-harmonic load impedance space. The UCCF mode uses $\alpha$ to describe the magnitude of the drain current conduction angle and $pcr$ to describe the drain current peak-clipped ratio. An analysis of the effects of $pcr$ and $\alpha$ on the linearity and efficiency of the UCCF model is presented, establishing a robust theoretical foundation for achieving a balance between these two characteristics. Additionally, an examination of how $pcr$ and $\alpha$ influence the load impedance design space is conducted, demonstrating that the UCCF mode not only offers a broader finite third-harmonic load impedance space but also expands the fundamental and second-harmonic load impedance design space. For practical validation, a PA with frequency of 2.05–2.65 GHz is designed based on CGH40010F. The test results show that $S_{11}$ is less than −15 dB, the drain efficiency is 67.0–73.2%, and the output power is 40.1–41.0 dBm. The linearity is tested using a 5G NR (New Radio) signal with a bandwidth of 100 MHz and a peak-to-average power ratio of 8 dB at 2.35 GHz. The worst adjacent channel power ratio (ACPR) is −34.8 dBc without digital predistortion (DPD), and −57.8 dBc with DPD. An average output power ($P_{ave}$) of around 32.4 dBm and an average DE ($D{E}_{ave}$) of 34.39% were obtained. Full article

This article presents a new broadband three-way series Doherty power amplifier (DPA) topology, which enables a broadband output power back-off (OBO) efficiency enhancement of up to 10 dB or higher. The proposed DPA topology achieves Doherty load modulation and three-way power combining through a transformer, which requires only a low coupling factor, thus facilitating its implementation in double-sided PCBs or monolithic microwave integrated circuit (MMIC) processes. The design equations for the proposed DPA topology are proposed and analyzed in detail. A proof-of-concept PA at the 2.1–2.8 GHz band using commercial GaN transistors was designed and fabricated to validate the proposed concept. Within the operating frequency band, it achieves a saturated output power ($P_{\mathrm{sat}}$) of 44.5–46.5 dBm with a peak drain efficiency (DE) of 60–72%, and 43–52% DE at 10 dB OBO. Moreover, under a 20 MHz long-term evolution (LTE)-modulated signal, the PA demonstrates a 36.8–37.5 dBm average output power ($P_{avg}$) and 47–53% average drain efficiency (${DE}_{avg}$). Notably, the adjacent channel leakage ratio (ACLR) is as low as −35–−28.2 dBc without any digital predistortion (DPD). Full article

This paper introduces the structure and characteristics of an internal-matching high-power Doherty power amplifier based on GaN HEMT devices with 0.25 μm process platforms from the Nanjing Electronic Devices Institute. Through parameter extraction and load-pull testing of the model transistor, an EE_HEMT model for the 1.2 mm gate-width GaN HEMT device was established. This model serves as the foundation for designing a high-power three-stage Doherty power amplifier. The amplifier achieved a saturated power gain exceeding 9 dB in continuous wave mode, with a saturated power output of 49.7 dBm. The drain efficiency was greater than 65% at 2.6 GHz. At 9 dB power back-off point, corresponding to an output power of 40.5 dBm, the drain efficiency remained above 55%. The performance of the amplifier remains consistent within the 2.55–2.62 GHz frequency range. The measured power, efficiency, and gain of the designed Doherty power amplifier align closely with the simulation results based on the EE_HEMT model, validating the accuracy of the established model. Furthermore, the in-band matching design reduces the size and weight of the amplifier. The amplifier maintains normal operation even after high and low-temperature testing, demonstrating its reliability. In conjunction with DPD (digital pre-distortion) for the modulated signal test, the amplifier exhibits extremely high linearity (ACLR < −50.93 dBc). This Doherty power amplifier holds potential applications in modern wireless communication scenarios. Full article

Space-based communications at the very high frequency (VHF) band for air traffic management is a new technology application under development that requires energy-efficient architectures to mitigate the power limitations of satellite platforms. The usage of high-efficiency radiofrequency (RF) transmitters can help reduce the power consumption, but nonlinearities concerning the amplified signal in wide fractional bandwidth systems are a problem to solve. This paper proposes a high-efficiency (RF) power amplifier (PA) for satellite communications at the VHF band that aims to reduce the envelope distortion inherent to wide fractional bandwidth multicarrier polar-mode transmitters. Its design is based on a solution called hybrid-coupled switching voltage PA in combination with gallium nitride (GaN) high electron mobility transistor (HEMT) technology. The developed VHF PA prototype delivers up to 95 W from a 28 V power supply, with a drain efficiency about 80% within the 118 MHz to 138 MHz operating band. To test its linearity performance, operating in a polar-mode configuration, a GaN-based wideband envelope amplifier (EA) has been developed to modulate the RF PA supply port. This EA improves its power efficiency by combining it with a slow envelope power supply (SEPS). Some measurements have been taken for a 100 W peak envelope power (PEP) and 10 MHz (maximum carrier spacing) four-tone digitally-modulated test signal, where any distortion product is attenuated 46 dB below the average power of the amplified signal without applying any digital predistortion (DPD) technique. Full article