Adjacent Channel Leakage Ratio Research Articles

Guard Band Protection Scheme to Facilitate Coexistence of 5G Base Stations and Radar Altimeters

Reformation of the 3.7–4.0 GHz band to expand 5G communication deployment poses a risk of 5G signals disrupting radar altimeter operation, leading to data loss or inaccuracies. Thus, this paper proposes a guard band protection method to facilitate the coexistence of 5G base stations and radar altimeters operating in the 4.2–4.4 GHz band. To enhance the adjacent channel leakage ratio (ACLR), we implemented spectral regrowth on an oversampled waveform using a high-power amplifier model, filtering out-of-band spectral emissions. The results demonstrated that a 150 MHz guard band enables coexistence, except in the case of the 16-by-16 antenna array in rural environments. Notably, for the 4-by-4 antenna array in urban environments, coexistence can be achieved using a 50 MHz guard band. The proposed mitigation techniques may also be extended to promote coexistence between non-terrestrial networks and 5G communication systems, including satellites, unmanned aerial vehicles, and hot air balloons.

A Broadband Three-Way Series Doherty Power Amplifier with Deep Power Back-Off Efficiency Enhancement for 5G Application

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 (Psat) 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 (Pavg) and 47–53% average drain efficiency (DEavg). Notably, the adjacent channel leakage ratio (ACLR) is as low as −35–−28.2 dBc without any digital predistortion (DPD).

Enhanced channel prediction in large‐scale 5G MIMO‐OFDM systems using pyramidal dilation attention convolutional neural network

AbstractIn order to enhance communication while minimizing complexity in 5G and beyond, MIMO‐OFDM systems need accurate channel prediction. In order to enhance channel prediction, decrease Error Vector Magnitude, Peak Power, and Adjacent Channel Leakage Ratio, this study employs the Pyramidal Dilation Attention Convolutional Neural Network (PDACNN). Simplified clipping with filtering (SCF) reduces PAPR data, and this technique employs a PDACNN trained with the reduced data. By combining attention techniques with pyramidal dilated convolutions, the suggested PDACNN architecture is able to extract OFDM channel parameters across several scales. Attention approaches enhance channel prediction by allowing the model to dynamically concentrate on essential information. The primary objective is to make use of the network's ability to comprehend intricate spatial–temporal connections in OFDM channel data. The goal of these techniques is to make channel forecasts more accurate and resilient while decreasing concerns about EVM, Peak Power, and ACLR. To confirm the effectiveness of the suggested CP‐LSMIMO‐OFDM‐PDACNN, we measure its spectral efficiency, peak‐to‐average power ratio, bit error rate (BER), signal‐to‐noise ratio (SNR), and throughput. Throughput gains of 23.76%, 30.45%, and 18.97% are achieved via CP‐LSMIMO‐OFDM‐PDACNN, while bit error rates of 20.67%, 12.78%, and 19.56% are reduced. PAPRs of 21.66%, 23.09%, and 25.11% are also decreased.

A 6-/12-dB back-off reconfigurable Doherty-like load modulated balanced amplifier with compact area and wide bandwidth

This article presents a Doherty-like Reconfigurable Load Modulated Power Amplifier (R-LMBA) topology, which enables a broadband 6-/12-dB power back-off (PBO) reconfiguration by rearranging the bias voltages of the sub-amplifiers with compact area. The proposed R-LMBA guarantees proper phase differences among the three sub-PAs across the entire operating frequency band without the need for a bulky phase shifter that is adopted in conventional LMBAs. The design equations for the R-LMBA are proposed and analyzed in detail. A proof-of-concept PA has been designed in 0.1 μm GaAs pHEMT process to verify the proposed concept. In Mode-1, from 30 to 40 GHz, it achieves saturated output power (Psat) of 27.7–29.1 dBm with peak power added efficiency (PAE) of 28.5–34.4%, and 16.8–22.1% PAE at 6-dB PBO with its best 1.29 × efficiency enhancement over a Class-B counterpart. In Mode-2, it exhibits 28 dBm Psat with 30% peak PAE, and a PAE of 25%/13.6% at 6-/12-dB PBO, which is 1.67 × /1.81 × over an ideal Class-B PA. Besides, in Mode-1/-2, the PA demonstrates 21.3/20.3 dBm average output power (Pavg) and 17.9%/22.1% average PAE (PAEavg) with −28.1/-23.8 dB error vector magnitude (EVM) and −29.1/-25.9 dBc adjacent channel leakage ratio (ACLR) under 6-Gb/s 64-QAM modulated signal at 35 GHz.

Adjacent-Channel Compatibility Analysis of International Mobile Telecommunications Downlink and Digital Terrestrial Television Broadcasting Reception in the 470–694 MHz Frequency Band Using Monte Carlo Simulation

This paper delves into the imperative need for coexistence and compatibility in the 470–694 MHz frequency band, as mandated by the World Radiocommunication Conference 2015 (WRC-15) and the WRC-23. It focuses on challenges in the coexistence of Digital Terrestrial Television Broadcasting (DTTB) and International Mobile Telecommunications-2020 (IMT-2020) services in downlink-only mode, particularly in adjacent-channel scenarios. Using Monte Carlo simulations, the study evaluates the probability of interference from IMT base stations with DTTB reception. The analysis thoroughly investigates the impact of the IMT transmitter’s Adjacent Channel Leakage Ratio (ACLR) and the DTTB receiver’s Adjacent-Channel Selectivity (ACS) on the probability of interference. The results demonstrate a significant degradation in the DTTB reception probability at the edge of coverage based on standard assumptions. To address these challenges, this paper provides recommendations for mitigating interference. These include defining enhanced ACLR regulations for IMT base stations, implementing antenna discriminations, providing specialized filters, and establishing national coordination procedures. The research provides valuable insights for informed decision making in spectrum management within the 470–694 MHz band, aiming to facilitate the coexistence of DTTB and IMT-2020 services, in line with international regulations and best practices.

A Dual-Mode CMOS Power Amplifier with an External Power Amplifier Driver Using 40 nm CMOS for Narrowband Internet-of-Things Applications

The narrowband Internet-of-Things (NB-IoT) has been developed to provide low-power, wide-area IoT applications. The efficiency of a power amplifier (PA) in a transmitter is crucial for a longer battery lifetime, satisfying the requirements for output power and linearity. In addition, the design of an internal complementary metal-oxide semiconductor (CMOS) PA is typically required when considering commercial applications to include the operation of an optional external PA. This paper presents a dual-mode CMOS PA with an external PA driver for NB-IoT applications. The proposed PA supports an external PA mode without degrading the performances of output power, linearity, and stability. In the operation of an external PA mode, the PA provides a sufficient gain to drive an external PA. A parallel-combined transistor method is adopted for a dual-mode operation and a third-order intermodulation distortion (IMD3) cancellation. The proposed CMOS PA with an external PA driver was implemented using 40 nm-CMOS technology. The PA achieves a gain of 20.4 dB, a saturated output power of 28.8 dBm, and a power-added efficiency (PAE) of 57.8% in high-power (HP) mode at 920 MHz. With an NB-IoT signal (200 kHz π/4-differential quadrature phase shift keying (DQPSK)), the proposed PA achieves 24.2 dBm output power (Pout) with a 31.0% PAE, while satisfying −45 dBc adjacent channel leakage ratio (ACLR). More than 80% of the current consumption at 12 dBm Pout could be saved compared to that in HP mode when the proposed PA operates in low-power (LP) mode. The implemented dual-mode CMOS PA provides high linear output power with high efficiency, while supporting an external PA mode. The proposed PA is a good candidate for NB-IoT applications.

Inverted sequential load-modulated balanced amplifier for extending dynamic power range over wide bandwidth

This paper propose an inverted sequential load-modulated balanced amplifier (ISLMBA) for extending the dynamic power range of a power amplifier (PA) over a wide bandwidth. The proposed ISLMBA consists of a control amplifier (CA) and a balanced PA (BPA) pair. A composited impedance inverter is inserted between each BPA transistor and the output coupler. The composited impedance inverter is composed by the intrinsic elements and output matching network (OMN) of the BPA transistor. In this way, the intrinsic elements can be fully absorbed into the impedance inverter over a wide bandwidth. Meanwhile, the load modulation trajectories of the BPA transistors can be optimized over a wide bandwidth by tuning the characteristic impedance of the impedance inverter. The theoretical current, voltage and load-modulation profiles of the ISLMBA are comprehensively analyzed. It is illustrated that the proposed ISLMBA could maintain high efficiency at deep output back-off power level over a wide bandwidth. Moreover, this work designs and fabricates an ISLMBA operating over 1.3–2.55 GHz to verify the proposed PA architecture. The fabricated ISLMBA exhibits a saturation drain efficiency (DE) of 54.5%–73.8% and a saturation output power of 42.9–45.9 dBm. At the same time, the fabricated ISLMBA achieves a 10 dB back-off DE of 42.1%–63.9% over the frequency band of interest. When the fabricated ISLMBA is stimulated by a 20 MHz wideband signal with a peak-to-average power ratio (PAPR) of 10.2 dB at 2.0 GHz, the measured adjacent channel leakage ratios (after predistortion) are −47.7 and −48.8 dBc at the lower and upper bands, respectively.

Multi-windowing Technique for 5G and Beyond

Recently, the development of mobile technology has reached a point that requires a high data rate with high waveform aspects. So, traditional ways are no further tolerable. With the dawn of the fifth generation (5G), researchers have been investigating its waveforms and experimenting the methods to improve it. This research examines universal filter multi-carrier (UFMC) for a novel strategy by employing multi-windowing UFMC-based (MW-UFMC) to boost the power spectral density (PSD). This was accomplished by lowering out-of-band emission (OOBE), bit error rate (BER), and adjacent channel leakage ratio (ACLR). The 256quadrature amplitude modulation (256QAM) mapping modulation method was employed in this work. 256QAM is the maximum modulation level that is standard for the third-generation partnership project (3GPP). The proposed MW-UFMC is compared with the conventional UFMC and cyclic prefix orthogonal frequency division multiplexing (CP-OFDM). The proposed multi-windowing technique presents a multistage service that offer a diversity of options to the network operator, which exhibits several advantages over existing methods. These include a lower BER, improved PSD, enhanced spectral efficiency (SE), reduced OOBE that increases capacity for accommodating more bits, decreased ACLR, and lower latency.

Dual-Band Dual-Output Four-Way Doherty Power Amplifier for Unsynchronized Time-Division Duplexing

This article proposes a dual-input dual-output dual-band four-way Doherty power amplifier (DPA) architecture, capable of linearized operation at one frequency band without being disturbed by arbitrary load switching at the other frequency band. The proposed technique is demonstrated through the design, implementation, and measurement of a prototype circuit operating at 1.85-and 2.65-GHz bands with 70-MHz bandwidth for each band. The prototype dual-band DPA (DB-DPA) achieves a peak output power of 49.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 0.2 dBm for the 1.85-GHz band and 49.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 0.5 dBm for the 2.65-GHz band. Furthermore, the measured drain efficiency at 9-dB power back-off (PBO) is 59%–64% and 60%–65% for the 1.85-and 2.65-GHz bands, respectively. Concurrent dual-band performance, dynamic power sharing capability, and utility of the proposed DB-DPA in unsynchronized time-division duplexing (TDD) applications are demonstrated by using 20-MHz new radio (NR) signals with 9-dB peak-to-average power ratio (PAPR). For an average output power of 39 dBm per band, the concurrent dual-band measurement yields 49% average drain efficiency and better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 48-dBc adjacent channel leakage ratio (ACLR).

Ka-band stacked and pseudo-differential orthogonal load-modulated balanced power amplifier in 22 nm CMOS FDSOI

Abstract This paper presents an integrated power amplifier (PA) following the orthogonal load-modulated balanced amplifier (OLMBA) topology. The fixed-phase prototype in this paper is implemented with 22 nm complementary metal oxide semiconductor (CMOS) fully depleted silicon-on-insulator (FDSOI) process. The proposed PA operates at 26 GHz frequency range, where it achieves 19.5 dBm output power, 16.6 dB gain, 15.7% power added efficiency, and 18.3 dBm output 1-dB compression point ( $P_{\rm 1\,dB}$ ). The PA is also tested with high dynamic range modulated signals, and it achieves, respectively, 11.4 dBm and 4.9 dBm average output power (Pavg) with 100 MHz and 400 MHz 64-QAM third-generation partnership project/new radio frequency range 2 signals, and 14 dBm Pavg with 0.6 Gb/s (120 MHz) single carrier 64-QAM signal, measured at 26 GHz and using −28 dBc adjacent channel leakage ratio and −21.9 dB (8%) error vector magnitude as threshold values. The proposed OLMBA is also compared to a stand-alone quadrature-balanced PA. Modulated measurements show that the stand-alone quadrature-balanced PA has better linearity in deep back-off, but the OLMBA has better efficiency.

A Wideband and Highly Efficient Circulator Load Modulated Power Amplifier Architecture

A complete theoretical analysis is presented for a highly efficient power amplifier (PA) architecture based on a non-reciprocal combiner. The architecture consists of two amplifier branches and a microwave circulator acting as the output combiner, referred to as the circulator load-modulated amplifier (CLMA). The continuous-mode (CM) design technique has been further exploited for the CLMA to demonstrate the wideband capabilities of the architecture. The analysis reveals that the CLMA performs active load modulation to maintain high PA efficiency performance across a wide bandwidth and large output power dynamic range. As a proof of concept, a CLMA demonstrator circuit based on gallium nitride (GaN) transistors and a microwave circulator, is designed and characterized with continuous-wave and modulated-signal measurements. The implemented CLMA prototype circuit experimentally demonstrates Doherty-like efficiency enhancement over a large bandwidth covering 2.1 to 3.5 GHz. In measurements, the prototype exhibits a drain efficiency of 46.7-57.5% at peak output power and 35.6-50.6% at 7-dB output power back-off level, within the design bandwidth. When tested with a 60-MHz multi-carrier orthogonal frequency-division multiplexing (OFDM) signal having a 7-dB peak-to-average power ratio (PAPR), an average efficiency of 48.5% with better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 47.5-dBc adjacent channel leakage ratio (ACLR) is achieved after applying digital pre-distortion (DPD).

Multiobjective Bayesian optimization for a 15‐dB back‐off high‐efficiency load modulated balanced amplifier design

AbstractIn this article, multiobjecive Bayesian optimization (MBO) with a non‐penalization strategy is proposed to design a 15‐dB back‐off high‐efficiency load modulated balanced amplifier (LMBA). Applying the proposed method, the output matching networks of the LMBA are optimized to achieve proper load modulation behaviors that providing good performance. To verify the proposed method, a 2.0‐GHz LMBA is designed and measured. Experimental results show that LMBA achieves an output power of 44.5 dBm with a gain higher than 6.6 dB at saturation. The measured drain efficiency (DE)/power‐added efficiency (PAE) are 67%/52% at saturation, 54%/43% at 9‐dB back‐off, and 52%/46% at 15‐dB back‐off, respectively. Tested with 20‐MHz signal with 10‐dB peak‐to‐average power ratio (PAPR) and a 256‐quadrature amplitude modulation (QAM) scheme, the LMBA achieves adjacent channel leakage ratio (ACLR) levels of −46.7/−47.5 dBc and an error vector magnitude (EVM) of 1.2% after digital predistortion.

An Online Sideband Suppression Architecture for PA With Strong Nonlinear Distortion

For power amplifier (PA) linearization under strong distortion scenarios, the inverse transfer function of conventional digital predistortion (DPD) might be unstable, and it would be quite difficult for DPD to work properly. In this letter, an online sideband suppression architecture is proposed for PA with strong distortion. In this architecture, an iterative learning control (ILC) algorithm is modified and unrolled into a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$</tex-math> </inline-formula> -stage cascade structure, which could be readily implemented for online applications. For predistorted signal generation, only the PA’s out-of-band (OOB) distortion needs to be used for accurate model fitting, and the estimated model parameters are updated into the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$</tex-math> </inline-formula> -stage cascade structure. Moreover, in order to improve linearization performance, three parameter updating strategies are explored to track the PA’s nonlinear feature and update the nonlinear models within this cascade structure. Finally, experimental results verify that the proposed method could significantly improve the adjacent channel leakage ratio (ACLR) performance by 22 dB when the PA is driven to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 24-dBc ACLR.

Divisional Load-Modulated Balanced Amplifier With Extended Dynamic Power Range

With the prevalence of complex modulated signals, it is of utmost significance to research the extension of the dynamic power range of radio frequency (RF) power amplifiers (PAs). This article proposes a divisional load-modulated balanced amplifier (DLMBA) for extending the high-efficiency power range. The proposed DLMBA is composed of a local modulated Doherty PA (DPA) and a class-C biased balanced PA (BPA) pair. The output signal of the local DPA is fed into the isolation port of the output coupler of the BPA pair, forming a global load modulation. The design parameters of the DLMBA are derived after a comprehensive analysis. It is illustrated that the dynamic power range of the DLMBA can be extended beyond 12 dB by combining a local DPA and a BPA pair. Meanwhile, each subamplifier of the DLMBA is presented with a modulated impedance over the whole dynamic power range, avoiding voltage oversaturation. As a validation, a DLMBA operating over 1.85–2.05 GHz is fabricated and measured in this article. The fabricated DLMBA delivers a maximum output power of more than 44.8 dBm, a saturation drain efficiency (DE) of more than 53%, and a 13 dB back-off DE of more than 44% in the interested frequency band. Meanwhile, when the DLMBA is excited by a 20-MHz wideband signal with a peak-to-average ratio of 10.2 dB, the measured adjacent channel leakage ratio reaches <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 47.4 dBc after digital predistortion.

Analysis of passive intermodulation in cascaded connectors with transmit‐receive systems

AbstractPassive intermodulation (PIM) is usually expressed by the third‐order intermodulation power excited by two‐tone signal, which has limitations in characterising nonlinear distortion of signal in actual communication system. The effect of PIM on modulated signals are analysed at both the transmit and receive port with multiple passive nonlinear sources. Four types of coaxial connectors are adopted to represent four different levels of PIM. The equivalent circuits of PIM sources in series or parallel are proposed. With the circuit simulations and theoretical modelling, the effect of PIM on the analog and the digital modulation signals are analysed respectively. Two indexes of adjacent channel leakage ratio and error vector magnitude are modelled, showing the PIM effect at transmit port. A system model of a transmit‐receiver is provided, investigating the effect of PIM on the symbol error rate in a receiver. The effects of PIM distortion on different modulated signals are observed both in experimental measurements and simulation tests, verifying the theoretical models.

Design of a dual‐band power amplifier over an octave bandwidth employing dual‐band resonators

AbstractIn this article, a compact dual‐band resonator is proposed for designing dual‐band power amplifiers (DBPAs). The proposed resonator has the characteristics of the band‐pass filters, suppressing the out‐of band signals. It is illustrated the proposed resonator has a simple circuit topology without sacrificing the performances of the DBPA. To verify the methodology, a high efficiency DBPA prototype operating at 1.72 and 3.48 GHz is fabricated and measured. The DBPA obtains a bandwidth of 100 and 50 MHz at the low and high frequency bands, respectively. The measurement results show that the DBPA delivers a saturation power of 43.1 and 40.8 dBm at 1.72 and 3.48 GHz, respectively. The measured drain efficiencies of the DBPA are 75.4% and 68.6% at 1.72 and 3.48 GHz, respectively. Meanwhile, when the DBPA is stimulated by a 20 MHz LTE signal with a peak to average power ratio (PAPR) of 7 dB, the measured adjacent channel leakage ratios are lower than −50 dBc at both 1.72 and 3.48 GHz after digital predistortion.

Single-Input Broadband Hybrid Doherty Power Amplifiers Design Relying on a Phase Sliding-Mode of the Load Modulation Scheme

This work introduces a novel design theory for a single-input hybrid Doherty power amplifier (PA) inspired by the design space existing within the previously reported dual-input Doherty–Chireix (outphasing) continuum. Unlike the conventional <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /4$ </tex-math></inline-formula> Doherty PA inverter which only performs the correct load modulation at its center frequency, the hybrid Doherty PA (HD <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> -PA) combiner network achieves a wideband load modulation using the frequency dependence of the electrical length of the output combiner lines versus frequency for sliding the PA mode of operation. A modified theory is presented in this work to allow for a single-input PA implementation. In this new design, the outphasing angle is only changing with frequency and not the input power. A transmission line phase shifter is used to provide the correct frequency-dependent input phase offset ensuring the correct wideband load modulation performed by the output combiner. A novel methodology is also proposed to select the optimal input phase offset to reduce the variation in the saturation power versus frequency and minimize the circuit size. A proof-of-concept demonstrator PA circuit is designed to operate from 2.5 to 3.3 GHz. When the fabricated PA is excited by a 20-MHz long-term evolution (LTE) modulated signal with 6-dB peak-to-average-power ratio (PAPR), an average efficiency of 45%–59% and adjacent channel leakage ratio (ACLR) less than −50 dBc are achieved after digital predistortion (DPD) across the entire band. When the fabricated PA is excited by a 5G-like 50-MHz orthogonal frequency-division multiplexing (OFDM) signal with 10-dB PAPR, an average efficiency of 33%–41% and ACLR less than −44 dBc are achieved after DPD across the entire band.

A 39-GHz CMOS Bidirectional Doherty Phased- Array Beamformer Using Shared-LUT DPD With Inter-Element Mismatch Compensation Technique for 5G Base Station

This article demonstrates a 39-GHz CMOS phased-array beamformer aiming for power-efficient and area-efficient fifth-generation (5G) dual-polarized multiple-in–multiple-out (DP-MIMO) applications. To address the digital pre-distortion (DPD) implementation issue in the massive beamformer elements with Doherty technique integrated, an inter-element mismatch compensation technique is introduced for improving the shared-lookup table (LUT) DPD performance over the process, voltage and temperature (PVT) variations. A bidirectional Doherty power amplifier (PA)-LNA is proposed to enhance the power back-off (PBO) efficiency regarding the high peak-to-average power ratio (PAPR) 5G signals, meanwhile cost down the system by the unbalanced neutralized bidirectional operation. The proposed phased-array beamformer chip is fabricated in 65-nm CMOS technology and packaged in a wafer-level chip-scale package (WLCSP). Each element occupies only a 0.82-mm2 chip area, including the on-chip low-dropout regulator (LDO). The measured stand-alone Doherty PA-LNA achieves 18.9-dBm saturated output power with 17.8% power-added efficiency (PAE) at 6-dB PBO in PA mode and obtains a 4.8-dB noise figure (NF) at 40 GHz in LNA mode. By utilizing the proposed mismatch compensation, the measured 64-quadrature amplitude modulation (QAM) orthogonal frequency-division multiple access (OFDMA)-mode error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) with the shared-LUT DPD are improved from −22.4 to −25.0 dB and from −28.7 to −32.1 dBc, respectively. The 64-element module achieves a 55.2-dBm saturated effective isotropic radiated power (EIRP) and supports 21-Gb/s single-carrier (SC) mode data streaming. The measured 64-element transmitter (TX) EVM is −25.2 dB at 43.2 dBm with 3.5-GSymbol/s baud rate in 64 QAM, and the corresponding 64-to-4 elements TX-to-receiver (RX) EVM is −22.5 dB. The consumed power for each element is 402 mW at saturation output point in TX mode and 87 mW in RX mode.

Techniques for Adaptive Input-Power Distribution in Doherty Power Amplifier and Load Modulation of Its Driver-Stage Power Amplifier

Techniques for adaptive input-power distribution in Doherty power amplifier (DPA) with the modified Wilkinson power divider and load modulation of its driver-stage PA are described. Combination of these techniques improves the linearity and efficiency of the two-stage PA with DPA as a final stage. Both the techniques leverage the nonlinearity of the input impedance of the auxiliary power amplifier in the DPA. The first technique is applied to a 3.5-GHz 32-W single-stage DPA using GaN high electron mobility transistor (HEMT) devices. Evaluation results showed that by using the technique, adjacent channel leakage ratio (ACLR) improvement of 9 dB was obtained under 8.5-dB peak to average power ratio (PAPR) 10-MHz long-term evolution (LTE) signal without digital predistortion (DPD), and the demonstrator achieved an average drain efficiency (DE) of 55% and ACLR of −50 dBc with DPD. Using the same DPA as a final stage, a two-stage PA was also designed and fabricated to verify the second technique. Due to the load modulation of the driver stage PA, efficiency improvement of 2.6% for the two-stage power added efficiency (PAE) is confirmed by simulation, and the demonstrator achieved a two-stage PAE of 45.4% under 8.5-dB PAPR 20-MHz LTE signal with ACLR of −50 dBc with DPD.

Amplified radio-over-fiber system linearization using recurrent neural networks

Ubiquitous communication is an emergent feature of the future sixth generation of mobile communication (6G) networks. One of the main challenges of this upcoming mobile network is providing broadband communication wherever connectivity is necessary, including rural areas. Up to now, all previous generations of mobile networks have not satisfactorily accomplished this task, and the high cost of deploying and maintaining complex communication infrastructure in remote areas is one of the main reasons. The centralized radio access network might play an important role in overcoming it, since it enables all baseband centralization in a central office (CO), simplifying network deployment and reducing operating/maintenance costs. Additionally, in this scenario, the radio over fiber (RoF) system might be used for transporting analog signals from the CO to a simplified remote base station, composed only of an optical detector and radio-frequency front-end. However, the Mach–Zehnder modulator and power amplifier, commonly employed in RoF systems, introduce undesired nonlinear effects that can severely degrade overall system performance and prohibitively increase the out-of-band emission. We investigate the use of machine learning (ML) algorithms applied to the linearization of an electrical-amplified RoF system. Particularly, a memory recurrent neural network (RNN) linearization is proposed and compared with a memoryless multilayer perceptron linearization. The root mean square error vector magnitude, normalized mean square error, and adjacent channel leakage ratio metrics have been calculated to evaluate the performance of our ML-based approach. Numerical results demonstrate promising linearization performance when the RNN memory depth is equal to or higher than the amplified-RoF system memory depth.