Digital predistortion of envelope-tracking power amplifiers under average power back-off and long-term average power efficiency for base-station applications

In many base-station applications, the load/usage fluctuates over time periods of hours to days, thereby varying the required transmit power by as much as 10 dB. It is desirable to maintain high efficiency and linearity in the power amplifier under these back-off conditions in order to achieve high long-term efficiency. This paper demonstrates a scalable digital predistortion (DPD) approach that can be applied under different power back-off levels in envelope-tracking (ET) amplifiers and quantifies the associated efficiency. Efficiency comparisons are made with other amplifier configurations such as Class B and Doherty. Efficiency of 60% at full power (35 W average power) and >30% efficiency at 10 dB average power back-off are measured in an ET amplifier with a 7.54 dB peak-to-average ratio (PAPR) single-carrier WCDMA signal while meeting linearity specifications. Long-term base-station usage probability functions are presented. The long-term efficiency of the ET amplifiers is simulated to be greater than that of Class B and Doherty amplifiers.

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Machine-Learning Assisted Optimisation of Free-Parameters of a Dual-Input Power Amplifier for Wideband Applications

Sensors ◽

10.3390/s21082831 ◽

2021 ◽

Vol 21 (8) ◽

pp. 2831

Author(s):

Teng Wang ◽

Wantao Li ◽

Roberto Quaglia ◽

Pere L. Gilabert

Keyword(s):

Power Amplifier ◽

Power Efficiency ◽

Average Power ◽

Long Term Evolution ◽

Input Power ◽

Global Optimisation ◽

Power Ratio ◽

Term Evolution ◽

Free Parameters

This paper presents an auto-tuning approach for dual-input power amplifiers using a combination of global optimisation search algorithms and adaptive linearisation in the optimisation of a multiple-input power amplifier. The objective is to exploit the extra degrees of freedom provided by dual-input topologies to enhance the power efficiency figures along wide signal bandwidths and high peak-to-average power ratio values, while being compliant with the linearity requirements. By using heuristic search global optimisation algorithms, such as the simulated annealing or the adaptive Lipschitz Optimisation, it is possible to find the best parameter configuration for PA biasing, signal calibration, and digital predistortion linearisation to help mitigating the inherent trade-off between linearity and power efficiency. Experimental results using a load-modulated balanced amplifier as device-under-test showed that after properly tuning the selected free-parameters it was possible to maximise the power efficiency when considering long-term evolution signals with different bandwidths. For example, a carrier aggregated a long-term evolution signal with up to 200 MHz instantaneous bandwidth and a peak-to-average power ratio greater than 10 dB, and was amplified with a mean output power around 33 dBm and 22.2% of mean power efficiency while meeting the in-band (error vector magnitude lower than 1%) and out-of-band (adjacent channel leakage ratio lower than −45 dBc) linearity requirements.

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Experimental Validation of Improved Exponential Companding Technique for SC-FDMA Systems Using WARP Hardware

Journal of Circuits System and Computers ◽

10.1142/s0218126620501546 ◽

2019 ◽

Vol 29 (10) ◽

pp. 2050154

Author(s):

K. Shri Ramtej ◽

S. Anuradha

Keyword(s):

Power Level ◽

Average Power ◽

Original System ◽

Threshold Value ◽

Single Carrier ◽

Power Spectral ◽

Research Platform ◽

Scatter Plots ◽

Subcarrier Mapping

As single-carrier frequency division multiple access (SC-FDMA) is used in long-term evolution (LTE) uplink communications, high peak-to-average power ratio (PAPR) increases power consumption in mobile devices. It is severe when localized subcarrier mapping is used with higher-order modulations. Companding is an attractive technique that offers a tradeoff between PAPR and bit error rate (BER) performances. This paper proposes an exponential companding technique that uses two companding levels based on a threshold, to reduce PAPR in SC-FDMA systems. It does not increase the average power level of transmitted signal and maintains the BER level without significant degradation from the original system. The proposed scheme has three parameters that can be adjusted for a tradeoff between PAPR, BER, and power spectral density (PSD) performances. Hence it offers more flexibility than the conventional exponential companding scheme. We also present scatter plots to find the optimum threshold value and companding levels. Finally, we verify the proposed technique considering a real-time indoor channel by using a wireless open-access research platform (WARP).

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A 10-W S-band class-B GaN amplifier with a dynamic gate bias circuit for linearity enhancement

International Journal of Microwave and Wireless Technologies ◽

10.1017/s1759078713000962 ◽

2013 ◽

Vol 6 (1) ◽

pp. 3-11 ◽

Cited By ~ 1

Author(s):

Pierre Medrel ◽

Audrey Martin ◽

Tibault Reveyrand ◽

Guillaume Neveux ◽

Denis Barataud ◽

...

Keyword(s):

Output Power ◽

Trajectory Optimization ◽

High Efficiency ◽

Average Power ◽

Gate Bias ◽

Error Vector Magnitude ◽

Power Added Efficiency ◽

Class B ◽

Band Class ◽

A Minor

In the present paper, we present a dynamic gate biasing technique applied to a 10 W, S-band GaN amplifier. The proposed methodology addresses class-B operation of power amplifiers that offers the potential for high efficiency but requires a careful attention to maintain good linearity performances at large output power back-off. This work proposes a solution to improve the linearity of class-B amplifiers driven by radio frequency-modulated signals having large peak to average power ratios. An important aspect of this work concerns the characterization of the dynamic behavior of GaN devices for gate bias trajectory optimization. For that purpose, the experimental study reported here is based on the use of a time-domain envelope setup. A specific gate bias circuit has been designed and connected to a 10 W – 2.5 GHz GaN amplifier demo board from CREE. Compared to conventional class-B operation with a fixed gate bias, a 10-dB improvement in terms of third-order intermodulation is reached. When applied to the amplification of 16-QAM signals the proposed technique demonstrates significant ACPR reduction of order of 6 dB along with error vector magnitude (EVM) improvements of five points over 8 dB output power back-off with a minor impact on power-added efficiency performances.

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Investigation on the PAPR performance of odd-bit QAM constellations for DFT spread OFDM systems

Indonesian Journal of Electrical Engineering and Computer Science ◽

10.11591/ijeecs.v21.i2.pp1005-1013 ◽

2021 ◽

Vol 21 (2) ◽

pp. 1005

Author(s):

Ahmed M. Sana ◽

Amer T. Saeed ◽

Yaseen Kh. Yaseen

Keyword(s):

Communication Systems ◽

Adaptive Modulation ◽

Average Power ◽

Transmission Efficiency ◽

Distribution Functions ◽

Cumulative Distribution ◽

Ofdm Systems ◽

Single Carrier ◽

Papr Performance

<p>Adaptive quadrature amplitude modulation (QAM) is a crucial scheme that enables the modern communication systems to overcome the adverse effects of channel fluctuations and maintain an acceptable spectral efficiency. In order to enhance adaptive modulation even further, adoption of odd-bit QAM constellations alongside even constellations had been suggested to improve the transmission efficiency of adaptive QAM modulation. Hence, odd-bit QAM had been extensively studied, analyzed, and tested by many researchers for various patterns, sizes, and communication systems in terms of bit error rate (BER) and peak to average power ratio (PAPR). However, the PAPR performance of odd-bit QAM constellation with single carrier transmission systems adopted in the uplink of the 4G long term evolution (LTE) standards caught almost no research interest. In this paper, the PAPR performance of both cross and rectangular odd-bit QAM constellations are investigated for DFT-S-OFDM systems. Complementary cumulative distribution functions (CCDFs) and probability density functions (PDFs) curves for PAPR are also obtained. Finally, an equation for PAPR PDF is empirically derived for odd-bit cross QAM based DFT-S-OFDM. The results show that cross odd-bit QAM outperforms the rectangular odd-bit QAM in terms of PAPR by 1.02 dB for 8-QAM and 1.3 dB for 32-QAM. This proves that cross odd-bit QAM is a better choice in terms of PAPR for DFT-S-OFDM systems. </p>

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Cross-seasonal Experimental Study on the Comprehensive Performance of C-Si PV Window

Energies ◽

10.3390/en13215684 ◽

2020 ◽

Vol 13 (21) ◽

pp. 5684

Author(s):

Wei Zhang ◽

Wei Wang ◽

Lingzhi Xie ◽

Hao Tian ◽

Mo Chen ◽

...

Keyword(s):

High Efficiency ◽

Average Power ◽

Experimental Tests ◽

Different Seasons ◽

Long Term Experiment ◽

Outdoor Test ◽

Simulation Estimation ◽

High Level ◽

Autumn And Winter

PV windows can potentially produce electricity, reduce the air-conditioning load, and provide natural light. Cross-seasonal experimental tests for long period could eliminate the gap between real outdoor test and simulation estimation. In this research, the lighting-thermal-electricity performance of high-efficiency c-silicon PV windows was tested, and the improvement has been put forward according to the conditions. The long-term experiment was conducted cross different seasons, including summer, autumn, and winter seasons. The highest average power generation, 50W/m2, could be found in autumn. The average outside surface temperature of the PV window would reach 48 °C in sunny days in the autumn, which was higher than other seasons. Although the c-Si PV window maybe block the partial daylighting, the daylighting requirement still could be satisfied with the most days. Furthermore, the average Useful Daylight Illuminance was the highest in summer up to 0.79, and the average illumination uniform could be achieved at a high level in all seasons. For the improvement suggestions, some measures could be taken to reduce the indoor cooling load in summer. During winter, appropriate inner shading measures might be taken to prevent excessive illumination in the building, and allow the electricity and thermal performance of PV window.

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An envelope tracking RF power amplifier with capacitive charge pump modulator

International Journal of Microwave and Wireless Technologies ◽

10.1017/s175907871600043x ◽

2016 ◽

Vol 8 (4-5) ◽

pp. 683-690 ◽

Cited By ~ 2

Author(s):

Gavin Tomas Watkins ◽

Konstantinos Mimis

Keyword(s):

Power Amplifier ◽

Supply Voltage ◽

Average Power ◽

Charge Pump ◽

Power Ratio ◽

Rf Power ◽

Envelope Tracking ◽

Rf Power Amplifier ◽

3Gpp Long Term Evolution

An envelope tracking (ET) radio frequency (RF) power amplifier (PA) is described intended for handsets and applications where a large number of PAs are needed. Instead of the usual split frequency architecture, a linear tracking charge pump structure is proposed. This allows the supply voltage of an RF PA to increase during the peaks of a high peak-to-average power ratio signal. When combined with an LDMOS RF PA, 42.9% efficiency was achieved at 31.3 dBm output power (POUT) when amplifying a 5 MHz bandwidth 8 dB PAPR 3rd Generation Partnership Project (3GPP) long term evolution signal. The first channel adjacent power ratio (ACPR) without digital pre-distortion was −30.4 dBc, meeting the 3GPP handset emission mask. The ACPR could be improved to −32.5 dBc by adopting a curved envelope shaping function at a reduced efficiency of 38.9%.

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