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Modern communication networks require improved signal quality and spectrum efficiency. Modern wireless communication relies heavily on the multiple input multiple output (MIMO) technology to improve spectrum efficiency and achieve faster data rates. However, the performance of MIMO systems is significantly hampered by non-linear distortions in power amplifiers (PA), especially under dynamic operating conditions. Traditional methods to reduce these distortions often lack the adaptability required for effective optimization. The proposed dynamic nonlinear distortion adaptive optimization analysis (DNDAOA) therefore introduces an adaptive approach that dynamically adjusts the pre-distortion signals using real-time feedback mechanisms. DNDAOA effectively reduces non-linear distortions and thus improves the performance of MIMO systems. Simulation results show that DNDAOA significantly increases spectrum efficiency, reduces error rates, and improves signal quality. This method is widely used in areas such as wireless telecommunications, internet of things (IoT), autonomous vehicles, and smart infrastructure, driving advances in connectivity, reliability, and data integrity. [ABSTRACT FROM AUTHOR]

This paper presents a new high-efficiency two-way Doherty Power Amplifier (DPA) with a modified output matching structure for Wideband Code Division Multiple Access (W-CDMA) low-to-medium power base station applications. A blended design is proposed using the symmetrical topology of equal rated power amplifying devices with unequal output impedances for the carrier and peaking amplifier to achieve enhanced efficiency and desired linearity in 1900 MHz band. The proposed output circuit modifications encompass the usage of parasitic capacitor compensation technique for the carrier amplifier, optimum offset line along with the Doherty combiner to achieve high efficiency over 6 to 10 dB extended range of back-off operation. The measured results of the DPA demonstrate a Power Added Efficiency (PAE) of more than 49.9% at +34 dBm W-CDMA signal power, which is between 8 and 8.5 dB back-off from the peak power level of 42.2 dBm. The DPA has a large signal power gain of 13 dB at 1960 MHz. Further, the PAE is 39.5% and linearised Adjacent Channel Power Ratio (ACPR) is −46.2 dBc, both at 10 dB back-off from peak power. In these back-off power levels, this implementation provides significant efficiency improvement using symmetrical devices and with excellent linearity. [ABSTRACT FROM AUTHOR]

Computational intelligent systems are becoming an increasingly attractive solution for power amplifier (PA) behavioural modelling, due to their excellent approximation capability. This paper utilizes an adaptive fuzzy logic system (AFLS) for the modelling of the highly nonlinear MIMIX CFH2162-P3 PA. Moreover, PA’s inverse model based also on AFLS has been developed in order to act as a pre-distorter unit. Driving an LTE 1.4 MHz 64 QAM signal at 880 MHz as centre frequency at PA’s input, very good modelling performance was achieved, for both PA’s forward and inverse dynamics. A comparative study of AFLS and neural networks (NN) has been carried out to establish AFLS as an effective, robust and easy-to-implement baseband model, which is suitable for inverse modelling of PAs and capable to be used as an effective digital pre-distorter. Pre-distortion system based on AFLS achieved distortion suppression of 84.2%, compared to the 48.4% gained using the NN-based equivalent scheme. [ABSTRACT FROM AUTHOR]

Digital signal processing (DSP) with both linear equalization and nonlinear compensations are studied in this paper for the single-carrier 400G system based on 65-GBaud 16-quadrature amplitude modulation (QAM) signals. The 16-QAM signals are generated and pre-processed with pre-equalization (Pre-EQ) and Look-up-Table (LUT) based pre-distortion (Pre-DT) at the transmitter (Tx)-side. The implementation principle of training-based equalization and pre-distortion are presented here in this paper with experimental studies. At the receiver (Rx)-side, fiber-nonlinearity compensation based on digital backward propagation (DBP) are also utilized to further improve the transmission performances. With joint LUT-based Pre-DT and DBP-based post-compensation to mitigate the opto-electronic components and fiber nonlinearity impairments, we demonstrate the unrepeatered transmission of 1.6Tb/s based on 4-lane 400G single-carrier PDM-16QAM over 205-km SSMF without distributed amplifier. [ABSTRACT FROM AUTHOR]

This paper presents a sub-2-dB Noise Figure (NF) wideband differential Common Gate (CG) Low Noise Amplifier (LNA) in 0.18 µm CMOS technology. The circuit benefits from several new techniques to improve the overall performance. A new current bleeding scheme is proposed in which not only enhances the gain of the circuit but also improves transconductance and noise performance simultaneously. In addition, double positive feedback is employed with only an auxiliary NMOS transistor to break the trade-off between noise and input matching condition of the CG structure. Moreover, the added transistor is biased in moderate inversion region to form pre-distortion performance and sink third order nonlinearity of main transistors at the input. Thus, low noise figure is obtained simultaneous with good linearity. Post-layout simulation results in TSMC 0.18 µm RF-CMOS show a voltage gain of 20.1 dB with a −3 dB bandwidth of 0.38–2.7 GHz, while S 11 is below −10 dB over the frequency band. The minimum NF equals to 1.88 dB and an average NF of 2.04 dB is achieved over the frequency band. Third Input Intercept Point (IIP3) of the proposed circuit is +6 dBm. The circuit occupies an area of 0.055 mm 2 while consuming 2.55 mA from a 1.2-V supply voltage. [ABSTRACT FROM AUTHOR]

This paper presents an Ultra Wide-Band (UWB) high linear low noise amplifier. The linearity of Common Gate (CG) structure is improved based on pre-distortion technique. An auxiliary transistor is used at the input to sink the nonlinear terms of source current, resulting linearity improvement. Furthermore, an inductor is used in the gate of the main amplifying transistor, which efficiently improves gain, input matching and noise performance at higher frequencies. Detailed mathematical analysis show the effectiveness of both linearity improvement and bandwidth extension techniques. Post-layout simulation results of the proposed LNA in TSMC 0.18 µm RF-CMOS process show a gain of 13.7 dB with −3 dB bandwidth of 0.8–10.4 GHz and minimum noise figure (NF) of 3 dB. Input Third Intercept Point (IIP3) of 10.3–13 dBm is achieved which shows 8 dB improvement compared to conventional common gate structure. The core circuit occupies an area of 0.19 mm 2 including bond pads, while consuming 4 mA from a 1.8-V supply. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear autoregressive with exogenous inputs (NARX) digital pre-distortion scheme to linearize power amplifiers is proposed. The proposed NARX digital pre-distortion gives better accuracy and spectral leakage suppression compared with other commonly used Volterra-based techniques. The stability criterion of the NARX digital pre-distortion is derived from the frequency domain analysis. Simulation is carried out with a 20 MHz single carrier long-term evolution signal and two-carrier long-term evolution signal and instantaneous to average ratio of 6.2 dB at 0.01% complementary cumulative distribution function (CCDF). The results of simulation analysis show a slight improvement in adjacent channel leakage ratio performance with 30% reduction in the number of floating point operations compared with conventional pre-distortion techniques. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel technique to improve the linearity of Low Noise Amplifier (LNA) based on pre-distortion in the input matching circuit is proposed. The linearization technique is applied to a Capacitive Cross Coupled Common Gate (CCC-CG) structure. An auxiliary transistor operating in weak inversion region is used to adjust the input matching circuit nonlinearity. It has been shown that the nonlinearity of input matching circuit can efficiently compensate the nonlinearity of transconductance ( G m ) of the amplifier, and improves the third Input Intercept Point (IIP3). Furthermore, the added transistor is used in a feedback path which provides a noise canceling scheme. Thus, linearity improvement is achieved in addition to low Noise Figure (NF). Post-layout simulation results in TSMC 0.18 µm CMOS technology, show a gain of 18.55 dB with an upper −3 dB frequency of 2.96 GHz, the minimum NF equals to 2.63 dB and IIP3 of 11 dBm, while consuming 2.77 mA from a 1.5 V supply. [ABSTRACT FROM AUTHOR]

This paper describes a novel scheme for the fusion of spectrum sensing information in cooperative spectrum sensing for cognitive radio applications. The scheme combines a spectrum-efficient, pre-distortion-based fusion strategy with an energy-efficient censoring-based fusion strategy to achieve the combined effect of reduction in bandwidth and power consumption during the transmissions of the local decisions to the fusion center. Expressions for computing the key performance metrics of the spectrum sensing of the proposed scheme are derived and validated by means of computer simulations. An extensive analysis of the overall energy efficiency is made, along with comparisons with reference strategies proposed in the literature. It is demonstrated that the proposed fusion scheme can outperform the energy efficiency attained by these reference strategies. Moreover, it attains approximately the same global decision performance of the best among these strategies. [ABSTRACT FROM AUTHOR]

A phase-delay cold-FET pre-distortion linearizer technique is proposed to improve the gain compensation ability compared with the conventional cold-FET pre-distortion linearizer. The gain expansion analysis of the power amplifier (PA) cascading with a pre-distortion linearizer and the comparison with the conventional linearizer and the proposed phase-delay linearizer are provided in this paper. To demonstrate the feasibility of this concept, a single-ended V-band cascode PA with the 90^\circ phase-delay linearizer and a differential K-band common-source PA with the 180^\circ phase-delay linearizer are developed to verify the characteristics. The V-band PA implemented in 90-nm CMOS process exhibits the output 1-dB compression power (OP1~dB) of 13.7 dBm and the power-added efficiency (PAE) at OP1~dB of 14.3%. The K-band PA implemented in 0.18- \mum CMOS process demonstrates 17.5-dBm OP1~dB and 13.6% PAE at OP1~dB. [ABSTRACT FROM AUTHOR]

In this article, analysis of a linearised travelling tube amplifier (TWT) using multi-tone signal under the digital modulation schemes is presented. The pre-distortion lineariser circuit based on the Schottky diodes is used to compensate for the nonlinear behaviour of the TWT amplifier in the noisy channel. The stability of the TWTA in combination with the lineariser has also been investigated through simulations. The 4-QAM and QPSK modulators are utilised and applied before linearised TWTA and capture results. The data passing through the linearised TWTA is analysed by using advanced design system (ADS). Constellation and eye diagrams are obtained from different modulation schemes and compared with each other in the same environment. Finally, the bit-error-rate (BER) performance of the system is evaluated using Monte Carlo estimation for three different values of input-back-off (IBO). It is shown that the performance is improved by applying the proposed signal pre-distortion lineariser. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a novel all-optical scheme is proposed to reduce fiber nonlinear distortions in high-speed dense wavelength division multiplexed (DWDM) optical fiber communication systems by applying time-domain fractional Fourier transform (FRFT) based on the time–space duality theory. The modulated optical pulses will be pre-distorted by an FRFT module before being launched into fiber links. It has been validated that the pre-distorted signal performs better fiber nonlinearity tolerance compared to that without pre-distortion. Simulation results show that the received bit error rate (BER) is improved by several orders of magnitude for a 40Gbit/s carrier-suppressed return-to-zero on-off keying (CSRZ-OOK) DWDM system, which can be used in a current 40Gbit/s system easily to improve the nonlinearity effect tolerance. [Copyright &y& Elsevier]

Abstract: An optical waveform pre-distortion method is proposed in reducing the temporal broadening of pulse based on the optical implementation of time domain fractional Fourier transform (FRFT). Moreover, a new analysis of the dispersion and self-phase modulation effects is investigated. The simulation results show that prechirp coefficient and proper fractional orders of FRFT can be beneficial in mitigating pulse broadening. [ABSTRACT FROM AUTHOR]

For adaptive improvement of linearity above a 12 dB PAPR for 64QAM WiMAX, a complementary feedback loop in a differential amplifier is adopted as a pre-distorter that is realized using an NMOS cell operating in the triode region in order to compensate the gm3, the third order transconductance, of the differential amplifier. The power amplifier has been implemented in 0.18 μm CMOS technology, and the chip size is 870 μm × 1050 μm. The proposed PA obtains the 42% efficiency at P1dB while improving the IMD by more than 10 dB above 15 dBm output power levels. It shows a gain of as much as 14.5 dB, and a return loss below -12 dB for 2.3–2.4 GHz operation. Finally, the fabricated PA complies with the spurious emission of WiMAX standards up to 22 dBm. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:833–836, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25062 [ABSTRACT FROM AUTHOR]

It is well known that HPAs (High Power Amplifiers) are inherently nonlinear devices and many researches have focused on the predistortion for memoryless HPAs. However, memory effects of HPAs can no longer be ignored when communication systems have wider bandwidth. Memoryless predistortion techniques proposed previously seldom have satisfactory effectiveness for typical wideband applications such as OFDM (Orthogonal Frequency Division Multiplexing) systems. In this paper, an improved adaptive predistortion method called 2D LUT (2-dimension look-up table) with different accuracy levels is presented to linearize HPAs with memory effects. Simulation and experimental results show that 2D LUT implements excellent performance in mitigating the signal deterioration caused by memory effects, both rectifies the signal constellation distortion and suppresses the spectrum emission. Large scale matrix computation is also avoidable in these adaptive algorithms, which makes them feasible when a real-time system is necessary. [ABSTRACT FROM AUTHOR]

The nonlinearity inherent in the traveling wave tube (TWT) amplifier distorts amplified signals and results in reduced efficiency and bandwidth, limiting its use in communication and electronic countermeasure applications. Signal predistortion is an effective technique for suppressing nonlinear distortion in TWTs that provides high suppression and requires simple circuits for implementation. While conventional predistortion linearizers are based on third-order intermodulation (MM) injection, this paper proposes using second-order (second-harmonic) signal injection in predistortion circuits. A detailed experimental investigation and comparison of second-order versus third-order signal predistortion is presented. It is observed that both schemes result in suppression of up to 30 dB (55 dBc) for the 31M distortion products. However, experimental results indicate that second-harmonic signal injection performs better than 31M in suppressing higher order products. The paper also investigates spatial evolution of the wave spectrum along the TWT axis with and without injection, and sensitivity of the suppression to injected signals amplitude, phase and the fundamental frequency. [ABSTRACT FROM AUTHOR]

For the power amplifier (PA) used in code-division multiple-access cellular phones, the supply voltage is switched from around 1.5 to 3.5 V at the boundary transmission power of several decibels higher than 10 dBm using a dc-dc converter to improve operation efficiency. Recently, however, this boundary transmission power is being raised. We applied the second harmonic injection to reduce distortion and maximize the boundary transmission power under low supply voltage. This paper presents the design concept of the PA's load impedance and bias network with second harmonic injection using Volterra-series analysis. We also present a design of the final stage of the PA under low supply voltage and show that the final stage has a drain efficiency of 53% at an output power of 21 dBm. [ABSTRACT FROM AUTHOR]

In this paper, we consider the optimization of the performance of QPSK and 16-QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non-linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non-linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non-linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10-3 when compared to QPSK COFDM without the predistortion scheme and 16-QAM COFDM provides a gain of 0.5 dB output back-off and 1.2 dB signal to noise ratio at a BER of 3×10-5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10-4 for QPSK and 16-QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work, the nonlinear behavior on pulse-amplitude-modulation (PAM) and their impact on the performance of RGB light-emitting-diodes (LED) based visible light communications (VLC) is presented. Particularly, how the limited source bandwidth affects the nonlinearity of fully modulated RGB LEDs is investigated. It is found that when symbol-rate is higher than the channel bandwidth the nonlinearity gradually diminishes. It causes the symbol-rate dependent nonlinearity. When applying PAM in VLC links, a pre-distortion method is often applied to compensate for the nonlinearity. Due to this symbol-rate dependency, however, the conventional pre-distortion method has a limitation on linearizing the non-linear VLC channel, especially in the case of applying various symbol-rates according to the channel condition. Although it can be adaptively compensated by nonlinear equalizers, their complexity is considerably high. In this work, the characteristics of multi-level PAM scheme in a band-limited nonlinear channel is presented. Also, the feasibility of a low complex but efficient pre-distortion method derived from monotonically decreasing characteristics of the frequency dependent nonlinearity is investigated. [ABSTRACT FROM AUTHOR]