Presence Of Nonlinear Distortions Research Articles

Effectiveness Evaluation of Coded FTN Signaling in the Presence of Nonlinear Distortion Under Multipath Fading Channels

Effectiveness Evaluation of Coded FTN Signaling in the Presence of Nonlinear Distortion Under Multipath Fading Channels

CRNN-based spatial active noise control in spherical harmonics domain

In this work, an active noise control (ANC) in the spherical harmonics (SH) domain, along with a learning model, is developed. The traditional ANCs are built on the adaptive signal processing framework and fail in the presence of nonlinear distortions. Further, these algorithms are limited to the horizontal plane only. In contrast, the proposed work develops the ANC in the 3D space using the SH representation with the spherical microphone array (SMA) as the error microphone. The SH decomposition calculates the SH pressure coefficients from the SMA recordings. Subsequently, a convolutional recurrent neural network (CRNN) is trained to estimate the real and imaginary spectrograms from the SH coefficients as the input features. The output of the CRNN is the canceling signal that eliminates or attenuates the primary noise in the ANC system. A delay-compensated method addresses ANC system latency. According to simulations and experiments, the proposed learning-based spatial ANC reduces wideband noise and generalizes to untrained noises.

A Novel Approach to Study the Time-Varying Additive Activity during the Electrorefining of Copper

Electrodeposition additives are key components to enhance the electrochemical deposition of metals, either in pure plating applications or during the electrorefining of metals. Many different additives, either organic or inorganic, are applied in industry, depending on the type of process. This work focusses on thiourea and chloride as common additives used for copper electrorefining. This electrochemical industrial process consumes an impure copper anode and produces a pure (99.995 %) copper cathode, while the anode impurities remain in the electrolyte. Additives assist the electroreduction process to produce smooth copper deposits, essential to avoid short circuits and the formation of unwanted cathode morphologies which can entrap impurities.Thiourea is a crucial but complex additive in copper refining. It is known to degenerate into formamidine disulfide (FDS) and both thiourea as FDS can undergo interactions with either copper ions in the solution or the cathode surface. Time dependent additive studies and fundamental knowledge of the effect of aged electrolyte on the cathodic part of the electrorefining process are scarce.The approach applied in this work enables the investigation of the time dependent effect of additives, in this case thiourea and chlorides, assisting the electroplating of copper. Fundamental knowledge of the assisted plating process is extended to create a corner stone for applied research, subsequently, semi-industrial circumstances are used to describe the additive behaviour in industrial relevant conditions. Operando Odd Random Phase Electrochemical Impedance Spectroscopy (ORP-EIS) is used to study the electrochemistry of the additive system [1,2]. Hereby, a multisine input signal is added to the DC current to perform the ORP-EIS experiment simultaneously with the plating process. This measurement technique allows an in situ monitoring of the electrochemical system for hour-long electrodeposition processes. The ORP-EIS technique enables a quantification of the nonlinearities and non-stationarities during the EIS experiment [3]. Additionally, the present non-stationarities are modelled and the nonlinearities are considered as nuisance factor to result in a best linear time-varying approximation [4,5]. An equivalent electrical circuit is used as model to extract the relevant physical parameters from the impedance data. The EIS study is complemented with an ex situ analysis of the thiourea concentration, through ion chromatography, as a function of plating time. Correlations could be made between electrochemical parameters and actual thiourea concentrations [2].[1] T. Collet, et al., An operando ORP-EIS study of the copper reduction reaction supported by thiourea and chlorides as electrorefining additives, Electrochimica Acta (2021) 138762. [2] T. Collet, et al., The time-varying effect of thiourea on the copper electroplating process with industrial copper concentrations, Electrochimica Acta (2022) 141412. [3] Van Gheem, et al., Electrochemical impedance spectroscopy in the presence of non-linear distortions and non-stationary behaviour part i: Theory and validation, Electrochimica Acta 49 (2004) 4753–4762. [4] N. Hallemans, et al., Detection, Classification, and Quantification of Nonlinear Distortions in Time-Varying Frequency Response Function Measurements, IEEE Transactions on Instrumentation and Measurement, 70 (2021) 6500814. [5] N. Hallemans, et al., Best Linear Time-Varying Approximation of a General Class of Nonlinear Time-Varying Systems, IEEE Transactions on Instrumentation and Measurement, 70 (2021) 6503814.

Deep MCANC: A deep learning approach to multi-channel active noise control

Traditional multi-channel active noise control (MCANC) is based on adaptive filtering and usually uses a separate control unit for each channel. This paper introduces a deep learning based approach for multi-channel active noise control (ANC). The proposed approach, called deep MCANC, encodes optimal control parameters corresponding to different noises and environments, and jointly computes the multiple canceling signals to cancel or attenuate the primary noises captured at error microphones. A convolutional recurrent network (CRN) is employed for complex spectral mapping where the summated power of error signals is used as the loss function for CRN training. Deep MCANC is a fixed-parameter ANC approach and large-scale multi-condition training is employed to achieve robustness against a variety of noises. We explore the performance of deep MCANC with different setups and investigate the impact of factors such as the number of loudspeakers and microphones, and the position of a secondary source, on ANC performance. Experimental results show that deep MCANC is effective for wideband noise reduction and generalizes well to untrained noises. Moreover, the proposed approach is robust against variations in reference signals and works well in the presence of nonlinear distortions.

Self-balancing collaboration between linear and nonlinear adaptive sub-filters for hybrid active noise control

Conventional adaptive filters for active noise control (ANC) are troubled by the trade-off between convergence speed and steady state error, especially when nonlinearity plays an important role in system model. In this paper, a hybrid ANC algorithm called FBFLANN is constructed by the collaboration of FIR and bilinear functional link artificial neural network. The characteristics of linear and nonlinear sub-filters are analyzed and utilized to facilitate the adaptability in noise reduction. A convex factor is employed to automatically balance the contribution of two sub-filters, achieving faster convergence and higher accuracy in the presence of nonlinear distortions. The mathematical working and updating rules of the controller are derived to regulate the ANC process theoretically. The effectiveness of the proposed FBFLANN algorithm is demonstrated by numerous simulation studies considering diverse nonlinear acoustic path models as well as acoustic feedback interference. Hardware ANC platform is built up to verify the real-time noise control performance in physical noisy environments. The simulation and experiment results confirm the applicability and prospects for further development of the presented architecture in noise control scenarios.

Impact of HPA nonlinearity on the performance of power domain OFDM-NOMA system

Non-orthogonal multiple access (NOMA) is expected to be used in beyond fifth-generation (B5G) and sixth-generation (6G) mobile networks to support ultra-massive connectivity. Since the two preceding mobile networks generations used orthogonal frequency division multiplexing (OFDM), NOMA is expected to be combined with OFDM. Unfortunately, the OFDM signal suffers from a high peak to average power ratio (PAPR) that limits its performance as it passes through the nonlinear high power amplifier (HPA). In literature, few works have studied the effect of nonlinear distortion on OFDM-NOMA. Furthermore, the HPA models used in previous works to describe the impact of nonlinear distortion on OFDM-NOMA in downlink (DL) were impractical or inaccurate. In contrast, this work uses the well-known soft limiter (SL) model with input back-off (IBO) as a practical controlling parameter. Also, instead of investigating the effect of nonlinear distortion on OFDM-NOMA in DL only, this work investigated this effect in both DL and uplink (UL). In particular, during this work, the performance of the OFDM-NOMA system in the presence of nonlinear distortion in both UL and DL is investigated in terms of users’ achievable data rate, sum rate capacity, system fairness, and the bit error rate (BER) of each user. Results showed that, in DL, the NU is the most affected by the nonlinear distortion, while, in UL, the nonlinear distortion caused by the NU’s HPA is more severe than the nonlinear distortion caused by other users.

Effectiveness evaluation of FTN signaling in the presence of nonlinear distortion under multipath fading channels

Effectiveness evaluation of FTN signaling in the presence of nonlinear distortion under multipath fading channels

Multiple sub filter based proportionate filtering for nonlinear acoustic echo cancellation

This paper presents a multiple sub-filter-based improved nonlinear acoustic echo cancellation (NAEC) framework to enhance the echo cancellation performance of the NAEC in the presence of nonlinear distortion. The proposed algorithm uses a novel combination of adaptive multiple sub-filter approach and proportionate filtering to enhance the convergence rate of the existing proportionate functional link-based NAEC algorithm by reducing the adaption time needed for updating the coefficients of the adaptive filter. In addition to that, the convergence and the steady-state analysis of the proposed algorithm are presented. The proposed NAEC framework is subjected to speech signal input corrupted with both white as well as colored noise as background noise and the colored noise input at low-to–high SNR conditions for a comprehensive analysis of the echo cancellation performance. The experimental results comprising of the echo return loss enhancement, spectrograms, and the perceptual evaluation of speech quality demonstrate the improvements brought by the proposed algorithm. At all signal-to-noise ratio conditions, the proposed algorithm has shown a 4 dB improvement in mean echo return loss enhancement compared to the existing algorithms validating the improvement in the proposed NAEC scheme’s performance.

Deep ANC: A deep learning approach to active noise control

Traditional active noise control (ANC) methods are based on adaptive signal processing with the least mean square algorithm as the foundation. They are linear systems and do not perform satisfactorily in the presence of nonlinear distortions. In this paper, we formulate ANC as a supervised learning problem and propose a deep learning approach, called deep ANC, to address the nonlinear ANC problem. The main idea is to employ deep learning to encode the optimal control parameters corresponding to different noises and environments. A convolutional recurrent network (CRN) is trained to estimate the real and imaginary spectrograms of the canceling signal from the reference signal so that the corresponding anti-noise can eliminate or attenuate the primary noise in the ANC system. Large-scale multi-condition training is employed to achieve good generalization and robustness against a variety of noises. The deep ANC method can be trained to achieve active noise cancellation no matter whether the reference signal is noise or noisy speech. In addition, a delay-compensated strategy is introduced to solve the potential latency problem of ANC systems. Experimental results show that deep ANC is effective for wideband noise reduction and generalizes well to untrained noises. Moreover, the proposed method can achieve ANC within a quiet zone and is robust against variations in reference signals.

Broadband Impedance Measurement of Lithium-Ion Battery in the Presence of Nonlinear Distortions

The impedance of a Lithium-ion (Li-ion) battery has been shown to be a valuable tool in evaluating the battery characteristics such as the state-of-charge (SOC) and state-of-health (SOH). Recent studies have shown impedance-measurement methods based on broadband pseudo-random sequences (PRS) and Fourier techniques. The methods can be efficiently applied in real-time applications where the conventional electrochemical-impedance spectroscopy (EIS) is not well suited to measure the impedance. The techniques based on the PRS are, however, strongly affected by the battery nonlinearities. This paper presents the use of a direct-synthesis ternary (DST) signal to minimize the effect caused by the nonlinearities. In such a signal, the second- and third-order harmonics are suppressed from the signal energy spectrum. As a result, the effect of the second- and third-order nonlinearities are suppressed from the impedance measurements. The impedance measurements are carried out for a nickel manganese cobalt Li-ion battery cell. The performance of the method is compared to the conventional EIS, as well as to other PRS signals which are more prone to battery nonlinearities. The Kronig–Kramers (K–K) transformation test is used to validate the uniqueness of the measured impedance spectra. It is shown that the measurement method based on the DST produces highly accurate impedance measurements under nonlinear distortions of the battery. The method shows a good K–K test behavior indicating that the measured impedance complies well to a linearized equivalent circuit model that can be used for the SOC and SOH estimation of the battery. Due to the good performance, low measurement time, and simplicity of the DST, the method is well suited for practical battery applications.

Synchronization System for Semiconductor Frequency Converters with a Power Supply Network

This article provides a detailed description of synchronization node operation based on the well-known method of a phase-locked loop. It is shown that the phase-locked loop method can be successfully applied in synchronization nodes of valve frequency converters provided that the amplitude of the reverse phase sequence does not exceed 20%. The dependence of the transient time of the measured variable voltage in the synchronization device is obtained depending on the level of asymmetry of the supply voltage, which was estimated by the amplitude of the voltage component of the reverse phase sequence. The dependence of the transition time on the amplitude of the reverse phase sequence is quadratic because of the need to reduce the uniform bandwidth of the second-order filter. The results of the refinement calculation of the metrological characteristics of the synchronization device with account for nonlinear distortions showed that, with the simultaneous presence of nonlinear distortions in the supply voltage curve and asymmetry of the supply voltage, the permissible level of the amplitude of the negative sequence voltage is limited to 10%.

Performance Analysis of NOMA in 5G Systems With HPA Nonlinearities

In this paper, we provide an analytical performance assessment of downlink non-orthogonal multiple access (NOMA) systems over Nakagami-m fading channels in the presence of nonlinear high-power amplifiers (HPAs). By modeling the distortion of the HPA by a nonlinear polynomial model, we evaluate the performance the NOMA scheme in terms of outage probability (OP) and ergodic sum rate. Hence, we derive a new closed-form expression for the exact OP, taking into account the undesirable effects of HPA. Furthermore, to characterize the diversity order of the considered system, the asymptotic OP in the high signal-to-noise (SNR) regime is derived. Moreover, the ergodic sum rate is investigated, resulting in new upper and lower bounds. Our numerical results demonstrate that the performance loss in presence of nonlinear distortions is very substantial at high data rates. In particular, it is proved that in presence of HPA distortion, the ergodic sum rate cannot exceed a determined threshold which limits its performance compared to the ideal hardware case. Monte-Carlo simulations are conducted and their results agree well with the analytical results.

Optimized self-interference cancellation based on optical dual-parallel MZM for co-frequency and co-time full duplex wireless communication under nonlinear distortion and emulated multipath effect.

Co-frequency and co-time full duplex (CCFD) technique has the potential to further improve the capacity of the fifth-generation (5G) system. However, in a CCFD-based transceiver, the self-interference-cancellation (SIC) module is essential because the transmitted signal is also captured by the receiving antenna. In this paper, an optimized SIC technique is proposed based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In addition to the multipath effect between the transmitting and receiving antennas, the nonlinear distortion induced by the used optical and electrical components is considered and analyzed for the first time. In this scheme, one of the children MZMs is biased at 90°. The bias points of the other child MZM and the parent MZM are swept for SIC optimization. Compared to the traditional SIC scheme using DP-MZM, the power of the received signal is increased by 6 dB and the robustness to the bias point drift is improved. In our experiment, over 35 dB cancellation ratio is achieved for 200 MHz filtered orthogonal frequency division multiplexing (F-OFDM) interference signal with carrier frequency from 2.5 GHz to 6 GHz. To mitigate the influence of multipath effect and nonlinear distortion, the recursive least squared (RLS) linear equalizer and the RLS Volterra equalizer are designed and compared. Finally, 42 dB cancellation ratio is achieved for 200 MHz F-OFDM signal with carrier frequency of 4.5 GHz in the presence of nonlinear distortion and emulated multipath effect.

Performance improvement of multi-user MIMO system in the presence of nonlinear distortion

In the presence of nonlinear distortion, the performance degradation of multiuser multiple-input multiple-output (MU-MIMO) systems becomes significant. The performance loss comes not only from the in-band nonlinear distortion, but also from the imperfect cancellation of multiuser interference (MUI) due to the nonlinear distortion. In this regard, we analyze characteristics of nonlinear distortion in an MU-MIMO system. Numerical results show that even tiny nonlinear distortion severely degrades the performance of MU-MIMO system. A nonlinear minimum mean square error (NMMSE) detection algorithm is proposed to improve the system performance. The proposed detection algorithm improves the system performance at low additional cost.

Recognition of Music Scores with Non-Linear Distortions in Mobile Devices

Optical music recognition (OMR), when the input music score is captured by a handheld or a mobile phone camera, suffers from severe degradation in the image quality and distortions caused by non-planar document curvature and perspective projection. Hence the binarization of the input often fails to preserve the details of the original music score, leading to a poor performance in recognition of music symbols. This paper addresses the issue of staff line detection, which is the most important step in OMR, in the presence of nonlinear distortions and describes how to cope with severe degradations in recognition of music symbols. First, a RANSAC-based detection of curved staff lines is presented and staves are segmented into sub-areas for the rectification with bi-quadratic transformation. Then, run length coding is used to recognize music symbols such as stem, note head, flag, and beam. The proposed system is implemented on smart phones, and it shows promising results with music score images captured in the mobile environment.

Linear System Identification in a Nonlinear Setting: Nonparametric Analysis of the Nonlinear Distortions and Their Impact on the Best Linear Approximation

This article addresses the following problems: 1) First, a nonlinearity analysis is made looking for the presence of nonlinearities in an early phase of the identification process. The level and the nature of the nonlinearities should be retrieved without a significant increase in the amount of measured data. 2) Next it is studied if it is safe to use a linear system identification approach, even if the presence of nonlinear distortions is detected. The properties of the linear system identification approach under these conditions are studied, and the reliability of the uncertainty bounds is checked. 3) Eventually, tools are provided to check how much can be gained if a nonlinear model were identified instead of a linear model. Addressing these three questions forms the outline of this article. The possibilities and pitfalls of using a linear identification framework in the presence of nonlinear distortions will be discussed and illustrated on lab-scale and industrial examples. In this article, the focus is on nonparametric and parametric black box identification methods, however the results might also be useful for physical modeling methods. Knowing the actual nonlinear distortion level can help to choose the required level of detail that is needed in the physical model. This will strongly influence the modeling effort. Also, in this case, significant time can be saved if it is known from experiments that the system behaves almost linearly. The converse is also true. If the experiments show that some (sub-)systems are highly nonlinear, it helps to focus the physical modeling effort on these critical elements.

Synchronization of voltage frequency converters with the grid in the presence of notching

Purpose – In the dispersed generation system, power electronic converters allow for coupling between energy sources and the power grid. The requirements of Transmission System Operators are difficult to meet when the share of distributed energy sources of the total energy balance increases. These requirements allow to increase penetration of distributed generation sources without compromising power system stability and reliability. Therefore, in addition to control of active or reactive power, as well as voltage and frequency stabilization, the modern power electronic converters should support power grid in dynamic states or in the presence of nonlinear distortions. The paper aims to discuss these issues. Design/methodology/approach – The research methodology used in this paper is based on three steps: Mathematical modelling and simulation studies, Experiments on laboratory test stand, Analyzing obtained results, evaluating them and formulating the conclusions. Findings – The authors identified two algori...

Waveform design solutions for EHF broadband satellite communications

The problematic RF environment experienced by broadband satellite communications at EHF frequency bands, in particular Q/W bands, call for the use of novel waveforms. This paper presents a detailed comparison of several waveforms in presence of nonlinear distortions and typical values of phase noise introduced at Q/W band. Two main types of waveforms have been compared: Constant Envelope multicarrier waveforms (CE-OFDM and CE-SCFDMA) and single carrier impulse-based waveforms (TH-UWB, DS-UWB and PSWF-based PSM). This comparison will allow to draw some practical guidelines for the waveforms design of EHF broadband satellite communications.

Multicarrier waveforms with I/Q staggering: uniform and nonuniform FBMC formats

Abstract Starting from the well-known uniform filter bank multicarrier (FBMC) format with Nyquist spectral shaping of frequency-limited orthogonal (FLO) subchannels and its dual time-frequency, time-limited orthogonal (TLO) form, we introduce an orthogonal frequency division multiplex of nonuniformly spaced subchannels with unequal width. The orthogonality conditions for nonuniform FBMC (Nu-FBMC) were evaluated through simulations using the ‘extended orthogonal frequency division multiplexing (OFDM)’ framework, as well as through analytical derivation in a rather pragmatic manner. The referent filter bank impulse responses were defined in frequency domain by straightforward aggregations of the pertaining uniform filter bank subchannels spectral shapes for FLO and by transforming the frequency domain of appropriately aggregated time-limited referent impulse responses of uniform TLO configuration. Nonsymmetrical spectral shaping of subchannels in the FLO case format has also been proposed. The spectral efficiency has been evaluated in the presence of nonlinear distortions caused by high power amplifier (HPA), and results have been given in accordance with power spectral density (PSD) constraints defined by IEEE 802.11a standard.

Optimization of 16-APSK by Maximizing Mutual Information Criteria in SC-FDMA Communication Systems

Single Carrier Frequency Division Multiplexing (SC-FDMA) scheme has been considered to be promising technology for the uplink of the 4G mobile communication systems. The main disadvantage of SC-FDMA is the high envelope fluctuation of signal resulting in a presence of nonlinear distortion in transmitted signal due to the transmitter high power amplifier (HPA). In order to improve the SC-FDMA performance, the 16-ary Amplitude Phase Shift Keying (16-APSK) is proposed as a base-band modulation scheme for SC-FDMA instead of conventional M-QAM. The different types of 16-APSK modulations will be investigated and positions of constellation points will be optimized according to maximizing Mutual Information (MI) criteria. For given value of SNR will be found optimal 16-APSK modulation and it will be proposed adaptive approach of 16-APSK modulation. The performance properties of adaptive approach of 16-APSK and 16-QAM based SC-FDMA transmission scheme will be illustrated using numerical results. The obtained results will show that optimized 16-APSK modulation in SC-FDMA transmitted system provide better performance than 16-QAM SC-FDMA system if the nonlinear model of HPA has to be assumed.