Nonlinear Cancellation Research Articles

Interference cancellation for higher harmonics of supply-modulated efficient RF power amplifier systems

In building highly efficient transmitters of today, one is forced to sacrifice linearity for efficiency. Some of the highest power amplifier efficiency figures are reported by envelope tracking (ET) amplifiers. These amplifiers can generate strong higher-order harmonics, which can lead to interference with receivers operating at the harmonic frequencies. Using non-linear interference cancellation, we can help to remove the interference being caused in those receivers. This paper looks at the problem of modeling the third and second-order harmonic emission from an ET amplifier. It derives the non-linear kernel for estimating such interference. This kernel has been rigorously expanded to show its correlation with the various harmonics and its effectiveness in predicting the harmonic content. We then set up an envelope amplifier test-bench to capture harmonic signal content and cancel it using the derived kernel model. The experiment yields excellent agreement with theory and provides a validation of the system and concept.

Spectral-Efficient Cellular Communications With Coexistent One- and Two-Hop Transmissions

The cellular communications scenario involving the coexistence of the one-hop direct transmission and the two-hop relaying is studied in this paper. In contrast to conventional cellular systems featuring orthogonal information flows served by decoupled channel resources via, e.g., time division, we propose a novel protocol in which two information flows are served simultaneously via the shared channel resource, thus constituting a spectral-efficient solution for cellular communications. On the other hand, however, an inevitable issue associated with the proposed protocol is the interflow interference, which may lead to serious deterioration on both information flows. To tackle this issue, we develop an overhearing-based protocol that utilizes the overheard interference as useful side information in the receiver design. Specifically, depending on the interference levels, an adaptive linear minimum mean squared error (MMSE) and nonlinear MMSE successive interference cancellation (SIC) receiver exploiting the overheard interference at the direct mobile terminal is developed. To balance between the two information flows, we develop the asymptotically optimum superposition coding at the base station (BS) in the high-power regime. Furthermore, the optimum relay beamforming matrix maximizing the bottleneck of the achievable rates of the two information flows is developed subject to a finite power constraint. Finally, simulations demonstrate a remarkable throughput gain over the conventional cellular systems.

Iterative nonlinear ISI cancellation in optical tilted filter-based Nyquist 4-PAM system

Abstract The conventional double sideband (DSB) modulation and direct detection scheme suffers from severer power fading, linear and nonlinear inter-symbol interference (ISI) caused by fiber dispersion and square-law direct detection. The system’s frequency response deteriorates at high frequencies owing to the limited device bandwidth. Moreover, the linear and nonlinear ISI is enhanced induced by the bandwidth limited effect. In this paper, an optical tilted filter is used to mitigate the effect of power fading, and improve the high frequency response of bandwidth limited device in Nyquist 4-ary pulse amplitude modulation (4-PAM) system. Furtherly, iterative technique is introduced to mitigate the nonlinear ISI caused by the combined effects of electrical Nyquist filter, limited device bandwidth, optical tilted filter, dispersion, and square-law photo-detection. Thus, the system’s frequency response is greatly improved and the delivery distance can be extended.

Optical diversity transmission using WDM signal and phase-conjugate lights through multi-core fiber.

This paper proposes a maximum-ratio combining (MRC) scheme for a WDM signal and phase-conjugate pair (PCP) diversity transmission to cancel nonlinear phase-shift. A transfer function approximation for nonlinear phase-shift cancellation is formulated. It shows, with the help of a numerical calculation, that span-by-span chromatic dispersion compensation is more effective than the lumped equivalent at the receiver. This is confirmed in a 2-core diversity 5 channel WDM transmission experiment over 3-spans of 60km MCF with 25 Gbit/s-QPSK PCP. The peak Q-value was enhanced by 3.6dB through MRC, resulting in superior bitrate-distance product and optical power density limit, compared to twice the single core transmission.

Novel self-interference suppression schemes based on Dempster-Shafer theory with network coding in two-way full-duplex MIMO relay

A two-way full-duplex multiple-input multiple-output (MIMO) relay provides effective spectral efficiency and system capacity improvement. However, self-interference (SI) as a serious problem limits the development of a full-duplex relay. In this paper, the novel SI suppression schemes based on the Dempster-Shafer (DS) evidence theory are proposed to suppress SI in the two-way full-duplex MIMO relay. DS evidence theory can appropriately characterize uncertainty and make full use of multiple evidence source information by DS combination rule to obtain reliable decisions. The first proposed DS network coding (DS-NC) scheme adopts DS evidence theory to detect the signal of each source node, considering SI suppression in the basic probability assignment computation in the multiple access phase. Moreover, different from the DS-NC scheme, the further proposed DS physical-layer network coding (DS-PNC) scheme considers SI suppression from the vector space perspective and combines the PNC mapping rule with the DS theory to obtain a network-coded signal without estimating each source node signal. In the broadcast phase, antenna selection is adopted at the relay and DS evidence theory is also applied at each source node for SI suppression. Meanwhile, the effects of imperfect SI channel estimation and the intended channel estimation on the proposed schemes are also studied. Finally, the proposed DS-PNC scheme is studied with the SI signal model which considers analog radio frequency cancellation, the effects of I/Q modulator imbalances, and power amplifier nonlinearity of the transmitter. Simulation results reveal that the proposed DS-PNC scheme is a little more sensitive to the channel estimation errors than the traditional spatial-domain schemes. However, with the perfect channel state information, the proposed DS-NC with one iteration and DS-PNC schemes outperform traditional spatial-domain schemes. Furthermore, considering the SI signal model with nonlinear distortion and radio frequency cancellation, the DS-PNC scheme is also superior to the traditional schemes. Meanwhile, the DS-PNC scheme is more robust to the SI and achieves the same diversity gain as the ideal cancellation.

Wide range temperature sensor with adaptive nonlinearity cancellation (ANC) technique for HVICs

A new temperature sensor utilising an adaptive nonlinearity cancellation circuit is proposed among two base-emitter voltages (VBEPT and VBEIO) of the diode-connected bipolar junction transistors driven in saturation region with a proportional to absolute temperature current and an independent of absolute temperature current, respectively. In this way, the nonlinear effect originated from the temperature dependence of saturation current (IS) drift can be cancelled adaptively through subtraction circuits. The measurements indicate that the proposed temperature sensor can achieve a sensitivity of −9.75 mV/°C with linearity up to 99.95% over the temperature range of 170°C (−40–130°C).

Highly Linear Open-Loop Amplifiers Using Nonlinearity Cancellation and Gain Adapting Techniques

Highly Linear Open-Loop Amplifiers Using Nonlinearity Cancellation and Gain Adapting Techniques

Nonlinear Acoustic Echo Cancellation by Exact-Online Adaptive Alternating Minimization

Nonlinear Acoustic Echo Cancellation by Exact-Online Adaptive Alternating Minimization

Optimized WDM Transmission Impairment Mitigation by Multiple Phase Conjugations

Multiple phase conjugations within a transmission-optimized fiber link enable significant nonlinearity cancellation in the wavelength division multiplexed (WDM) systems. In particular, we demonstrate the fiber impairment mitigation of WDM $24\times 48$ Gb/s dual-polarization quadrature phase shift keying (DP-QPSK) signals using 12 optical phase conjugations (OPC). The power excursion and dispersion-tailored transmission line in which the phase conjugations acted periodically, enabled an 8-dB higher nonlinearity threshold for the WDM 1.1-Tb/s DP-QPSK signals. With the nearly perfect nonlinearity cancellation, large input powers per span became available. Under these circumstances, we also present a first approach to the analysis of the impact of multiple phase conjugations in a distributed Raman amplified link. The analysis considers the performance of the experimentally measured OPC subsystem within an optimized transmission line limited only by an amplified spontaneous emission noise. This raw estimate gives insight into the linear noise performance limit of the employed phase conjugator when inserted multiple times in such a transmission system.

A simplified IDA-PBC design for underactuated mechanical systems with applications

We develop a method to simplify the partial differential equations (PDEs) associated to the potential energy for interconnection and damping assignment passivity based control (IDA-PBC) of a class of underactuated mechanical systems (UMSs). Solving the PDEs, also called the matching equations, is the main difficulty in the construction and application of the IDA-PBC. We propose a simplification to the potential energy PDEs through a particular parametrization of the closed-loop inertia matrix that appears as a coupling term with the inverse of the original inertia matrix. The parametrization accounts for kinetic energy shaping, which is then used to simplify the potential energy PDEs and their solution that is used for the potential energy shaping. This energy shaping procedure results in a closed-loop UMS with a modified energy function. This approach avoids the cancellation of nonlinearities, and extends the application of this method to a larger class of systems, including separable and non-separable port-controlled Hamiltonian (PCH) systems. Applications to the inertia wheel pendulum and the rotary inverted pendulum are presented, and some realistic simulations are presented which validate the proposed control design method and prove that global stabilization of these systems can be achieved. Experimental validation of the proposed method is demonstrated using a laboratory set-up of the rotary pendulum. The robustness of the closed-loop system with respect to external disturbances is also experimentally verified.

A multichannel nonlinear adaptive noise canceller based on generalized FLANN for fetal ECG extraction

In this paper, a multichannel nonlinear adaptive noise canceller (ANC) based on the generalized functional link artificial neural network (FLANN, GFLANN) is proposed for fetal electrocardiogram (FECG) extraction. A FIR filter and a GFLANN are equipped in parallel in each reference channel to respectively approximate the linearity and nonlinearity between the maternal ECG (MECG) and the composite abdominal ECG (AECG). A fast scheme is also introduced to reduce the computational cost of the FLANN and the GFLANN. Two (2) sets of ECG time sequences, one synthetic and one real, are utilized to demonstrate the improved effectiveness of the proposed nonlinear ANC. The real dataset is derived from the Physionet non-invasive FECG database (PNIFECGDB) including 55 multichannel recordings taken from a pregnant woman. It contains two subdatasets that consist of 14 and 8 recordings, respectively, with each recording being 90 s long. Simulation results based on these two datasets reveal, on the whole, that the proposed ANC does enjoy higher capability to deal with nonlinearity between MECG and AECG as compared with previous ANCs in terms of fetal QRS (FQRS)-related statistics and morphology of the extracted FECG waveforms. In particular, for the second real subdataset, the F1-measure results produced by the PCA-based template subtraction (TSpca) technique and six (6) single-reference channel ANCs using LMS- and RLS-based FIR filters, Volterra filter, FLANN, GFLANN, and adaptive echo state neural network (ESNa) are 92.47%, 93.70%, 94.07%, 94.22%, 94.90%, 94.90%, and 95.46%, respectively. The same F1-measure statistical results from five (5) multi-reference channel ANCs (LMS- and RLS-based FIR filters, Volterra filter, FLANN, and GFLANN) for the second real subdataset turn out to be 94.08%, 94.29%, 94.68%, 94.91%, and 94.96%, respectively. These results indicate that the ESNa and GFLANN perform best, with the ESNa being slightly better than the GFLANN but about four times more computationally expensive than the GFLANN, which makes the GFLANN a good alternative for NI-FECG extraction.

A Bayesian network approach to linear and nonlinear acoustic echo cancellation

This article provides a general Bayesian approach to the tasks of linear and nonlinear acoustic echo cancellation (AEC). We introduce a state-space model with latent state vector modeling all relevant information of the unknown system. Based on three cases for defining the state vector (to model a linear or nonlinear echo path) and its mathematical relation to the observation, it is shown that the normalized least mean square algorithm (with fixed and adaptive stepsize), the Hammerstein group model, and a numerical sampling scheme for nonlinear AEC can be derived by applying fundamental techniques for probabilistic graphical models. As a consequence, the major contribution of this Bayesian approach is a unifying graphical-model perspective which may serve as a powerful framework for future work in linear and nonlinear AEC.

A Hybrid Nonlinear ANC for Speech Recovery Using Both Bone- and Air-Conducted Measurements

<div class=""abs_img""> <img src=""[disp_template_path]/JRM/abst-image/00270005/08.jpg"" width=""300"" /> Denoising nonlinear filter</div> Speech recovery in the presence of very harsh noise is calling for R&D that take approaches different from those established to date, as the conventional systems and algorithms for speech denoising may suffer from serious performance degradation. In this paper, we propose a hybrid nonlinear adaptive noise canceller (ANC) to perform the speech enhancement task using both bone- and air-conducted measurements. In the proposed ANC, the bone-conducted speech serves as a reference signal while the air-conducted measurement with very large additive noise is adopted as a primary noise. A Volterra filter and a functional link artificial neural network (FLANN) are placed in parallel, forming a hybrid nonlinear ANC. Simulations using real bone- and air-conducted speech measurements are provided to demonstrate that the proposed system outperforms ANCs equipped with FIR filter or Volterra filter or FLANN alone. </span>

Nonlinear Acoustic Echo Cancellation Using Voltage and Current Feedback

Acoustic echo cancellation (AEC) is a well studied problem. The underlying assumption in most echo cancellation solutions is that the echo path following the reference signal is completely linear. However, in many handheld devices, the echo path following the reference signal is nonlinear. The reason for this nonlinearity in the echo path is the use of smaller inexpensive loudspeakers and the desire for generating high sound pressure levels. This brings about the need for a nonlinear echo canceler to maintain the required echo return loss enhancement (ERLE). Many software-based solutions have been proposed to solve this problem, but the computational complexity of these solutions is prohibitively high for practical implementation. This paper analyzes the sources of nonlinearities in smartphones and proposes a simple, elegant hardware modification to significantly reduce nonlinear echo. Thorough analysis and intensive testing results show that up to 6 dB of improvement in ERLE in a real device is possible using the proposed technique.

Dynamic range tuning of graphene nanoresonators

From sensing perspective, smaller electromechanical devices, in general, are expected to be more responsive to the stimuli. This enhanced performance, however, is contingent upon the noise sources remaining unchanged and the onset of nonlinear behavior not being precipitated by miniaturization. In this paper, we study the effect of strain on the nonlinearities and dynamic range in graphene nanoresonators. The dynamic response and the onset of nonlinearity in these devices are sensitive both to the electrostatic field used to actuate the device and the strain. By tuning the strain of the device by two orders of magnitude, we observe an enhancement of 25 dB in the dynamic range leading to a mass resolution of 100 yoctogram. The increase in dynamic range in our devices is modeled as a combined effect of strain and partial cancellation of elastic and electrostatic nonlinearities.

Nonlinear Acoustic Echo Cancellation Using a Nonlinear Postprocessor With a Linearly Constrained Affine Projection Algorithm

This brief presents a nonlinear acoustic echo cancellation algorithm comprising a postprocessor that can model the saturation-type nonlinear distortion of a microphone circuit. To support fast adaptation to the acoustic echo environment, the linear filter is adapted using an affine projection algorithm where the reference input vectors subject to linear operation are dynamically selected to update the coefficient vector. We consider the hard-clipper and sigmoid functions for the postprocessor, and their parameters are adaptively updated using the least-mean-square algorithm. The simulation results confirm that the proposed algorithm achieves fast and stable convergence under saturation-type microphone distortion, and it can have better performance than conventional algorithms.

Overcoming limitations of nanomechanical resonators with simultaneous resonances

Dynamic stabilization by simultaneous primary and superharmonic resonances for high order nonlinearity cancellation is demonstrated with an electrostatically actuated, piezoresistively transduced nanomechanical resonator. We prove experimentally how the combination of both the third-order nonlinearity cancellation and simultaneous resonances can be used to linearly drive a nanocantilever up to very large amplitudes compared to fundamental limits like pull-in occurrence, opening the way towards resonators with high frequency stability for high-performance sensing or time reference.

Global solutions to nonisentropic hydrodynamic models for two-carrier plasmas

This paper is concerned with nonisentropic hydrodynamic models for two-carrier plasmas, which take the form of Euler equations for conservation laws of mass density, current density and energy density for two-carrier plasmas, coupled to Poisson’s equation for self-consistent electronic field. Due to the nonlinear coupling and cancellation between electrons and ions, the expected dissipation rates of densities for two carriers are no longer available in comparison with the one-carrier case, which leads to the lack of exponential stability near constant equilibrium in the whole space. In order to capture the weaker dissipation and obtain global solutions in spatially critical Besov spaces, calculus techniques which have been recently developed in Chemin–Lerner spaces, will be further applied.

Tracking control for a hydraulic drive with a pressure compensator

A problem of tracking control is considered for a hydraulic drive with a pressure compensator that is widespread in the equipment of heavy-duty machines. Method. The control problem is solved by means of a switching sliding-mode controller coupled with static nonlinear compensation and desired velocity feedforward. Main Results. Mathematical model of a hydraulic drive is given in view of the pressure compensator presence. Traditional model of a hydraulic drive is formulated for a system with a spool valve; purpose and principles of operation of the pressure compensator in hydraulic systems are described, and the extended model is presented illustrating compensator contribution to overall system dynamics. It is shown that the obtained model has an input static nonlinearity; the nonlinearity cancellation method is proposed giving the possibility for injection of a desired velocity feedforward term. The control law is chosen as a switching one and two chattering attenuation methods are studied: equivalent control estimation via filtering and sign function integration. Experimental studies are performed at a forestry hydraulic crane prototype and illustrate high tracking accuracy achieved for typical crane motions. Practical Significance. The results are suitable for heavy-duty hydraulic machines automation in construction, road building and forestry.

Iterative Cancellation of Non-Linear Distortion Noise in Digital Communication Systems

In this paper, an iterative receiver that performs non-linear distortion noise cancellation is presented. The performance is assessed for time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA) waveforms. Even though a return link setup is considered, the receiver is equally applicable in the forward link, taking into account the differences in the data multiplexing and the channel. Analytical modeling of the received electrical signal-to-noise ratio (SNR) is carried out for OFDMA with one iteration of non-linear distortion noise cancellation. The performance is assessed in terms of power efficiency and spectral efficiency, where the total degradation (TD) of the received SNR in a non-linear channel is minimized. The modulation formats of the DVB-RCS2 satellite return link standard and a respective non-linear channel have been used. OFDMA shows the highest power efficiency gain of 1.1–2.5 dB with 2 iterations of non-linear noise cancellation across the different modulation orders. In SC-FDMA, the gain is in the range of 0.3–1.1 dB, while gains of 0.1–0.8 dB and 0.2–1.9 dB are presented in TDMA with 20% roll-off and 5% roll-off, respectively.