Nonlinear Cancellation Research Articles

Sub-band Implementation of Adaptive Nonlinear Filter for Adaptive Nonlinear Echo Cancellation

The adaptive Volterra filter has been successfully applied in nonlinear acoustic echo cancellation (AEC) systems and nonlinear line echo cancellation systems, but its applications are limited by its required computational complexity and slow convergence rate, especially for systems with long memory length. In this paper, we first apply a more general nonlinear filter, the function expansion nonlinear filter, in the acoustic echo cancellation - the Volterra filter can be regarded as special case of the function expansion nonlinear filter. Then by leveraging to a multi-channel configuration of the function expansion nonlinear filter and the sampling theory for nonlinear systems, we extend linear sub-band delay-less adaptive filter techniques to develop an efficient sub-band implementation of the adaptive function expansion nonlinear filter. The developed sub-band configuration of the adaptive nonlinear filter can greatly improve the convergence rate and reduce the computational complexity of nonlinear echo cancellers, which is shown by analyses and simulations.

Adaptive neuro-fuzzy inference systems based approach to nonlinear noise cancellation for images

The adaptive neuro-fuzzy inference system (ANFIS) is an effective tool that can be applied to induct rules from observations, e.g. pattern recognition. In this paper, we extend the nonlinear noise cancellation method using ANFIS from 1-D signals to 2-D counterpart images. First, the image restoration contaminated with Gaussian noise is investigated in nonlinear passage dynamics of order 2. We inspect eight types of membership functions (MF): bell MF, triangle MF, Gaussian MF, two sided Gaussian MF, pi-shaped MF, product of two sigmoidal MFs, difference of two sigmoidal MFs, and trapezoidal MF. In addition, the other parameters, such as the training epochs, the number of MFs for each input, the optimization method, the type of output MFs, and the over-fitting problem, are investigated. For comparison with the noise cancellation using ANFIS, we simulate 22 conventional filtering techniques: spatial filters, optimal Wiener filter, frequency domain filters, wavelet, wavelet packet, 2-D adaptive filters, etc. The quality in terms of mean square error (MSE) of image restoration using the proposed noise cancellation using ANFIS (Pi-shaped MF) is at least 75 times better for Gaussian noise than that derived using any of these conventional filtering techniques.

A ROBUST NONLINEAR CONTROL DESIGN FOR PATH FOLLOWING OF A MARINE SURFACE VESSEL

The problem of path following for marine surface vessels using rudder angle is addressed in this paper. A 4 degrees of freedom nonlinear surface vessel model, together with the Serret-Frenet equations, is introduced to describe the ship dynamics and path following error dynamics. While similar models have been used and reported in literature for path following control algorithm development, the novelty of the approach presented in this work lies in the following aspects: (a) The back-stepping nonlinear controller design is based on feedback dominance, instead of feedback linearization and nonlinearity cancellation; (b) Relying on feedback dominance, the resulting controller is almost linear, with very benign nonlinearities allowing for analysis and evaluation; (c) Performance of the nonlinear controller, in terms of path following, is analyzed for robustness in the presence of rudder saturation and rate limits, delays in the control execution, as well as measurement noises. Because of its simple form, very limited on-board computational power is required to implement the control. The simulation results are presented to verify and illustrate the analytic development and the effectiveness of the resulting control.

A Mixer With Third-Order Nonlinearity Cancellation Technique for CDMA Applications

A feedforward technique to improve the third-order nonlinearity of mixers in a direct conversion transceiver is presented. The third-order intermodulation (IM3) generated by the main transconductance (G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m </sub> ) stage of mixer with inductively degenerated emitter is cancelled by that generated by the sub-G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> stage with degeneration resistor. The circuit allows the mixer to be optimized independently, and has minimal impact on noise figure (NF), gain, area, and current consumption. The proposed technique reduced IM3 by approximately 16 dB with a current increase of approximately 7%. The mixer achieved an input-referred third-order intercept point of 5 dBm, a gain of 37 dB, and an NF of 9.8 dB drawing 7.9 mA from a 2.85-V supply. The transceiver including the calibration circuitry was implemented in a SiGe bipolar transistor with f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> = 35GHz for U.S. cellular code division multiple access application

A Highly Linear Low-Noise Amplifier

A low-noise amplifier (LNA) that achieves high third-order input intercept point (IIP3) at RF frequencies using a nonlinearity cancellation technique is proposed. The circuit tackles the problem of the effect of the second-order nonlinearity on IIP3 at RF frequencies. The circuit functionality is analyzed using Volterra series. The linear LNA was designed and fabricated in a TSMC 0.35-mum CMOS process. An IIP3 of +21 dBm was achieved with a gain of 11.5 dB, noise figure of 2.95 dB, and a power consumption of 9 mA at 2.5 V

A High Precision Motion Control System With Application to Microscale Robotic Deposition

Decreasing the minimum feature size of solid free-form (SFF) fabrication techniques requires advancements in both the SFF process and the actuating hardware. Microscale robotic deposition (mu-RD) is an ink-deposition SFF process where recent advances in ink design coupled with a high-precision motion system can lead to the fabrication of parts with microscale-sized features. This paper presents a control algorithm that combines nonlinearity compensation and a learning feedforward approach to achieve high-precision tracking with a standard, off-the-shelf motion system. The off-the-shelf motion system is affected by several nonlinear disturbances that severely inhibit the accuracy of linear models for small motions. Iterative learning control (ILC) is used in an inverse identification procedure to obtain accurate maps of the disturbances. These maps are used in the controller to yield a linear system after nonlinearity cancellation. As a further improvement, ILC is used to increase accuracy in tracking the repetitive portion of specific part trajectories. The combined approach yields extremely low contour tracking errors and is used to fabricate two types of periodic parts demonstrating high aspect ratios and spanning elements. Although high-precision tracking can also be achieved with an expensive, customized system, the off-the-shelf system combined with the control technique presented here provides a more cost-effective solution. The proposed control technique is effective for improving performance of repeatable, but uncertain nonlinear systems

Compensation of Loudspeaker Nonlinearity in Acoustic Echo Cancellation Using Raised-Cosine Function

The nonlinearity of a power amplifier or loudspeaker in a large-signal situation gives rise to a nonlinear distortion of acoustic signal. A conventional acoustic echo canceller using linear adaptive filters is not able to eliminate the nonlinear echo component. In this brief, a novel nonlinear echo cancellation technique is presented by using a nonlinear transformation in conjunction with a conventional linear adaptive filter. The nonlinear transformation is derived from a raised-cosine function and is exploited to compensate for the nonlinearity of a loudspeaker. The transformation parameters are updated using the normalized least mean square algorithm according to the unknown nonlinear characteristic of the loudspeaker. Computer simulations show that the proposed method yields, in general, a satisfactory cancellation performance while having a very low computational complexity

DS-CDMA Non-linear Interference Canceller with Multiple-Beam Reception

In this paper, a multistage parallel interference canceller (MPIC) with multiple-beam reception for a DS-CDMA system is proposed to suppress multiple access interference (MAI) effectively. Its aim is to reduce the computational complexity of the conventional MPIC cascaded with an adaptive array antenna. It employs multiple fixed beams based on phased array and selects suitable beams to demodulate the transmitted signal of each user. Then it suppresses residual interference signals by the MPIC cascaded with multiple-beam receiver. Its bit error rate (BER) performance is evaluated by computer simulations assuming an uplink single-chip-rate multiple-spreading-factor DS-CDMA system over both exponentially decaying 5-path and equal average power 2-path Rayleigh distributed channels. When there are 16 users in an 120°-sectored single cell, the proposed receiver with 6-element array antenna and 2-stage MPIC shows better or comparable BER performance compared with that of the conventional receiver. Moreover, the proposed receiver with 8 beams can reduce the number of complex multiplications to about 40% of that of the complexity-reduced conventional receiver over 5-path channels.

Design and implementation of a sliding-mode controller and a high-gain observer for output tracking of a three-axis pickup

A novel decoupling actuation scheme applied to a new three-axis four-wire optical pickup is synthesized in this study based on theories of sliding-mode control and high-gain observer. The three-axis pickup owns the capability to move the lens holder in three directions of focusing, tracking and tilting. This capability is required particularly for higher data-density optical disks to annihilate the non-zero lens tilting. To achieve control design, Lagrange's equations are first employed to derive equations of motion for the lens holder. A sliding-mode controller is then designed to perform dynamic decoupling and nonlinearity cancellation with the aims of precision tracking, focusing and no tilting. A full-order high-gain observer is next forged to estimate the velocities of the moving lens holder in order to provide low-noised feedback velocity signals for the designed sliding-mode controller. Simulations are carried out to choose appropriate parameter values of the designed controller and observer. Finally, experiments are conducted to validate the effectiveness of the controller for annihilating lens tilting and the capability of the observer for reducing the effects of digital noises on pickup positionings.

Advanced detection and coding techniques for nonlinear intersymbol interference cancellation in 40 Gb/s systems

To mitigate the fibre nonlinearities in high-speed transmission (at 40 Gb/s or higher), the use of maximum a posteriori probability (MAP) symbol decoding supplemented with iterative decoding is proposed. The MAP detector operates on the channel trellis to correct the corrupted data and to provide soft outputs processed further in an iterative decoder. Impressive performance improvement is demonstrated.

Non-linear cancellation of the parametric resonance in elastic beams: Theory and experiment

A non-linear control strategy is applied to a simply supported uniform elastic beam subjected to an axial end force at the principal-parametric resonance frequency of the first skew-symmetric mode. The control input consists of the bending couples applied by two pairs of piezoceramic actuators attached onto both sides of the beam surfaces and symmetrically with respect to the midspan, driven by the same voltage, thus resulting into symmetric control forces. This control architecture has zero control authority, in a linear sense, onto skew-symmetric vibrations. The non-linear transfer of energy from symmetric motions to skew-symmetric modes, due to non-linear inertia and curvature effects, provides the key physical mechanism for channelling suitable control power from the actuators into the linearly uncontrollable mode. The reduced dynamics of the system, constructed with the method of multiple scales directly applied to the governing PDE’s and boundary conditions, suggest effective forms of the control law as a two-frequency input in sub-combination resonance with the parametrically driven mode. The performances of different control laws are investigated. The relative phase and frequency relationships are designed so as to render the control action the most effective. The control schemes generate non-linear controller forces which increase the threshold for the activation of the parametric resonance thus resulting into its annihilation. The theoretical predictions are compared with experimentally obtained results.

Widely linear reception strategies for layered space-time wireless communications

A new class of receivers based on widely linear data processing has been recently proposed for data detection in communication systems affected by improper complex noise. In this paper, it is shown that this detection strategy may be applied to wireless communication systems employing multiple transmit and receive antennas and adopting a noncircular modulation. Improved versions of the linear decorrelating and minimum mean square error (mmse) receivers, and of the nonlinear nulling and cancellation (V-BLAST) receiver are, thus, developed and analyzed. In particular, we show that the improved receivers outperform the conventional ones both in terms of the error probability and of the capacity to cope with the power disparities that the fading channel may induce on the data streams transmitted by different antennas. Moreover, the improved receivers exhibit satisfactory performance also in systems with a number of transmit antennas exceeding the number of receive antennas. Finally, we also consider the situation in which the propagation channel is not perfectly known to the receiver, and show that the performance of the improved receivers is less sensitive to the channel estimation errors than the conventional receivers.

An Implementation of Nonlinear Multiuser Detection in Rayleigh Fading Channel

A blind nonlinear interference cancellation receiver for code-division multiple-access- (CDMA-) based communication systems operating over Rayleigh flat-fading channels is proposed. The receiver which assumes knowledge of the signature waveforms of all the users is implemented in an asynchronous CDMA environment. Unlike the conventional MMSE receiver, the proposed blind ICA multiuser detector is shown to be robust without training sequences and with only knowledge of the signature waveforms. It has achieved nearly the same performance of the conventional training-based MMSE receiver. Several comparisons and experiments are performed based on examining BER performance in AWGN and Rayleigh fading in order to verify the validity of the proposed blind ICA multiuser detector.

Iterative detection and decoding with an improved V-BLAST for MIMO-OFDM systems

Multiple-input-multiple-output (MIMO) systems provide a very promising means to increase the spectral efficiency for wireless systems. By using orthogonal frequency-division multiplexing (OFDM), wideband transmission can be achieved over frequency-selective fading radio channels. First, in this paper, we introduce an improved vertical Bell Labs layered space-time (V-BLAST) receiver which takes the decision errors into account. Second, we propose an iterative detection and decoding (IDD) scheme for coded layered space-time architectures in MIMO-OFDM systems. For the iterative process, a low-complexity demapper is developed by making use of both nonlinear interference cancellation and linear minimum mean-square error filtering. Also, a simple cancellation method based on hard decision is presented to reduce the overall complexity. Simulation results demonstrate that the proposed IDD scheme combined with the improved V-BLAST performs almost as well as the optimal turbo-MIMO approach, while providing tremendous savings in computational complexity.

Knight Shifts around Vacancies in the 2D Heisenberg Model

The local response to a uniform field around vacancies in the two-dimensional spin-1/2 Heisenberg antiferromagnet is determined by numerical quantum Monte Carlo simulations as a function of temperature. It is possible to separate the Knight shifts into uniform and staggered contributions on the lattice which are analyzed and understood in detail. The contributions show interesting long- and short-range behavior that may be of relevance in NMR and susceptibility measurements. For more than one impurity, remarkable nonlinear enhancement and cancellation effects take place. We predict that the Curie impurity susceptibility will be observable for a random impurity concentration even in the thermodynamic limit.

Orthogonalized power filters for nonlinear acoustic echo cancellation

Standard approaches for the cancellation of acoustic echoes in telecommunication systems assume that the echo path to be identified can be modeled by a linear system. However, in applications such as echo cancellation for mobile communication terminals, non-negligible nonlinear distortions are introduced by loudspeakers and their amplifiers, resulting in a significant degradation of the performance of purely linear approaches. In this contribution we consider so-called power filters in order to cope with these kinds of nonlinear echo paths. By combining time-domain orthogonalization methods with a DFT-domain implementation of power filters we derive corresponding quasi-complete orthogonalized versions. As the statistical properties of speech input are non-stationary, the orthogonalization must follow this time-variance, too. Furthermore, we introduce a step-size control for the adaptation of the equivalent orthogonalized structure. Experiments with real hardware show that, with the proposed nonlinear approach, an increase in echo attenuation can be achieved, if the loudspeaker system introduces saturation-type nonlinearities in the echo path.

Techniques for nonlinearity cancellation into embedded links by optical phase conjugation

One of the main causes of signal degradation in high-bit-rate transmission systems is the interplay between fiber nonlinear effects and dispersion. Different techniques to compensate nonlinear effects in transmission systems, by using an optical phase conjugator, have been proposed in the literature. In this paper, two different innovative setups allowing nonlinearity cancellation in an embedded link are disclosed. The proposed schemes are simpler than those previously described and strongly improve systems performances. The physical mechanism allowing nonlinearity compensation is depicted, and the effectiveness of the proposed solutions is numerically demonstrated. Moreover a new practical method, useful for performance optimization of systems including a phase conjugator, is presented. Results apply to any bit-rate and modulation format.

Cancellation Moderating Factor Control for DS-CDMA Non-linear Interference Canceller with Antenna Diversity Reception

In a CDMA non-linear interference canceller, a generated replica of an interference signal is multiplied by a positive number smaller than unity, which is called cancellation moderating factor (CMF), to prevent interference enhancement due to inaccurate replica subtraction. In this paper, two CMF controlling schemes applicable to a multistage parallel interference canceller with multi-antenna (spatial diversity) reception are proposed. They control CMF by using the mean square error of the complex channel gain or by using the ratio of the estimated power of each interference signal to remaining interference signals' power, in order to mitigate the replica subtraction error due to inaccurate channel estimation. The performance of the proposed schemes are evaluated by computer simulations assuming an asynchronous uplink single chip-rate variable spreading factor DS-CDMA system. The simulation results show that the proposed schemes with higher order diversity reception improve the bit error rate (BER) performance compared with a conventional scheme considering the tentative decision error or fixed CMF settings. Their performance improvement is by 0.1--0.9 dB in terms of the required Eb/N0 at an average BER of 10-5 over exponentially decaying 5-path Rayleigh distributed channels when the number of receiving antennas is 6.

A Novel CMOS Realization of the Differential Input Balanced Output Current Operational Amplifier and its Applications

In this paper a new realization of the differential input balanced output current opamp is proposed, operating with ±1.5 V supplies. Its architecture is based on the use of current inverters to sense the input currents while providing a very low input resistance, 23 ?. The opamp provides a maximum output swing of 700 ?A, with an input offset current of 3.5 nA. The differential gain achieved is 65.5 dB, and the differential structure adopted in the design provided a high CMRR, 89.5 dB, the proposed circuit is compared to other realizations with single and differential inputs. The applications of the current opamp are exploited some new applications are presented such as: MOSFET-C integrators, full non-linearity cancellation for MOS transistors, and finally a digitally tuned current-mode variable gain amplifier, which has a gain tuning range of 25 dB with a 0.05 dB step.

Nonlinear Distortion Cancellation Using LINC Transmitters in OFDM Systems

The LInear amplification using Nonlinear Components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system, such as Digital Video Broadcasting (DVB) system, which is based on a very sensitive to nonlinear distortions OFDM modulation scheme. The major drawback of LINC transmitters is the inherited sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method, which corrects any gain and phase imbalances in LINC transmitters mainly due to the un-matching of the two amplifier paths, is described. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficients to correct gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator impairments. A computer simulation has been carried out to verify method functionality.