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Nat. Methods 12, 131–133 (2015); published online 15 December 2014; corrected after print 6 February 2015 In the version of this article initially published, the Hendrickson formula in the Figure 2 legend incorrectly had (2NA/NP)1/2 divided by (f''/Zeff); these terms should have been multiplied. Theerror has been corrected in the HTML and PDF versions of the article.

Most available control algorithms for active noise control (ANC) require identification of the secondary path. This estimation not only increases the control system complexity, but it can add to the residual noise power and even cause the adaptive system to diverge when the identification is not sufficiently close to the real system. We use a geometrical analysis of the filtered-x LMS algorithm to introduce a new ANC algorithm for a single frequency and narrowband noise where no identification of the secondary path is required. We then extend our new ANC algorithm without secondary path identification to the active control of broadband noise through the use of a sub-band ANC implementation. When compared to other available control algorithms requiring no secondary path identification, our method possesses a simple structure, good performance, and a reasonable convergence rate. Simulation results confirm the effectiveness of our proposed algorithms.

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, by leveraging a multi-channel configuration of the Volterra 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 Volterra filter. The developed sub-band configuration of the adaptive Volterra filter can greatly improve the convergence rate and reduce the computational complexity of nonlinear echo cancellers, which is shown by analyses and simulations.

This paper introduces a novel signal exclusive adaptive average (SEAA) filter that offers good image denoising performance in applications characterized by impulsive or impulse-like noise. The proposed algorithm works well in suppressing impulse noise with noise ratios from 3% up to 60%. We begin by introducing a digital differentiation preprocessing step to quantify the increments in each local neighborhood of the noisy image. A homogeneity level map is then derived by adaptive thresholding and used to designate pixels as noise candidates. The initial selection is refined using a novel connected components labeling algorithm. Finally, the noise is attenuated by estimating the values of the noisy pixels with a linear filter applied exclusively to those neighborhood pixels not labeled as noise candidates. This approach bears similarity to several nonlinear techniques including alpha-trimmed means, selective averaging, and WMMR filters. Simulation results indicate that SEAA is better able to preserve 2-D edge structures from the original image and delivers better performance with less computational overhead as compared to competing nonlinear denoising algorithms

It has been proven that adaptive nonlinear predistorters based on direct adaptation have many advantages over ones based on indirect adaptation. In this work, we develop two affine projection based direct adaptation algorithms for adaptive nonlinear predistorter: nonlinear filtered-x affine projection algorithm and nonlinear adjoint affine projection algorithm. Compared with available least mean square (LMS) based direct adaptation predistorters, predistorters based the new developed algorithms have the advantages fast convergence and efficient computational complexity. The nonlinear adjoint affine projection algorithm is computationally more efficient than the nonlinear filtered-x affine projection algorithm. Simulation results confirm the better performance of our developed algorithms.

Implementation of digital signal processing (DSP) algorithms in hardware, such as field programmable gate arrays (FPGAs), requires a large number of multipliers. In this paper, we introduce a new multi-input Canonical Signed Digit (CSD) multiplier unit, which requires fewer shift/add/subtract operations and less CSD number conversion overhead; as a result, we can greatly reduce the power consumption and area requirements in the hardware implementation of DSP algorithms. Furthermore, because all the products are produced simultaneously, the multiplication speed and thus the throughput are improved. The developed multi-input multiplier unit is applied to implement digital filters with non-fixed filter coefficients, such as adaptive filters. The implementation cost of these digital filters can be further reduced by limiting the wordlength of the input signal with little or no sacrifice to the filter performance, which is confirmed by our simulation results. The proposed multiplier unit can also be applied to other DSP algorithms, such as digital filter banks or matrix and vector multiplications.

The constrained minimum output variance method (CMOV), which is also known as the constrained minimum output energy method (CMOE), has been applied to directly blind equalize a linear channel and proven effective with white inputs (Tsaisanis et al. (1999)). It is believed that the method introduced in Tsaisanis can work for a linear system with colored source. In this paper, we correct this misunderstanding, and prove that a colored input will cause the equalizer to incorrectly converge. Consequently, we introduce a new blind channel equalizer algorithm based on the CMOV, but with different constraints. Our proposed algorithm works for channels with either white or colored input, and performs equivalently to the trained minimum mean-square-error (MMSE) equalizer under high SNR. Our proposed algorithm may be regarded as a generalized version of the CMOV in Tsaisanis. However, unlike CMOV, the proposed method exploits the input sequence statistics. As a result, the proposed method performs better than the original CMOV even when the input is white.

One-dimensional (In,Ga)As quantum dot (QD) arrays are created on planar singular, vicinal, and shallow mesa-patterned GaAs (100) substrates by self-organized anisotropic strain engineering of an (In,Ga)As/GaAs quantum wire (QWR) superlattice template in molecular beam epitaxy. On planar singular substrates, highly uniform single QD arrays along [0–11] are formed. On shallow [0–11] and [011] stripe-patterned substrates, the generated type-A and -B steps distinctly affect the surface migration processes which are crucial for QWR template development, i.e., strain-gradient-driven In adatom migration along [011] and surface-reconstruction-induced Ga/In adatom migration along [0–11]. In the presence of both type-A and -B steps on vicinal substrates misoriented towards [101], the direction of adatom migration is altered to rotate the QD arrays. This establishes the relationship between self-organized anisotropic strain and step engineering, which is exploited on shallow zigzag-patterned substrates for the realization of complex QD arrays and networks with well-positioned bends and branches, exhibiting high structural and optical quality. ©2005 American Institute of Physics

In this paper, we present a geometric based analysis of the "filtered" LMS algorithms such as the filtered-x LMS algorithm and the adjoint LMS algorithm. Using this method, the maximum step size, the effects of the secondary path estimation error and the relationship between the adjoint, secondary path equalization and FXLMS LMS algorithms can be easily obtained. Furthermore, our introduced method yields these conditions with some geometrical meaning and intuitive explanation. Based on our introduced method, we also discuss the convergence speed of the filtered-x LMS algorithm for the first time

In this paper, we discuss the sub-space based blind nonlinear channel equalization problem. The conditions required for exciting the zero force equalizer and an MMSE equalizer based on the sub-space algorithm are given. Using these conditions, we propose several efficient sub-space-based blind nonlinear channel equalization algorithms. These provide: 1) a blind zero force equalizer for a nonlinear channel whose linear portion has maximum memory length, 2) an MMSE equalizer for a nonlinear channel whose nonlinear distortion is weak and 3) an MMSE equalizer for a nonlinear channel whose linear part has minimum memory length while the inputs to the linear and nonlinear parts are uncorrelated to each other. Our proposed algorithms are more efficient than currently available methods and work over a broader range of channels. As a result, our algorithms have significant practical application

In this work, we develop novel control algorithms suitable for the smart shock absorber (SSA) component of the intelligent vehicle and bridge system (IVBS). The SSA control serves two IVBS purposes: 1) working as the vehicle suspension to increase driver comfort and controllability when the vehicle is on the pavement, and 2) reducing the vibration of highway bridges and thus prolonging bridge life. We propose and discuss in this paper algorithms targeted at the first purpose. Based on the application of active noise control techniques to an active suspension system, we introduce the clipped active noise control (clipped ANC) algorithm. The main advantage of this algorithm is that because it is adaptive, it can effectively balance the comfort and controllability. A simplified control algorithm based on the clipped ANC is also proposed to reduce the implementation cost. The simplified algorithm has no requirements for system modeling, so it substantially reduces the implementation cost. The effectiveness of our proposed algorithm is indicated by analyses, simulations and laboratory testing.

Vibration mitigation has become increasingly vital for the current highway bridge system. Since the main source of bridge vibrations comes from heavy trucks passing by, we propose a control system that can be installed on the trucks to help reduce bridges' vibration. The approach is based on the nonlinear black-box model of the truck-bridge interaction.

Adaptive filtering is a widely used technique in active noise control (ANC). In order to make the adaptive filter in an FXLMS (filtered-x LMS) ANC system stable, the reference signal must pass through an estimation filter whose phase response is within /spl plusmn/90/spl deg/ of the phase of the secondary path. In this paper, we study the quantization effects on the filter phase response and the relationship between the phase response and the location of the zeros and poles. In addition, we propose a filter structure and nonuniform quantization method in which we quantize the filter coefficients so they each contain a small number of nonzero bits, based on the distance of the zeros/poles to the unit circle, to guarantee that the /spl plusmn/90/spl deg/ allowable phase deviation is met - greatly reducing the implementation cost. We combine these ideas with that of multiplierless implementations of adaptive FIR filters to realize an efficient active noise control using field programmable gate arrays or other digital hardware.

The filtered-X LMS algorithm is successfully applied in linear active noise control and linear active vibration control. However, when it comes to non-linear noise or vibration control, or when the secondary path has a non-linearity, this algorithm must be modified to ensure that it converges and that it is unbiased. Some modified algorithms have been proposed for active control of nonlinear noise with a linear secondary path [L.Z. Tan and J. Jiang, Aug. 2001] or a weakly non-linear secondary path [V. DeBrunner and D. Zhou, 2002]. In this paper, we extend 'a non-linear filtered-X LMS' algorithm to solve the active non-linear noise control (ANNC) and active non-linear vibration control (ANVC) with non-linearities in the secondary path using an adaptive Volterra filter for the first time. Two improved versions of the non-linear adaptive filters that improve the stability and reduce the computational complexity are proposed and discussed in detail. Simulations show their effectiveness.

The filter-X LMS algorithm is successfully applied in linear active noise control and linear active vibration control. However, when it comes to nonlinear noise or vibration control, or the secondary path has a nonlinearity, this algorithm needs to be modified to ensure that it converges and that it is unbiased. We proposed configurations [V. DeBrunner, et al., 2003] that solve both the main path nonlinearity and the secondary path nonlinearity problems where the nonlinearity can be expressed by Volterra series. However, in practices some nonlinear system can be expressed in much simple form such as a linear filter followed by a memoryless nonlinearity (Wiener model), a memoryless nonlinearity followed by linear filter (Hammerstein model), a linear filter, a memoryless nonlinearity and another linear filter connected in series (LNL model). Such kinds of nonlinear system structure can greatly reduce the computation burden and simplify the implementation structure. In this paper, we give out active nonlinear noise control (ANNC) with these kinds of secondary path nonlinearity. We find with these kinds of nonlinear structure in the secondary path, the ANNC will have much simpler structure and the computation burden can be further reduced.

Xu, Y. et al. (see IEEE T-IP, vol.3, no.6, 1994) proposed an effective wavelet based spatially selective denoising algorithm. The performance of the algorithm depends on the noise power estimation. Pan, Q. et al. (see IEEE T-SP, vol.47, no.12, 1999) tried to improve the performance via a small modification. However, our simulation shows that both of these methods are sensitive to noise estimation. We analyze the sensitivity of these two methods and introduce a new spatially selective noise filter based on the UDWT (undecimated wavelet transform) that uses spatial correlation thresholding. Theoretic analysis and simulations show our algorithm improves the denoising effect. They also show that our proposed method is robust to errors in the noise power estimate. Because our approach is robust, we can relax the requirements for the estimation of the threshold without sacrificing performance, and so our method is more computationally efficient. We also put some perspective on the impact of employing nonorthogonal representations. Simulation results show the effectiveness of our proposed algorithm.

In this paper, we address the problem of adaptive control of a nonlinear noise process in the presence of a weakly nonlinear secondary path; This problem is common in many cases of Active Vibration Control (AVC) and Active Noise Control (ANC) where the secondary path nonlinearity is due to the presence of a weak nonlinear actuator. Our proposed configuration turns out to be subsumed by a method called the filtered-A LMS algorithm proposed by Klippel [1997]. In that paper, Klippel attempted to linearize a weakly nonlinear plant (main or primary path) using an adaptive inverse control method so that the nonlinear plant will track an input signal. He certainly did not consider our configuration or usage. Thus some effort to connect these two algorithms is required. Furthermore, we also determine that as the nonlinear secondary path becomes linear, and there is thus only a nonlinear primary path, the filtered-A LMS algorithm and our configuration gives the so-called Volterra filtered-x LMS (VFLMS) algorithm [2001] developed by Tan and Jiang. In this paper, we connect the algorithms. Detailed implementation information is provided. Extensive simulations show that the algorithm works well for our AVC problem.

This paper considers a range of channel allocation schemes for High Speed Circuit Switched Data (HSCSD) over GSM and reports performance (blocking probability) and efficiency results. The channel allocation schemes studied differ in the way channels are packed (First Fit, Best Fit and Repacking), and in the connection admission policy. An overall performance comparison of the schemes is provided in order to gain insight into simplicity/efficiency tradeoffs.

This paper reports on a simulation-based investigation of a wavelength diverse free-space optical link with an emphasis on identifying design choices that optimize the performance of the system under different operating scenarios. The simulation incorporates experimental data into the theoretical calculations for optical propagation to better describe the performance of the physical designs. The performance is evaluated in terms of the coverage area at the receiver, which is a measure of misalignment tolerance and is dependent not only on wavelength but on other key parameters, such as link length, transmitted power, the pattern of transmitters, beam divergence, and the receiver construction. The investigation finds that the coverage area of the receiver can be optimized for a given wavelength by proper choices of these parameters, and that parameter choices exist that minimize the change in performance when switching between wavelengths or for variations in link parameters. The interrelationships among key parameters and their impact on the potential system performance are investigated. The results provide guidance on the further development of the overall system.

Purpose To retrospectively evaluate the safety and retrievability of the Celect IVC filter. Materials and Methods All patients undergoing Celect filter placement and retrieval between 2007 and 2012 were assessed for complications and retrievability. Results Of 690 patients who had Celect filter placement, 143 presented for removal. The indwelling time in these patients was 176.2 ± 150.3 days (range, 2-1413 d). A total of 125 filters (87.4%) were removed; 18 filters were left in situ for the following reasons: filter embedment (7), caval occlusion (3), retained thrombus (3), large floating thrombus in IVC (4), or tilt > 15° (1). With filters in place, 6 patients developed new pulmonary embolism and 2 others presented with severe abdominal pain. The available 135 pairs of placement and removal cavagrams suggested limb penetration in 112 cases (86.1%); intracaval migration > 2 cm in 5; secondary tilt > 15° in 8; filter deformity in 10; retained thrombus within filters in 13; and IVC occlusion in 3. Among 52 available CT scans, 11 cases (21%) demonstrated asymptomatic limb penetration to the duodenum (6), aortic wall (3), kidney (1) and liver (1). No filter fracture was found. Conclusion This study showed a high penetration rate for Celect IVC filters, including penetrations that were symptomatic or involved adjacent structures. Penetration appears to correlate with indwelling time, suggesting that the filter should be removed as soon as PE protection is no longer indicated. Although most of the filters were removed, 5.6% of retrievals were unsuccessful because of technical failure.

Volatiles emitted by healthy, mechanically damaged, and weevil-infested Artemisia ordosica (Asteraceae) were obtained through a dynamic headspace method and analysed by automatic thermal desorption/gas chromatography/mass spectrometry (ATD/GC/MS). Twenty-eight compounds in all were identified, and the qualitative as well as quantitative differences were compared. The green leaf volatiles 2-hexenal, (Z)-3-hexen-1-ol, 2-hexen-1-ol, 1-hexanol, and (Z)-3-hexen-1-ol acetate were present in all of the damaged plants, but in relatively lower portions when plants were infested by the weevil Adosopius sp., while the terpenoids α-copaene, β-cedrene, and (E,E)-α-farnesene and the ester methyl salicylate were only present in weevildamaged plants. The volatiles from healthy and weevil-infested leaves were dominated by D-limonene, whereas mechanically damaged leaves emitted β-pinene as the dominant compound

International audience; We report on the uniformity improvement of InAs quantum dashes (QDHs) grown by molecular beam epitaxy on InP (100) through optimizing double cap technique. Broad-area lasers were fabricated with an emission wavelength of 1.58 μm. A threshold current density of 360 A/cm2 was achieved for a five stack QDH structure and a cavity length of 1.2 mm. This results from a reduced inhomogeneous broadening (62 meV) and lower internal optical losses (7 cm-1). The achievement paves the way toward ultralow threshold semiconductor laser for telecommunications.

The authors report lateral positioning and number control of InAs quantum dots (QDs) on truncated InP (100) pyramids by selective-area metal organic vapor-phase epitaxy. With reducing QD number, sharp emission peaks are observed from individual and single QDs with wavelength tuned into the 1.55μm telecom region by insertion of ultrathin GaAs interlayers beneath the QDs. Regrowth of a passive waveguide structure around the pyramids establishes submicrometer-scale active-passive integration for efficient microcavity QD nanolasers and single photon sources.

We report on the optical properties of threefold stacked InGaAs sidewall quantum wires (QWires) with quaternary InGaAsP barriers grown on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent quantum wells (QWells) into the QWires at low temperature, thermally activated repopulation of the QWells at higher temperature, and negligible localization of carriers along the QWires. Strong broadening of power dependent PL indicates enhanced state filling in the QWires compared to that in the QWells. Clear linear polarization of the PL from the QWires confirms the lateral quantum confinement of carriers. These results demonstrate excellent optical quality of the sidewall QWire structures with room temperature PL peak wavelength at 1.55μm for applications in fiber-based optical telecommunication systems.

Highly strained InAs quantum dots (QDs) embedded in InGaAsP are formed at the fast- growing [01-1] mesa sidewall on shallow-patterned InP (311)A substrates by chemical beam epitaxy.Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent dashlike QDs in the planar areas to the larger sidewall QDs resulting in well-distinguishable emission around 80 K. The large high-energy shift of the PL from the sidewall QDs as a function of excitation power density is ascribed to the screening of the internal piezoelectric field. The linear polarization of the PL from the sidewall QDs is reversed compared to that of the quantum dashes in the planar areas due to the more symmetric shape and possible nonuniform strain in the sidewall QDs.

Tsatsanis and Xu have applied the constrained minimum output variance (CMOV) principle to directly blind equalize a linear channel—a technique that has proven effective with white inputs. It is generally assumed in the literature that their CMOV method can also effectively equalize a linear channel with a colored source. In this paper, we prove that colored inputs will cause the equalizer to incorrectly converge due to inadequate constraints. We also introduce a new blind channel equalizer algorithm that is based on the CMOV principle, but with a different constraint that will correctly handle colored sources. Our proposed algorithm works for channels with either white or colored inputs and performs equivalently to the trained minimum mean-square error (MMSE) equalizer under high SNR. Thus, our proposed algorithm may be regarded as an extension of the CMOV algorithm proposed by Tsatsanis and Xu. We also introduce several methods to improve the performance of our introduced algorithm in the low SNR condition. Simulation results show the superior performance of our proposed methods.

Several channel allocation schemes for high speed circuit switched data (HSCSD) over GSM are studied. The schemes differ in the way channels are packed (first fit, best fit and repacking), and in the connection admission policy. We study their blocking probability and utilisation. The performance of the schemes is studied with special focus on their simplicity/efficiency tradeoffs.