Sampling In Frequency Domain Research Articles

Improvement of the envelope – transient S-parameters' simulation in circuit and system simulation

This paper focuses on the behavioral modeling of the passive RF blocks from frequency-domain samples. This work is based on vector fitting (VF) approach which is a robust method for MIMO system identification in the frequency domain. This paper addresses firstly the problem of convergence using envelope transient (ET) on complex circuits, i.e. power amplifiers (PAs), where linear sub-circuits are widely described through S-parameters matrices derived from ElectroMagnetic (EM) simulations. An alternative way leads to combine VF method with an RLC synthesis process at the circuit level. This approach is validated on a simple circuit case and generalized to MIMO systems. Second application is the behavioral modeling of MIMO blocks at system level in a high-level spice-like system simulation tool which allows “Control Flow” simulations. The proposed approach combines on one hand the VF method with and impulse responses evaluation on the other hand. In consequence, bilateral behavioral models of MIMO system can be efficiently achieved irrespective of the number of access. This method is validated at once on simple and complex MIMO blocks. As a result, the topological behavioral modeling of complex PAs, which distinguish linear sub-circuits and nonlinear ones, is now possible in a high-level time-domain CAD tool.

Sequential geoacoustic inversion using frequency coherent processing

Insufficient sampling in frequency domain results in range aliasing that affect geoacoustic inversion. Range aliasing and its effects on source localization and environmental parameter inversion are demonstrated on data collected during the MAPEX2000 experiment. Using a source and geoacoustic particle filter mitigates range aliasing caused by using just a few frequencies. Particle filters are sequential Bayesian techniques that provide dynamic estimation of both the geoacoustic parameters and their evolving uncertainties. This approach allows for side lobe suppression due to prior information supplied by the particle filter and hence improved source localization that results in better geoacoustic inversion.

Range aliasing in frequency coherent geoacoustic inversion

This paper discusses the effects of frequency selection on source localization and geoacoustic inversion methods that use frequency coherent objective functions. Matched-field processors based on frequency-coherent objective functions often have rapidly fluctuating range ambiguity surfaces. Insufficient sampling in frequency domain results in range aliasing terms that affect geoacoustic inversion. Range aliasing and its effects on source localization and environmental parameter inversion are demonstrated on data collected during the MAPEX2000 experiment. Guidance for frequency selection to avoid range aliasing is provided.

Damped sinusoidal signals parameter estimation in frequency domain

Parameter estimation of noisy damped sinusoidal signals in the frequency domain is presented in this paper. The advantage of the frequency domain approach is having the spectral energy concentrated in frequency domain samples. However, the least squares criterion for frequency estimation using frequency domain samples is nonlinear. A low complexity three-sample estimation algorithm (TSEA) for solving the nonlinear problem is proposed. Using the TSEA for initialization, a frequency domain nonlinear least squares (FD-NLS) estimation algorithm is then proposed. In the case of white Gaussian noise, it yields maximum likelihood estimates, verified by simulation results. A time domain NLS (TD-NLS) estimation algorithm is also proposed for comparison. The Cramer–Rao lower bound (CRLB) of the frequency domain estimation algorithms is derived. The theoretical analysis shows that the FD-NLS can yield a near-optimal performance with few energy-concentrated samples. On the other hand, the TD-NLS does not have the energy concentration property and requires more time domain samples to perform satisfactory estimation. Simulation results verify that the frequency domain estimation algorithms provide better tradeoff between computational complexity and estimation accuracy than time domain algorithms.

Analysis of the radar range extension in open-ended waveguide type geometries

High frequency EM backscatter modeling of large waveguide type geometries is a difficult task. In analysis of radar range profile, wider bandwidths make modeling even more challenging. Here, a new dispersive scattering center model is used based on Model Based Parameter Estimation (MBPE) approach. The model is capable of representing the radar range extension according the nonlinear variations of the scattering phase. A population-based Maximum Likelihood (ML) algorithm is used to calculate the parameters. The PRONY method is used for initialization. Wideband sparse measured frequency domain samples are the inputs of the model. The results are compared with IFFT outcomes.

WIDEBAND DISPERSION ANALYSIS OF WAVEGUIDE GEOMETRIES USING FINITE SAMPLED DATA

Wideband analysis of frequency dispersive geometries is a challenge in inverse scattering problems. Waveguide duct is an important case in aerial targets with dominant returns. Its dispersive behavior afiects the range proflle analysis due to occurrence of unwanted range extension. A new high frequency analysis using model based parameter estimation (MBPE) approach is presented. A group delay criteria derived from the nonlinear scattering phase response represents the duct length. Wideband sparse measured frequency domain samples of various waveguides are used as inputs to the model. Comparison is made with joint time-frequency analysis (JTFA) and inverse fast Fourier transform (IFFT) results.

A frequency domain subspace blind channel estimation method for trailing zero OFDM systems

The technique of orthogonal frequency division multiplexing (OFDM) is widely used for high-speed data transmission in indoor and outdoor communication networks. Trailing zero (TZ) OFDM systems possess some favorable features compared to conventional cyclic prefixed OFDM systems. In this paper, we propose a blind channel estimation method for TZ-OFDM systems in the frequency domain. The significance of the proposed method is threefold. First, it gives an insight into the characteristics of TZ-OFDM systems from a frequency domain perspective. The characteristics revealed are not clearly manifest in the time domain. Second, by exploiting the desirable property brought by the trailing zeros and making use of the frequency domain samples available at the TZ-OFDM receiver, the frequency domain subspace based blind channel estimator is straightforward in concept and algorithm derivation as opposed to a time domain formulation. Third, the proposed method explicitly addresses the issue of unknown channel length. The new method is theoretically proven and numerically shown to work effectively for channels of unknown length. Simulation results demonstrate the satisfactory performance of the proposed method as compared to the existing methods and its robustness to channel overestimation.

Cleaning-up dirty isotachopherograms in time and frequency domain

In chromatography and electrophoresis S/N is increased by time or frequency domain filtering, multiple injections or sample stacking (in case of CZE). Bottom line is noise reduction without peak distortion. Isotachophoresis (ITP) using conductivity detection is also relevant because of its entirely different information content and the importance in CZE stacking. Several time- and frequency domain filters (Fourier & Walsh transform) were compared. Results were:•Time domain filters can be equally applied to either integral or differential signal;•Fourier and Walsh transforms are likewise suitable, whereas Walsh better preserves sharp boundaries;•Disturbance by detector transfer function can only be partly un-done with de-convolution; conditions are critical.

Frequency domain sampling and receiving method for ultla-wideband pulse signal

Frequency domain sampling and receiving method for ultla-wideband pulse signal

A Maximum Likelihood Fine Timing Estimation for Wireless OFDM Systems

Orthogonal frequency division multiplexing (OFDM) systems are more sensitive to timing synchronization than single carrier systems. This paper presents a fine timing synchronization scheme which utilizes the channel impulse response (CIR) estimated from frequency-domain samples at OFDM receivers. A maximum likelihood estimate (MLE) of timing offset is derived based on the probability distribution of the estimated CIR under time-varying multipath fading. The ML timing scheme is further developed for both integer precision and real-valued precision implementations. In the real-valued timing precision case, a delay locked loop (DLL) structure is devised as an effective way to implement the MLE. Both analysis and simulations of the proposed MLE showed significant improvement over existing schemes under time-varying multipath fading channels.

Quantitation and mapping of tissue optical properties using modulated imaging

We describe the development of a rapid, noncontact imaging method, modulated imaging (MI), for quantitative, wide-field characterization of optical absorption and scattering properties of turbid media. MI utilizes principles of frequency-domain sampling and model-based analysis of the spatial modulation transfer function (s-MTF). We present and compare analytic diffusion and probabilistic Monte Carlo models of diffuse reflectance in the spatial frequency domain. Next, we perform MI measurements on tissue-simulating phantoms exhibiting a wide range of l values (0.5 mm to 3 mm) and (micro(s) (')micro(a)) ratios (8 to 500), reporting an overall accuracy of approximately 6% and 3% in absorption and reduced scattering parameters, respectively. Sampling of only two spatial frequencies, achieved with only three camera images, is found to be sufficient for accurate determination of the optical properties. We then perform MI measurements in an in vivo tissue system, demonstrating spatial mapping of the absorption and scattering optical contrast in a human forearm and dynamic measurements of a forearm during venous occlusion. Last, metrics of spatial resolution are assessed through both simulations and measurements of spatially heterogeneous phantoms.

MRI image enhancement by PROPELLER data fusion

Magnetic Resonance Imaging (MRI) image reconstruction, based on the frequency-domain Super-Resolution (SR) algorithm, is presented in this paper. It is shown that the approach improves MRI spatial resolution in cases where Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction (PROPELLER) sequences are used. The PROPELLER MRI method collects data in rectangular 'blades' rotated around the origin of the k-space. Inter-blade patient motion is the premise for the use of SR technique. Images obtained from sets of irregularly located frequency-domain samples are combined into the high-resolution MRI image. The SR reconstruction replaces the usually applied direct averaging of low-resolution images. This is an expanded version of a paper presented at the 3rd IEEE International Workshop on Medical Measurements and Applications, 9 10 May 2008, Ottawa, ON, Canada.

Application of PRO-ESPRIT algorithm in identification of surface acoustic wave identification-tags

The surface acoustic wave (SAW) identification (ID)-tags have great potential for application in radio frequency identification (RFID) due to their characteristics of wireless sensing and passive operation. In the measurements based on the frequency domain sampling (FDS), to expand the range of detection and allow the system work in harsh environments, it is necessary to enhance the identification capability at low SNR. In addition, to identify the tags in real time, it is important to reduce identification time. Therefore, estimation of signal parameters based on the Procrustes rotations via the rotational invariance technique (PRO-ESPRIT) is adopted. Experimental results show that good identification capability is achieved with a relatively faster measurement speed.

Wideband receiver design in the presence of strong narrowband interference

In the presence of narrowband interference (NBI), detection of weak wideband signals faces foremost challenges in analog-to-digital conversion (ADC), due to the dynamic range problem encountered when the weak signal cannot be amplified adequately to achieve sufficient quantization accuracy. Building on a parallel frequency-domain sampling structure for ADCs, this letter derives a new quantization bit allocation scheme that effectively removes strong NBI. Frequency bins hosting NBIs are allocated with no quantization bits. Optimal rules for symbol detection and quantization bit allocation are derived by jointly minimizing the mean square error of the decoding output.

Applications of Multipath Transform-Domain Charge-Sampling Wide-Band Receivers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Transform-domain (TD) receivers expand the received signal over a basis set, and then operate on the basis coefficients. An analog computation of the basis coefficients efficiently parallelizes the signal for digital processing, relaxing the sampling requirements and enabling parallel digital processing at a much lower rate. Frequency-domain (FD) sampling, as a special case of TD sampling, has been proposed to parallelize the sampling process in broad-band communication receivers. The flexibility and scalability of TD receivers allow for the design of receivers that can cope with a large range of narrow-band and broad-band communications standards. A theoretical TD receiver design example is provided which is capable of processing GSM, Bluetooth, IEEE802.11g, Wimax, and UWB in just one configurable front-end. An example of spectrum sensing in cognitive radio is also provided. </para>

Inherent homogenous media dispersion compensation in frequency domain optical coherence tomography by accurate k-sampling

Depth dependent broadening of the axial point spread function due to dispersion in the imaged media, and algorithms for postprocess correction, have been previously described for both time domain and frequency domain optical coherence tomography. We show that homogeneous media dispersion artifacts disappear when frequency domain samples are acquired with uniform spacing in circular wavenumber, as opposed to uniform sampling in optical frequency. We further explicate the source of this point spread broadening and simulate its magnitude in aqueous media. We experimentally demonstrate media dispersion compensation in high dispersion glass by choosing sample frequencies at equal intervals of media index of refraction divided by vacuum wavelength, and we recover unbroadened reflections without an additional postprocessing step.

Automatic pathological voice evaluation based on auditory model

Sustained vowel analysis is an important method in pathological voice evaluation system. In view of the fact that conventional methods generally analyzes the hand-cut samples in FFT frequency domain, an auditory model is proposed as an accurate and robust method for use in pathological vowel analysis. An automatic sample cutting method increases the stability of analysis. Expertiment showed this method is more effective and robust.

High resolution MRI image reconstruction from a PROPELLER data set of samples

Magnetic Resonance Imaging (MRI) image reconstruction, based on the frequency domain Super-Resolution (SR) algorithm, is presented in the paper. It is shown that the approach improves MRI spatial resolution in cases where Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction (PROPELLER) sequences are used. The PROPELLER MRI method collects data in rectangular 'blades' rotated around the origin of the k-space. Inter-blade patient motion is the premise for the use of SR technique. Images obtained from sets of irregularly located frequency domain samples are combined into the high resolution MRI image. The SR reconstruction replaces the usually applied direct averaging of low-resolution images.

Identifying surface acoustic wave ID-tags using the total least squares-estimating signal parameters via the rotational invariance technique algorithm

Tags based on surface acoustic wave techniques have a great amount of potential for application in radio frequency identification because of their characteristics of wireless sensing and completely passive operation. Since time domain sampling requires high-speed radio frequency switches in the transmitter and fast data acquisition in the receiver, frequency domain sampling (FDS) is used for measurement and frequency-stepped continuous wave is adopted as the interrogation signal. FDS requires, however, the traditional inverse fast Fourier transform method which has a resolution restriction and decreases the identification probability. To identify the tag reliably with higher probability, a high-resolution algorithm is required. In actual measurement, the echo signal attenuates greatly as the distance between the transceiver and the tag increases. Furthermore, the perturbations in the environment also dampen the echo signal. To increase the identification range and allow the system work in harsher environments, it is necessary to enhance the identification capability at low signal noise ratio (SNR). The application of total least squares-estimating signal parameters via the rotational invariance technique is presented. The experimental results show that an excellent identification capability at low SNR is achieved.

Corrosion Study of an AZ91 Magnesium alloy by EIS and LEIS

The electrochemical impedance diagrams obtained at the corrosion potential for pure Mg or for AZ91 alloy presented the same shape after an immersion time of few days. It was thus assumed that the magnesium matrix of the AZ91 alloy corrodes first. The diagrams are characterized by two capacitive loops and an inductive one. It was shown that the diagrams measured in different electrolytes (Na2SO4 or NaCl) and on a large pH range (from 2 to 12) also presented the same shape and can be reduced to one diagram if the impedance is normalized by the maximum value of the modulus. Considering the experimental data and taking also into account the Negative Difference Effect (NDE), a kinetic model was proposed. Local Electrochemical Impedance Spectroscopy (LEIS) was carried out with the bi-electrode technique. Both anodic and cathodic sites were evidenced when mapping the sample in the low frequency domain. These sites could be linked to the microstructure of the AZ91 alloy. With a larger bi-electrode, a local average of the impedances corresponding to the anodic and cathodic sites was obtained. Thus, local impedance diagrams were similar to those measured for the global impedance on the overall AZ91 electrode (1 cm2). The analysis of LEIS data obtained along the radius of the electrode gave some new information on the origin of the CPE behavior of the global impedance in the high frequency range.