Time-domain Delay Research Articles

Variable kernel‐based computing algorithms for estimating sparse multipath channels

SummaryAccurate channel estimation algorithms are required to mitigate the frequency‐selective fading in the broadband wireless communication systems. Many physical experiments revealed that finite impulsive responses are distributed as sparse in delayed time domain. Hence, the inherent sparse information can be exploited by state‐of‐the‐art computing algorithms, in order to improve channel accuracy. Existing computing algorithms, zero‐attracting recursive least square (ZA‐RLS) and reweighted ZA‐RLS (RZA‐RLS), have been developed to exploit channel sparsity. However, optimization theory implies that accuracy of the computing algorithms can be further improved to exploit more sparsity information. To further improve the estimation performance, this paper proposes a correntropy induced metric (CIM)‐penalized RLS (CIM‐RLS) based sparse channel estimation algorithm. Here, sparse constraint is performed by CIM function, while error constraint term is computed by RLS. In particular, Gaussian kernel is adopted for computing the CIM, and its variable kernel width (VKW) is computed for adaptively exploiting the channel sparsity. Monte Carlo simulation results are conducted to verify the proposed algorithm in different scenarios.

フィードフォワード型能動制御による重機騒音の低減効果

The construction machineriy noises have a sound peak in low frequency region(approximately less than 100 Hz). Active noise control (in the following, ANC) is one of the methods to reduce the low frequency noise. ANC is a system that reduce noises by interference between noise and sound wave from a speaker that has reverse phase against the noise. In recent years, ANC is occasionally applied to reduce noise of construction machineries like backhoes and rough terrain cranes. As usual, the control method of the ANC is feedback that has only error microphone, or feedforward that has the reference microphone and the error microphone. In the construction sites, there are many kinds of noise sources like backhoes, cranes, power generator, roadheader, etc., therefore the ANC using feedback control may lose the target noise. Also, most of construction machineries move around in the construction site during operation, for safety it is hard to set up two microphones on the machineries for feedforward control. So we developed an active noise control system for noise of construction machineries that can be set up on moving noise source like backhoes and can control stably. We considered about the applicability of the feedforward control which uses only reference signal, uses no Ĉ. Then, we proposed control methods of the ANC which estimate a predominant frequency and calibrate an amplitude ratio and a phase delay in time domain. To estimmate a dominant frequancy in time domain, the proposed control method uses the optimized filter of LMS algorism. The LMS algorism minimizes the difference of input signal and the band-pass- filtered signal in the ANC system. The coefficient of the optimized filter is updated by each sampling time, the estimated frequency at n+1(n means a time number. n=1, 2...) is mainly derived from the estimated freqency at n, and the ratio of the coefficient of the optimized filter at n+1 to the coefficient of the optimized filter at n. As for the calibration of an amplitude ratio and a phase delay in time domain, the proposed control method uses correction values of amplitude and phase delay in each frequency, which are obtained in advance from the comparison o of the input signal and the output signal of the ANC system. When the control starts, at first, the system takes out the correction value of the estimated frequency. Next, the system subtracts the number of data of the correction value from the number of data of one wavelength for the estimated frequency. At last, the system takes out the past data at the point of calculated difference from the start point, and the data multiply by the correction value of amplitude is the output signal. To confirm the usefulness of the proposed method, we carried out numerical simulations. In the simulation, we used some fixed sin waves of 50Hz to 100Hz, and fluctuated sin waves such as 40Hz to 50Hz or 40Hz to 100Hz, as input signal. As a result, the proposed methods can control stably and the control speed of proposed method is faster than that of conventional feedforward control and conventional feedback control. Then, we carried out experiments in a laboratory to verify the effectiveness of ANC system using proposed method. Some fixed sin waves of 50Hz to 100Hz and construction machinery noises are used as input signal. As a result, the ANC reduced fixed sine waves by maximum about 20dB, and the ANC reduced construction machinery noise by about 10dB.

Delay Estimation Using Instantaneous Frequency and Phase Difference--Simulation Study.

We propose a time-domain delay estimator that takes the slope of the best fit line crossing the origin in the instantaneous frequency-phase difference plane as the delay estimate. This formulation differs from existing phase-based estimators in two respects. First, we find the instantaneous frequency at all individual sample points, including large and abrupt spikes caused by destructive interference in the coherent scattering process. This differs from Loupas which finds a smoothed-out center frequency estimate within an observation window. We show that under high signal-to-noise ratio (SNR), the information from these spikes can be properly used. Second, we show that error ought to be considered as the deviation of the phase difference from the best fit line rather than deviation from the averaged phase difference. Without considering instantaneous frequency, phase-based estimators make the following two errors: samples with phase difference far away from the center frequency need not be errors as they naturally have large phase difference when their instantaneous frequency is large; samples with phase difference close to the center frequency may in fact be errors if their instantaneous frequency is large. We derive the Gauss-Markov least-squares best fit line and then propose an iterative variant that removes samples from the line-fitting process if its deviation from the best fit line is sufficiently large. The iterative version can reduce the effect of aliasing for larger delays and also further reduce the root-mean-square error (RMSE) of the estimate. Simulation studies using various bandwidth, SNR, and delay parameters indicate that iterative phase least squares (PLS) begins to outperform correlation phase Loupas at between SNR of 30 dB (for larger bandwidths and larger delays) and 60 dB (for smaller bandwidths and smaller delays). As SNR increases, iterative PLS can reach a 30- to 50-dB increase in performance over correlation phase Loupas with respect to RMSE in the most favorable conditions.

Ultralow-Voltage High-Speed Flash ADC Design Strategy Based on FoM-Delay Product

This paper discusses the ultralow-voltage (ULV) design strategy for high-speed flash analog-to-digital converters (ADCs). A lower supply voltage decreases the energy consumption at the cost of conversion speed. In this paper, a new index, the figure-of-merit (FoM)-delay (FD) product, is introduced to provide a balance between the energy efficiency and conversion speed. As a prototype, a 0.5 V, 420-MS/s, and 7-bit, flash ADC is developed using a 90-nm CMOS technology to demonstrate the validity of ULV operation. To overcome the challenges associated with a reduced supply voltage, a double-tail latched comparator with a variable capacitance calibration technique using metal–oxide–metal capacitors is implemented. An all-digital time-domain delay interpolation technique further enhances the resolution with very little additional power consumption. Using two-way time-interleaving, the prototype ADC achieves an effective number of bits (ENOB) of 5.5 bits while operating at 420 MS/s consuming a total power of 4.1 mW. The lowest measured FoM is the 195 fJ/conv.-step during single-channel operation at 210 MS/s, which results in an extremely low FD product of 0.93 pJ $\times $ ns/conv.-step.

Fast Algorithms for Low-Delay TDAC Filterbanks in MPEG-4 AAC-ELD

The MPEG committee has completed development of a new audio coding standard called MPEG-4 advanced audio coding-enhanced low (AAC-ELD). AAC-ELD uses low delay spectral band replication (LD-SBR) technology together with a low delay time domain alias cancellation (LD TDAC) filterbank in the encoder to achieve both high coding efficiency and low algorithmic delay. In this paper, we present fast algorithms for implementing LD-TDAC filterbanks in AAC-ELD. Two types of fast algorithms are presented. In the first, we map LD-TDAC analysis and synthesis filterbanks to modified discrete cosine transform (MDCT) and inverse modified discrete cosine transform (IMDCT), respectively. Since MDCT/IMDCT are already extensively used in AAC and they have many fast algorithms, this mapping not only provides a fast implementation but also allows a common implementation of the filterbanks in AAC Low Complexity (AAC-LC), AAC Low Delay (AAC-LD) and AAC-ELD codecs. In the second algorithm, we provide a mapping to discrete Cosine transform of type II. The mapping to DCT-II allows the merger of the matrix operations with the windowing stage that precedes or follows them. This further reduces the number of multiplications and leads to an algorithm with the lowest known arithmetic complexity. For filterbanks of lengths 1024 and 960, we also present a new fast factorization of 15-point DCT-II that requires only 14 irrational multiplications, 3 dyadic rational multiplications and 67 additions.

Research on the Accuracy of Mine Tremor Location in Coal Mine

In order to improve the location accuracy of mine tremor in coal mine, the P wave is utilized to calculate the location and the wavelet analysis method is used to pick more exact first arrival time by filtering noise and extracting weak tremor signal. According to the principle of choosing station number, the optimal channel number participating in the location calculation for A is 6 and 10 for B. The result obtained onsite show that: (1) The wavelet method can reconstruct the mine tremor signal and extract the weak tremor signal, while not causing time delay in time domain; (2) Compared to the grid search method, the average source location error is reduced from 255m to 115m and the epicenter location error is reduced from 191m to 50m by the proposed method.

The simulation of far-field wavelets using frequency-domain air-gun array near-field wavelets

Air-gun arrays are used in marine-seismic exploration. Far-field wavelets in subsurface media represent the stacking of single air-gun ideal wavelets. We derived single air-gun ideal wavelets using near-field wavelets recorded from near-field geophones and then synthesized them into far-field wavelets. This is critical for processing wavelets in marineseismic exploration. For this purpose, several algorithms are currently used to decompose and synthesize wavelets in the time domain. If the traveltime of single air-gun wavelets is not an integral multiple of the sampling interval, the complex and error-prone resampling of the seismic signals using the time-domain method is necessary. Based on the relation between the frequency-domain phase and the time-domain time delay, we propose a method that first transforms the real near-field wavelet to the frequency domain via Fourier transforms; then, it decomposes it and composes the wavelet spectrum in the frequency domain, and then back transforms it to the time domain. Thus, the resampling problem is avoided and single air-gun wavelets and far-field wavelets can be reliably derived. The effect of ghost reflections is also considered, while decomposing the wavelet and removing the ghost reflections. Modeling and real data processing were used to demonstrate the feasibility of the proposed method.

Time-dependent effects of corticosterone on reward-based decision-making in a rodent model of the Iowa Gambling Task

Corticosteroid hormones, released after stress, are known to change neuronal activity in two time-domains: within minutes via non-genomic pathways and with a delay of >1 h through pathways involving transcriptional regulation. Recent evidence in rodents and humans indicates that these two modes of corticosteroid action differently affect cognitive tasks. Here, we investigated whether reward-based decision-making, in a rat model of the Iowa Gambling Task (rIGT), is also differently altered by rapid versus delayed actions of corticosterone. We targeted the rapid and delayed time domain by injecting corticosterone (CORT, 1 mg/kg, s.c.) at 30 min (rapid) or 180 min (delayed) respectively prior to behavioural testing, during the final 3 days of the behavioural paradigm. In saline treated rats, the number of visits to the disadvantageous arm decreased over trial blocks, whilst this was attenuated when CORT was administered 30 min before testing. This attenuation was associated with a significantly increased c-Fos expression in the lateral orbitofrontal cortex and insular cortex, and a trend for an increase in the infralimbic cortex. The rapid corticosteroid effect contrasted with treatment 180 min before testing, where the number of visits to the disadvantageous arm as well as c-Fos labelling was not affected. These findings indicate that rapid corticosteroid actions impair reward-based decision-making.

CMOS Fluorometer for Oxygen Sensing

This letter presents an integrated complementary metal-oxide semiconductor fluorometer that utilizes frequency-domain fluorescence lifetime imaging spectroscopy for oxygen-sensing applications. The implemented fluorometer chip consists of a p+/n-well/p-substrate photodiode, a phase readout circuit with integrated zero-crossing detection to extract the frequency-domain phase shift into a time-domain delay, and a high-resolution time-to-digital converter for digital quantization of the converted time delay. The fabricated fluorometer consumes less than 8.3 mW power and has a temporal resolution of 110 ps. During oxygen-sensing experiments, a ruthenium complex was used as an oxygen-sensitive dye whose lifetime was measured as a function of the of the oxygen concentration in water.

Transient Simulation of Distributed Networks Using Delay Extraction Based Numerical Convolution

This paper presents a numerical convolution based approach for transient simulation of distributed networks characterized by band limited frequency domain data when terminated with arbitrary nonlinear circuits. The proposed algorithm uses time-frequency decompositions to extract multiple propagation delays of a distributed network and the associated attenuation losses in a piecewise manner, and implements inverse fast Fourier transform to efficiently convert the frequency response into a sum of delayed time domain responses. Numerical examples illustrate that the proposed algorithm shows significantly more accurate results for networks with multiple long delays when compared to existing numerical convolution techniques.

Effect of time delays in characterizing the continuous mixing of non-Newtonian fluids in stirred-tank reactors

Aqueous xanthan gum solutions are pseudoplastic fluids possessing yield stress. Their continuous mixing is an extremely complicated phenomenon exhibiting non idealities such as channeling, recirculation and dead zones within the stirred-tank reactors. To characterize the continuous mixing of xanthan gum solutions, three dynamic models were utilized: (1) a dynamic model with 2 time delays in discrete time domain, (2) a dynamic model with two time delays in continuous time domain, and (3) a simplified dynamic model with a single time delay in discrete time domain. A hybrid genetic algorithm was employed to estimate the model parameters through the experimental input–output dynamic data. The extents of channeling and fully mixed volume were used to compare the performances of these three models. The dynamic model parameters exerting strong influence on the response predicted by the dynamic model were identified. It was observed that the models with 2 time delays gave a better match with the experimental results.

RFID Transponder Collision Control Algorithm

Transponder collision problem can be significant when a large number of RFID (radio frequency identification) transponders exist in field. Most existing anti-collision algorithms can solve this problem. However, problem arises when all or part of these transponders are having identical UID (unique identification). This paper proposes a new transponder collision control algorithm to overcome overlapping that occurs among transponders with identical UID in RFID large scale deployment (e.g., in a large warehouse), so that the RFID reader can successfully identify the quantity of transponders for each particular UID with high identification accuracy. The proposed anti-collision algorithm adopts a modified version of frequency domain method by adding stochastic delays in time domain. The obtained results show that the proposed method can achieve optimum frequency bandwidth utilization and at the same time poses high identification accuracy (almost 100%) with low identification delay.

A Miniature Planar Antenna for Bluetooth and UWB Applications

The paper puts forward a miniature microstrip antenna at the operating frequency of 2.4–2.5 GHz (Bluetooth) and 3.1–10.6 GHz (UWB). The omnidirectional radiation patterns can be obtained at the whole operating frequency band by cutting the ground conductor and adding a branch at the top of the antenna. Simulated results show that the antenna has attractive characteristics such as stable phase center, constant group delay, linear phase and good time-domain impulse response. Both the reflection coefficient and radiation patterns of the antenna are in good agreement with measured results. Experiment also shows that the cross polarization level is very low with flat gain. Consequently, the proposed antenna can well meet the requirements of wireless communication in both the Bluetooth and UWB bands.

Minimization of geometric-beam broadening in a grating-based time-domain delay line for optical coherence tomography application: reply to comment

Minimization of geometric-beam broadening in a grating-based time-domain delay line for optical coherence tomography application: reply to comment

Minimization of geometric-beam broadening in a grating-based time-domain delay line for optical coherence tomography application: comment

This is a comment on "Minimization of geometric-beam broadening in a grating-based time-domain delay line for optical coherence tomography application," J. Opt. Am. A24, 3808 (2007).

Minimization of geometric-beam broadening in a grating-based time-domain delay line for optical coherence tomography application

This paper discusses a dispersion effect in a grating-based time-domain delay line that is different from the second- or higher-order dispersion in a grating-based Fourier-domain delay line. When the lateral broadening of the beam profile after grating dispersion exceeds the collection aperture of the reference fiber, the peripheral spectrum is decoupled by the fiber. The loss of reference spectral bandwidth by this geometric-beam broadening thus degrades the axial resolution. The polarizing-beam reflector used in the Fourier-domain delay line for suppression of lateral beam walk-off is implemented in this grating-based time-domain delay line to minimize geometric-beam broadening. Theoretical analysis and experiments are given to validate the axial resolution improvement after geometric-beam broadening is minimized. In vitro and in vivo imaging results are presented to demonstrate the improvement. It is also shown that geometric-beam broadening may exist in other optical coherence tomography reference arm configurations.

Bit Error Rate Analysis of OFDM with Pilot-Assisted Channel Estimation

SUMMARY The objective of this paper is to develop the theoretical foundation to the pilot-assisted channel estimation using delay-time domain windowing for the coherent detection of OFDM signals. The pilotassisted channel estimation using delay-time domain windowing is jointly used with polynomial interpolation, decision feedback and Wiener filter. A closed-form BER expression is derived. The impacts of the delay-time domain window width, multipath channel decay factor, the maximum Doppler frequency are discussed. The theoretical analysis is confirmed by computer simulation.

Delay-time/code division multi-access in frequency-selective channel

A new hybrid multi-access technique, called delay-time/code division multi-access (DT/CDMA), is proposed. Multiplexing is accomplished in both the delay-time domain and code domain. Delay-time division multiplexing is achieved by assigning different cyclic time delays to the same spreading sequence. At a receiver, frequency-domain equalisation, despreading, and demultiplexing are performed simultaneously in the frequency domain. The bit error rate performance when using the proposed DT/CDMA in a frequency-selective Rayleigh fading channel is evaluated by computer simulation.

Synthesis, characterization and laser flash photolysis studies of some naphthothiophenes bearing electron donor and acceptor functional groups

Photoinduced electron transfer processes have been investigated in a rigid naphthothiophene moiety which contains both electron donor (methoxy group, OCH 3) and acceptor (dicyanovinyl or methoxycarbonyl group) functional groups at its two different ends. Both steady state absorption and fluorescence measurements coupled with the estimation of electronic coupling matrix elements, H DA , show the possibilities of occurrence of charge separation reactions within the donor and acceptor functional groups. Transient absorption measurements by laser flash photolysis technique using different delays in microsecond time domain demonstrate the presence of ion-pair in the triplet state and the stabilization of the radical ions within β -cyclodextrin ( β CD) cavity against destructive charge recombination process. It appears that β CD microenvironment serves as the suitable medium to achieve one of the key requirements (enhancement of the survival duration of charge-separated species by retarding the charge recombination) for developing artificial photosynthetic device.

On the Compensation of Delay in the Discrete Frequency Domain

The ability of a DFT filterbank frequency domain filter to effect time domain delay is examined. This is achieved by comparing the quality of equalisation using a DFT filterbank frequency domain filter with that possible using an FIR implementation. The actual performance of each filter architecture depends on the particular signal and transmission channel, so an exact general analysis is not practical. However, as a benchmark, we derive expressions for the performance for the particular case of an allpass channel response with a delay that is a linear function of frequency. It is shown that a DFT filterbank frequency domain filter requires considerably more degrees of freedom than an FIR filter to effect such a pure delay function. However, it is asserted that for the more general problem that additionally involves frequency response magnitude modifications, the frequency domain filter and FIR filters require a more similar number of degrees of freedom. This assertion is supported by simulation results for a physical example channel.