Time-domain Delay Research Articles

Sequential monitoring of cancer immunotherapy trial with random delayed treatment effect

ABSTRACT Cancer immunotherapy trials are frequently characterized by a delayed treatment effect that violates the proportional hazards assumption. The log-rank test (LRT) suffers a substantial loss of statistical power under the nonproportional hazards model. Various group sequential designs using weighted LRTs (WLRTs) have been proposed under the fixed delayed treatment effect model. However, patients enrolled in immunotherapy trials are often heterogeneous, and the duration of the delayed treatment effect is a random variable. Therefore, we propose group sequential designs under the random delayed effect model using the random delayed distribution WLRT. The proposed group sequential designs are developed for monitoring the efficacy of the trial using the method of Lan-DeMets alpha-spending function with O’Brien-Fleming stopping boundaries or a gamma family alpha-spending function. The maximum sample size for the group sequential design is obtained by multiplying an inflation factor with the sample size for the fixed sample design. Simulations are conducted to study the operating characteristics of the proposed group sequential designs. The robustness of the proposed group sequential designs for misspecifying random delay time distribution and domain is studied via simulations.

A novel compact semicircular defected ground structure ultrawideband monopole antenna integrated with Ku band for breast cancer detection

SummaryA compact and novel ultrawideband (UWB) antenna integrated with Ku band for microwave imaging applications is reported. The reported antenna consists of a novel patch structure along with a tapered feed structure on top of FR‐4 substrate having a compact dimension of 16 × 22 mm2 and novel semicircular defected ground structure (SC‐DGS) etched below the substrate. The proposed antenna covers a wide impedance bandwidth of 15.07 GHz spanning from 3.51 to 18.58 GHz with a fractional bandwidth (FBW) of 136%. The intended antenna performance is analyzed for S11, peak gain, efficiency, and radiation patterns in frequency domain, and group delay, isolation (S21), and linear phase response in time domain. The simulated and measured results of reported antenna are well matched for the usage in practical portable UWB applications. More importantly, the proposed antenna system is simulated for the detection of breast cancer tissue by comparison of S21 results, current densities, and specific absorption rate with and without tumor conditions. These findings show that the radiator and the whole system work well in detecting the breast tumor.

Stochastic dynamic analysis of composite plates in thermal environments using nonlinear autoregressive model with exogenous input in polynomial chaos expansion surrogate

The application of composite materials has increased manifolds in aerospace and high-speed vehicle industries, where structures experience dynamic loads along with temperature variation. To ensure safety of these structures, the stochastic dynamic analysis in varying thermal environments is essential. The generalized polynomial chaos (gPC) expansion method is a well-known metamodel used to quantify uncertainties in engineering systems instead of using the direct Monte Carlo simulation. Though the gPC expansion method is used extensively for engineering systems, its classical version has some limitations while implementing in dynamical systems. The accuracy of the gPC expansion method reduces in delayed time domain and can be improved to some extent by increasing the order of polynomial, which though is computationally intensive. Furthermore, the classical gPC expansion method is suitable for low-dimensional problems having independent random parameters. To overcome these limitations in the classical gPC expansion method, a system identifier, i.e., nonlinear autoregressive model with exogenous input (NARX) is coupled with it to avoid response degeneration in delayed time domain. The temperature-dependent material properties of composite lamina can be random and correlated, however the classical gPC expansion method is unable to accommodate the correlated random parameters. To address these challenges, the NARX-gPC expansion method is modified to conduct stochastic dynamic analysis of composite plates using correlated random material properties of the composite lamina in varying thermal environments. The study indicates that the correlation has a significant effect on the stochastic dynamic response at low and high temperatures for cross-ply laminates in comparison with angle-ply laminates, which is not captured through uncorrelated random material properties. The prediction efficiency of the developed surrogate by using the adaptive NARX-gPC expansion method is established even though it is trained using data in a shorter time domain, thereby computational performance is enhanced. Additionally, this surrogate is implemented effectively for higher order randomness in the input parameters.

Transformer Oil Temperature Variation Based on Terahertz Time-domain Spectroscopy

The transmission terahertz time-domain spectroscopy system is used to measure the transformer oil terahertz spectrum at different temperatures, the time and frequency domain, time delay, and refractive information of transformer oil with different temperatures are tested. The terahertz wave of the time-domain delay of transformer oil at different temperatures is obtained, the variation of time-domain delay and refractive index with different temperatures in the terahertz band were calculated and the linear variation trend was fitted.

Joint Compensation of TX/RX IQ Imbalance and Channel Parameters for OTSM Systems

Orthogonal time sequency multiplexing (OTSM), robust to doubly-selective fading channel, performs similar to orthogonal time frequency space (OTFS) system with less modulation/demodulation complexity. Direct conversion OTSM system suffers from hardware impairments such as in-phase and quadrature phase (IQ) imbalance at the transmitter (TX) and receiver (RX). At high frequencies, hardware imperfections are inevitable and should be compensated for better performance. In this Letter, we propose joint estimation of TX and RX IQ imbalance and estimate channel parameters in the delay time domain using pseudo noise based training sequence approach. The mean square error of the estimated channel parameters reduce with increase in training sequence length and power. With matched filtered Gauss-Seidel iterative method of detection of low complexity, it is shown that the compensated system performs close to ideal system under fractional delay and fractional Doppler.

Quantitative analysis of time-varying delay for real-time hybrid simulation

Real-time hybrid simulation is an effective method to study the seismic performance of large or complex structures. Time delay of the hydraulic servo system is unavoidable, which affects test accuracy and may cause instability. Previous studies shown that the reality of time-varying delay has a substantial negative effect on system stability than the assumption of constant delay. However, there is currently a lack of research for the actuating system with time-varying delay in the reality time domain. Therefore, a quantitative analysis method of time-varying delay is proposed in this study. The advantage is that only the command and the measured displacement signals are needed to obtain the time-varying delay in the time domain without any prior knowledge of the system. To overcome the influence of the amplitude error on the solution results, a processing method for the amplitude modulation of the measured displacement is proposed. To accurately search for the command corresponding to the measured signal, it is proposed to solve the time-varying delay by taking segment operation on the signal according to the maximum and minimum points. The efficiency of the proposed method is verified by numerical simulation, actuator displacement tracking test, and RTHS.

Time and Frequency Synchronization for OTFS

In this letter, we propose timing offset (TO) and carrier frequency offset (CFO) estimators for orthogonal time frequency space modulation (OTFS). The proposed estimators do not require any additional training overheads as they deploy the same pilot signal that is used for channel estimation. Hence, no additional training overhead is required for synchronization, thanks to the periodic properties of the pilot signal in the delay-time domain. Our proposed TO estimator finds the start of each OTFS block by searching for a periodic sequence in delay and time dimensions. The CFO is then estimated by finding the mean of the angles of a two-dimensional correlation function at the best timing instant. As a novel aspect of these estimators, the multipath diversity of the channel is exploited to achieve a high estimation accuracy. Finally, we show the efficacy of our proposed synchronization techniques through extensive simulations.

Digital Compensation of IQ Imbalance, DC Offset for Zero-Padded OTFS Systems

Next generation communication systems (e.g., 6G) foresee higher mobility, higher data rates with higher constellations and with high levels of integration in a small form factor. Direct conversion orthogonal time frequency space modulation (OTFS) systems suffer from hardware impairments such as in-phase and quadrature (IQ) imbalance, direct current (DC) offset causing image Doppler interference (IDI) among the sub-carriers in the delay Doppler (DD) domain. In this letter, we propose a novel method of estimation and compensation of hardware impairments for zero padded (ZP) OTFS systems in the delay time (DT) domain. A dual pilot approach with a phase difference of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\frac {\pi }{2}}$ </tex-math></inline-formula> between these symbols is followed in DD domain with which hardware impairments are estimated with less computational complexity in DT domain. It is found that the compensated system performs close to ideal system. The mean square error (MSE) of the estimated channel is computed and MSE reduces with increase in signal to noise ratio (SNR), pilot power ratio (PPR) and with reduction in mobility.

Estimation and Compensation of IQ Imbalance for OTSM Systems

Recently, orthogonal time sequency multiplexing (OTSM) waveform was proposed using Walsh Hadamard transform (WHT) for doubly-dispersive channels at a lower modulation/demodulation complexity than orthogonal time frequency space (OTFS) waveform. At high frequencies, hardware imperfections such as in-phase and quadrature (IQ) imbalance is prominent at the transceiver. In this letter, the input-output (I/O) relation in the delay-sequency domain is derived under these impairments at the receiver. The impairment parameters are estimated in the delay-time domain and are compensated in the time domain using proposed dual pilot approach. The normalized mean square error (NMSE) of the estimated imbalance parameters is evaluated and it is observed that NMSE reduces with increase in SNR and with reduction in mobility. The results are evaluated with OTFS system and it is observed that the NMSE performance of OTSM is similar to OTFS under high pilot power and high SNR at no excess pilot power. The bit error rate performance of the compensated system is evaluated and its performance is close to the ideal system.

Acoustic Estimation of the Direction of Arrival of an Unmanned Aerial Vehicle Based on Frequency Tracking in the Time-Frequency Plane.

The development of unmanned aerial vehicles (UAVs) opens up a lot of opportunities but also brings some threats. Dealing with these threats is not easy and requires some good techniques. Knowing the location of the threat is essential to deal with an UAV that is displaying disturbing behavior. Many methods exist but can be very limited due to the size of UAVs or due to technological improvements over the years. However, the noise produced by the UAVs is still predominant, so it gives a good opening for the development of acoustic methods. The method presented here takes advantage of a microphone array with a processing based on time domain Delay and Sum Beamforming. In order to obtain a better signal to noise ratio, the UAV’s acoustic signature is taken into account in the processing by using a time-frequency representation of the beamformer’s output. Then, only the content related to this signature is considered to calculate the energy in one direction. This method enables to have a good robustness to noise and to localize an UAV with a poor spectral content or to separate two UAVs with different spectral contents. Simulation results and those of a real flight experiment are reported.

Coordinated Formation Control of Discrete-Time Autonomous Underwater Vehicles under Alterable Communication Topology with Time-Varying Delay

This paper is concerned with the coordinated formation control problem of multiple autonomous underwater vehicles (AUVs) under alterable communication topology and time-varying delay in discrete time domain. Firstly, the multi-AUV system is divided into one leader and multiple followers, and the communication topology is divided into two parts. The coupled nonlinear AUV model is linearized into a second-order integral model using state feedback. Secondly, two types of coordinated controllers in discrete time are proposed: the controller for multi-AUV system without delay, the controller for multi-AUV system with time-varying delay. Then, the formation control issue for multiple AUVs with alterable topology is treated as the asymptotic stability of an error system. The stability analysis of the error system consisting of the state errors between each follower and the leader is performed, to obtain some novel sufficient conditions for achieving the formation control objective. Finally, some simulation results are presented to demonstrate the effectiveness of the theoretical results, and the comparisons describe the effects of communication topology and delay on the performance of the control system.

Reflections and standing waves on the Tianlai cylinder array

In 21 cm intensity mapping, the spectral smoothness of the foreground is exploited to separate it from the much weaker 21 cm signal. However, the non-smooth frequency response of the instrument complicates this process. Reflections and standing waves generate modulations on the frequency response. Here we report the analysis of the standing waves in the bandpass of the signal channels of the Tianlai Cylinder Array. By Fourier transforming the bandpass into the delay time domain, we find various standing waves generated on the telescope. A standing wave with time delay at ∼142 ns is most clearly identified which is produced in the 15-meter feed cable. We also identify a strong peak at a shorter delay of τ < 50 ns, which may be a mix of the standing wave between the reflector and feed, and the standing wave on the 4 m intermediate frequency (IF) cable. We also show that a smoother frequency response could be partially recovered by removing the reflection-inducted modulations. However, the standing wave on the antenna is direction-dependent, which poses a more difficult challenge for high precision calibration.

Underwater channel estimation exploiting multipath feature morphology.

Real-time accurate channel estimation has been an ongoing challenge because of diverse oceanic events that cause rapid fluctuations of high-energy multipath activity across the delay spread. This work leverages current compressed sensing and sparse optimization techniques with topological signal processing to improve estimation time and localize channel estimation to salient parts of the delay spread. This work improves the estimation time by tracking the channel as a union of overlapping multipath and other scattering events, which are modeled as "feature braids" in the delay-time domain. A channel feature braid may be intuitively visualized as the topologically connected trajectory of a group of channel delay taps, which represent the support of dominant or persistent scattering events, e.g., surface bounce multipath scattering. We present algorithms that harness support-constrained mixed norm optimization techniques to track the evolving support of channel feature braids. We validate our channel feature tracking algorithm independently in experimental field data as well as BELLHOP channel simulations across a diversity of oceanic conditions. This work shows that braiding used in estimation can improve estimation time and track high-energy events that develop within the delay vs time channel representation.

A 100–750 MS/s 11-Bit Time-to-Digital Converter With Cyclic-Coupled Ring Oscillator

This paper presents the first measured cyclic-coupled ring oscillator (CCRO) time-to-digital converter (TDC). The CCRO realizes a robust true time-domain delay interpolation with sub-gate-delay resolution. The architecture employs real-time quantization to reduce conversion time and hence maximize bandwidth. Furthermore, the CCRO phase progression is encoded with a bubble error suppression logic, thereby building resilience to delay mismatches from circuit/layout imperfections. The prototype circuit implemented in a 28 nm CMOS process demonstrates a combination of high resolution and high sample rate over wide range of sample rates. The TDC achieves its peak figure-of-merit (FoM) of 0.051 pJ/conv.-step at 100 MS/s while delivering 8.38-bit linear resolution and 15.4 ps time resolution, operating from a 0.55 V supply. The TDC demonstrates the highest reported linear resolution of 9.29 bits among converters operating above 100 MS/s, at 125 MS/s and 0.9 V supply, while achieving 4.4 ps time resolution and 0.16 pJ/conv.-step FoM. Further, the real-time quantizing architecture allows fast operation up to 750 MS/s, where the TDC delivers 6-bit linear resolution and 0.48 pJ/conv.-step FoM operating from 0.9 V supply.

A Method of Deflection of the Vertical Measurement Based on Phase Correction

The combination of the strapdown inertial navigation system (SINS) and the global navigation satellite system (GNSS) is an ingenious means to measure the deflection of the vertical (DOV). The error characteristics of the traditional direct difference model show that the DOV cannot be recovered by the traditional method because of the ignorance of the frequency characteristics of DOV. The error propagation relationship considering frequency domain characteristics between the horizontal attitude angles error and DOV is established. The Bode diagrams of the transfer functions between the horizontal attitude angles error and DOV show that there is a phase lag in the transfer functions, which is shown as a time delay in time domain, when the frequency of DOV in time domain is in the range of $7\times 10^{-4}{rad} \mathord {\left /{ {\vphantom {rad s}} }\right. } s . Then the improved direct difference model considering the time delay is established, and is simplified according to the spherical harmonic characteristics of gravity field. The simulation results show that the improved model with phase correction can recover the high-frequency component of DOV with the error standard deviations of $\delta \xi =1.0{5}^{\prime \prime }$ and $\delta \eta =0.9{9}^{\prime \prime }$ . Finally, the model is also verified by a section of ship test data, and the error standard deviations of the DOV recovered are $\delta \xi =1.4{6}^{\prime \prime }$ and $\delta \eta =1.2{4}^{\prime \prime }$ .

Maximum likelihood distance estimation algorithm for multi‐carrier radar system

In this study, a maximum likelihood distance estimation algorithm is proposed for a multi-carrier radar system to estimate the time delay of non-integer sampling intervals. Particularly, the equivalent relationship between time domain delay and frequency domain phase shift and the relationship between target delay and channel impulse response is used. The idea of maximum likelihood estimation is to find the estimation value that maximises the likelihood function. Therefore, the core idea of this algorithm is the peak search. First, channel estimation is performed on the sampled signal in frequency domain to obtain the channel impulse response. Second, phase compensation and peak search is done to estimate the target delay. Finally, for multiple estimation results, the authors statistic the probability density distribution of the target. In addition, they deduce the Cramer–Rao bound (CRB) of the variance of time delay estimation. The measurement accuracy of the algorithm that they proposed approaches the CRB in the high signal-to-noise regime.

Parametric study on pump noise processing method of continuous wave mud pulse signal based on dual-sensor

Continuous wave pulse transmission technology has become the forefront development direction of measurement while drilling and logging information transmission with its high transmission rate and strong anti-interference ability. In this paper, the denoising principle of time-domain delay differential method based on two pressure sensors is analyzed in detail. The acquisition signals of two sensors with different sensor intervals and SNRs (Signal-to-Noise Ratio) are constructed. The denoising ability of the time-domain delay differential method in different cases, i.e., stable and unstable pump noise, the amplitude and frequency distortion of the original pulse signal, and the structural change of the original pulse signal, are emphatically studied. Simulations show that this method can effectively suppress the pump noise even when there is a significant fluctuation in the fundamental frequency and amplitude of pump noise. This method can also obtain well-formed reconstructed signal when the pulse signal has high frequency and amplitude distortion. Besides, a general method for deriving an optimal dual-sensor installation interval is discussed for a BFSK (Binary Frequency Shift Keying) transmission signal, which consists of high-frequency and low-frequency carrier waves, and a reference installation interval is given. Finally, this method is applied to denoise the actual dual-sensor acquisition signal, and satisfactory results are obtained.

An Active Rectifier with Time-Domain Delay Compensation to Enhance the Power Conversion Efficiency

An Active Rectifier with Time-Domain Delay Compensation to Enhance the Power Conversion Efficiency

Dynamics and Stability of Turn-Milling Operations With Varying Time Delay in Discrete Time Domain

Turn-milling machines are widely used in industry because of their multifunctional capabilities in producing complex parts in one setup. Both milling cutter and workpiece rotate simultaneously while the machine travels in three Cartesian directions leading to five axis kinematics with complex chip generation mechanism. This paper presents a general mathematical model to predict the chip thickness, cutting force, and chatter stability of turn milling operations. The dynamic chip thickness is modeled by considering the rigid body motion, relative vibrations between the tool and workpiece, and cutter-workpiece engagement geometry. The dynamics of the process are governed by delayed differential equations by time periodic coefficients with a time varying delay contributed by two simultaneously rotating spindles and kinematics of the machine. The stability of the system has been solved in semidiscrete time domain as a function of depth of cut, feed, tool spindle speed, and workpiece speed. The stability model has been experimentally verified in turn milling of Aluminum alloy cut with a helical cylindrical end mill.

Wireless Channel Optimization of Internet of Things

Research on the optimization of Internet of Things wireless channel has received widespread attention. First, this paper analyzed the Internet of Things wireless channel, including multichannel analysis, Doppler effect analysis, MIMO channel model analysis, and channel correlation characteristics simulation. On this basis, a three-path channel neural network curve approximation model was established, and the CDF and PDF curves of Rayleigh and Rice fading channels were approximated and analyzed. The results showed that the neural network model basically conformed to the reality. According to the 3GPP2 standard, the time domain delay model of the FIR filter is optimized, and the design model has the characteristics of fast calculation speed and high precision. In addition, this paper also used the neural network to approximate the amplitude-frequency characteristics of the 64-order fading shaping filter and the 120-order interpolation filter. The simulation results met the requirements. Finally, based on the neural network MIMO channel model, a neural network model of additive white Gaussian noise channel under certain conditions was established. Based on the simulation data, the polarization antenna was optimized for path loss and different tilt angles, and the optimization could be performed at high speed while achieving the minimum error.