Phase Offsets Research Articles

Modeling and application of the time-varying GPS differential code bias between C1 and P1 observations

Considering the time-varying characteristic of the GPS differential code bias between C1 and P1 observations (DCB (C1-P1)), the method for estimating the time-varying DCB (C1-P1) is presented. The time-varying characteristic of the DCB (C1-P1) is analyzed using the estimated values with the twelve-month (1 Jan-31 Dec 2018) GPS data set from 120 International GNSS Service (IGS) stations. The estimated results show that the DCB (C1-P1) has the evident variation with the periods of 12, 8, 6, 4, 3.4286 h. Based on the noticed periods, the estimated single-day DCB (C1-P1) series is modeled with a harmonics-based function. The results show that the initial phase offsets (θi(i=1~5)) have the characterization of linear variation and these variations are very evident, while the amplitudes (yi(i=1~5)) of each satellite irregularly vary with time. The time-varying DCB (C1-P1) is used in single point positioning (SPP) to validate its effect on positioning. The SPP results show that the three-dimensional positioning results can be improved, when the time-varying part of the DCB (C1-P1) is corrected. The results for the 120 IGS stations indicate that the average three-dimensional positioning improvement for three days is about 3 cm. These improvements further advise that the time-varying part of DCB (C1-P1) should be corrected in GPS data processing and be serviced by IGS. The prediction performance shows that the correction rates of the predicted results for all satellites reach more than 40% accuracy and the mean prediction accuracy can reach 70%.

Phascope: Fine-Grained, Fast, Flexible Motion Profiling based on Phase Offset in Acoustic OFDM Signal

Acoustic Doppler shift estimation is a cost-effective way to implement Human-Computer Interaction applications across existing smart devices such as smart phones and smart spekaers. However, due to the inherent uncertainty principle in the traditional time-frequency analysis, it remains challenging to profile motions accurately and timely. In this paper, phase offset in acoustic OFDM signal is leveraged for developing Phascope, a fine-grained, fast and flexible motion profiling scheme. We evaluate Phascope using simulation and experiment on COTS devices. Sub-millisecond response time is achieved for Phascope in our experiment. Besides, with optimal subcarrier selection and SNR of 30 dB over all subcarriers, Phascope can estimate motion speed of 0.1 m/s with 6.75% root-mean-square error (RMSE) compared to optimized FFT method.

Microstrip antenna with high self‐interference cancellation using phase reconfigurable feeding network for in‐band full duplex communication

AbstractThis article presents a bistatic microstrip circular patch antenna with high self‐interference cancellation (SIC) through phase reconfigurable differential feeding network. The proposed microstrip antenna consists of closely spaced transmitter and receiver patches having orthogonal polarization with respect to each other. To achieve high SIC, the phase reconfigurable of feeding network can assist in tracking the phase offsets of self‐interference signal caused by fabrication error or scattering nearby objects. From the experiment, the proposed antenna provided higher than 75 dB (65 dB) SIC bandwidth for 36 MHz (50 MHz) at the center frequency of 2.50 GHz. The proposed antenna is a good candidate for in‐band full duplex communication system because of its simple design.

Referenceless multi-channel signal combination: A demonstration in chemical-shift-encoded water-fat imaging.

Without explicit coil sensitivity information acquired by means of a reference body coil, multi-channel signal combination for water-fat separation (WFS) can be challenging due to channel-dependent phase offsets and chemical-shift dependent phase shifts. This study aims to develop a referenceless, robust, accurate, and fast channel combination method for WFS. A dual-step multi-channel combination method is proposed. In the first step, channel-dependent phase offsets are estimated with a preliminary WFS estimation. In the second step, the multi-channel data are combined after removing phase offsets. Thereafter, WFS is performed to obtain final results. Numerical simulations (4-64 coils) and in vivo experiments (8, 16, 28 coils) at 3T field strength are conducted to compare the proposed method to previous methods. Channel combination with a body-coil scan serves as the reference for in vivo experiments. The proposed method estimates channel-dependent phase offsets accurately. It shows improved robustness to phase singularities than weighted mean and adaptive reconstruction. It is faster than adaptive reconstruction (e.g., 25.45 versus 46.34 s with 28 coils) and the channel-by-channel WFS method (e.g., 21.77 versus 50.04 s with 8 coils). It provides comparable fat quantification accuracy to the reference under various reasonable signal-to-noise ratio conditions (e.g., Pearson correlation coefficient r = 0.981 with P < 0.01, for in vivo fat fractions using flip angle = 10°). The proposed referenceless channel combination method may be beneficial to both qualitative and quantitative water-fat imaging.

Virtualization of Industrial Real-Time Networks for Containerized Controllers.

The virtualization technology has a great potential to improve the manageability and scalability of industrial control systems, as it can host and consolidate computing resources very efficiently. There accordingly have been efforts to utilize the virtualization technology for industrial control systems, but the research for virtualization of traditional industrial real-time networks, such as Controller Area Network (CAN), has been done in a very limited scope. Those traditional fieldbuses have distinguished characteristics from well-studied Ethernet-based networks; thus, it is necessary to study how to support their inherent functions transparently and how to guarantee Quality-of-Service (QoS) in virtualized environments. In this paper, we suggest a lightweight CAN virtualization technology for virtual controllers to tackle both functionality and QoS issues. We particularly target the virtual controllers that are containerized with an operating-system(OS)-based virtualization technology. In the functionality aspect, our virtualization technology provides virtual CAN interfaces and virtual CAN buses at the device driver level. In the QoS perspective, we provide a hierarchical real-time scheduler and a simulator, which enable the adjustment of phase offsets of virtual controllers and tasks. The experiment results show that our CAN virtualization has lower overheads than an existing approach up to 20%. Moreover, we show that the worst-case end-to-end delay could be reduced up to 78.7% by adjusting the phase offsets of virtual controllers and tasks.

Secrecy Rate Analysis of Open-Loop Analog Collaborative Beamforming Under Position Estimation Error of Virtual Antenna Array

As the importance to guarantee confidentiality against security attacks by eavesdroppers has attracted significant attention, there has been much effort to enhance the security performance through cooperative beamforming (CB) in the context of physical layer security (PLS). In particular, analog CB (ACB), which requires vastly lower overhead compared to digital CB, can provide significantly higher secrecy rate compared to the PLS methods with co-located array. In this letter, we focus on ACB with open-loop architecture that requires low complexity, and consider phase offsets across multiple virtual antenna array (VAA) elements for ACB, which are caused by position estimation error of VAA. We investigate the impact of the phase offsets in ACB in terms of the secrecy throughput loss.

A Femtosecond Pulse Train with a Selectable Carrier–Envelope Offset Phase

A method and a scheme of obtaining a femtosecond pulse train without frequency comb offset and selectable carrier–envelope offset phase are proposed.

Joint equalization of linear impairments using two-stage cascade Kalman filter structure in coherent optical communication systems

In this paper, instead of adopting different algorithms to deal with the different impairments separately based on different signal processing structures, we proposed a joint linear impairment equalization scheme using a two-stage cascade Kalman structure in which the first stage solves the residual chromatic dispersion (rCD), the rotation of state of polarization (RSOP) and polarization mode dispersion (PMD), and the second stage compensates for the carrier frequency offset (CFO) and carrier phase noise (CPN). The structures of the two stages are similar with a seamless connection and possess a clear logic architecture. The stages are compatible with each other and achieve excellent performance. We aim to use this two-stage Kalman scheme as a comprehensive DSP equalization scheme to replace the combined algorithms of the constant modulus algorithm (CMA), improved Mth-power algorithm (IMP), and blind phase search (BPS). Simulations based on a 28 Gbaud polarization division multiplexed quadrature-phase shift keying coherent optical communication system show that the proposed two-stage Kalman scheme comprehensively outperforms the CMA-IMP-BPS scheme in solving the problems of RSOP, PMD, rCD, CFO, and CPN. The experimental results confirm the simulation results. In addition, the complexity of the proposed Kalman scheme is relatively less than the CMA-IMP-BPS scheme.

An X-ray and optical study of the outbursting behaviour of the SMC Be X-ray binary SXP 91.1

ABSTRACT In this paper we report on the optical and X-ray behaviour of the Be X-ray binary, SXP 91.1, during a recent type I outburst. We monitored the outburst using the Neil Gehrels Swift Observatory. These data were supported by optical data from the Southern African Large Telescope and the Optical Gravitational Lensing Experiment (OGLE) to show the circumstellar disc activity. Matter from this disc accretes on to the neutron star, giving rise to the X-ray outburst as seen in the synchronous evolution of the optical and X-ray light curves. Using data taken with OGLE we show that the circumstellar disc has exhibited stable behaviour over two decades. A positive correlation is seen between the colour and magnitude from the OGLE and massive compact halo object observations, which indicates that the disc is orientated at relatively low-inclination angles. From the OGLE and Swift data, we demonstrate that the system has shown relative phase offsets that have persisted for many years. The spin period derivative is seen to be at maximum spin-up at phases when the mass accretion rate is at maximum. We show that the neutron star in SXP 91.1 is an unusual member of its class in the sense that it has had a consistent spin period derivative over many years, with the average spin-up rate being one of the highest for known Small Magellanic Cloud pulsars. The most recent measurements of the spin-up rate reveal higher values than the global trend, which is attributed to the recent mass accretion event leading to the current outburst.

Phase Offset Based Channel Estimation Method for Optical OFDM/OQAM Systems

In this letter, we developed a novel phase offset (PHO)-based channel estimation method for optical orthogonal frequency division multiplexing (OFDM)/offset quadrature amplitude modulation (OQAM). In this approach, the suppression of intrinsic imaginary interference (IMI) induced by both the linear and nonlinear impairment could be improved by increasing the pseudo pilot power with the using of PHO. As demonstrated in the numerous Montel Carlo simulation results, PHO outperforms the interference approximation methods (IAMs) for both the suppressing IMI and combating the fiber nonlinearity induced interference.

Timing Estimation Based on Higher Order Cyclostationarity for Faster-Than-Nyquist Signals

Faster-than-Nyquist (FTN) transmission is a promising technique to increase the spectral efficiency at a fixed constellation size. However, traditional timing synchronization algorithms mostly rely on the eye diagram opening after matched-filtering (e.g., Gardner and zero-crossing). Such approaches are, thus, unsuitable in the presence of the FTN-induced intersymbol interference. In this letter, we first show that FTN signals exhibit cyclostationarity at the $l$ th order ( $l > 2$ ) according to their bandwidth and symbol period. Then, we derive non-data-aided timing offset estimators from the cyclic temporal cumulant function. Besides its relevance for strong FTN scenarios, the proposed solution is also robust to frequency and phase offsets.

Design and Implementation of a Tree-Based Blind Modulation Classification Algorithm for Multiple-Antenna Systems

This paper presents the design and testbed implementation of a tree-based algorithm, which classifies many of the linearly modulated signals, such as binary phase-shift keying (PSK), quadrature PSK (QPSK), offset QPSK, $\pi $ /4-QPSK, 8-PSK, minimum shift keying, and 16-quadrature amplitude modulation. The proposed modulation classification algorithm is applicable to spatially multiplexed multiple antenna systems over frequency-selective fading channels. It works in the presence of timing, phase, and frequency offsets, without having prior knowledge of the channel state information. Classification is performed by utilizing the combined properties of the correlation functions, cyclic cumulant (CC), and cumulant. The correlation function of the received baseband signal exhibits peaks at a particular set of time lag, which represents distinctive features for the modulation formats. The CC uses the position of nonzero cycle frequency of the received baseband signals to classify modulation formats, while the cumulant employs threshold values. To authenticate the proposed algorithm, implementation and measurement are performed in an indoor propagation environment by using a National Instrument testbed setup. The performance of the proposed algorithm is compared with existing methods via Monte Carlo simulations.

RoArray: Towards More Robust Indoor Localization Using Sparse Recovery with Commodity WiFi

With the multi-antenna design of WiFi interfaces, phased array has become a promising mechanism for accurate WiFi localization. State-of-the-art WiFi-based solutions using Angle-of-Arrival (AoA), however, face a number of critical challenges. First, their localization accuracy degrades dramatically due to low Signal-to-Noise Ratio (SNR) and incoherent processing. Second, they tend to produce outliers when the available number of packets is low. Moreover, the prior phase calibration schemes are not multipath robust and accurate enough. All of the above degrade the robustness of localization systems. In this paper, we present ROArray, a RObust Array based system that accurately localizes a target even with low SNRs. The key insight of ROArray is to use sparse recovery and coherent processing across all available domains, including time, frequency, and spatial domains. Specifically, in the spatial domain, ROArray can produce sharp AoA spectrums by parameterizing the steering vector based on a sparse grid. Then, to expand into the frequency domain, it jointly estimates the Time-of-Arrival (ToAs) and AoAs of all the paths using multi-subcarrier OFDM measurements. Furthermore, through a novel multi-packet fusion scheme, ROArray is enabled to perform coherent estimation over multiple packets. Such coherent processing not only increases the virtual aperture size, which enlarges the number of maximum resolvable paths but also improves the system robustness to noise. In addition, ROArray includes an online phase calibration technique that can eliminate random phase offsets while keeping communication uninterrupted. Our implementation using off-the-shelf WiFi cards demonstrates that, with low SNRs, ROArray significantly outperforms state-of-the-art solutions in terms of localization accuracy; when medium or high SNRs are present, it achieves comparable accuracy.

Off-resonance correction for pseudo-continuous arterial spin labeling using the optimized encoding scheme

Pseudo-continuous arterial spin labeling (PCASL) MRI has become a popular tool for non-invasive perfusion imaging and angiography. However, it suffers from sensitivity to off-resonance effects within the labeling plane, which can be exacerbated at high field or in the presence of metallic implants, leading to spatially varying signal loss and cerebral blood flow underestimation. In this work we propose a prospective correction technique based on the optimized encoding scheme, which allows the rapid calculation of transverse gradient blips and RF phase modulations that best cancel phase offsets due to off-resonance at the locations of the feeding arteries within the labeling plane. This calculation is based upon a rapidly acquired single-slice fieldmap and is applicable to any number and arrangement of arteries. In addition, this approach is applicable to both conventional PCASL and a vessel-selective variant known as vessel-encoded PCASL (VEPCASL). Through simulations and experiments in healthy volunteers it was shown that in the presence of off-resonance effects a strong bias in the strength of the perfusion signal across vascular territories can be introduced, the signal-to-noise ratio (SNR) efficiency of PCASL and VEPCASL can be severely compromised (∼40% reduction in vivo), and that vessel-selective signal in VEPCASL can be incorrectly assigned. Distortion of the spatial regions placed in the label or control conditions in the presence of off-resonance effects was confirmed in phantom experiments. The application of the proposed correction restored SNR efficiency to levels present in the absence of off-resonance effects and corrected errors in the vascular territory maps derived from VEPCASL. Due to the rapid nature of the required calculations and fieldmap acquisition, this approach could be inserted into protocols with minimal effect on the total scan time.

Inherent Geometry Correction for Diffusion EPI Using the Reference Echoes as Navigators

Diffusion-weighted EPI has become an indispensable tool in body MRI. Geometric distortions due to field inhomogeneities are more prominent at large field–of–view and require correction for comparison with T2W TSE. Several known correction methods require acquisition of additional lengthy scans, which are difficult to apply in body imaging. We implement and evaluate a geometry correction method based on the already available non phase-encoded EPI reference data used for Nyquist ghost removal. The method is shown to provide accurate and robust global geometry correction in the absence of strong, local phase offsets. It does not require additional time for calibrations and is directly compatible with parallel imaging methods. The resulting images can serve as improved starting point for additional geometry correction methods relying on feature extraction and registration.

A novel 3D measurement technique for rigid moving objects with a determined movement trajectory and constant movement speed

When phase-shifting (PS) and temporal-phase-unwrapping algorithms are employed for three-dimensional (3D) shape measurement, the measured object must be kept static during the projection and acquisition. If the measured object is moving, deviation among multiple fringe images will inevitably occur, which results in the 3D measurement error. In this paper, a novel 3D measurement technique for rigid moving objects obtained by using the PS algorithm and the three-pitch heterodyne-unwrapping (TPHU) algorithm is proposed, which consists of six steps. First, the pixel offset is estimated based on a centroid deviation calculation. Second, the phase offsets among multiple fringes are calculated. Third, a novel set of fringes for the projection is generated. Fourth, we offset the captured fringe images according to the pixel offsets to generate a new set of captured fringe images for the phase calculation. Fifth, the wrapped phase is calculated by the PS algorithm. Finally, the unwrapped phase is calculated by the TPHU algorithm. The proposed method can be applied to the 3D shape reconstruction of a rigid movement object with a determined movement trajectory and constant movement speed. This approach not only greatly improves the measurement efficiency but also inherits the high accuracy and robustness of the PS and TPHU algorithms.

Dichotic phase effects on frequency following responses reveal phase variant and invariant harmonic distortion products

The dichotic frequency following responses (FFR) have been used in studies to infer about dichotic auditory processing. In the present study, we hypothesize that the proximity of the binaural neural generators of the FFR would result in interference of the volume-conducted electrical fields. This might lead to contamination of the scalp-recorded dichotic FFRs due to which it might be difficult to infer about true dichotic processing in the putative neural generators. We investigated this by recording FFRs to binaurally presented 200 Hz pure tone with graded dichotic phase offsets (0°, 90°, 180° and 270°) in normal hearing young adults. Spectral analysis of the FFRs was performed for the estimation of the magnitude and phase at the component frequencies. FFR spectra were compared using non-parametric paired randomizations within the subjects. We found that the brainstem responses to a 200 Hz pure tone consisted of prominent peaks at 200 Hz, and at frequencies corresponding to the harmonics of 200 Hz. The FFR spectral magnitude at 200 Hz diminished with a phase offset of 180°. Phase offsets of 90° and 270° showed reduced spectral magnitudes at 200 Hz than those in the 0° condition. Our findings, in line with the hypothesis, show that the dichotic FFRs do not reflect true dichotic processing and that they are contaminated during volume conduction. Additionally, we found harmonic distortion products (HDP) in the FFRs. We found that the response at 200 Hz and the 3rd HDP systematically varied with a change in phase of the stimulus, while the even HDPs (2nd and 4th) were phase-invariant. Based on our findings, and modeling FFRs using auditory models, we propose a rectification process as the contributors for the generation of HDPs. We also discuss the implications of this HDP generating mechanism in understanding the pitch represented in FFRs.

Phase Offset Analysis of Asymmetric Communications Infrastructure in Smart Grid

Synchrophasor advancement has the conversant to the smart grid applications, which is turned into necessary integral parts of digital communication frameworks that include transmission of electrical signals measured crosswise over various parts, which synchronized the grid applications utilizing external precise time source. The existing Communication protocol IEC 61850 for substation automation in Smart Grid today is being used with the support of up to 12 RS232/485 and 6 Ethernet ports, SCADA server, and PMUs. However, there is still having timing and control issue in the digital smart grid applications. Therefore, this paper proposes the hybrid synchronization scheme. The design considerations of the proposed scheme are mainly IP enabled broadband connectivity, IEEE 1588 clock server, and C37.118 functionalities. The result shows that the proposed scheme performs better than the existing systems. DOI: 10.5755/j01.eie.25.2.23209

Performance Comparison between DPSK and OQPSK modulation approaches in multi environments channels with Matlab Simulink models

Phase shift keying modulation approaches are widely used in the communication industry. Differential phase shift keying (DPSK) and Offset Quadrature phase shift keying (OQPSK) schemes are chosen to be investigated is multi environment channels, where both systems are designed using MATLAB Simulink and tested. Cross talk and unity of signals generated from DPSK and OQPSK are examined using Cross-correlation and auto-correlation, respectively. In this research a proposed system included improvement in bit error rate (BER) of both systems in the additive white Gaussian Noise (AWGN) channel, by using the convolutional and block codes, by increasing the ratio of energy in the specular component to the energy in the diffuse component (k) and the diversity order BER in the fading channels will be improved in both systems.

Calibrating Phase Offsets for Commodity WiFi

The calibration of phase offsets between RF chains on commodity WiFi chips has been an key obstacle for many WiFi-based applications. In this paper, we conduct extensive experiments to explore the characteristics of the phase offsets. The real experimental results reveal that the phase offsets are actually deterministic. We explain such a phenomena via the circuit design of WiFi chips. We also show that the phase offsets are even the same among different chips. With extensive experiments, we obtain and report the measured phase offset values for the commodity Intel 5300 and Atheros AR9380 WiFi chips. With the observation illustrated in this paper, the calibration of the phase offsets can be simplified greatly.