In-phase Components Research Articles

Expansion of the Impedance and Frequency Measurement Ranges of AC Shunt Resistors

For expanding the impedance and frequency ranges of a calibration system for ac shunt resistors, a current bridge method with cascaded current transformers (CTs) has been developed. An ac shunt resistor with a nominal value of 10 $\text{m}\Omega $ is evaluated by the current bridge method using cascaded CTs and the results of the calibration system using this method are validated. It is demonstrated that the calibration system for ac shunt resistors using the current-bridge method with the cascaded CTs can be used successfully for both in-phase and quadrature components up to 3 kHz. Further, for expanding the frequency range, a voltage difference method is proposed. The measurement results obtained by the current-bridge method and the proposed method are consistent with each other within the measurement uncertainties. In addition, for expanding the impedance range at higher frequencies, a combination method with an inductive voltage divider and a current transformer is proposed. The measurement results using the combination method are consistent with the results of the current-bridge method within the measurement uncertainties. The test current in this paper was limited up to 10 A because of the specification of shunt resistors.

A portable embedded contactless system for the measurement of metallic material conductivity and lift-off

This paper describes the development, implementation and characterization of a portable embedded measurement system for the contactless estimation of a metallic material conductivity and of the lift-off between the system probe and the metallic material surface. The system consists on an absolute probe with compensation and is capable of measuring the in-phase and in-quadrature components of the probe output voltage using as a reference the probe stimulus voltage. The stimulus module includes a direct digital synthesizer (DDS) to set the measurement frequency, while the acquisition module includes analog voltage amplification and analog-to-digital conversion. A microcontroller is used to control the measurement, process the acquired voltage samples, estimate the desired parameters and perform USB communication. The final dimensions of the pen-like system, its capability of communication with a smartphone and its ability to power the system from the smartphone make it highly portable and especially suited for non-destructive testing (NDT) and field measurements.

X-mode raw data analysis of the new AUG ICRF antenna edge density profile reflectometer

The new multichannel X-mode reflectometer installed on ASDEX Upgrade measures the plasma density profile evolution at different positions in front of the ICRF antenna. The reflectometer operates in the extended U-band (40–68GHz) microwave region, measuring density profiles up to 2×1019m−3 with magnetic fields between 1.5T and 2.7T. In this heterodyne reflectometer architecture, the signal reflected by the plasma is down-shifted and quadrature detectors demodulate its in-phase and quadrature (IQ) components. In this work we analysed the acquired IQ signals from the different reflectometer antennas, and describe the waveguide dispersion calibration and filtering of the raw signal. The effect of spurious reflections, such as the multiple reflections from the ICRF antenna metal straps, are analysed and taken into account on the data processing software. In high plasma density and high magnetic field scenarios, both the lower and upper X-mode cut off frequencies are detected in the probing range. The first fringe (FF) reflection of the upper cut off indicates the start of the plasma signal and must be determined robustly to reduce density profile errors. Existing FF estimation algorithms based on signal amplitude and spectral information may still fail in the presence of both upper and lower cut off reflections.

Expendable Current Profiler for Measuring the Electric Field Induced by Ocean Currents

In this study, an expendable current profiler sensor is developed to satisfy the actual requirements of an expendable current profiler for measuring electric fields induced by ocean currents. The electric field induced by ocean currents is an important process variable for investigating the motion characteristics of ocean currents; however, accurate measurement thereof is affected by various factors. Amplitude modulation is used to modulate the measured signals into narrow-band, single-frequency signals, thereby reducing the noise level of the sensor when measuring the electric field induced by ocean currents and for extracting ocean current signals in the nanovolt range under high background noise. In this study, front-end weak signal processing circuits are designed, strong interfering signals induced by the descent of the expendable current profiler probe are partially offset by a compensation circuit for the in-phase electric field component, and useful signals are extracted using a filter circuit. System on a programmable chip technology is used for the digital processing module of the expendable current profiler probe, thereby achieving rapid development, rapid optimization, and software/hardware integration of the digital processing module, as well as enhancing the overall performance of the system. In addition, dynamic data transmission technology using an enameled wire with a diameter of 0.1 mm and a length of 2 km is developed to achieve dynamic data transmission requirements for the expendable current profiler surface float. Finally, the ocean current electric field data and ocean temperature data are acquired through experiments.

Adaptive Control of Low-Level Radio Frequency Signals Based on In-Phase and Quadrature Components

This research work presents a low-level radio frequency (RF) control method based on the in-phase, $I$ , and quadrature, $Q$ , components of the RF signal. The proposed method uses only the main four arithmetic operations, i.e., addition, subtraction, multiplication, and division, which makes this control method suitable for implementation on the field-programmable gate array. The control scheme is adaptive in the sense that it estimates the system response on-the-fly, and therefore, it is robust against changes in the loop phase and/or gain during the operation.

Study of an expendable current profiler detection method

In this study, the induced electric field model for current movement is established, and the measurement principle of an expendable current profiler (XCP) is obtained through model analysis. Based on this analysis, a method is proposed for the measurement of the nanovolt-scale ocean-current-induced electric field. The proposed procedure moves the frequency of the ocean-current-induced electric field signal to the super-low noise range of the ocean current electric field sensor though amplitude modulation. This is then followed by amplifier filter extraction, while compensating the ocean-current-induced electric field, in terms of the circuit, to offset the strong interference of the induced electric field caused by the subsidence of the XCP probe. Inside the XCP probe, the ocean current electric field signal and the compass coil signal are converted into the in-phase component In, quadrature component Qn, and baseline component Bn, and the data processing method that calculates the eastward and northward relative velocity components of the ocean current from the values of In, Qn, and Bn is established.

Quadrature Compressive Sampling for Multiband Radar Echo Signals

In multiband/multifunction radars, the received echoes are usually multiband signals consisting of several subbands with different carrier frequencies. Digital acquisition of the in-phase and quadrature ( ${I}$ and ${Q}$ ) components of each subband is important for the extraction of radar targets. However, the existing acquisition methods are inefficient because their sampling rates are at least twice of the effective bandwidth, also known as the Landau rate. In this paper, we merge the quadrature compressive sampling into the uniform sampling technique for multiband signals, and develop a multiband quadrature compressive sampling (MQuadCS) system. The MQuadCS system first applies the random modulation to generate a compressive multiband signal, and then utilizes the uniform sampling to output the samples of the compressive multiband signal at its Landau rate. As the Landau rate of the compressive multiband signal is much less than that of the received echo, the MQuadCS achieves the sub-Landau rate sampling. With the assumption of sparse targets, the $I$ and $Q$ components of each subband can be independently recovered by the corresponding samples separated from the compressive multiband samples. For the independent recovery, we establish the model of MQuadCS system parameters and provide a sufficient condition to ensure the existence of the system parameters. To guarantee successful recovery of each subband, we introduce the frequency domain representation of the MQuadCS and then derive the reconstructability condition via restricted isometry property analysis. Furthermore, we design a system parameter optimization scheme to improve the recovery performance. Theoretical analyses and simulations validate the efficiency of the MQuadCS system.

The Complexα-μFading Channel with OFDM Application

The aims of this paper are threefold: (i) to present a model for the complexα-μfading channel; (ii) to propose an efficient, simple, and general method to generate complexα-μsamples; (iii) to make use of this channel in order to assess the bit error rate performance of an OFDM system. An analytical framework is then used, whose output is validated through Monte Carlo simulation. Several important conclusions concerning the system performance as a function of the channel parameters, namely, nonlinearity, clustering, and power imbalance of in-phase and quadrature components, are drawn.

GPS L5 Signal Acquisition and Tracking under Unintentional Interference or Jamming

The GPS signal consists of several signals transmitted at the L1, L2, and L5 carrier frequencies. The signal at L1 = 1575.42 MHz and L2 =1227.6 MHz consists of the civilian C/A code signals with pseudorandom sequences of length 1023 and chipping frequency of 1.023 MHz and the P(Y) code signals of length 1 week and chipping frequency of 10.23 MHz. The new L5 signal is QPSKmodulated, centered on 1176.45 MHz. Its two components have each a different spreading code at chipping frequency of 10.23 MHz. The in-phase component carries the navigation message, at 100 symbols per second (50 bits per second with a convolutional encoder) while the quadrature component, called the pilot channel, carries no message at all. Most GPS receivers, whether military or civilian, are designed in a way that the acquisition of the P(Y) code depends on the acquisition and tracking of the C/A code. Moreover, if the acquisition of the P(Y) code is lost, due to reasons that are explained in the paper, then the reacquisition of the P(Y) code will again depend on the acquisition and tracking of the C/A code. Therefore, for most commercially available receivers, the reliable acquisition and tracking of the C/A code is critical for the entire operation of a GPS receiver. However, it is well-known the vulnerability of the GPS C/A code signal, to unintentional interference or jamming. The main theme of this paper is the reexamination of the GPS C/A code signal acquisition and tracking under the situation of the unintentional interference or jamming. A variety of jamming signals are considered such as: (1) periodic, deterministic; (2) aperiodic, deterministic; and (3) noisy type signals or non-deterministic. However, the majority of vendors are still producing correlator type receivers. As shown by the simulation results of this paper and other previous publications a sliding correlator type of receiver used to acquire and track the C/A code or L5 code can be easily jammed by a similar C/A code replica or L5 code replica at power levels 10 dB or higher above noise power. GAMES, GILS, and GIANT are not the most economically viable solutions in the market to handle GPS protection of the civilian receivers. A maximum likelihood GPS receiver which considers all the signals in the environment can be used to acquire and track successfully the C/A and the L5 GPS signals when the jamming signal power are in the range or 10dB or higher above the noise power. In summary, the direction of designing acquisition and tracking receivers for future C/A L1 code or L5 GPS signals should go towards joint signal acquisition and tracking. There are three main challenges with these types of receivers: (1) algorithm complexity, (2) computational power, and (3) test with real data. All these remain to be studied and analyzes further in the future. I think it is going to be a breakthrough in the state of the art of GPS receivers when these algorithms are ultimately implemented and a lot more work is required to arrive at that point which some of it is going to be published in future publications.

Sliding discrete Fourier transform based frequency‐locked loop for adaptive carrier tracking of bi‐phase signals

For bi-phase signals, an adaptive carrier tracking method based on sliding discrete Fourier transform (SDFT) frequency-locked loop (FLL) is proposed. Magnitude and phase spectra of closed-loop SDFT filter provide almost flat response around the centre frequency. However, the small magnitude and phase errors observed at the SDFT in-phase and quadrature components are corrected by adaptive sampling frequency control. The carrier frequency is estimated by computing the frequency error. Hence, the input frequency variation due to Doppler shift could be estimated for the bi-phase signal. Experimental investigations with digital implementation demonstrate the suitability of the FLL for bi-phase signals.

High-Bandwidth Demodulation in MF-AFM: A Kalman Filtering Approach

Emerging multifrequency atomic force microscopy (MF-AFM) methods rely on coherent demodulation of the cantilever deflection signal at multiple frequencies. These measurements are needed in order to close the z -axis feedback loop and to acquire complementary information on the tip–sample interaction. While the common method is to use a lock-in amplifier capable of recovering low-level signals from noisy backgrounds, its performance is ultimately bounded by the bandwidth of low-pass filters. In light of the demand for constantly increasing imaging speeds while providing multifrequency flexibility, we propose to estimate the in-phase and quadrature components with a linear time-varying Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a field programmable gate array. Tracking bandwidth and noise performance are verified experimentally, and trimodal AFM results on a two-component polymer sample highlight the applicability of the proposed method for MF-AFM.

Optimization and Performance of Non-Uniform Rotated Constellations With Multi-RF Transmission Techniques

Non-Uniform Constellations (NUC) have been introduced in ATSC 3.0 (Advanced Television Systems Committee - Third Generation) as one of the main novelties to improve the performance compared to uniform Quadrature Amplitude Modulation (QAM) constellations. NUCs are optimized by means of signal geometrical shaping, considering the signal-to-noise ratio (SNR) and the channel model. ATSC 3.0 implements two types of NUC, depending on the number of real-valued dimensions in which they are optimized: 1D-NUC and 2D-NUC. However, the gain of NUCs becomes almost non-existent at high SNRs, especially when optimizing for fading channels. In that particular case, Rotated Constellations (RC) can be used to further improve the overall system performance. RCs may become especially effective when using multi-radio frequency (multi-RF) SNR averaging techniques such as Channel Bonding (CB) or Time-Frequency Slicing (TFS), where in-phase (I) and quadrature (Q) components are transmitted in different RF channels. 2D-NUCs can be rotated without increasing the demapping complexity, since a 2D-demapper is also needed. In this paper, we propose an optimization method designed for rotated 2D-NUCs, in which the rotation angle is considered as an additional variable, together with the symbol positions. The SNR gain obtained in fading channels is also provided for three different use cases: single-RF transmissions, CB with 2 RF channels as adopted in ATSC 3.0, and extension of multi-RF techniques to 4 RF channels.

Robust Training Symbol Assisted Least Squares Estimation for Direct Conversion Receivers with Oscillator IQ-Imbalance

The direct conversion receiver is attractive for being able to provide low-cost and compact receiver design for wireless communications. However, the oscillator imbalance in the in-phase and quadrature components of its mixing sinusoid introduces additional self-image interference, which is a non-linear effect to the received signal. Relying on just one OFDM training symbol, we formulate the joint estimation of oscillator imbalance, DC offset, and channel response as a linear model. A low-complexity least squares (LS) estimation method is then proposed. The transformation matrix in our model is shown to be of full rank with probability 1, which allows our LS approach to be realizable for a variety of training OFDM symbols. Justified by simulation results, our method outperforms the other three LS methods in the literature.

Gridless quadrature compressive sampling with interpolated array technique

Quadrature compressive sampling (QuadCS) is a sub-Nyquist sampling scheme for acquiring in-phase and quadrature (I/Q) components in radar. In this scheme, the received intermediate frequency (IF) signals are expressed as a linear combination of time-delayed and scaled replicas of the transmitted waveforms. For sparse IF signals on discrete grids of time-delay space, the QuadCS can efficiently reconstruct the I/Q components from sub-Nyquist samples. In practice, the signals are characterized by a set of unknown time-delay parameters in a continuous space. Then conventional sparse signal reconstruction will deteriorate the QuadCS reconstruction performance. This paper focuses on the reconstruction of the I/Q components with continuous delay parameters. A parametric spectrum-matched dictionary is defined, which sparsely describes the IF signals in the frequency domain by delay parameters and gain coefficients, and the QuadCS system is reexamined under the new dictionary. With the inherent structure of the QuadCS system, it is found that the estimation of delay parameters can be decoupled from that of sparse gain coefficients, yielding a beamspace direction-of-arrival (DOA) estimation formulation with a time-varying beamforming matrix. Then an interpolated beamspace DOA method is developed to perform the DOA estimation. An optimal interpolated array is established and sufficient conditions to guarantee the successful estimation of the delay parameters are derived. With the estimated delays, the gain coefficients can be conveniently determined by solving a linear least-squares problem. Extensive simulation results evidently demonstrate the superiority of the proposed algorithms in achieving super-resolution time-delay estimation and high-accuracy sparse signal reconstruction.

Multiple resolution chirp reflectometry for fault localization and diagnosis in a high voltage cable in automotive electronics

A multiple chirp reflectometry system with a fault estimation process is proposed to obtain multiple resolution and to measure the degree of fault in a target cable. A multiple resolution algorithm has the ability to localize faults, regardless of fault location. The time delay information, which is derived from the normalized cross-correlation between the incident signal and bandpass filtered reflected signals, is converted to a fault location and cable length. The in-phase and quadrature components are obtained by lowpass filtering of the mixed signal of the incident signal and the reflected signal. Based on in-phase and quadrature components, the reflection coefficient is estimated by the proposed fault estimation process including the mixing and filtering procedure. Also, the measurement uncertainty for this experiment is analyzed according to the Guide to the Expression of Uncertainty in Measurement. To verify the performance of the proposed method, we conduct comparative experiments to detect and measure faults under different conditions. Considering the installation environment of the high voltage cable used in an actual vehicle, target cable length and fault position are designed. To simulate the degree of fault, the variety of termination impedance (10 , 30 , 50 , and 1 ) are used and estimated by the proposed method in this experiment. The proposed method demonstrates advantages in that it has multiple resolution to overcome the blind spot problem, and can assess the state of the fault.

Simultaneous all-optical phase noise mitigation and automatically locked homodyne reception of an incoming QPSK data signal.

Simultaneous phase noise mitigation and automatic phase/frequency-locked homodyne reception is demonstrated for a 20-32 Gbaud QPSK signal. A phase quantization function is realized to squeeze the phase noise of the signal by optical wave mixing of the signal, its third-order harmonic, and their corresponding delayed variant conjugates, converting the noisy input into a noise-mitigated signal. In a simultaneous nonlinear process, the noise-mitigated signal is automatically phase- and frequency-locked with a "local" pump laser, avoiding the need for feedback or phase/frequency tracking for homodyne detection. Open eye-diagrams are obtained for in-phase and quadrature-phase components of the signal and ∼2 dB OSNR gain is achieved at BER 10-3.

Derivation of a reflectogram using digital lock-in detection in coherent FMCW reflectometry based on a uniformly pumped Brillouin grating

We used digital lock-in detection to demodulate in-phase and quadrature components from a balanced mixer output in coherent FMCW reflectometry based on a uniformly pumped Brillouin grating. All the frequency components contributing to a reflectogram were extracted without attenuation by using a rectangular window in the frequency domain. We succeeded in reshaping a deformed reflectogram into a step-wise reflectogram for a single mode fiber that consisted of two fibers with different Brillouin frequencies. We found multiplicative noise to be dominant in the retrieved reflectograms, whose signal levels typically varied between ±7 and ±10%. We compared the observed changes with those estimated from power fluctuations in the amplified probe and pump light waves.

Near-Coherent QPSK Performance With Coarse Phase Quantization: A Feedback-Based Architecture for Joint Phase/Frequency Synchronization and Demodulation

As communication systems scale up in bandwidth, the limited resolution in high-speed analog-to-digital converters (ADCs) is a key challenge in realizing low-cost “mostly digital” transceiver architectures. This motivates a systematic effort to understand the limits of such architectures under the severe quantization constraints imposed by the use of low-precision ADCs. In particular, we investigate a canonical problem of blind carrier phase and frequency synchronization with coarse phase quantization in this paper. We develop a Bayesian approach to blind phase estimation, jointly modeling the unknown data, unknown phase and the quantization nonlinearity. We highlight the crucial role of dither, implemented via a mixed signal architecture with a digitally controlled phase shift prior to the ADC. We show the efficacy of random dither, and then improve upon its performance with a simple feedback control policy that is close to optimal in terms of rapidly reducing the mean squared error of phase estimation. This initial blind phase acquisition stage is followed by feedback-based phase/frequency tracking using an Extended Kalman Filter. Performance evaluations for a QPSK system show that excellent bit error rate (BER) performance, close to that of an unquantized system, is achieved by the use of 8 phase bins (implementable using 4 one-bit ADCs operating on linear combinations of in-phase and quadrature components).

Mono-component AM–FM Signal Decomposition Based on Discrete Second-Order Generalized Integrator Phase-Locked Loop

A mono-component AM---FM signal decomposition method is proposed using discrete second-order generalized integrator and phase-locking scheme. A discrete second-order generalized integrator (SOGI) is employed in the algorithm as a quadrature signal generator for a center carrier frequency. The outputs from SOGI are in-phase and quadrature components of the AM---FM signal. These components are processed in the discrete phase-locked loop to estimate instantaneous frequency variation and instantaneous amplitude variation. The estimated instantaneous frequency variation is fed back to SOGI to adjust the center frequency. Proposed mono-component AM---FM demodulator is implemented in FPGA platform. The algorithm offers good acquisition time, accuracy, and operating range. Experimental investigations performed on the algorithm prove the efficacy and suitability of the algorithm for mono-component AM---FM demodulation.

Study of I/Q imbalances in QAM communication systems adopting multi-antenna receivers

This paper investigates the inphase/quadrature phase (I/Q) imbalance problem in quadrature amplitude modulation (QAM) communication systems with multi-antenna receivers. Two application scenarios are considered: adaptive beamforming and multi-user detection based on blind source separation (BSS). Our analysis illustrates that, in both scenarios, the effect of the transmitter and receiver I/Q imbalance can be mitigated through straightforward digital signal processing methods. For adaptive beamforming systems, increasing the number of receiver branches automatically suppresses the interference induced by transceiver I/Q imbalances. For the multi-user detection application, a simple alternative expression of the signal model can be adopted, which separately lists the inphase and quadrature phase components of the received signals and the source signals. As a result, the BSS estimation of all user signals can be conducted in the presence of transceiver I/Q imbalances. Simulation results confirmed the effectiveness of the presented I/Q imbalance correction techniques.