Phase Of Reference Signal Research Articles

On the Effect of Imperfect Reference Signal Phase Recovery on Performance of PSK System Influenced by TWDP Fading.

We examine the effects of imperfect phase estimation of a reference signal on the bit error rate and mutual information over a communication channel influenced by fading and thermal noise. The Two-Wave Diffuse-Power (TWDP) model is utilized for statistical characterization of propagation environment where there are two dominant line-of-sight components together with diffuse ones. We derive novel analytical expression of the Fourier series for probability density function arising from the composite received signal phase. Further, the expression for the bit error rate is presented and numerically evaluated. We develop efficient analytical, numerical and simulation methods for estimating the value of the error floor and identifying the range of acceptable signal-to-noise ratio (SNR) values in cases when the floor is present during the detection of multilevel phase-shift keying (PSK) signals. In addition, we use Monte Carlo simulations in order to evaluate the mutual information for modulation orders two, four and eight, and identify its dependence on receiver hardware imperfections under the given channel conditions. Our results expose direct correspondence between bit error rate and mutual information value on one side, and the parameters of TWDP channel, SNR and phase noise standard deviation on the other side. The results illustrate that the error floor values are strongly influenced by the phase noise when signals propagate over a TWDP channel. In addition, the phase noise considerably affects the mutual information.

Processing methods of the pipeline crack detection signal by a balanced field electromagnetic technique based on phase characteristics

The balanced field electromagnetic technique is an effective way of in-line inspection to detect cracks in pipelines. A signal demodulation method based on phase characteristics is proposed for the problem of interference signals generated by the sensor tilt shaking during the detection, which affects the judgment of the cracks. The method uses a reference signal whose phase is orthogonal to the signal generated by the sensor shaking to demodulate the detection signal to eliminate the shake interference. The generation principles of crack detection signals and interference signals generated by sensor shaking are analyzed, and the influence of sensor lift-off on detection is compared. A demodulation model is established based on the characteristic of that same frequency and different phases of crack and shake signals. The feasible conditions of the method are analyzed by simulation, and the phase value of the reference signal in the demodulation method is determined. The platform detection experiment and pulling tests at different speeds are carried out, respectively, to verify the effectiveness of the proposed method. The results show that there is a significant phase difference between the signals generated by the sensor shaking and the crack. For carbon steel pipelines, the signal phase of different shake angles is −4°. When the sensor structure and excitation frequency in this study are used, the reference signal phase is chosen to be 86°. The method preserves the detection signal characteristics before processing and enables the linear output responses to be obtained for different depths of cracks.

Fluidic Oscillator with Active Phase Control

This paper demonstrates the closed-loop control of the frequency and phase of a fluidic oscillator using acoustic excitation. It is shown experimentally that the use of acoustic excitation modifies the passive feedback mechanism and slows down the jet switching process. Closed-loop control is employed to vary the oscillation frequency at a fixed flow rate and track a sinusoidal reference target without phase error, using measurements from a pitot probe in the device. The controller is demonstrated to be effective at rejecting disturbances, which is illustrated with both time and frequency domain data. The controller’s ability to track step changes to the reference signal phase is tested, and the closed-loop bandwidth is shown to be around 20% of the oscillation frequency, in close agreement with the theoretical prediction.

An Efficient Cross-Correlation Method for a Digital Phase Noise Measurement System

In this paper, we propose a digital phase noise measurement using a 10-bit digital oscilloscope MXR608A from Keysight Technologies. The digital oscilloscope’s four channel data are used for digital phase noise measurement: two channels are assigned for the equally divided SUT (source under test), while the other two are assigned for the equally divided reference signals. First, we propose a cross correlation method to identify the phase noises added by the ADCs in the digital oscilloscope from the measured phase noises. Then, we propose a novel cross correlation method to extract the SUT phase noise. The cross-correlation output of the proposed method yields only the SUT phase noise and does not contain the reference signal phase noise unlike the traditional method. The proposed method was applied to measure the phase noises of the two SUTs, Keysight’s synthesized signal generator E8257D and function generator 33600A. The measured phase noises of the two SUTs were compared and found to show remarkable agreements with those measured using Keysight’s signal source analyzer E5052B. The phase noise floor of our digital phase noise measurement system is about -160 dBc/Hz.

Design of an RF Reference Distribution System for the RISP Linac

The heavy-ion accelerator of the Rare Isotope Science Project (RISP) in Korea has been developed. The RF reference distribution system must deliver phase reference signals to all low-level RF (LLRF) systems and BPM systems with low phase noise and low phase drift. The frequencies of the RISP linac are 81.25 MHz, 162.5 MHz and 325 MHz, and 30 LLRF systems and 60 BPMs are used for SCL3, and 210 LLRF systems and 60 BPMs are used for SCL2. A signal with a frequency of 81.25 MHz is chosen as the reference frequency signal, and a 1-5/8″ rigid coaxial line is installed with temperature control. This paper address aspects of the design for the RF reference distribution system, such as the reference frequency, phase noise on master oscillator, phase stability, temperature influence, and reference line attenuation.

Simplified Fourier Series Based Transistor Open-Circuit Fault Location Method in Voltage-Source Inverter Fed Induction Motor

Transistors in three-phase voltage-source inverter often suffer from open-circuit failures due to the lifting of bonding wires caused by thermic cycling, resulting in performance degradation with ripple torque and current harmonics. Current-spectral-analysis based methods are widely applied to failure diagnosis; however, high calculation consumption and complex implementation limit their application in some real-time occasion. In this paper, a simplified Fourier series method is proposed by the product between reconstructed phase currents and reference signals. Meanwhile, a novel normalized method for DC and fundamental components of simplified Fourier series are proposed to locate twenty-one transistor open-circuit faults. Numerical results show that the proposed Fourier series method coincides with that of Fast Fourier Transform. Experimental results and the comparison with previous methods show high efficiency and merits of its application to transistor open-circuit fault location in the voltage-source inverter.

A low level radio frequency system drift compensation technique by time-multiplexing pick-up/reference signals

The Low Level radio frequency system long-term stability is critical for the operation of accelerator facilities. The RF cavity field phase drift observed at the Tsinghua Thomson scattering X-ray source showed the correlations with devices temperature characteristic. We proposed a drift compensation technique by time-multiplexing cavity pick-up and phase reference signals, which guaranteed that they shared the same route with the same change. The preliminary ∼84 h Dual-Receiver out-of-loop stability test showed phase drift of 100 fs peak-peak (∼45 fs rms) when the reference signal phase changed ∼40 ps peak-peak.

Measurement of the Absolute Phase Error of Digitizers

This paper proposes a method for the measurement of digitizer absolute phase errors, defined as the phase displacement between the digitized output and the input analog waveform. The measurement procedure is based on the use of a phase reference signal (PRS), which is theoretically synchronous with the input analog waveform and that triggers the digitizer sampling clock. From the characterization of the waveform generator phase response and the measurement of the time delay of the digitizer sampling clock with respect to the PRS, an accurate evaluation of the digitizer absolute phase error is obtained. The method has been applied to a high-performance digitizer, measuring the absolute phase errors of two different channels. The expanded uncertainty of the method has been quantified as a few microradians at 50 Hz and 150 $\mu $ rad at 20 kHz.

Order spectrogram visualization for rolling bearing fault detection under speed variation conditions

Abstract For rotating machinery condition monitoring and fault diagnosis under speed variation conditions, order tracking has been considered as a very powerful non-stationary vibration signal analysis method, when compared with the frequency analysis methods based on stationary assumption. However, the conventional order tracking methods require additional hardware to provide a phase reference signal. This constraint limits the conventional methods in industrial applications significantly. In order to further improve the applicability of the conventional order tracking methods, some tacho-less order tracking methods have been proposed in the past few years. Despite the tacho-less order tracking methods successfully getting rid of reference signal, the algorithms are very complex and the computational burden is increased correspondingly. To address the aforementioned shortcomings, a straightforward tacho-less order tracking method based on order spectrogram visualization is proposed in this paper. In the proposed method, a ridge extraction approach is used to estimate the instantaneous frequency of a certain rotating frequency harmonic. And then the vibration signal is resonance demodulated and the time-frequency distribution of the demodulated signal is obtained. A subsequent transform is conducted and the frequency axis of the time-frequency distribution is rescaled based on the estimated instantaneous frequency of rotating shaft. Then, an order spectrogram is constructed and thereby the non-stationary interference introduced by rotating speed fluctuation is suppressed. Finally, fault orders are uncovered and bearing fault type can be identified. The effectiveness of the proposed method has been validated by both simulated and experimental rolling bearing vibration signals. The results illustrate the improved features regarding previously developed tacho-less order tracking method in bearing diagnosis under speed variation conditions.

Polarization-Multiplexed Quadrature Amplitude Modulation for Continuous-Variable Quantum Key Distribution

We propose a continuous-variable quantum key distribution (CV-QKD) scheme by using polarization-multiplexing (Pol-Mux) technique. As an effective way to promote spectral efficiency, quadrature amplitude modulation (QAM) has ability to provide substantial capacity. However, it may encounter the problem when discriminated symbols with increasing d. The star-QAM with different ring radii is utilized to tolerate greater phase jitter and improve the stability. In the proposed scheme, an optical phase reference signal is multiplexed to the quantum signal through the optical fiber to provide phase reference for local oscillator signal, which enables secure key distribution. However, the quadrature amplitude modulation could obtain the high modulation efficiency at the cost of increased complexity. And we utilize the low-density parity-check (LDPC) codes with little computational cost reconciliation scheme to deal with the extra data. From the numerical results, the proposed scheme achieves a good performance in terms of the key generation rate. The secure bound is derived with the presence of a Gaussian channel and the analysis shows the performance of the proposed scheme can be further improved by altering the effective parameters.

A Method for the Measurement of Digitizers’ Absolute Phase Error

A lot of engineering applications, from telecommunications to power systems, require accurate measurement of phase angles. Some of them, like synchrophasor measurement and calibration of instrument transformers with digital output, in order to reach high phase measurement accuracy, require the knowledge of phase error of digitizers. Therefore, in this paper a method for the measurement of digitizers’ absolute phase errors is proposed. It adopts a sinewave and two square waves, that are the digitizer sample clock and a phase reference signal. Combining the measurements of the relative phase differences between the adopted signals it is possible to accurately evaluate the absolute phase error of a digitizer.

Joint Uplink Radio Access and Fronthaul Reception Using MMSE Estimation

In cloud-based radio access networks, remote radio units and central baseband units are connected by fronthaul links, which are commonly assumed to be error-free. However, especially for wireless millimeter wave fronthaul links, this might be challenging to achieve, as they face a more unreliable environment than the conventionally used fiber links. In this paper, we hence aim to mitigate the impact of imperfect fronthaul links. For this, we propose the concept of joint radio access and fronthaul reception, which considers to recover the transmitted messages correctly at the centralized baseband unit, rather than to ensure a nearly perfect fronthaul transmission in between. Based on the Bayesian minimum mean square error criterion, we develop a joint access and fronthaul estimation scheme that can be utilized for various signals transported over the fronthaul, including in-phase/quadrature phase (I/Q) samples, soft-bits, synchronization, and reference signals. In addition, we develop an approximated variant of the scheme to reduced complexity, and an iterative extension to further improve the performance. We demonstrate that our scheme can operate under less reliable fronthaul than conventional approaches by numerical simulation for different signals, and show that our method can be implemented in a parallel architecture to achieve a reasonable computational complexity.

A Real-Time Harmonic Detection Method for Single-Phase Active Power Filters

Abstract: Harmonics, due to the increasing use of nonlinear loads, such as converters and solid state switching devices, has become a serious problem in power systems. Active power filters (APFs) have been used effectively to eliminate harmonic components. Precision of harmonic detection is one of the most important factors of APFs. This paper describes a novel circuit is proposed for real-time harmonic detection as an alternative to conventional approaches. This circuit is based on a switched capacitor band-pass filter and a Phase Locked Loop (PLL) which has low distortion sine wave output. This PLL follows not only phase of reference signal but also its amplitude. Harmonic components have been obtained by subtracting produced fundamental component with PLL from distorted signal. Fundamental and harmonic components of distorted line voltage and current have been successfully separated experimentally.

Phase correction autocorrelation-based frequency estimation method for sinusoidal signal

To improve the precision of frequency estimation, a phase correction autocorrelation-based frequency estimation method for sinusoidal signal is proposed. Firstly, a phase correction autocorrelation is developed to reduce the effect of non-half period sampling signal on autocorrelation. Secondly, reference signal is generated according to phase correction autocorrelation signal. Finally, an error function between phase correction autocorrelation signal and reference signal is constructed and frequency estimation is obtained by calculating the minimum of error function. To demonstrate the superiority of the proposed method, computational complexity is analyzed, simulations and experiments are performed. Theoretical analysis and simulations demonstrate that the proposed method reduces the influence of non- half period sampling signal and has better frequency estimation performance than the interpolated DFT method, the modified covariance method for correlation, the two-stage autocorrelation method and the expanded autocorrelation method. The measurement experiments of LFMCW radars validate the effectiveness and superiority of the proposed method in practice.

A cointegration-based monitoring method for rolling bearings working in time-varying operational conditions

Most conventional diagnostic methods for fault diagnosis in rolling bearings are able to work only for the case of stationary operating conditions (constant speed and load), whereas, bearings often work at time-varying conditions. Some methods have been proposed for damage detection in bearings working under time-varying speed conditions. However, their application might increase the instrumentation cost because of providing a phase reference signal. Furthermore, some methods such as order tracking methods can only be applied for limited speed variations. In this study, a novel combined method for fault detection in rolling bearings based on cointegration is proposed for the development of fault features which are sensitive to the presence of defects while in the same time they are insensitive to changes in the operational conditions. The method makes use solely of the measured vibration signals and does not require any additional measurements while it can identify defects even for considerable speed variations. The signals acquired during run-up condition are decomposed into zero-mean modes called intrinsic mode functions using the performance improved ensemble empirical mode decomposition method. Then, the cointegration, which is finding stationary linear combination of some non-stationary time series, is applied to the intrinsic mode functions to extract stationary residuals. The feature vectors are created by applying the Teager–Kaiser energy operator to the obtained stationary residuals. Finally, the feature vectors of the healthy bearing signals are utilized to construct a separating hyperplane using the one-class support vector machine method. Eventually the proposed method was applied to vibration signals measured on an experimental bearing test rig. The results confirm that the method can be successfully applied to distinguish between healthy and faulty bearings even if the shaft speed changes dramatically.

Supply Frequency Tracking in Resistance-Based Induction Motor's Rotor Temperature Estimation

In resistance-based rotor temperature estimation schemes, a grid-connected induction motor's rotor temperature is derived from a resistance quantity based on an equivalent circuit model. This temperature is susceptible to fluctuations in the motor's supply frequency. In this paper, the relationship between supply frequency fluctuations and accuracy in resistance-based rotor temperature estimates is analyzed, and a complex adaptive phase discriminator is proposed to track the supply frequency fluctuations for grid-connected induction motors. A complex voltage vector is constructed from polyphase voltage measurements and passed through a frequency-selective digital filter to attenuate harmonics and interference. The complex adaptive phase discriminator then operates on the filtered voltage signal, iteratively adapting a complex reference signal's phase to align it with the filtered voltage signal. The power grid's supply frequency is directly estimated from the adapted phase on a sample-by-sample basis. Experimental results demonstrate that the proposed complex adaptive phase discriminator helps produce rotor temperature estimates with increased accuracy.

A phase stability control system in radiointerferometry experiments

A phase-stability control system of the radio-receiving section of a radio telescope, used in radiointerferometry observations, is presented. The system contains a picosecond pulse generator the phase of output pulses of which is synchronized with the reference-signal phase. The generator pulses with a 40-ps duration are applied to the input of the receiving unit, and, having passed the same path, as a signal received from celestial sources, are intended to compensate a signal-phase change occurring in the receiving-converting section by the correlation processing. The designed system controls the phase stability with an accuracy of 10 ps.

Performance of SC Receiver over Generalized K Fading Channel in the Presence of Imperfect Reference Signal Recovery

This paper considers a partially coherent detection of quadrature phase-shift keying (QPSK) signals in a composite generalized K (KG) fading channel. At the reception the selection combining is applied, while the branches of the combiner are not identically distributed. The extraction of the reference carrier from non-modulated pilot signal is performed in a phase-locked loop (PLL) circuit. The difference between received signal phase and extracted reference signal phase is a stochastic variable with Tikhonov probability density function. The influence of the fading parameters, the standard deviation of phase error and the number of diversity branches on the system performance is examined. The bit-error rate is used as a measure of the reception quality. Ill. 6, bibl. 17 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.115.9.746

Computation-Based Phase Measurement of RF Power-Amplifier Intermodulation Products

Computation-based phase measurement is a relatively new intermodulation measurement method. It differs from other major methods in that no external phase reference signal is needed. This paper studies modulation phase measurement procedures from the viewpoint of the information envelope domain. This leads to further development of the time-zero cancelation technique and simplification of the computation-based phase measurement. Noncoherent calibrated two-tone phase measurement procedures are shown to be feasible as one validation of the proposed ideology.

A simple method to measure phase difference between sinusoidal signals

In this paper, a novel and simple method to measure the phase difference between two sinusoidal signals is presented. Basically, the method consists of subtracting two sinusoidal signals with same frequencies and measuring the resulting signal amplitude: this amplitude being a minimum whenever there is a coincidence between both signal phases. In order to test this method, an adjustable phase reference signal has been generated using a direct digital synthesizer device. Employing this reference signal, it can be demonstrated that the phase difference between two signals can be evaluated with errors smaller than 0.3° for signals with frequencies up to 1.25 MHz.