Common Reference Signal Research Articles

An enhanced stochastic subspace identification incorporating time variables and its application to large-span sea-crossing suspension bridges

Structural health monitoring and assessment are essential to large-span sea-crossing bridges, and modal identification is the most effective method for achieving them, with the stochastic subspace identification (SSI) method dominating. However, when analyzed in open traffic scenarios with SSI for a large-span sea-crossing bridge, the contour of the vibration mode is distorted. Related affecting factors such as the measuring conditions, user-defined parameters, and traffic are explored, and traffic is verified as the essential component. To address this issue, an enhanced SSI algorithm incorporating time variables is created to automatically identify and rectify vibration mode shapes. Feature heterotopic signals are first matched with a common reference signal to perform modal identification. Advanced particle swarm optimization is applied to estimate critical parameters. The SSI algorithm with the density-based spatial clustering of applications with noise (DBSCAN) algorithm is then utilized to extract the modal characteristics. Both simulated misalignment and real records are applied to verify the suggested approach's performance. Comparative analysis with state-of-the-art techniques, such as the error norm, cross correlation, phase transform-β, mean phase deviation, and genetic algorithm, shows that the recommended approach is dependable and successful at identifying the large-span sea-crossing bridge's vibration mode shapes and computationally more accurate and efficient.

Output-only modal analysis for non-synchronous data using stochastic sub-space identification

The stochastic subspace identification (SSI) method has been recognized as the most dominant and popular system identification technique in the time domain. Nevertheless, it cannot cope with the non-synchronicity of dynamic response measurements that happens sometimes in structural health monitoring practice. To overcome this, this study proposes a strategy for the SSI algorithm to realize system identification from non-synchronous dynamic response measurements. The modal identification is carried out in a pairwise manner by pairing a time-shifted signal with a common reference signal. The state space model is employed to fit the pair of reference and time-shifted signals and the SSI algorithm is exploited to extract the modal parameters. The core of the strategy is the tactical usage of the mean phase deviation (MPD) of the mode for seeking out the actual time lag as well as the actual mode shape components simultaneously. By so doing, the strategy fulfills integrated time lag estimation and modal extraction for non-synchronous dynamic response measurements. Furthermore, the strategy also overcomes the difficulty to determine the model order with the use of the stabilization diagram and reduces the computational cost substantially with the help of the periodicity of the MPD. To examine the performance of the strategy, intensive validations are conducted by making use of the non-synchronous acceleration measurements of the Jiangyin Bridge subjected to a ship collision and the artificially misaligned acceleration measurements of the Canton Tower struck by an earthquake. Both the time lags and the mode shapes identified by the strategy can be well validated, indicating that the proposed strategy is competent for modal identification of non-synchronous dynamic response measurements.

A Digital Interconnected Bus Providing Voltage Synchronization for the Modular Series-Connected Inverters

The input port or the output port series-connected system is very suitable for medium- or high-voltage applications. For the output series-connected modular inverter system, the important issue is to guarantee that the phase angle of the different modules are exactly the same, otherwise, the total output voltage cannot meet the requirement. This letter proposes a digital synchronization strategy, which adopts a digital interconnected bus to provide the common reference signal for the composed modules. The operation principle, circuit schematic, and control design of the proposed strategy are explained in detail in this letter, and finally, the performance of the strategy is verified on a three-module series-connected inverter system.

Enhanced interference cancellation techniques for downlink of LTE-A heterogeneous networks

The formation of Heterogeneous Network (HetNet) into the cellular system improves the overall spectral efficiency and network capacity of the system. Although the forming of the heterogeneous cellular network increases the complexity and overall interference of the system, the interference between the macro cell and smaller cells like femto/pico reduces the overall performance of the system in the downlink. In downlink, the Common Reference Signal (CRS) is used at the User Element (UE) to estimate the channel characteristics and is available throughout the entire frequency band. The presence of CRS of the neighbouring cells creates interference to the users. Linear Minimum Mean Square Error (LMMSE) based equaliser is proposed to reduce the effect of the non-colliding CRS at the UE. Enhanced space alternating generalised expectation maximisation-maximum a posteriori probability (ESAGE-MAP) estimator is used at the UE to mitigate colliding CRS interference. The simulation results have proved that the proposed LMMSE and ESAGE-MAP interference cancellation techniques perform better than the existing methods.

Enhanced interference cancellation techniques for downlink of LTE-A heterogeneous networks

The formation of Heterogeneous Network (HetNet) into the cellular system improves the overall spectral efficiency and network capacity of the system. Although the forming of the heterogeneous cellular network increases the complexity and overall interference of the system, the interference between the macro cell and smaller cells like femto/pico reduces the overall performance of the system in the downlink. In downlink, the Common Reference Signal (CRS) is used at the User Element (UE) to estimate the channel characteristics and is available throughout the entire frequency band. The presence of CRS of the neighbouring cells creates interference to the users. Linear Minimum Mean Square Error (LMMSE) based equaliser is proposed to reduce the effect of the non-colliding CRS at the UE. Enhanced space alternating generalised expectation maximisation-maximum a posteriori probability (ESAGE-MAP) estimator is used at the UE to mitigate colliding CRS interference. The simulation results have proved that the proposed LMMSE and ESAGE-MAP interference cancellation techniques perform better than the existing methods.

Low-Cost Polarization Sensing System for Self-Oscillating Circularly-Polarized Active Integrated Antenna

A simple, low-cost yet efficient polarization sensing system, capable of determining the polarization state of a self-oscillating circularly-polarized active integrated antenna (CPAIA), is proposed and demonstrated. The newly developed sensing system is capable of retrieving the phase difference information between the orthogonal field components of a CPAIA without the need of a common synchronous reference signal as that in a conventional pattern measuring system. The two orthogonal electrical fields are captured and mixed to retrieve the relative phase difference information as dc voltages. As a proof of concept, the polarization sensing system has been successfully developed on a printed circuit board, while a typical passive circularly-polarized antenna and a self-oscillating CPAIA were fabricated as a pair of antennas under test (AUTs). On one hand, the passive AUT characterized by the sensing system was supported by data from a commercial measuring setup to validating the accuracy of the newly developed system. On the other hand, the proposed sensing system is believed to be the first demonstration dedicated to retrieving the polarization information of a self-oscillating CPAIA, and hence pave a new way to fully characterize this special sort of active antennas.

Uncertainty Analysis of an Equivalent Synchronization Method for Phasor Measurements

This paper deals with the accuracy evaluation of a method for gathering synchronized phasor measurements of electrical quantities in nodes of power networks. Usually, this task is performed using commercially available instrumentation, for instance, the phasor measurement unit. They rely on a common time reference signal provided usually by the GPS system. After a brief recall of two methods already presented by authors in previous papers, which do not require a common time reference for providing synchronized phasors of voltages at the network nodes, the major sources of uncertainty in the measurement chain (lengths of the branches of the network; per-unit length reactance of the cables; and effect of the instrument transformers) are considered and investigation on their contribution, in one of the two methods, to the overall uncertainty performed.

Joint Power Waveforming and Beamforming for Wireless Power Transfer

In the Internet of Things, wireless devices need more easily accessible energy resources, which motivates the development of wireless power transfer (WPT) using radio frequency signals. Beamforming technique has been widely adopted by using multiple transmit antennas to form a sharp energy beam toward an intended receiver. However, few of them have considered the potential gain of multipath propagation. In this paper, we propose a joint power waveforming and beamforming in the time domain for WPT, in which the waveforms on multiple transmit antennas driven by a common reference signal are designed to maximize the gain of energy delivery efficiency. We consider both nonperiodic and periodic reference signals and propose low-complexity waveforms that can achieve near-optimal performance. It is found that the energy delivery efficiency gain of the proposed approach increases with the waveform length until saturation. We theoretically analyze the outage probability of the proposed approach under a uniform power delay channel profile, which quantifies the impact of the number of antennas and multipaths. Simulations are performed to validate the theoretic analysis and the effectiveness of the proposed joint power waveforming and beamforming approach.

2D Active Antenna Array Design for FD-MIMO System and Antenna Virtualization Techniques

Full dimension MIMO (FD-MIMO) is one of the key technologies presently studied in the 3GPP for the next generation long-term evolution advanced (LTE-A) systems. By incorporating FD-MIMO into LTE/LTE-A systems, it is expected that system throughput will be drastically improved beyond what is possible in conventional LTE systems. This paper presets details on the 2D active antenna array design for FD-MIMO systems supporting 32 antenna elements. The FD-MIMO system allows for dynamic and adaptive precoding to be performed jointly across all antennas thus achieving more directional transmissions in the azimuth and elevation domains simultaneously, to a larger number of users. Finally, we discuss 2D antenna array port virtualization techniques for creating beams with wide coverage, necessary for broadcasting signals to all users within a sector, such as the CRS (Common Reference Signal).

Spatial Power Combining of Multi-Sine Signals for Wireless Power Transmission Applications

This paper presents two transmitter architectures for wireless power transmission (WPT) applications. These architectures aim at transmitting high peak-to-average power ratio (PAPR) multi-sine signals, which have demonstrated to improve the RF-dc conversion efficiency of rectifier circuits, such as the ones in the receiving end of a WPT system. In order to overcome the challenges associated to the amplification of high PAPR signals, the proposed schemes make use of the spatial power combining concept, in which the individual signal components are amplified, radiated, and then combined in free space. In order to achieve the high PAPR signals, proper synchronization of the individual tones is required. Two architectures are proposed. The first one is based on the transmission of single-tone signals that are externally locked to a common reference signal that establishes the necessary phase reference. The second architecture is based on a mode-locked oscillator scheme that requires no external reference signal. Instead, this scheme takes advantage of the synchronization phenomena in oscillator circuits to establish the phase reference. Measurements are presented to validate both schemes and to show their effectiveness in improving the RF-dc conversion efficiency in rectifier circuits.

Single agent control for multi-agent dynamical consensus systems

The problem of controlling a single agent in a multi-agent consensus system is studied in order to make states of all agents in the system follow a common reference signal. It is shown that if every two agents in a given system are connected and a reference signal is a step function, then every controller locally stabilising one single agent gives rise to a successful tracking of all agents. When a proportional control is employed, the relations between overall tracking performance, interconnection topology and the choice of a controlled agent are analytically investigated. A numerical study is also performed to substantiate theoretical findings.

Design of a wideband multi-channel system for time reversal hyperthermia

Purpose: To design and test a wideband multi-channel amplifier system for time reversal (TR) microwave hyperthermia, operating in the frequency range 300 MHz–1 GHz, enabling operation in both pulsed and continuous wave regimes. This is to experimentally verify that adaptation of the heating pattern with respect to tumour size can be realised by varying the operating frequency of the antennas and potentially by using Ultra-wideband (UWB) pulse sequences instead of pure harmonic signals.Materials and methods: The proposed system consists of 12 identical channels driven by a common reference signal. The power and phase settings are applied with resolutions of 0.1 W and 0.1°, respectively. Using a calibration procedure, the measured output characteristics of each channel are interpolated using polynomial functions, which are then implemented into a system software algorithm driving the system feedback loop.Results: The maximum output power capability of the system varies with frequency, between 90 and 135 W with a relative power error of ±6%. A phase error in the order of ±4° has been achieved within the entire frequency band.Conclusions: The developed amplifier system prototype is capable of accurate power and phase delivery, over the entire frequency band of the system. The output power of the present system allows for an experimental verification of a recently developed TR-method on phantoms or animals. The system is suitable for further development for head and neck tumours, breast or extremity applications.

Submillimeter-Wave Phasor Beam-Pattern Measurement Based on Two-Stage Heterodyne Mixing With Unitary Harmonic Difference

A near-field phasor beam measurement system is developed for the characterization of heterodyne receiver optics at submillimeter-wave frequencies. The system synthesizes a pair of submillimeter-wave signals as the RF and local oscillator (LO) sources from common reference sources. The synthesized harmonic numbers of the RF and LO sources are arranged with difference by one, which makes this a new configuration with a unitary harmonic difference. The coherent RF and LO signal are down-converted by the receiver under test, then mixed with the microwave-frequency common reference signal to generate the second-order IF signal around 100 MHz for amplitude and phase comparison. The amplitude and phase fluctuation of the measurement system at 683 GHz is within plusmn0.2 dB and plusmn4deg in a 1-h period, respectively. The system dynamic range at 683 and 250 GHz can be as high as 43 and 47 dB, respectively. The system is then used to measure the receiver beam patterns at 683 and 250 GHz with different RF transmitting probe antennas.

Classification of active sonar detections with class specific method

The use of the Class Specific Method (CSM) [P. M. Baggenstoss, Trans. Sig. Proc. 47, 3428–3432 (1999)] is demonstrated with numerically simulated data. The two models of a cylindrical shell and a fish school are shown to generate sufficient statistics with appropriate assumptions. The common reference signal for the CSM is Gaussian white noise. An interpretation of the resulting conditional probability density functions is given, which leads to a numerical regularization. The resulting implementation of the CSM is demonstrated using numerically modeled data of variable bandwidth with variable amounts of additive Gaussian white noise. This approach enables the evaluation of bandwidth requirements for sufficient classification performance. The method is shown to be generalizable to include effects of propagation. [Work supported by the Office of Naval Research.]

Harmonic quality of multilevel cascade inverters with random carrier phase pulse width modulation

The output harmonic quality of N series connected full-bridge dc-ac inverters is investigated. The inverters are pulse width modulated using a common reference signal but randomly phased carrier signals. Through analysis and simulation, probability distributions for inverter output harmonics and vector representations of N carrier phases are combined and assessed. It is concluded that a low total harmonic distortion is most likely to occur and will decrease further as N increases.

Phase Synchronization Measurements Using Electroencephalographic Recordings: What Can We Really Say About Neuronal Synchrony?

Phase synchrony analysis is a relatively new concept that is being increasingly used on neurophysiological data obtained through different methodologies. It is currently believed that phase synchrony is an important signature of information binding between distant sites of the brain, especially during cognitive tasks. Electroencephalographic (EEG) recordings are the most widely used recording technique for recording brain signals and assessing phase synchrony patterns. In this study, we address the suitability of phase synchrony analysis in EEG recordings. Using geometrical arguments and numerical examples, employing EEG and magnetoencephalographic data, we show that the presence of a common reference signal in the case of EEG recordings results in a distortion of the synchrony values observed, in that the amplitudes of the signals influence the synchrony measured, and in general destroys the intended physical interpretation of phase synchrony.

Single molecule studies by means of the two-photon fluorescence distribution.

We have characterized a commercial confocal scanning head for the detection of single molecule fluorescence by two-photon excitation. We have verified that the distribution of the fluorescence emitted by dyes and labeled proteins on glass substrates is discrete with quanta proportional to a common reference signal. We describe and test a simple and quantitative tool to discriminate between single molecules and molecular aggregates on single snapshots based on the analysis of the intensity distribution. We have verified the square dependence of the fluorescence intensity vs. the excitation power, suggesting that no appreciable saturation and fast photo-damage of the chromophores takes place at the excitation power employed here.

Functional coupling of human right and left cortical motor areas demonstrated with partial coherence analysis

Although a linear correlation between oscillatory activities in the right and left motor cortices during movements has been shown in monkeys, there has been a debate whether scalp-recorded EEG coherence in human reflects a similar association. By applying partial coherence analysis, we demonstrated that interhemispheric coherence during movements cannot be explained by contamination from the occipital alpha rhythm or common reference signal. A significant increase of net interhemispheric communication in the beta1 band was shown during movements. We propose that the partial coherence method can be a useful tool to measure cortico-cortical functional coupling reliably.

Acoustic current meter

First Page

Doppler Dispersion Losses in the Reduced Averaging Processor for the Linear Swept FM Pulse

Reduced averaging processing of the linear swept FM pulse signal has been studied by the technique of using one common reference signal with one common set of step oscillators for multiple acoustic channels. Doppler dispersion effects versus the doppler resolution accuracy in both point and a special type of extended target are considered. Under the matched echo and reference signal slopes, the stated processing technique acts as the matched filter processor for both point and extended targets. Under the mismatched echo and reference signal slopes for the point target case, the Doppler dispersion loss is negligible and the stated processing technique does not degrade the resolution performance from the system that provides more than one reference signal. When the target is extended and both echo and reference signal slopes are mismatched, the stated processing technique indicates the serious dispersion loss; therefore, the resolution accuracy is jeopardized. In other words, it is necessary to have multiple reference signals for the specified resolution accuracy.