Undesired Signals Research Articles

Development of the passive vibroacoustic isolation system for the path matched differential interferometry based fiber-optic sensors

Fiber-optic interferometric sensor arrays are very attractive for many applications. One of the common used interrogation approaches for fiber-optic sensor arrays is the path matched differential interferometry (PMDI). It allows to interrogate a large number of multiplexed fiber-optic sensors by using an auxiliary compensation interferometer (CIF). This approach with using the phase modulator allows to implement the phase-generated carrier demodulation for multiplexed fiber-optic sensors. However, this approach has the significant disadvantage, which is that environmental vibroacoustic impacts on the CIF produce undesirable phase signals from the sensor array. It leads to increasing the noise floor level of the measuring system. In this paper the development methodology and results of the experimental investigation of the passive vibroacoustic isolation system for the CIF in the PMDI-based fiber-optic interferometric sensor are presented. The proposed isolation system is implemented by using acoustic absorbing layers and the special mechanical suspension system for the CIF mounted in the single rack unit. It is shown that the proposed approach for the CIF isolation allows to reduce its sensitivity to vibroacoustic impacts by up to 30 dB in the frequency range up to 500 Hz. It is also demonstrated that potting of the CIF fiber-optic components reduces its isolation efficiency by an average value of 8.3 dB in the considered frequency range, that is not applicable for interferometric sensors. The presented methodology and obtained results might be used in PMDI-based fiber-optic interferometric sensors to improve their performance characteristics.

On the Influence of Diurnal and Subdiurnal Signals in the Normal Vector on Large Ring Laser Gyroscope Observations

The ring laser gyroscope (RLG) technique has been investigated for over 20 years as a potential complement to space geodetic techniques in measuring Earth rotation. However, RLGs are also sensitive to changes in their terrestrial orientation. Therefore in this paper, we review how the high-frequency band (i.e. signals shorter than 0.5 cycle per day) of the known phenomena causing site deformation contribute to the RLG observable, the Sagnac frequency. We study the impact of solid Earth tides, ocean tidal loading and non-tidal loading phenomena (atmospheric pressure loading and continental hydrosphere loading). Also, we evaluate the differences between available models of the phenomena and the importance of the Love numbers used in modeling the impact of solid Earth tides. Finally, we compare modeled variations in the instrument orientation with the ones observed with a tiltmeter. Our results prove that at the present accuracy of the RLG technique, solid Earth tides and ocean tidal loading effects have significant effect on RLG measurements, and continental hydrosphere loading can be actually neglected. Regarding the atmospheric loading model, its application might introduce some undesired signals. We also show that discrepancies arising from the use of different models can be neglected, and there is almost no impact arising from the use of different Love numbers. Finally, we discuss differences between data reduced with tiltmeter observations and these reduced with modeled signal, and potential causes of this discrepancies.

Generalized phase calibration method of liquid crystal spatial light modulator with absolute reference system of obnoxious background light

Spatial light modulators (SLMs) are widely used in many optical fields such as wavefront modulation, beam shaping and diffractive optical elements. It is necessary to calibrate SLM to determine the initial state of device before using it. Here a simple and generalized interferometry is proposed to calibrate the phase modulation curve with good robustness, stability and high precision, in which the obnoxious background light is no longer an undesired signal, but is utilized as an absolute reference system that provides the self-reference functionality. Combined with centroid localization algorithm, the phase modulation curve can be easily calculated by the fringes shift. Besides, multi-channel detector simultaneously provides three groups of data that further improve the calibration accuracy of gamma curve by weighted average algorithm. An experiment on phase-shifting holography was carried out and verified the validity of our proposed method. The larger the CCD target surface, the better the calibration accuracy is.

Eliminating unwanted signals in sound by using digital signal processing system

<p><a name="_Hlk536186602"></a><span style="font-size: 9pt; font-family: 'Times New Roman', serif;">Unwanted signals or noise signals in sound files are considered one of the major challenges and issues for a thousand users. It is impossible to reduce or remove these noise signals without identifying their types and ranges. Therefore, to address one of the big problems in the digital or analogue communication, which is noise signals or unwanted signals, an adaptive selection method and noise signal removal algorithm are proposed in this research. The proposed algorithm is done through specifying the types of undesirable signals, frequency, and time range, then utilizing digital signal processing system which includes design several types of digital filters based on the types and numbers of unwanted signals. Four digital filters are used in this research to remove noise signals from the sound file by implementing the proposed algorithm using Matlab Code. Results show that our proposed algorithm was done successfully and the whole noise signals were removed without any negative consequence in the output sound signal. </span><span style="font-family: 'Times New Roman', serif; font-size: 9pt;">Unwanted signals or noise signals in sound files are considered one of the major challenges and issues for a thousand users. It is impossible to reduce or remove these noise signals without identifying their types and ranges. Therefore, to address one of the big problems in the digital or analogue communication, which is noise signals or unwanted signals, an adaptive selection method and noise signal removal algorithm are proposed in this research. The proposed algorithm is done through specifying the types of undesirable signals, frequency, and time range, then utilizing digital signal processing system which includes design several types of digital filters based on the types and numbers of unwanted signals. Four digital filters are used in this research to remove noise signals from the sound file by implementing the proposed algorithm using Matlab Code. Results show that our proposed algorithm was done successfully and the whole noise signals were removed without any negative consequence in the output sound signal.</span></p>

Degrees of Freedom of Cache-Aided Wireless Cellular Networks

This work investigates the degrees of freedom (DoF) of a downlink cache-aided cellular network where the locations of base stations (BSs) are modeled as a grid topology and users within a grid cell can only communicate with four nearby BSs. We adopt a cache placement method with uncoded prefetching tailored for the network with partial connectivity. According to the overlapped degree of cached contents among BSs, we propose transmission schemes with no BS cooperation, partial BS cooperation, and full BS cooperation, respectively, for different cache sizes. In specific, the common cached contents among BSs are utilized to cancel some undesired signals by interference neutralization while interference alignment is used to coordinate signals of distinct cached contents. Our achievable results indicate that the reciprocal of per-user DoF of the cellular network decreases piecewise linearly with the normalized cache size $\mu$ at each BS, and the gain of BS caching is more significant for the small cache region. Under the given cache placement scheme, we also provide an upper bound of per-user DoF and show that our achievable DoF is optimal when $\mu\in\left[\frac{1}{2},1\right]$, and within an additive gap of $\frac{4}{39}$ to the optimum when $\mu\in\left[\frac{1}{4},\frac{1}{2}\right)$.

Simulation-Based Optical Threshold Component Design for Mitigating Four-Wave Mixing Effects in WDM Radio Over Fiber Systems

AbstractThe gigantic demand on high bandwidth and capacity has triggered the need to use the radio over optical fiber (RoF) systems. RoF systems offer several attractive features such as low attenuation loss, large bandwidth, less interference, etc., which can improve the communication system reliability and achieve high data rates. However, the RoF system suffers from linear and nonlinear fiber impairments, which result in signal distortion. Several solutions have been proposed to overcome linear impairments; on the other hand, the nonlinear impairments issue is still a challenging problem in RoF communication systems. Four-wave mixing (FWM) is the most dominating nonlinear impairments that impacts the performance of optical fiber communication systems and the RoF systems as well. In this article, we present a strategy to mitigate the FWM effect in wavelength division multiplexing (WDM) RoF systems. Specifically, we study the effect of FWM under high transmit power levels over long transmission distances. This proposed strategy aligns the optical and radio link parameters to alleviate the FWM effects. To achieve this objective, the impact of WDM RoF system parameters such as wavelength ($\lambda_i$), transmitted power, etc., on system performance is investigated. The main performance metrics are the total signal-to-noise ratio (SNR), optical SNR (OSNR), Q-factor, and bit error rate (BER). Given these metrics, our proposed strategy defines an optical threshold level that applies to the optical threshold component to get rid of the undesired signals generated by the FWM effect.

Development of hybrid shielding system for large-area Compton camera: A Monte Carlo study

Abstracts Compton cameras using large scintillators have been developed for high imaging sensitivity. These scintillator-based Compton cameras, however, mainly due to relatively low energy resolution, suffer from undesired background-radiation signals, especially when radioactive materials’ activity is very low or their location is far from the Compton camera. To alleviate this problem for a large-size Compton camera, in the present study, a hybrid-type shielding system was designed that combines an active shield with a veto detector and a passive shield that surrounds the active shield. Then, the performance of the hybrid shielding system was predicted, by Monte Carlo radiation transport simulation using Geant4, in terms of minimum detectable activity (MDA), signal-to-noise ratio (SNR), and image resolution. Our simulation results show that, for the most cases, the hybrid shielding system significantly improves the performance of the large-size Compton camera. For the cases investigated in the present study, the use of the shielding system decreased the MDA by about 1.4, 1.6, and 1.3 times, increased the SNR by 1.2–1.9, 1.1–1.7, and 1.3–2.1 times, and improved the image resolution (i.e., reduced the FWHM) by 7–8, 1–6, and 3–5% for 137Cs, 60Co, and 131I point source located at 1–5 m from the imaging system, respectively.

A Generalizable Optogenetic Strategy to Regulate Receptor Tyrosine Kinases during Vertebrate Embryonic Development

Ligand-independent activation of receptor tyrosine kinases (RTKs) allows for dissecting out the receptor-specific signaling outcomes from the pleiotropic effects of the ligands. In this regard, RTK intracellular domains (ICD) are of interest due to their ability to recapitulate signaling activity in a ligand-independent manner when fused to chemical or optical dimerizing domains. A common strategy for synthetic activation of RTKs involves membrane tethering of dimerizer–RTK ICD fusions. Depending on the intrinsic signaling capacity, however, this approach could entail undesirable baseline signaling activity in the absence of stimulus, thereby diminishing the system's sensitivity. Here, we observed toxicity in early Xenopus laevis embryos when using such a conventional optogenetic design for the fibroblast growth factor receptor (FGFR). To surpass this challenge, we developed a cytoplasm-to-membrane translocation approach, where FGFR ICD is recruited from the cytoplasm to the plasma membrane by light, followed by its subsequent activation via homo-association. This strategy results in the optical activation of FGFR with low background activity and high sensitivity, which allows for the light-mediated formation of ectopic tail-like structures in developing X. laevis embryos. We further generalized this strategy by developing optogenetic platforms to control three neurotrophic tropomyosin receptor kinases, TrkA, TrkB, and TrkC. We envision that these ligand-independent optogenetic RTKs will provide useful toolsets for the delineation of signaling sub-circuits in developing vertebrate embryos.

The Dependence of Spontaneous Charge Generation in Water on its Flow Rate in a Flow-Based Analytical System

Highly sensitive biosensor systems are particularly sensitive to the charge state of an analyte. This charge state can have either a positive (for instance, in case of increasing the efficiency of fishing of low-abundant proteins) or negative effect (for instance, in case of the appearance of charge jumps upon the injection of analyte solution into a measuring cell, what can cause undesirable parasitic signals). Previously, it was demonstrated that upon the pumping of analyte solution through polymeric communications of biosensors with a peristaltic pump at a low (~1 mL/min) flow rate, an accumulation of charge, transferred by the liquid drops from the feeding system into the measuring cell, is observed. At this point, the time dependence of charge accumulation has a linear-stepwise form. In the present study, the influence of the flow rate of water on the parameters of the time dependence of the accumulation of charge in such a system—including the influence on the stepwise charge accumulation—has been investigated. The measurements have been performed with a highly sensitive electrometer sensor at 38 °C, which corresponds to a pathological state of a human body. It has been found that a linear-stepwise time dependence of charge accumulation is observed in a wide range of water flow rates (V= 0.9 to 7.2 mL/min). At that point, upon increasing the flow rate with the transition from the drop-by-drop mode of water supply (0.9 mL/min) to the jet flow (7.2 mL/min), an increase in the absolute value of accumulated charge is observed, but the magnitude of the charge jumps does not change significantly. Thus, the amount of charge accumulated in the cell ambiguously depends on the water flow rate—i.e., this dependence can be non-linear. Accounting for the discovered phenomenon is important in the development of new, more accurate models describing physicochemical properties of aqueous solutions and hemodynamics. This effect should also be taken into account in the development of highly sensitive diagnostic systems intended for the detection of single biomarkers of pathologies in humans and crops, as well as in other living systems. In low-concentration systems, the occurrence of a charge can become a significant factor affecting the efficiency of detection of biomolecules and the reliability of the data obtained. The detection of biomolecules present in the solution at low concentrations is in high demand in medical diagnostics for the revelation of biomarkers at the early asymptomatic stage of various diseases, including aggressive forms of cancer.

On the performance of non-orthogonal multiple access (NOMA) using FPGA

In this paper, non-orthogonal multiple access (NOMA) is designed and implemented for the fifth generation (5G) of multi-user wireless communication. Field-programmable gate array (FPGA) is considered for the implementation of this technique for two users. NOMA is applied in downlink phase of the base-station (BS) by applying power allocation mechanism for far and near users, in which one signal contains the superposition of two scaled signals depending on the distance of each user from the BS. We assume an additive white Gaussian noise (AWGN) channel for each user in the presence of the interference due to the non-orthogonality between the two users’ signals. Therefore, successive-interference cancellation (SIC) is exploited to remove the undesired signal of the other user. The outage probability and the bit-error rate performance are presented over different signal-to-interference-plus-noise ratio (SINR). Furthermore, Monte-Carlo simulations via Matlab are utilized to verify the results obtained by FPGA, which show exact-close match.

GENERATION OF FREQUENCY SEXTUPLING IN THE MILLIMETER WAVE RANGE USING LITHIUM NIOBATE MACH ZENDER MODULATOR

Now a days the bandwidth for the broadband communication is not enough for the HD quality video transmission. The optical fiber with mm wave is an emerging technique to achieve error free performance in the communication field. The proposed system used to generate mm wave of 60 GHz from the 10 GHz micro wave frequency. This setup helps to reduce the congestion, propagation delay and fading effect from the data transmission process. The carrier suppression scheme is used to suppress the undesired signal by adjusting the voltage parameter in the LiNbO3 modulator for the generation of sextupling frequency. The data rate of 5 Gbps is attained over 50 km optical fiber. The results include optical, RF and BER spectrum visualizer to prove the robustness of the design

A Sparse Learning Approach to the Design of Radar Tunable Architectures With Enhanced Selectivity Properties

This article considers the design of tunable decision schemes capable of rejecting with high probability mismatched signals embedded in Gaussian interference with unknown covariance matrix. To this end, a sparse recovery technique is exploited to enhance the resolution at which the target angle of arrival is estimated with the objective to obtain high-selective detectors. The outcomes of this estimation procedure are used to devise detection architectures relying on either the two-stage design paradigm or heuristic design procedures based upon the generalized likelihood ratio test. Remarkably, the new decision rules exhibit a bounded-constant false alarm rate property and allow for a tradeoff between the matched detection performance and the rejection of undesired signals by tuning a design parameter. At the analysis stage, the performance of the newly proposed detectors is assessed also in comparison with existing selective competitors. The results show that the new detectors can outperform the considered counterparts in terms of rejection of unwanted signals, while retaining reasonable detection performance of matched signals.

Polarization Manipulated Fourier Domain Mode-Locked Optoelectronic Oscillator

We report a polarization manipulated Fourier domain mode-locked optoelectronic oscillator (FDML-OEO) using a polarization modulator (PolM). Frequency and bandwidth doubling linearly chirped microwave waveforms (LCMWs) are generated from a PolM-based FDML-OEO. The multiplying operation is capable of increasing the frequency and bandwidth of LCMWs, which doubles the time-bandwidth product of the LCMWs and makes it possible to increase the center frequency of the LCMWs beyond the bandwidth of the optical modulator. Moreover, by simply adding the other laser diode, it is also possible to generate a dual-chirp LCMW. The polarization manipulated of two optical signals avoids the undesired beating signals from optical carriers. Thus, an electrical bandpass filter which is essential in previous work is no longer required. To the best of our knowledge, this is the first time that polarization manipulation is used in FDML-OEO, which can further satisfy the demands of modern radars in terms of improved range-Doppler resolution, higher carrier frequency, and larger bandwidth.

Blind Source Separation for Clutter and Noise Suppression in Ultrasound Imaging: Review for Different Applications.

Blind source separation (BSS) refers to a number of signal processing techniques that decompose a signal into several "source" signals. In recent years, BSS is increasingly employed for the suppression of clutter and noise in ultrasonic imaging. In particular, its ability to separate sources based on measures of independence rather than their temporal or spatial frequency content makes BSS a powerful filtering tool for data in which the desired and undesired signals overlap in the spectral domain. The purpose of this work was to review the existing BSS methods and their potential in ultrasound imaging. Furthermore, we tested and compared the effectiveness of these techniques in the field of contrast-ultrasound super-resolution, contrast quantification, and speckle tracking. For all applications, this was done in silico, in vitro, and in vivo. We found that the critical step in BSS filtering is the identification of components containing the desired signal and highlighted the value of a priori domain knowledge to define effective criteria for signal component selection.

Optical excitation of atomic force microscopy cantilever for accurate spectroscopic measurements

Reliable operation of frequency modulation mode atomic force microscopy (FM-AFM) depends on a clean resonance of an AFM cantilever. It is recognized that the spurious mechanical resonances which originate from various mechanical components in the microscope body are excited by a piezoelectric elemen that is intended for exciting the AFM cantilever oscillation and these spurious resonance modes cause the serious undesirable signal artifacts in both frequency shift and dissipation signals. We present an experimental setup to excite only the oscillation of the AFM cantilever in a fiber-optic interferometer system using optical excitation force. While the optical excitation force is provided by a separate laser light source with a different wavelength (excitation laser : λ=1310 nm), the excitation laser light is still guided through the same single-mode optical fiber that guides the laser light (detection laser : λ=1550 nm) used for the interferometric detection of the cantilever deflection. We present the details of the instrumentation and its performance. This setup allows us to eliminate the problems associated with the spurious mechanical resonances such as the apparent dissipation signal and the inaccuracy in the resonance frequency measurement.

Research on Noise Reduction of Φ-OTDR Signal Based on Blind Source Separation Algorithm

Optical fiber sensing has become an important means of health and safety monitoring of large buildings and facilities due to its better sensing characteristics. Undesirable noise signals are inevitably generated during actual sensor data acquisition. This paper focuses on the noise reduction processing of optical fiber Φ-OTDR vibration signal. Firstly, the acquired signal is preprocessed with data, then the data is independently correlated, and finally the FastICA algorithm in blind source separation is used to filter the noise signal. In this paper, the traditional wavelet transform algorithm is compared to reduce noise. The experimental results show that the blind source separation algorithm has better separation effect on fiber vibration signals.

Electric Discharges Localization for Substation Fault Monitoring Using Two Elements Sensor

A substation is an important unit in the electric power system. Thus, the monitoring process must be carried out effectively to detect the operation status of the equipment, and pre-fault threat detection is necessary for safe operation. Many methods and intelligent techniques have been developed to provide a better way of fault detection. However, power authorities unwilling to adopt those techniques due to the high cost of installation and more sensors required to improve localization accuracy. Therefore, to reduce cost and increase the speed of detection, this paper presents a 2-element array antenna acted like a sensor to detect and localize the electric discharges from abnormal radiated electromagnetic activities in the substation based on the direction of arriving angle (DOA) received by the array antenna. Software implemented signal processor was used to obtain the radiation patterns for different value of DOA relative to the normalized Array Factor (AFN). This 2-element Sensor was proven to eliminate the undesired signals (such as electromagnetic signals from outside the substation) and maximize the signals in the direction of the desired signal by detecting the DOA of abnormal radiation from power apparatus (such as power transformer or circuit breaker bushings) inside the substation. It was proven that this cohesive unit was able to perform the two tasks by simultaneously eliminating or maximizing signals with very small (such as 0.0873 radians) angle difference between external radiation and radiation from apparatus inside the substation. By performing these tasks, the 2-element Sensor was promisingly able to detect and localize the abnormal electrical activities such as Electric Corona and Electric Arcs discharges that may occur in any substation based on the identified DOA from the power apparatus within the substation as a preventative approach for substation breakdown and to improve the efficiency and the performance of fault detection technique in future Substation Fault Monitoring.

Communication‐awareness joint beams and power allocation scheme of radar network for manoeuvring targets tracking

The coexistence of radar and communication system is a crucial task owing to the shortage of spectrum resources. In this study, the authors consider a multiple manoeuvring targets tracking problem via a radar network in the presence of several non-cooperative, spatially random, and spectral overlapped communication areas (CAs). Instead of costly inner pattern optimisation, a communication awareness joint beam and power allocation (CJBPA) scheme of radar network is proposed to achieve high flexibility in coexistence. In CJBPA, radars and CAs treat the signals from each other as interference, which are formulated and discussed from the perspective of spectrum and space. The CJBPA optimises the overall tracking performance, which is characterised by the posterior Cramer-Rao lower bound under the consideration of coexistence. The resultant non-convex problem is relaxed and decoupled as an integrated two-staged optimisation. To accelerate the numerical procedures of the optimisations, custom-built primal dual interior point methods are derived by the structure information of the problems. The effectiveness of the proposed CJBPA scheme is assessed through simulations, showing that by using spatial and spectral information of undesired signals, the tracking performance can be optimised while the impacts of interference on both radars and CAs are restricted.

Simulink implementation of RLS algorithm for resilient artefacts removal in ECG signal

Noise is the undesired signal which affects the desired signal. This noise has been a serious problem which is affecting the signals during transmission of information. In this project, two different noisy signals are considered they are speech signal and ECG signal. The speech signals are taken from the NOIZEUS database and ECG signals from Physio Net ECG database. The major noises affecting the ECG signal are baseline wander, electrode motion, power line interference, muscle artefact noises. The baseline wander noise which is caused due to patient movement, breathing and bad electrode contact to skin, electrode motion noise occurs when electrode moves away from the skin which leads to impedance changes resulting in variations in ECG, muscle artefact noise which is caused due to contraction of other muscles besides the heart. Simulink model is designed for cancelling the noise from the noisy signals. The adaptive algorithm that is chosen is the RLS algorithm because it has faster convergence rate when compared to other algorithms like LMS, NLMS and RLS. The Simulink model is tested for different cases to show that the model works efficiently and the performance can be observed from the mean square error obtained.

Third-order passive intermodulation distortion cancellation using a cubic Volterra filter for wireless relay systems

Passive intermodulation distortion (PIMD) is a phenomenon in which two or more transmission signal frequencies interfere with each other due to non-linearity in passive elements of a wireless communication system and undesired signals are generated. Such intermodulation distortion increases the noise level in the receive frequency band of the wireless communication system, thereby degrading the performance of the receiver. In this paper, a PIMD mitigation scheme based on a modified cubic Volterra filter is proposed to reduce a passive intermodulation distortion level to enhance the uplink signal receive performance. The performance of the proposed approach is evaluated by applying it to the data sampled at a repeater for the long term evolution (LTE) system. The proposed approach demonstrates a notable reduction of PIMD in the receive band. The conventional least mean square (LMS) approach is considered in this study for the purpose of comparison.