Narrowband Signals Research Articles

High-precision time delay estimation of narrowband radio signal by PHAT-LSTM

In this article, a novel method for high-precision time-delay estimation (TDE) of narrow-band signals is proposed. It is based on a cross-correlation function, phase spectrum, long short-term memory (LSTM) artificial neural network to unwrap the phase transform (PHAT) spectrum of the cross-correlation function. The PHAT-LSTM architecture consists of three parts. The first part is a wrapping parameter estimator (WPE) used to estimate the wrapping parameter of the base-band phase spectrum. The second part, a wrapping classifier (WCF), is a single output network used to compensate the drawbacks of the WPE. The third part, a synthesize and fine estimator, synthesizes the information from the WPE and WCF to unwrap the phase and estimate the delay according to the phase-delay model. The input of the PHAT-LSTM are fast Fourier transforms of snapshot data from two receiving channels. In addition, the dimension of the input signals was dramatically decreased compared with other deep learning-based TDE methods. Simulation results show that the root mean square error (RMSE) of the PHAT-LSTM is decreased in low signal-to-noise ratio (SNR) compared with traditional TDE methods. When the SNR = 10 dB or 0 dB, the RMSE of TDE was about ten times smaller than that of traditional methods.

Triple-step feed line-based compact ultra-wideband antenna with quadruple band-notch characteristics

ABSTRACT An ultra-wideband (UWB) antenna with quadruple-band-rejection characteristics and a size-miniaturised approach for portable wireless applications is designed and experimentally investigated. The proposed antenna consists of a unique trapezoidal-shaped patch, 50 Ω triple-step microstrip feed line and step–truncated ground plane. The patch tapering improves the bandwidth of an antenna to 2.8–12.5 GHz with fractional–bandwidth of 127%, covering an entire UWB (3.1–10.6 GHz). Consequently, it provides a nearly omnidirectional radiation pattern, better gain and excellent radiation efficiency. The three steps of the feed line increase the electrical length of the patch, achieving size reduction of the fabricated antenna to 20 mm × 29 mm. Generally, UWB systems suffer owing to strong narrowband signal interference from unlicensed wireless communication devices. To avoid this, the proposed antenna is designed with quadruple band-notch characteristics. It includes three inverted U-slots (length approaches half the guided wavelength), which are used to reject the 3.5, 4.5 and 5.2/5.8 GHz bands. Moreover, a C-strip pair besides the feed line is used to reject the 8.35 GHz X-band. The simulated results were also compared with the experimental performance of the prototype in terms of reflection coefficient, voltage standing wave ratio, radiation pattern, transfer function, group delay and gain of the antenna.

An optimized variational mode extraction method for rolling bearing fault diagnosis

The fault feature signal of rolling bearing can be characterized as the narrow-band signal with a specific resonance frequency. Therefore, resonance demodulation analysis is a powerful damage detection technique of bearings. In addition to the fault feature signal, the measured vibration signals carry various interference components, and these interference components become a serious obstacle of fault feature extraction. Variational mode extraction is a novel signal analysis method designed to retrieve a specific signal component from the composite signal. Variational mode extraction is founded on a similar basis as variational mode decomposition, while it shows better accuracy and higher efficiency compared with variational mode decomposition. In this study, variational mode extraction is introduced to the resonance demodulation analysis of bearing fault. As the results of variational mode extraction analysis are greatly influenced by the choice of two parameters, that is, the balancing factor α and the initial guess of center frequency ωd, an optimized variational mode extraction method is further developed. First, a new fault information evaluation index for measuring the richness of fault characteristics of the signal, termed ensemble impulsiveness and cyclostationarity, is formulated. Second, the ensemble impulsiveness and cyclostationarity is used as the fitness function of particle swarm optimization to automatically determine the optimal values of α and ωd. Finally, the validity of optimized variational mode extraction method is verified by simulated and experimental analysis, and the superiority of optimized variational mode extraction method is highlighted through comparison with two other advanced resonance demodulation analysis approaches, that is, the improved kurtogram and infogram. The analysis results indicate that optimized variational mode extraction method has a powerful capability of resonance demodulation analysis.

Synchronous Demodulation for Low Noise Measurements

This paper provides an overview of the applications of synchronous demodulators for low noise measurements in a tutorial manner. Synchronous demodulators have been around for nearly a century and used extensively for precise measurements and reduction of noise bandwidth in a wide range of applications. The purpose of this paper is to briefly introduce the method that is recognized and formalize its performance. The theory explains how to amplify a narrowband signal to reduce the amount of measurement noise and how the process can be simply considered as a multiplier followed by a low-pass filter. We also introduce some of the applications and design considerations for using synchronous demodulation. Some of the advanced topics are briefly discussed with reference to the most recent contribution in this field for those interested in a deeper understanding of the content.

Low-power DSSS transmitter and its VLSI implementation

An interesting area of application in wireless data communication is direct-sequence spread spectrum (DSSS). Spread spectrum communication techniques make the signals more robust against interference and jamming. These are based on a concept that narrowband signal is scrambled before transmission in such a way that the signals occupy a much larger part of the radio frequency spectrum. As the digital and the analogue system components are required on the same substrate in today’s mixed-signal chips, the DSSS transmitter system is proposed to be implemented in field-programmable gate array (FPGA)–based platforms and application-specific integrated circuits (ASICs). With a low-power very large-scale integration (VLSI) architecture, sophisticated processing of wide-bandwidth DSSS systems can be exploited in FPGAs/ASICs. In this article, binary pseudo-noise (PN) sequences are generated using a low-power linear feedback shift register (LFSR) in order to spread transmit signals extensively. The proposed low-power design of LFSR and DSSS transmitter with implementation results is illustrated in this paper. Dynamic power dissipation of the proposed DSSS transmitter is reduced up to 15% and 15.6% when compared to the conventional LFSR and the Gold code–based systems respectively. The proposed hardware is implemented in 180-nm technology and operates at 15.36-MHz frequency.

Total Focusing Method Damage Imaging in Frequency Domain Using Laser-Ultrasonic Lamb Wave Based on Time-domain Filtering in Multi-band

A fully non-contact experimental platform for ultrasonic Lamb wave damage detection was constructed, where laser exciting and the scanning laser Doppler vibrometer were used to realize the high-resolution pickup of the Lamb wave field in the structure, which has overcome the disadvantages of low spatial resolution caused by the conventional contact Lamb wave transducer. In order to suppress the dispersion effect of broadband laser-ultrasonic signal, we proposed time-domain filtering in multi-band method based on wavelet analysis to decompose the broadband signal into multiple narrowband ones and separate the scattering signals effectively without reference signal. On this basis, the total focusing method (TFM) was used for damage imaging. However, when the traditional TFM was applied to image based on ultrasonic Lamb wave, the inherent dispersion characteristic of ultrasonic Lamb wave could lead to the miscalculation of time delay, thus reducing the imaging precision. Therefore, the frequency-domain TFM was developed by applying phase delay in the frequency domain. The logical AND was introduced to synthesize the damage imaging results of multiple narrowband signals to obtain high-precision damage imaging. Our study has shown that the method of time-domain filtering in multi-band combining with frequency-domain TFM can realize non-contact and accurate damage detection in isotropic plate structures, and it is a potential effective method for application in engineering practice.

Unstable basis function for joint radar-communication systems

• A combined radar and communications system using basis functions derived from an unstable second-order system is described. • Using unstable systems with different frequencies allows for the creation of a set of orthogonal basis functions. • Both communications and radar signals may be decoded with linear analog circuits, leading to simple inexpensive receivers. • The radar properties are not sensitive to the encoded communications method. • Because of simplicity and low cost, the system could be used in applications where it was necessary to piggyback a radar signal on a communications signal. In this paper, we develop a joint radar-communication waveform based on the unstable basis function. Basis functions of a chaotic waveform are uncertain, vary continuously and hence the use of a traditional matched filter is not practical. Corron et al. [1,2] demonstrated a chaotic circuit for which an analytic matched filter could be constructed, solving the signal detection problem. The Corron circuit produced a narrow band signal, which is not optimal for spread spectrum communications and radar applications. In this paper, we adapt Corron’s concept of a chaotic signal composed of a linear combination of basis functions and show how the basis functions are used to design joint radar-communications systems that still have simple analytic matched filters. The form of the matched filter makes it useful for both the radar and communications systems where it is necessary to minimize weight or power consumption.

Integrated Silicon Fourier Transform Spectrometer with Broad Bandwidth and Ultra‐High Resolution

AbstractAn ultra‐high resolution Fourier transform spectrometer (FTS) realized in silicon photonic platform that can operate with broad band, narrow band as well as a combination of broad band and narrow band signals is reported. The ultra‐high resolution of the spectrometer is achieved by exploiting multiple techniques: a Michelson interferometer (MI) structure to increase the optical path delay (OPD), a hybrid waveguide design to reduce insertion loss, an optimized heater and air trenches to achieve higher thermal efficiency. Moreover, to further increase the OPD of the spectrometer to increase its resolution, a novel multiple interferometers approach is employed which combines balanced MI with N statically imbalanced MIs, thereby increasing the OPD of a single MI by factor of N + 1. An FTS spectrometer consisting of N = 2 such MIs is fabricated and experimentally characterized using unknown broad bandwidth input signal spectra of about 180 nm centered around 1550 nm, a narrow line laser input signal, and a combination of broad and narrow band signals demonstrating spectral resolution of about 0.16 nm.

Secure, Accurate, and Practical Narrow-Band Ranging System

Relay attacks pose a serious security threat to wireless systems, such as, contactless payment systems, keyless entry systems, or smart access control systems. Distance bounding protocols, which allow an entity to not only authenticate another entity but also determine whether it is physically close by, effectively mitigate relay attacks. However, secure implementation of distance bounding protocols, especially of the time critical challenge-response phase, has been a challenging task. In this paper, we design and implement a secure and accurate distance bounding protocol based on Narrow-Band signals, such as Bluetooth Low Energy (BLE), to particularly mitigate relay attacks. Narrow-Band ranging, specifically, phase-based ranging, enables accurate distance measurement, but it is vulnerable to phase rollover attacks. In our solution, we mitigate phase rollover attacks by also measuring time-of-flight (ToF) to detect the delay introduced by such attacks. Therefore, our protocol effectively combines the best of both worlds: phase-based ranging for accuracy and time-of-flight (ToF) measurement for security. To demonstrate the feasibility and practicality of our solution, we prototype it on NXP KW36 BLE chips and evaluate its performance and relay attack resistance. The obtained precision and accuracy of the presented ranging solution are 2.5 cm and 30 cm, respectively, in wireless measurements.

Broadband signal reconstruction for SHM: An experimental and numerical time reversal methodology

Structural Health Monitoring (SHM) aims to shift aircraft maintenance from a time-based to a condition-based approach. Within all the SHM techniques, Acoustic Emission (AE) allows for the monitoring of large areas by analyzing Lamb waves propagating in plate like structures. In this study, the authors proposed a Time Reversal (TR) methodology with the aim of reconstructing an original and unaltered signal from an AE event. Although the TR method has been applied in Narrow-Band (NwB) signal reconstruction, it fails when a Broad-Band (BdB) signal, such as a real AE event, is present. Therefore, a novel methodology based on the use of a Frequencies Compensation Transfer Function (FCTF), which is capable of reconstructing both NwB and real BdB signals, is presented. The study was carried out experimentally using several sensor layouts and materials with two different AE sources: (i) a Numerically Built Broadband (NBB) signal, (ii) a Pencil Lead Break (PLB). The results were validated numerically using Abaqus/CAETM with the implementation of absorbing boundaries to minimize edge reflections.

Multiple Narrowband Interferences Characterization, Detection and Mitigation Using Simplified Welch Algorithm and Notch Filtering

By increasing the demand for radio frequency (RF) and access of hackers and spoofers to low price hardware and software defined radios (SDR), radio frequency interference (RFI) became a more frequent and serious problem. In order to increase the security of satellite communication (Satcom) and guarantee the quality of service (QoS) of end users, it is crucial to detect the RFI in the desired bandwidth and protect the receiver with a proper mitigation mechanism. Digital narrowband signals are so sensitive into the interference and because of their special power spectrum shape, it is hard to detect and eliminate the RFI from their bandwidth. Thus, a proper detector requires a high precision and smooth estimation of input signal power spectral density (PSD). By utilizing the presented power spectrum by the simplified Welch method, this article proposes a solid and effective algorithm that can find all necessary interference parameters in the frequency domain while targeting practical implantation for the embedded system with minimum complexity. The proposed detector can detect several multi narrowband interferences and estimate their center frequency, bandwidth, power, start, and end of each interference individually. To remove multiple interferences, a chain of several infinite impulse response (IIR) notch filters with multiplexers is proposed. To minimize damage to the original signal, the bandwidth of each notch is adjusted in a way that maximizes the received signal to noise ratio (SNR) by the receiver. Multiple carrier wave interferences (MCWI) is utilized as a jamming attack to the Digital Video Broadcasting-Satellite-Second Generation (DVB-S2) receiver and performance of a new detector and mitigation system is investigated and validated in both simulation and practical tests. Based on the obtained results, the proposed detector can detect a weak power interference down to −25 dB and track a hopping frequency interference with center frequency variation speed up to 3 kHz. Bit error ratio (BER) performance shows 3 dB improvement by utilizing new adaptive mitigation scenario compared to non-adaptive one. Finally, the protected DVB-S2 can receive the data with SNR close to the normal situation while it is under the attack of the MCWI jammer.

A 0.75 V Sub-mW CMOS LNA employing transmitted signal suppression technique in a full-duplex wireless brain-machine interface transceiver

This paper presents a sub-milliwatt (sub-mW) low-voltage CMOS low-noise amplifier (LNA) that can be utilized in a full-duplex transceiver without using duplexer. The topology of the proposed LNA includes a wideband RLC network to suppress and isolate the receiver from a high-power ultra-wideband transmitted signal. This feature is comparable to other reported LNAs, which are only applicable to a narrowband signal instead of a wideband signal. In addition, the combination of a source-degenerated cascode LNA with an inverter-based LNA in the proposed topology achieves an ultra-low-voltage low-power operation with a 0.75 V bias voltage. Analytical results and the circuit implementation in a 180 nm CMOS technology verify that the proposed LNA presents an noise figure (NF) of less than 3.45 dB over a 200 MHz bandwidth at a carrier frequency of 2.4 GHz. Simulation results also demonstrate a 14 dB gain (S21), less than −11 dB input return loss (S11) and 50 dB transmitted signal attenuation rather than the desired signal. The power consumption is only 980 μW at a 0.75 V supply. The input-referred third-order intercept point (IIP3) is about −8 dBm, and the chip occupies an area of 0.37 mm2.

Design and Development of Adaptive filter for Real Time Signal Processing

In Communication the signal is distorted due to noise and the notch filters are used for eliminating unwanted frequencies For filtering the signal in a specific band Notch filter is used. Notch filter can pass the signal below and above notch frequency. In most of the signal processing applications frequency estimation of narrow band signals in noisy environment are required For frequency detection and tracking Adaptive IIR filter or Adaptive FIR filters can be used. Adaptive FIR Filter is more stable than Adaptive IIR filter. In most practical applications Adaptive IIR Notch Filter (AIIRNF)is used The advantage of Adaptive IIR notch filter over FIR Filter is less number of filter coefficients and less complexity in design In this paper Adaptive IIR Notch filter is designed for real time applications. The performance of designed adaptive IIR Notch filter is evaluated based on Magnitude and Frequency response.

Development of a module for broadband detection of digital transmissions for a radio broadcast monitoring system using parallel computing means

Short-wave communication is a means of trunk, zone, mobile and industrial communication for general and departmental use. Taking into account its technical potential, economic efficiency, strategic role as a necessary reserve, the task of monitoring the use of radio frequency resources in the short-wave range remains relevant. The main problem is the search for digital modes of transmission in the entire shortwave band. The purpose of the study is to develop a module for broadband signal detection operating in real time and integrate it into an operating radio monitoring system. The methodology of the work includes an analysis of the literature of foreign and domestic authors on solving monitoring problems, methods for detecting signals in the short-wave range; method of systematization and generalization of facts about the problems of choosing software and hardware for broadband signal detection. The features of short-wave communication have been studied, and the choice of comparison of signals has been made in this paper. The choice was made taking into account the computational complexity of the algorithms. Modules of broadband and narrowband signal detectors have been developed, the places of their integration into the existing radio monitoring system, as well as interfaces for their interaction, have been determined. During the pilot industrial operation the developed modules effectively coped with the solution of the problems of radio monitoring of the short-wave range in real time, so appropriate conclusions are formulated.

Photonic Armstrong method enabled by direct detection for wideband electrical PM generation.

Wideband signal generation using frequency/phase modulation (FM/PM) is the key fundamental function for various applications such as radar and analog communication systems. It is well known that analog FM/PM communication systems can dramatically improve signal quality by spectral expansion. In classical communication theories, the Armstrong indirect method is one of the most popular methods for bandwidth expansion of FM signals. In the Armstrong method, a narrowband signal is converted to a broadband signal with the help of a nonlinear frequency multiplier. In this paper, we propose a photonic Armstrong method enabled by direct detection. By utilizing the nonlinearity caused by direct detection, we can increase bandwidth so that it is double that of the original signal in the photonic Armstrong method. Also, it completely eliminates signal-to-signal beat interference (SSBI) at the same time. We conducted an experiment to verify the concept and confirmed these advantages experimentally.

A Search for Technosignatures around 31 Sun-like Stars with the Green Bank Telescope at 1.15–1.73 GHz

Abstract We conducted a search for technosignatures in 2018 and 2019 April with the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. These observations focused on regions surrounding 31 Sun-like stars near the plane of the Galaxy. We present the results of our search for narrowband signals in this data set, as well as improvements to our data processing pipeline. Specifically, we applied an improved candidate signal detection procedure that relies on the topographic prominence of the signal power, which nearly doubles the signal detection count of some previously analyzed data sets. We also improved the direction-of-origin filters that remove most radio frequency interference (RFI) to ensure that they uniquely link signals observed in separate scans. We performed a preliminary signal injection and recovery analysis to test the performance of our pipeline. We found that our pipeline recovers 93% of the injected signals over the usable frequency range of the receiver and 98% if we exclude regions with dense RFI. In this analysis, 99.73% of the recovered signals were correctly classified as technosignature candidates. Our improved data processing pipeline classified over 99.84% of the ∼26 million signals detected in our data as RFI. Of the remaining candidates, 4539 were detected outside of known RFI frequency regions. The remaining candidates were visually inspected and verified to be of anthropogenic nature. Our search compares favorably to other recent searches in terms of end-to-end sensitivity, frequency drift rate coverage, and signal detection count per unit bandwidth per unit integration time.

Active noise control using remotely placed sources: Application to magnetic resonance imaging noise and equivalence to the time reversal inverse filter

This paper explores the feasibility of active control of noise from magnetic resonance imaging (MRI) systems using control sources placed outside of the region that MRI scanners are sensitive to ferrous materials. Active noise control (ANC) is shown here to be equivalent to the time reversal (TR) inverse filter technique with a 180° phase shift. Since TR is capable of remotely focusing sound energy to a point in space, it follows that ANC may also be remotely focused. This paper explores the remote delivery of a noise-canceling signal to a desired location (e.g. a patient’s ears). A parameterization study testing frequency dependence and signal length is conducted to determine the effectiveness of the remote delivery. The reduction of MRI noise using ANC is demonstrated using recordings of MRI noise. The parameterization and MRI noise reduction studies are conducted in a reverberation chamber and in a laboratory room with a lower reverberation time. Frequencies below 1 kHz and narrowband signals are easier to control, with reductions up to 20 dB. MRI noise is reduced by up to 18 dB in overall sound pressure level. These results utilized a single control loudspeaker; further reductions should be possible with multiple control sources.

Attenuation of Several Common Building Materials: Millimeter-Wave Frequency Bands 28, 73, and 91 GHz

Future cellular systems will make use of millimeter wave (mmWave) frequency bands. Many users in these bands are located indoors, i.e., inside buildings, homes, and offices. Typical building material attenuations in these high frequency ranges are of interest for link budget calculations. In this paper, we report on a collaborative measurement campaign to find the attenuation of several typical building materials in three potential mmWave bands (28, 73, 91 GHz). Using directional antennas, we took multiple measurements at multiple locations using narrow-band and wide-band signals, and averaged out residual small-scale fading effects. Materials include clear glass, drywall (plasterboard), plywood, acoustic ceiling tile, and cinder blocks. Specific attenuations range from approximately 0.5 dB/cm for ceiling tile at 28 GHz to approximately 19 dB/cm for clear glass at 91 GHz.

Exchanging Bandwidth With Aperture Size in Wireless Indoor Localization - Or Why 5G/6G Systems With Antenna Arrays Can Outperform UWB Solutions

The localization of wireless devices in indoor scenarios presents a major challenge because of multipath propagation. Hence, the majority of the research community has focused on increasing the available bandwidth of localization systems, leading to the emergence of the ultra wide band (UWB) radar. However, the hardware implementation of UWB transceivers is challenging itself and, hence, their utilization in commercial low-cost wireless devices is not to be expected in the near future. Hence, instead of evaluating frequency dependent phases via UWB, the measurement of spatially distributed phases represents a valuable alternative. Therefore, this article presents a comparison of phase-difference-of-arrival (PDOA) and time-of-arrival (TOA) systems. For this purpose, we compare the measurement sensitivity, the effects of multipath propagation, and the hardware complexity. Based on the results, the applicability of typical position estimators is discussed. Thereby, we argue that PDOA-based localization with large receiver arrays appears to be the better choice to localize wireless devices, because it enables highly accurate positioning using narrow band signals without elaborated transmitter–receiver synchronization. To validate this, indoor localization measurements are presented and compared with UWB results in extant literature.

The Calculation Method of PV Direct Current Energy Based on Modulated Broadband Mode Decomposition and Compound Simpson Integral Algorithm

The application of photovoltaic power is becoming more and more extensive presently, when the existing time-frequency analysis methods are used to analyze photovoltaic mutation signals such as transient rise and transient fall, the cornered signal will produce Gibbs phenomenon and leads to errors. Thus, the Broadband Mode Decomposition (BMD) method is proposed. The main idea of BMD is to search in the associated dictionary that contains the wideband and narrowband signals. However, the BMD algorithm may treat the wideband signal as several narrowband components, when applied to a wideband signal interfered by strong noise, because the relative bandwidth is not sufficiently small. Therefore, a modulated broadband modal decomposition (MBMD) based on the modulation differential operator is proposed. By multiplying a high-frequency single-frequency signal, the relative bandwidth of the effective wideband signal is much smaller than 1, and the wideband signal is processed as an approximate wideband signal. Meanwhile, because the errors of the traditional dot product sum algorithm in DC energy measurement cannot be positive and negative offset, while the compound Simpson integral algorithm has small error and high calculation accuracy. Therefore, a photovoltaic DC power calculation method based on the MBMD and compound Simpson integration is proposed.