Doppler Interference Research Articles

Reduction of peak-to-average power ratio for FBMC/OQAM signals under the general linear non-symmetrical companding transform with a Laplace distribution

The filter bank multi-carrier with offset quadrature amplitude modulation (FBMC/OQAM) is extensively utilized in communication scenarios characterized by severe Doppler interference, owing its remarkable ability for precise time–frequency positioning concentration. However, the distinctive staggered superposition structure leads to an additional increase in peak-to-average power ratio (PAPR). In this letter, we discover that the unique superposition structure results in a high likelihood of abnormal minima in FBMC/OQAM, consequently diminishing the efficacy of the general companding transform scheme relying on Gaussian distribution for PAPR reduction. Thus, we introduce a general companding transform scheme based on the Laplace distribution. The simulation results demonstrate that the proposed scheme offers a 3 dB advantage in PAPR reduction compared to the traditional general companding scheme, while also maintaining a nearly 1 dB advantage in BER.

Estimation of Target Motion Parameters from the Tonal Signals with a Single Hydrophone.

In the shallow-water waveguide environment, the tonal signals radiated by moving targets carry modal interference and Doppler shift information. The modal interference can be used to obtain the time of the closest point of approach (tCPA) and the ratio of the range at the closest point of approach to the velocity of the source (rCPA/v). However, parameters rCPA and v cannot be solved separately. When tCPA is known, the rCPA and the v of the target can be obtained theoretically by using the Doppler information. However, when the Doppler frequency shift is small or at a low signal-to-noise ratio, there will be a strong parametric coupling between rCPA and v. In order to solve the above parameter coupling problem, a target motion parameter estimation method from tonal signals with a single hydrophone is proposed in this paper. The method uses the Doppler and modal interference information carried by the tonal signals to obtain two different parametric coupling curves. Then, the parametric coupling curves can be used to estimate the two motion parameters. Simulation experiments verified the rationality of this method. The proposed method was applied to the SWellEx-96 and speedboat experiments, and the estimation errors of the motion parameters were within 10%, which shows the method is effective in its practical applications.

Digital Compensation of IQ Imbalance, DC Offset for Zero-Padded OTFS Systems

Next generation communication systems (e.g., 6G) foresee higher mobility, higher data rates with higher constellations and with high levels of integration in a small form factor. Direct conversion orthogonal time frequency space modulation (OTFS) systems suffer from hardware impairments such as in-phase and quadrature (IQ) imbalance, direct current (DC) offset causing image Doppler interference (IDI) among the sub-carriers in the delay Doppler (DD) domain. In this letter, we propose a novel method of estimation and compensation of hardware impairments for zero padded (ZP) OTFS systems in the delay time (DT) domain. A dual pilot approach with a phase difference of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\frac {\pi }{2}}$ </tex-math></inline-formula> between these symbols is followed in DD domain with which hardware impairments are estimated with less computational complexity in DT domain. It is found that the compensated system performs close to ideal system. The mean square error (MSE) of the estimated channel is computed and MSE reduces with increase in signal to noise ratio (SNR), pilot power ratio (PPR) and with reduction in mobility.

Analysis, Estimation and Compensation of Hardware Impairments for CP-OTFS Systems

Orthogonal time frequency space (OTFS) waveform, which is robust to doubly-selective fading channels is a strong contender for the Fifth generation (5G) communications. At high frequencies, hardware imperfections are prominent in practice at the transceivers. In this letter, we consider impairments such as carrier frequency offset (CFO), direct current (DC) offset and in-phase and quadrature (IQ) imbalance at the transmitter (Tx) and receiver (Rx) for cyclic prefix (CP) OTFS system. We derive the input-output (I/O) relation in the delay-Doppler (DD) domain under these impairments and show that due to the DC offset and IQ imbalance, image Doppler interference (IDI) appears along the Doppler domain and the CFO becomes part of the channel parameters. We estimate impairment parameters in the DD domain and compensate these at Tx and Rx in the time domain. The normalized mean square error (NMSE) of the estimated imbalance parameters are evaluated and it is observed that NMSE reduces with increase in, pilot power, number of Doppler bins and with windowing techniques applied in time-frequency (TF) domain.

Correlation coefficient local capping REMD adaptive filtering method for laser interference signal.

Considering the issue of noise reduction associated with Laser Doppler Interference (LDI) signal, the paper presented a correlation coefficient local capping robust empirical mode decomposition (REMD) filter algorithm for LDI laser sensor that enables more robust reconstruction of the displacement information from an LDI signal. The performance of the algorithm is studied, and it is shown that the algorithm is capable of removing high-frequency noise. Useful information can be extracted more easily by this method, and the Hilbert phase unwrapping displacement reconstructions method based on this algorithm has been experimentally validated. The experimental results show that the proposed method can improve the frequency separation performance in experiments, and is robust against noise interference.

Space-Time Adaptive Cancellation in Passive Radar Systems

A critical issue in the realization of passive radar systems is the effective suppression of the zero Doppler interference (ZDI). The performance of the clutter cancellation relies much on the used algorithms. Several state-of-the-art approaches consist in the independent use of spatial and temporal algorithms for ZDI suppression. In this paper, a novel interference cancellation algorithm is proposed, which jointly exploits the available information from both space and time domains. We call this novel method Space-Time Adaptive Cancellation (STAC), and it differs from previous schemes included among the tools of Space-Time Adaptive Processing (STAP). The STAC algorithm is able to cancel out the high power direct and multipath signals on all the surveillance antenna channels prior to the beamforming and other space domain processing methods. The proposed preprocessing technique facilitates the detection of targets even in the direction of the illuminator or large static scatterers. Moreover, the interference rejection capability is also enhanced in the space domain. The performance of the presented algorithm is verified through simulations and field measurements. The experiments show improvement over the currently available filtering techniques.

Single-Arm Self-Mixing Superluminescent Diode Interferometer for Flow Measurements

Laser-diode self-mixing interferometry is a noncontact technique widely used both in industries and laboratories. In this paper, we propose to extend the self-mixing approach to low-coherence sources such as superluminescent diodes. In particular, we present a fiber-based common-path interferometer exploiting a single-mode-pigtailed superluminescent diode. The developed measuring system has been demonstrated to be able to directly measure the flow in pipes. To the best of our knowledge, it is the first time that flow measurements have been performed by a single-arm self-mixing pigtailed superluminescent-diode. The measuring system exploits the Doppler interference pattern produced by the light back-reflected from the inner facet of the pipe wall and the light back-diffused by the moving particles. Then, the use of a low-coherence source allows to measure the velocity of the scattering particles in a fixed and well-defined region located close to the pipe wall, thus providing good robustness to variations of scatterers concentration and allowing to easily estimate the flow under the laminar flow assumption. Experimental results demonstrated a high linearity (Pearson coefficient of about 99 $\%$ ) and sensitivity of about 16.62 $\pm$ 1.1 cm $^{-3}$ , with flows ranging from 1 to 15 cm $^3$ /s and scatterers volume concentration ranging from 0.015 to 0.36 $\%$ .

Subarray compressive beamforming for midfrequency active sonar on a cylindrical array

Subarray compressive beamforming is adapted to a cylindrical array for midfrequency active sonar detection of low-Doppler targets in reverberant environments. Low Doppler targets are difficult to detect due to spreading caused by side-lobes and the width of the main lobe. Compressive beamforming and, in particular, subarray compressive beamforming will be shown to drastically mitigate Doppler spreading and interference from static objects. A straightforward application of compressive beamforming to simulated data results in nearly perfect suppression of spread due to sidelobes and good isolation of low Doppler targets from the zero Doppler ridge. Artificially subdividing the array allows for multiple fully resolved sparse estimates of the incident sound field. The set of estimates from the set of subarrays may be combined to form a single sparse estimate, often fully suppressing zero Doppler clutter. Performance of both compressive beamforming and subarray compressive beamforming will be demonstrated using simulated data having realistic Doppler spreading due to multipath and environmental sources of Doppler spreading. Performance will be compared to conventional beamforming methods on the cylindrical array. In addition to practical applications, some theoretical challenges with adaptation to the cylindrical array will be discussed. [Work supported by a NAVSEA Phase I SBIR award.]

Ideal signals and processing for continuous active sonar

The ideal signal for continuous active sonar would be linear in both time and Doppler and have no time or Doppler leakage. Here two signals/signal processing methods are presented that have half the requisite condition - zero time leakage. But we show a way to use the time property to eliminate Doppler interference (clutter) from zero Doppler reverberation (bottomed) sources and from direct arrivals. Here we develop an m-sequence processed with a matched filter approach and a special class of inverted binary sequences processed with a matched -inverse filter. In both cases, there is a perfect pulse correlation property; that is, a large signal when they line up in time and hard zero when they don't. This property is used to develop a Complete Ortho-Normal (CON) data sets in both waveform and pulse response space. The CON pulse response allows elimination of the easily identified zero Doppler reverberation arrivals. Then, reprocessing for Doppler, the zero Doppler signals are cleanly removed as is all of their Doppler leakage. In effect one has the ideal clutter free signal with leakage from direct arrivals and bottom reverberation removed and a target signal displayed in a time-Doppler plane against a noise only background.

The Fiber Measuring Method for Rotating Parts Comprehensive Vibration

Light propagation in the air is easily affected by the environment. Shaft bending vibration and torsional vibration are needed to be measured at the same time. The different vibration state are coupled each other. For these reasons, it is necessary to design the optical fiber laser Doppler measurement system and develop the integrated optical fiber system, which is in favor of various vibration modes decoupling and can improve the signal-to-noise ratio. The double parallel beam differential scheme is adopted in the torsional vibration measurement, which the light exposed in the air is coupled into the optical fiber. The optical fiber heterodyne Doppler interference measuring method is adopted in the bending vibration measurement. The laser Doppler vibration measurement technology is applied to a rotating shaft vibration measurement. Comprehensive measuring technology is developed, which can simultaneously measure bending vibration, torsional vibration and the rotation speed of shaft.

NoninvasiveIn-vivoMeasurements of Microvessels by Reflection-Type Micro Multipoint Laser Doppler Velocimeter

We have developed a micro multipoint laser Doppler velocimeter (µ-MLDV) that enables selective collection of Doppler interference photons. In previous report [H. Ishida et al.: Rev. Sci. Instrum. 82 (2011) 076104], developed the reflection-type µ-MLDV, and showed the results of demonstrations performed on transparent artificial flow channels. In this study, we attempted to perform in-vivo experiments using animals. It can measure absolute velocity and generate tomographs of blood vessels courses. The present system can perform noninvasive in-vivo measurements with a detection limit of about 0.5 mm/s and a spatial resolution in the x–y plane of 125 µm. It is thus able to image venulae. It was used to image venulae in a mouse ear and a subcutaneous blood vessel in a mouse abdomen at a depth of about 1.0 mm below the skin.

Noninvasive In-vivo Measurements of Microvessels by Reflection-Type Micro Multipoint Laser Doppler Velocimeter

We have developed a micro multipoint laser Doppler velocimeter (µ-MLDV) that enables selective collection of Doppler interference photons. In previous report [H. Ishida et al.: Rev. Sci. Instrum. 82 (2011) 076104], developed the reflection-type µ-MLDV, and showed the results of demonstrations performed on transparent artificial flow channels. In this study, we attempted to perform in-vivo experiments using animals. It can measure absolute velocity and generate tomographs of blood vessels courses. The present system can perform noninvasive in-vivo measurements with a detection limit of about 0.5 mm/s and a spatial resolution in the x–y plane of 125 µm. It is thus able to image venulae. It was used to image venulae in a mouse ear and a subcutaneous blood vessel in a mouse abdomen at a depth of about 1.0 mm below the skin.

An Approximation for the Doppler Broadening Function and Interference Term Using Fourier Series

The calculation of the Doppler broadening function and of the interference term are important in the generation of nuclear data. In a recent paper, Goncalves and Martinez proposed an analytical approximation for the calculation of both functions based in sine and cosine Fourier transforms. This paper presents new approximations for these functions, and , using expansions in Fourier series, generating expressions that are simple, fast and precise. Numerical tests applied to the calculation of scattering average cross section provided satisfactory accu- racy.

Common-path laser interferometer

A common-path laser interferometer is introduced. Its most important feature is that two optical arms are entirely in a common path. Laser Doppler and laser polarization interference technologies are used in the proposed optical system. An experiment setup is established. The primary experimental result shows that this common path method is very feasible. The resolution is 0.72 nm within a 0.01 mm range, and the highest velocity is 0.56 mm/s. There is much room to improve its performance.

Design of a symmetric multicarrier modulation for underwater acoustic communications

Mobile underwater acoustic (UWA) channels always exhibit large delay spread and Doppler spread. Multicarrier modulation is an efficient technique for the communications over multipath channels. However, the orthogonality of the transmit signals, e.g., OFDM signals, will be destroyed by the Doppler spread and interference will be produced. Thus, an equalizer is required in the receiver. For this reason, we argue that multicarrier modulation with Gaussian pulse (symmetric in time and frequency domains) as the transmit filter is more suitable for the UWA communication systems than the OFDM. The key problem for the multicarrier modulation is to design/optimize the number of carriers and the parameter alpha in the Gaussian pulse which will greatly affect the system performance. In this paper, we investigate the optimization problem for four kinds of channels: AWGN channel, frequency-selective channel, time-selective channel and doubly selective channel. Channel information is assumed known in the transmitter by feedback. Analytical results are obtained and the numerical examples are given. To achieve the cost function, a 2D MMSE-DFE equalizer is used. Finally, we propose the balanced design for the practical engineering.

Doppler interference in dissociative resonant photoemission

Resonant photoemission involving dissociative core excited states has been the subject of a great number of experimental and theoretical investigations in recent time. The resonant decay of such dissociating systems has been shown to lead to semiatomic Auger electron emission spectra, with particular angular behavior. In the present paper a detailed theoretical analysis of dissociative resonant photoemission spectra of homonuclear diatomic molecules is presented. The theory addresses both fixed in space and randomly oriented homonuclear molecules and emphasizes the Doppler effect and the role of the interference between channels referring to the Doppler split atomic fragments. It is shown that peaks originating from decay in the atomic fragments can be asymmetric and structured due to the Doppler interference effect. The predicted strong non-Lorentzian behavior of the substructure on the top of the Doppler broadened atomiclike contribution is traced to the interplay between decay channels leading to gerade and ungerade final states. Simulations based on wave-packet theory are compared with experimental data for molecular oxygen. Our numerical simulations of the atomiclike resonance of fixed in space molecules show that the spectral profile is very sensitive to the shape of interatomic potentials of core excited and final states. It is shown that the Doppler effect in the decay spectra depends upon the symmetry of the core excited state.

漁船の海中への放射雑音

The underwater noise emitted by fishing boats is one of the main noise sources in coastal fishing grounds. This paper intends to investigate the underwater noise emitted by fishing boats, by means of measuring both drifting and cruising noise for small trawlers and medium purse seiners. The spectrum of noise when drifting showed some harmonics (line component spectrum) of basic frequency which corresponded to the main engine and generator revolution pitch. The noise at cruising showed a powerful continuous component spectrum above 50 Hz frequency zone to the propeller influence as well as line components spectrum. It dominated when applied to full speed ahead and astern. The sound spectrogram of underwater noise emitted by fishing boats when cruising showed furthermore doppler phenominon and interference. These functions at cruising were influenced by distance from noise source, depth, reflection number, main engine and generator revo-lution, and cruising speed.

A circular passive synthetic array: an inverse problem approach

Based on the general concept of the inverse acoustic radiation problem, the temporal scanning of a stationary acoustic field along a closed contour is used to simplify the measurement approach for obtaining information on source directionality. The mathematical formulation is derived from a model of the two-dimensional acoustic field. The formulation of the inverse problem is also investigated to establish a methodology for improving the angular resolution of the array processing. The fundamental relationship between the sound sources and the circular passive synthetic array is explored, utilizing existing mathematical methods, in order to develop the processing algorithm. Other subjects of practical interest, such as directional ambiguity, effect of Doppler frequency, interference noise, and processing gain are discussed. It is concluded that the results can be used to establish guidelines for engineering design and deployment of this type of synthetic array, and to further exploit the new array signal processing technique. >

Dual diode preamplifier for detection of laser Doppler interference photons

A preamplifier circuit using two parallelly placed p-i-n diodes was constructed to detect the coherent light scattered from the moving object in the laser Doppler velocimeter. The preamplifier effectively eliminates the common mode light, noise due to laser mode variation, and 50-Hz pickup. The amplifier can be applied in various velocity measurements, e.g., determination of skin blood flow.

Simple Demonstrations of Doppler Effect, Interference, and Radiation Resistance Using a Sonalert

Simple Demonstrations of Doppler Effect, Interference, and Radiation Resistance Using a Sonalert