Time-domain Beamforming Research Articles

Time-domain delay-and-sum beamforming for time-reversal detection of intermittent acoustic sources in flows.

This study focuses on the identification of intermittent aeroacoustic sources in flows by using the time-domain beamforming technique. It is first shown that this technique can be seen as a time-reversal (TR) technique, working with approximate Green functions in the case of a shear flow. Some numerical experiments investigate the case of an array measurement of a generic acoustic pulse emitted in a wind-tunnel flow, with a realistic multi-arm spiral array. The results of the time-domain beamforming successfully match those given by a numerical TR technique over a wide range of flow speeds (reaching the transonic regime). It is shown how the results should be analyzed in a focusing plane parallel to the microphone array in order to estimate the location and emission time of the pulse source. An experimental application dealing with the aeroacoustic radiation of a bluff body in a wind-tunnel flow is also considered, and shows that some intermittent events can be clearly identified in the noise radiation. Time-domain beamforming is then an efficient tool for analyzing intermittent acoustic sources in flows, and is a computationally cheaper alternative to the numerical TR technique, which should be used for complex configurations where the Green function is not available.

Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles

Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.

Using a coherent hydrophone array for observing sperm whale range, classification, and shallow-water dive profiles.

Sperm whales in the New England continental shelf and slope were passively localized, in both range and bearing, and classified using a single low-frequency (<2500 Hz), densely sampled, towed horizontal coherent hydrophone array system. Whale bearings were estimated using time-domain beamforming that provided high coherent array gain in sperm whale click signal-to-noise ratio. Whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements. Multiple concurrently vocalizing sperm whales, in the far-field of the horizontal receiver array, were distinguished and classified based on their horizontal spatial locations and the inter-pulse intervals of their vocalized click signals. The dive profile was estimated for a sperm whale in the shallow waters of the Gulf of Maine with 160 m water-column depth located close to the array's near-field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array. By accounting for transmission loss modeled using an ocean waveguide-acoustic propagation model, the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing.

Impulsive sound source localization using peak and RMS estimation of the time-domain beamformer output

This paper presents a beamforming technique for locating impulsive sound source. The conventional frequency-domain beamformer is advantageous for localizing noise sources for a certain frequency band of concern, but the existence of many frequency components in the wide-band spectrum of impulsive noise makes the beamforming image less clear. In contrast to a frequency-domain beamformer, it has been reported that a time-domain beamformer can be better suited for transient signals. Although both frequency- and time-domain beamformers produce the same result for the beamforming power, which is defined as the RMS value of its output, we can use alternative directional estimators such as the peak value to enhance the performance of a time-domain beamformer. In this study, the performance of two different directional estimators, the peak and RMS output values, are investigated and compared with the incoherent measurement noise embedded in multiple microphone signals. The impulsive noise source is modeled as a triangular pulse, and the beamwidth and side lobe level of the time-domain beamformer are formulated as functions of the pulse duration, the microphone spacing, and the number of microphones. The proposed formula is verified via experiments in an anechoic chamber using a uniformly spaced linear array, and the results show that the peak estimation of beamformer output determines the location with better spatial resolution and a lower side lobe level than RMS estimation.

Hybrid Communication System Based on OFDM

A Hybrid architecture between terrestrial and satellite networks based on Orthogonal Frequency Division Multiplexing (OFDM) is employed here. In hybrid architecture, the users will be able to avail the services through the terrestrial networks as well as the satellite networks. The users located in urban areas will be served by the existing terrestrial mobile networks and similarly the one located in rural areas will be provided services through the satellite networks. The technique which is used to achieve this objective is called Pre-FFT adaptive beamforming also called time domain beamforming. When the data is received at the satellite end, the Pre-FFT adaptive beamforming extracts the desired user data from the interferer user by applying the complex weights to the received symbol. The weight for the next symbol is then updated by Least Mean Square (LMS) algorithm and then is applied to it. This process is carried out till all the desired user data is extracted.

Beampattern for Multiple Antennas in Hybrid Terrestrial Satellite Communications System (HTSCS)

The hybrid architecture of Terrestrial and Satellite networks discussed in this paper utilizes frequency reuse. However, at the same time the frequency reuse results in Co-Channel Interference (CCI). The CCI is caused by the mobile users to the satellite end because of the strong receiver on the satellite end. Mainly, this paper will focus on to tone down the CCI and would also show that how the OFDM based adaptive beamforming can be employed to mitigate this interference. The technique which is being used to mitigate this interference is Pre-FFT adaptive beamforming also called as time domain beamforming. In this paper, main task is to mitigate the CCI which is induced by the mobile users to the satellite end and will be considered that there are J users. Out of these J users there is one desired user and rest are interferers. When the interfered data is received at the satellite end, the Pre-FFT adaptive beamforming extracts the desired user data from the interferers by applying the complex weights to the received symbol. The weight for the next symbol is then updated by Least Mean Square (LMS) algorithm and then is applied to it. This process is carried out till all the desired user data is extracted from the interference signal.

A multiple-filter F detector method for medium-aperture seismometer arrays

S U M M A R Y The generalized F method, developed for teleseismic signal detection at small-aperture arrays, is extended to medium-aperture arrays and regional-distance signals using a multiple-filter technique. The technique allows the continuous estimate of the instantaneous amplitude and phase of the array seismograms, while at the same time allowing time-domain beamforming, making the method applicable to situations where the transit time of the signal across an array is much greater than the signal duration. The method is tested by application to waveform data from 22 seismometer arrays of the International Monitoring System, being set up to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty. A comparison with the results of the traditional signal detection method used by the International Data Centre (IDC) shows that the F detector increases candidate first P associations with IDC Reviewed Event Bulletin events, whereas at the same time halving the overall number of detections. The F method increases the number of associations at 21 of the 22 arrays, and for all signal slownesses.

Time-Domain Implementation of Broadband Beamformer in Spherical Harmonics Domain

Most of the existing spherical array modal beamformers are implemented in the frequency domain, where a block of snapshots is required to perform the discrete Fourier transform. In this paper, an approach to real-valued time-domain implementation of the modal beamformer for broadband spherical microphone arrays is presented. The microphone array data are converted to the spherical harmonics domain by using the discrete spherical Fourier transform, and then steered to the look direction followed by the pattern generation unit implemented using the filter-and-sum structure. We derive the expression for the array response, the beamformer output power against both isotropic noise and spatially white noise, and the mainlobe spatial response variation in terms of the finite impulse response (FIR) filters' tap weights. A multiple-constraint problem is then formulated to find the filters' tap weights with the aim of providing a suitable tradeoff among multiple conflicting performance measures such as directivity index, robustness, sidelobe level, and mainlobe response variation. Simulation and experimental results show good performance of the proposed time-domain broadband modal beamforming approach.

The Application of Time Domain Beamforming to Ultra-wideband Through-wall Imaging Radar

摘要: 超宽带穿墙成像雷达作为一种能够隔墙探测和定位的新型雷达系统,在很多领域得到应用。该文提出利用时域波束形成对穿墙雷达进行成像的方法。电磁波穿墙传播时产生速度变化、衰减和折射等现象。该文在电磁波穿墙传播的折射模型上用解析的方法计算电磁波的传播时间,在时域波束形成成像算法中考虑了墙体对电磁波的影响,并用FDTD模拟对成像方法进行验证。最后定性分析了墙体厚度、介电常数估计误差对成像的影响。 关键词: 成像雷达; 超宽带; 穿墙成像; 时域波束形成

An Efficient Digital CZT Beamforming Design for Near-Field 3-D Sonar Imaging

A planar array of sensors is required to collect the signals coming from a 3-D scene to generate volumetric underwater acoustic images. The method most frequently used to process the acquired signals is a digital beamforming algorithm. In general, owing to the high number of sensors and beam signals, the computational load is prohibitive for real-time image generation. In the literature, a frequency-domain beamforming technique based on the chirp zeta transform (CZT), which is efficient and computationally advantageous, has been introduced for linear and planar arrays working in the far field. This paper proposes an extension of the CZT beamforming that has been specifically devised to cope with the requirements of volumetric sonar imaging. In particular, the processing of wideband signals collected by a planar array and generated by a scene placed in both near-field and far-field conditions is enabled with a computational load that is one or two orders of magnitude lower than that of the traditional frequency-domain and time-domain beamforming implementations. To attain this result, the Fresnel delay approximation, a useful definition of steering angles, and the setting up of multiple focal regions are adopted. In addition, a computationally convenient technique to generate cubic resolution cells is introduced.

Time-Domain Transmit Beamforming for MIMO-OFDM Systems with Finite Rate Feedback

Transmit beamforming (BF) and receive combining are simple and popular methods for performance enhancement in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. In this paper, we propose a novel single-data stream, time-domain BF (TD-BF) scheme for MIMO-OFDM systems which uses cyclic BF filters (C- BFFs). Assuming perfect channel state information (CSI) at the transmitter, the C-BFFs are optimized for two different criteria, namely, maximum average mutual information (AMI) per sub-carrier and minimum average uncoded bit error rate (BER). If the C-BFF length Lg is equal to the number of sub-carriers Nc,closed-form solutions to both optimization problems exist. For the practically relevant case Lg < Nc we present numerical methods for calculation of the optimum C-BFFs for both criteria. Using a global vector quantization (GVQ) approach the C-BFFs are quantized for practical finite-rate feedback channels. Simulation results for typical IEEE 802.11 n channels confirm the excellent performance of the proposed scheme and show that TD-BF has a more favorable performance/feedback rate trade-off than previously proposed frequency-domain BF (FD-BF) schemes.

Evaluation of a Time-Domain Adaptive Beamformer for Regional Phase Detection

Abstract We evaluate the output from the time-domain adaptive beamformer (ABF) developed by Shen (1979) coupled to both incoherent (short-term average/long-term average [STA/LTA]) and coherent F -statistic (FSTAT) detectors. Detection test results on regional phases are compared to the baseline conventional beamformer output coupled to both STA/LTA and FSTAT detectors. Examples and test results are presented that demonstrate reduced detection thresholds, improved clutter rejection, and lower false-alarm rates with a time-domain ABF coupled to either STA/LTA or FSTAT detectors with significant reductions in the false-alarm rate observed for the ABF coupled to the FSTAT detector.

Chirp zeta transform beamforming for three-dimensional acoustic imaging

This letter considers the possibility of the generation of three-dimensional acoustic images with a limited computational load by considering the extension of Chirp zeta transform beam forming to the case of planar array and near-field conditions. This extension, with a few innovative solutions, allows for a dramatic reduction in the number of on-line operations over traditional time-domain beamforming.

Broadband Beamspace DOA Estimation: Frequency-Domain and Time-Domain Processing Approaches

Frequency-domain and time-domain processing approaches to direction-of-arrival (DOA) estimation for multiple broadband far field signals using beamspace preprocessing structures are proposed. The technique is based on constant mainlobe response beam-forming. A set of frequency-domain and time-domain beamformers with constant (frequency independent) mainlobe response and controlled sidelobes is designed to cover the spatial sector of interest using optimal array pattern synthesis technique and optimal FIR filters design technique. These techniques lead the resulting beampatterns higher mainlobe approximation accuracy and yet lower sidelobes. For the scenario of strong out-of-sector interfering sources, our approaches can form nulls or notches in the direction of them and yet guarantee that the mainlobe response of the beamformers is constant over the design band. Numerical results show that the proposed time-domain processing DOA estimator has comparable performance with the proposed frequency-domain processing method, and that both of them are able to resolve correlated source signals and provide better resolution at lower signal-to-noise ratio (SNR) and lower root-mean-square error (RMSE) of the DOA estimate compared with the existing method. Our beamspace DOA estimators maintain good DOA estimation and spatial resolution capability in the scenario of strong out-of-sector interfering sources.

Sound source imaging of low-flying airborne targets with an acoustic camera array

Two-dimensional images of sound source distribution from near-ground airborne sounds are created using an array of 32 microphones and time-domain beamforming. The signal processing is described and array configurations spanning a square area with a side length of 3.45 m, approximately five wavelengths for a 500 Hz sound, are examined. Simulations of a 32-element under-populated log 6 × log 6 spaced array are given for sound sources centered over the array at 250 Hz, 500 Hz, and 1000 Hz. Stochastically optimized array geometry with a simulated annealing algorithm is discussed and a 32-element array optimized for a 500 Hz source is given along with a simulated image for direct comparison with the log 6 spaced array. Images from field testing a 32-element under-populated log 6 × log 6 spaced array are provided for a small aircraft flyover. Results show that this type of acoustic camera generates accurate images of sound source location. Suggested uses include monitoring small aircraft flying too low to be detected by radar as well as monitoring ecological events, such as bird migration.

마이크로폰 어레이를 이용한 회전하는 소음원 가시화에 관한 연구

Acoustic analysis of a moving sound source required that the measured sound signals be do-Dopplerized and restored as of the original emission signals. The purpose of this research is development of beamforming technique can be applied to the rotor noise source identification. For the do-Dopplerization and reconstruction of emitted sound wave, Forward Propagation Method is applied to the time domain beamforming technique. And validation test were performed using rotating sound source constructed by bended pipe and horn driver. In the validation test using sinusoidal sound wave, sufficient performance of signal processing can be seen, and the effect of measuring duration for accuracy was compared. In the prop-rotor measurements, the acoustic source locations were successfully verified in varying positions for different frequencies and collective pitch angle, in hover condition.

Robust Beamforming of Microphone Array Using H Adaptive Filtering Technique

In ASR (Automatic Speech Recognition) applications, one of the most important issues in the real-time beamforming of microphone arrays is the inability to capture the whole acoustic dynamics via a finite-length of data and a finite number of array elements. For example, the reflected source signal impinging from the side-lobe direction presents a coherent interference, and the non-minimal phase channel dynamics may require an infinite amount of data in order to achieve perfect equalization (or inversion). All these factors appear as uncertainties or un-modeled dynamics in the receiving signals. Traditional adaptive algorithms such as NLMS that do not consider these errors will result in performance deterioration. In this paper, a time domain beamformer using H∞ filtering approach is proposed to adjust the beamforming parameters. Furthermore, this work also proposes a frequency domain approach called SPFDBB (Soft Penalty Frequency Domain Block Beamformer) using H∞ filtering approach that can reduce computational efforts and provide a purified data to the ASR application. Experimental results show that the adaptive H∞ filtering method is robust to the modeling errors and suppresses much more noise interference than that in the NLMS based method. Consequently, the correct rate of ASR is also enhanced.

Power allocation for OFDM using adaptive beamforming over wireless networks

The performance of a multiuser wireless network using orthogonal frequency-division modulation (OFDM), combined with power control and adaptive beamforming for uplink transmission is presented here. A network-wide adaptive power control algorithm is used to achieve the desired signal-to-interference-and-noise-ratio at each OFDM subcarrier and increase the power efficiency of the network. As a result, we can achieve a better overall error probability for a fixed total transmit power. With the assumption of fixed-modulation for all subcarriers, transmit powers and beamforming weight vectors at each subcarrier are updated jointly, using an iterative algorithm that converges to the optimal solution for the entire network. Unlike most of the loading algorithms, this approach considers fixed bit allocation and optimizes the power allocation and reduces the interference for the entire network, rather than a single transmitter. We also propose joint time-domain beamforming and power control to reduce the complexity resulting from the number of beamformers and fast Fourier transformed blocks. The proposed algorithm is also extended to COFDM and we show that it improves the performance of those systems.

ULTRASONIC IMAGING SYSTEM USING A 2D ENVELOPE BEAMFORMING TECHNIQUE: IN-HOMOGENEITIES LOCATION

An algorithm has been developed to implement synthetic aperture focusing technique for B-scan. This is made at a several transmitter/receiver locations to form a map of ultrasonic reflectivity on the insonified region, considering the path travelled by the ultrasonic pulse from the transducer to the target and back again. To reconstruct the image, a time domain beam-former is applied to the envelope of the detected signals. This method minimizes the side-lobe amplitude and the restriction of λ/2 distance between two adjacent transducer positions can be neglected without loosing image resolution. The present work is focused on the location of the in-homogeneities, caused by the presence of a phantom immersed in a water tank. The results are presented when the distance between two adjacent transducer positions are varied from 0.5λ to 2.5λ showing that the longitudinal resolution is not affected but the lateral resolution becomes poorer when the distance is about 2λ. The error in the longitudinal location of in-homogeneities is within the minimum detectable distance of the system, while the lateral location error is increased when the distance between any two adjacent transducer positions is larger than 1.5λ.

Direct sampled I/Q beamforming for compact and very low-cost ultrasound imaging

A wide variety of beamforming approaches are applied in modern ultrasound scanners, ranging from optimal time domain beamforming strategies at one end to rudimentary narrowband schemes at the other. Although significant research has been devoted to improving image quality, usually at the expense of beamformer complexity, we are interested in investigating strategies that sacrifice some image quality in exchange for reduced cost and ease in implementation. This paper describes the direct sampled in-phase/quadrature (DSIQ) beamformer, which is one such low-cost, extremely simple, and compact approach. DSIQ beamforming relies on phase rotation of I/Q data to implement focusing. The I/Q data are generated by directly sampling the received radio frequency (RF) signal, rather than through conventional demodulation. We describe an efficient hardware implementation of the beamformer, which results in significant reductions in beamformer size and cost. We present the results of simulations and experiments that compare the DSIQ beamformer to more conventional approaches, namely, time delay beamforming and traditional complex demodulated I/Q beamforming. Results that show the effect of an error in the direct sampling process, as well as dependence on signal bandwidth and system f number (f#) are also presented. These results indicate that the image quality and robustness of the DSIQ beamformer are adequate for low end scanners. We also describe implementation of the DSIQ beamformer in an inexpensive hand-held ultrasound system being developed in our laboratory.