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The increasing number of connected users as well as the availability of new services and mobile applications drive the need for higher data rates. In order to fulfill such expectations different strategies such as spatial multiplexing have been introduced. This thesis is centered on the Multi-User Uplink Channel where different users transmit to a single base station with multiple antennas. The purpose of this thesis is to design the transmitter and the receiver architectures so that the maximum sum rate of a Multi-User Uplink Channel reaches the capacity for single and multi-antenna users. In the literature there is a lack of practical implementations and not many studies exploit the multi-antenna user scenario. It is important to properly characterize the capacity region and define practical implementation schemes on the uplink direction to design the architecture for the Multi-User Downlink Channel also referred as the Broadcast Channel, which is a more complex problem based on the uplink solution. The design of the optimal transmitter is motivated by the analysis of capacity first for the single user scenario with Multi Input Multi Output Peer-to-Peer (MIMO P2P) communica- tions followed by the Multi-User scenario for single and multi-antenna users. At the receiver three types of beamformers are analyzed and compared: Zero Forcing, QR and Minimum Mean Squared Error beamformer. Results for the Bit Error Rate performance and maximum sum rate for the different receivers are provided. The thesis results show that the optimal architecture for the Multi-User Uplink with multi- antenna users that achieves capacity is the combination of the optimal MIMO P2P design, based on the Singular Value Decomposition of the channel matrix and the Water Filling power allocation. For the receiver part the Minimum Mean Squared Error beamformer is proven to achieve capacity. Channel State Information is needed at the transmitter and receiver, therefore a channel estimation algorithm is provided based on orthogonal sequences and is proven to deliver good Bit Error Rate results.

Ultrasound imaging is a largely used medical imaging system as it is safe, non-invasive, and capable of real-time imaging. In ultrasound imaging, different beamforming methods are used to obtain the image of the field of view. The image quality largely depends on the type of beamforming used in ultrasound imaging. To make the ultrasound imaging system portable, beamforming system needs to be implemented as compact hardware architecture. Dynamic focusing and adaptive apodization are used in beamforming systems to generate high-quality ultrasound images, however, their implementation into the hardware requires large hardware resource which consumes high power. This paper presents the implementation of a compact receive beamformer architecture using a hardware-efficient dynamic delay calculator, an IEEE single-precision arithmetic based adaptive apodization system architecture and a focusing mechanism. The proposed beamformer provides real-time beamforming output which can be used to display high quality ultrasound images. Field-II toolbox is used to simulate and verify the beamformer output. The proposed beamformer consumes 1370k NAND-2 gate equivalent logic resources in UMC 90 nm CMOS standard cell library.

In this paper, a set of transmission schemes are proposed for the delivery of multicast (MC) signals, in which an intelligent reflecting surface (IRS) assists the transmission from an access point (AP) to a set of multicast users. It is known that the large number of IRS reflecting elements have the potential to improve the transmission efficiency by forming an artificial signal path with strong channel gain. However, the joint optimization of the AP beamformer and the phases of the IRS reflecting elements is challenging due to the non-convex nature of the phase elements as well as the high computational complexity required for a large number of elements. A set composed of two AP beamformer schemes and a set with two IRS phase adjustment algorithms are proposed, which are sub-optimal but less computationally demanding. A semi-definite relaxation (SDR)-based scheme is considered along with a least squares (LS) based one for the AP beamformer design. For the IRS phase adjustment, an LS based optimization and a grouping method for the phase elements are suggested. From these two sets, four combinations of overall optimization can be built, and their performances can be compared with their merits and weaknesses revealed. The signal-to-interference-plus-noise power ratio (SINR) performance results are verified in various parameter conditions by simulation.

This paper reports on the design of frequency-dependent feed networks for linear antenna arrays with minimum half-power beamwidth (HPBW) variation in more than one octave of the frequency spectrum. The proposed approach is based on: i) frequency-dependent power dividers that gradually shift the RF power from the outer elements of the array to the inner ones with the increase of frequency and ii) uniformly or non-uniformly-spaced directive antenna elements. The operating principles and design trade-offs of the concept are presented through ideal simulations of four- and six-element antenna arrays shaped by isotropic or directive radiators. It is shown that by employing directive antenna elements and non-uniform spacing, minimum HPBW variation can be obtained in a broad bandwidth (BW, e.g., 3:1). For physical verification purposes, two frequency-dependent feed networks and Vivaldi antenna elements were designed, manufactured, and measured. The first network feeds a uniformly-spaced four-element array of Vivaldi antennas and demonstrates a 58% HPBW variation in a 3:1 of BW. The second network feeds a non-uniformly-spaced six-element Vivaldi array and results in a 67% HPBW variation in a 2.5:1 of BW.

This paper reports on the design and practical validation of monopole antenna arrays with reduced half-power beamwidth (HPBW) variation in a bandwidth (BW) greater than one octave of the RF spectrum. The HPBW variation is reduced by feeding the antenna elements with frequency-dependent feed networks. The feed networks are designed in such a way that the element power is gradually shifted from the outer elements at low frequencies to the inner elements at high frequencies. The operating principles of the proposed concept are explored through simulated examples of four-element arrays made of isotropic elements and then realistic monopole elements. Scalability of the concept to eight-element arrays is also explored using ideal simulations. For practical validation purposes, a four-element monopole antenna array and its corresponding feed network are designed and measured. The prototype resulted in a HPBW variation of 78% in a 2.6:1 BW, which is significantly reduced compared to the uniformly fed array, having a 216% variation.

In this paper, a beamforming scheme is proposed to maximize a secrecy multicast rate (SMR) in the multicast wiretap channel, in which the multiple unauthorized users overhear the multicast messages. The SMR is formulated by the ratio of multicast rate and information leakage in the numerator and denominator, respectively. By exploiting the SMR structure, we propose three doubly equalizing beamforming approaches: i) zero-forcing algorithm, ii) bottom-first algorithm, and iii) top-first algorithm. Depending on the algorithms, either the legitimate user channels or the unauthorized user channels are fully equalized, and the other set of channels are then equalized through a least-squares approach. While the zero-forcing algorithm optimizes the strength of legitimate user channels, the bottom-first and the top-first algorithms find the balance between the strengths of legitimate user channels and unauthorized user channels. The top-first algorithm encompasses the bottom-first algorithm, where the bottom-first algorithm encompasses the zero-forcing algorithm. Consequently, the proposed top-first algorithm outperforms the other two algorithms. The proposed top-first algorithm improves SMR by effectively preventing overhearing while sustaining almost maximum multicast rate and provide comparable SMR to the multicast rate obtained without unauthorized users. These results are verified by simulation.

This paper presents a multipath component (MPC) parameter estimator that uses a double-directional (D-D) channel sounding system in WiGig millimeter-wave bands. It employs low-cost commercial-off-the-shelf (COTS) RF transceivers capable of beam steering within an azimuth angle range of ±45°; the transmit power is approximately 31 dBm, equivalent isotropic radiated power (EIRP), including a total antenna gain of approximately 19 dBi. The half-power beam widths in the azimuth and elevation planes are 6° and 45°, respectively. A fast D-D channel acquisition in 360° full azimuth range can be achieved by developing a $4 \times 4$ multiple-input-multiple-output (MIMO) time division-multiplexing (TDM) scheme that enables simultaneous use of four antenna arrays at both sides of the transmitter and receiver. The beam switching for all combinations ( $48 \times 48 = 2304$ ) with 12 beams at each array requires less than 200 ms, excluding optional procedure related to data storage. A high-resolution MPC extraction method was developed from the D-D angular delay power spectra obtained using the sub-grid CLEAN algorithm, which is applicable when phase coherence among multiple snapshots obtained via the beam-switching measurement cannot be guaranteed. Furthermore, the operation of the developed system was validated via a measurement at 58.32 GHz in an office floor of a university laboratory. From the data analysis, the cluster properties and the corresponding scattering processes were identified.

Recently, more and more portable devices and software applications that interact with human are being developed. The needs for detecting position information are growing rapidly in both amount and accuracy. Approaches that using RF signals or light for active probing, analyzing the reflected signals by deep-learning attract the most attention. However, in order to realize a practical portable device, cost and hardware requirements must be reduced. In this paper, a position detecting system is proposed. By sending chirp signals via ultrasound speakers and receiving the reflection using MEMS microphone array, then position info can be reconstructed by digital signal processing.

Highlights • MEG may aid in the localization of the epileptogenic zone in the parietal lobe. • SAMepi – a novel kurtosis beamformer – results in localizations similar to those of the ECD analysis. • A unifocal result in both the ECD and the SAMepi analysis is associated with a good clinical outcome., Objective To evaluate a novel analysis method (SAMepi) in the localization of interictal epileptiform magnetoencephalographic (MEG) activity in parietal lobe epilepsy (PLE) patients in comparison with equivalent current dipole (ECD) analysis. Methods We analyzed the preoperative interictal MEG of 17 operated PLE patients utilizing visual analysis and: (1) ECD with a spherical conductor model; (2) ECD with a boundary element method (BEM) conductor model; and (3) SAMepi – a kurtosis beamformer method. Localization results were compared between the three methods, to the location of the resection and to the clinical outcome. Results Fourteen patients had an epileptiform finding in the visual analysis; SAMepi detected spikes in 11 of them. A unifocal finding in both the ECD and in the SAMepi analysis was associated with a better chance of seizure-freedom (p = 0.02). There was no significant difference in the distances from the unifocal MEG localizations to the nearest border of the resection between the different analysis methods. Conclusions Localizations of unifocal interictal spikes detected by SAMepi did not significantly differ from the conventional ECD localizations. Significance SAMepi – a novel semiautomatic analysis method – is useful in localizing interictal epileptiform MEG activity in the presurgical evaluation of parietal lobe epilepsy patients.

Imperceptible latency, uninterrupted communication, and the availability of inexhaustible bandwidth are conceptualized as essential milestones to revolutionize the modes by which societies generated, circulate, receive, and perceive information. The exponential increase in wireless data traffic has raised concerns to investigate suitable bands in the radio spectrum to satisfy the intensifying user's data rate requirements. Overall the wireless infrastructure needs development and exploitation to synchronize with the massive capacity and connectivity demands. The Terahertz (THz) frequency band (0.1-10 THz) is considered as a pivotal solution to fulfill the needs of applications and devices requiring the high speed transmission, and have received noticeable attention from the research community. Technologies in this spectrum are facing rapid development and hold high potentials in applications like ultra-fast short-range wireless communications, remote sensing, biological detection, and basic material research. The antenna is one of the critical components to support the THz systems and require a considerable attention in terms of precision. Compact high-gain antennas are desirable for low latency and high data rate THz wireless communication systems, specifically for applications having space limitation, for example, in the high speed interlink inside the high density wireless communication base station (BS). Nevertheless, there still exist many challenges, while designing the antenna for THz communications requiring innovative solutions. This paper serves an introductory guideline to address the challenges and opportunities, while designing a THz enabled antenna.

This paper considers speech enhancement of signals picked up in one noisy environment which must be presented to a listener in another noisy environment. Recently, it has been shown that an optimal solution to this problem requires the consideration of the noise sources in both environments jointly. However, the existing optimal mutual information based method requires a complicated system model that includes natural speech variations, and relies on approximations and assumptions of the underlying signal distributions. In this paper, we propose to use a simpler signal model and optimize speech intelligibility based on the Approximated Speech Intelligibility Index (ASII). We derive a closed-form solution to the joint far- and near-end speech enhancement problem that is independent of the marginal distribution of signal coefficients, and that achieves similar performance to existing work. In addition, we do not need to model or optimize for natural speech variations.

We propose a multistage approach for enhancing speech captured by a drone-mounted microphone array. The key challenge is suppressing the drone ego-noise, which is the major source of interference in such captures. Since the location of the target is not known a priori, we first apply a UNet-based deep convolutional autoencoder (AE) individually to each microphone signal. The AE generates a time-frequency mask is an element of [0, 1] per signal, where high values correspond to time-frequency points with relatively good signal-to-noise ratios (SNRs). The masks are pooled across all microphones and the aggregated mask is used to steer an adaptive, frequency domain beamformer, yielding a signal with an improved SNR. This beamformer output, after being fed back to the AE, now yields an improved mask - which is used for re-focussing the beamformer. This combination of AE and beamformer, which can be applied to the signals in multiple 'passes' is termed multistage beamforming. The approach is developed and evaluated on a self-collected database. For the AE - when used to steer a beamformer - a training target that preserves more speech at the cost of less noise suppression outperforms an aggressive training target that suppresses more noise at the cost of more speech distortion. This, in combination with max-pooling of the multi-channel mask - which also lets through more speech (and noise) compared with median pooling - performs best. The experiments further demonstrate that the multistage approach brings extra benefit to the speech quality and intelligibility when the input SNR is >= -10 dB, and yields comprehensible outputs when the input has a SNR above -5 dB.

This paper presents a method to generate antenna patterns for a Uniform Linear Array (ULA) having narrow beamwidth and low sidelobe levels (SLL) using the recently proposed Modified FRM (ModFRM) architecture. This allows it to direct the beams to specific ground cells for communications while mitigating inter-cell interference. The sharpness of the beam pattern defines the spatial discriminating performance of a ULA beamformer, while the SLL dictates the interference and noise suppression capabilities. Typically, a conventional ULA beamforming will demand high computational complexity and a large number of sensors to satisfy these requirements. Hence to reduce the system cost, using the ModFRM technique a sparse array is developed. With this strategy, the total number of sensors is drastically reduced compared to conventional ULA beamformers. The designed beamformers can be used in applications with stringent requirements where cost and size are concerned.

Space Situational Awareness (SSA) by ground-based Digital-Array Radar (DAR) systems has been attracting global attention in recent years. One of its fundamental tasks is to provide accurate collision forecast between space debris and active satellites, leading to increased avoidance probability. In a DAR system, this is achieved by a rigorous Signal Processing (SP) stage that successfully detects stray space debris and accurately estimates its parameters: range, Direction-of-Arrival (DOA), radial velocity, and more. However, classical SP methods, which are not tailored to the SSA environment, ultimately lead to sub-optimal performance. The objective of this thesis is to improve the DAR performance through the adaptation of the SP scheme to the SSA scenario. We present the shortcomings of several key traditional SP aspects and propose new methods for improved target detection and parameter estimation, supported by numerical demonstrations of a real SSA DAR. One such aspect is the SP of large DAR with a high number of receiving antenna elements, which contributes to a better target detection and DOA estimation. Commonly used data reduction transformations harness existing resources to serve only the target detection aspect, which is not necessarily optimal for SSA. We present a novel parameter-controlled design method to construct a lossless (or optimal) transformation, with respect to the available resources and an acceptable trade-off between detection and DOA estimation performance. Moreover, a new tool is provided to analyze the potential performance of a given array without the need for simulations. The abovementioned concept is also demonstrated in a multi-static radar network configuration, showing significant performance gain. A common topic in most radar systems is the DOA Maximum Likelihood Estimator (MLE). In SSA, we deal with targets in the Low Earth Orbit (LEO) region, moving at great orbital velocities. Pulsed radar systems therefore experience the so-called ‘DOA migration’ effect from pulse to pulse, where each pulse echo returns with changing DOA and unequal amplitude. With a classical MLE, these effects result in a large target localization estimation bias (in the order of kilometers). For that purpose, the orbital mechanics of LEO targets are implemented in the DOA motion model, rendering the estimation bias removed. Another issue of great impact is the target masking phenomenon. Classical SP gives rise to a miss-detection in two specific cases related to SSA. A far range target will go unnoticed in the presence of a short range target. In addition, a small target will remain undetected due to a nearby larger target. With this challenge in mind, two new waveform design concepts are successfully demonstrated. The above-mentioned techniques ultimately lead to superior estimation accuracy, higher resource efficiency, and robust detection capabilities, contributing to the SSA goal. Based on this research, new estimation methods and operational modes could be explored in the context of a single station and radar networks., Die Erfassung der Weltraumlage durch erdgebundene digitale Phased-Array-Radarsysteme hat in den letzten Jahren global an Bedeutung gewonnen. Eine ihrer grundlegenden Aufgaben ist es hochgenaue Kollisionsvorhersagen zwischen Weltraumschrott und aktiven Satelliten zu ermöglichen, sodass durch notwendige Ausweichmanöver die Kollisionswahrscheinlichkeit minimiert werden kann. Digitale Phased-Array-Radarsysteme erreichen dies durch eine komplexe Signalverarbeitung, welche erfolgreich Weltraumschrott detektiert und deren Parameter, unter anderem Entfernung, Einfallsrichtung und Radialgeschwindigkeit, präzise schätzt. Klassische, nicht auf die Weltraumumgebung zugeschnittene, Signalverarbeitungsmethoden führen jedoch zu einer suboptimalen Leistungsfähigkeit. Ziel dieser Arbeit ist es, die Leistungsfähigkeit eines digitalen Phased-Array-Radarsystems durch die Anpassung der Signalverarbeitung an das Weltraumszenario zu optimieren. Hierfür werden zunächst Schwachpunkte einiger Aspekte der klassischen Signalverarbeitung aufgezeigt und anschließend neue Methoden zur verbesserten Zielerfassung und Parameterschätzung eingeführt. Dies wird mit numerischen Beispielen eines realen digitalen Phased-Array-Radars zur Weltraumüberwachung unterstützt. Ein solcher Aspekt tritt besonders bei einer hohen Anzahl von Empfangselementen des digitalen Phased-Array-Radars auf, welche zu einer besseren Zieldetektion und Richtungsschätzung beiträgt. Aufgrund der mit der hohen Anzahl an Empfangselementen einhergehenden großen Datenmenge werden in solchen Systemen im Vorfeld der Signalverarbeitung häufig Transformationen zur Datenreduktion verwendet. Die gängigen Transformationen konzentrieren die vorhandenen Ressourcen ausschließlich auf die Leistung der Zieldetektion, was für das Weltraumszenario nicht notwendigerweise optimal ist. Wir präsentieren eine neuartige parametergesteuerte Design-Methode zur Konstruktion einer optimalen Transformation in Bezug auf die verfügbaren Ressourcen und einen akzeptablen Kompromiss zwischen den Leistungsfähigkeiten bezüglich Detektion und Richtungsschätzung. Des Weiteren wird ein neues Tool vorgestellt, welches die potenzielle Leistung eines gegebenen Phased-Array-Systems ohne erforderliche Simulation analysiert. Zusätzlich wird die vorgestellte Methode auf ein multistatisches Radarnetzwerk angewandt, welche einen signifikanten Leistungsgewinn zeigt. Ein in Radarsystemen gängiges Verfahren zur Schätzung der Einfallsrichtung ist der Maximum Likelihood (ML)-Richtungsschätzer. In der Weltraumüberwachung werden unter anderem Ziele im LEO betrachtet, welche sich mit sehr hohen Bahngeschwindigkeiten bewegen. Daher tritt bei gepulsten Radarsystemen die sogenannte "directionof- arrival" Migration von Puls zu Puls auf. Hierbei zeigt das Empfangssignal jedes Pulses eine veränderte Einfallsrichtung und Amplitude. Mit einem klassischen MLRichtungsschätzer führen diese Effekte zu einem Bias bei der Ziellokalisierung in der Größenordnung von Kilometern. Um diesen Bias zu beseitigen wird die Bahnmechanik von LEO-Zielen betrachtet und erfolgreich in das Bewegungsmodell des ML-Richtungsschätzers implementiert. Ein weiteres wichtiges Problem ist das Phänomen der Maskierung von Zielen. Mit der klassischen Signalverarbeitung kommt es in zwei für die Weltraumüberwachung spezifischen Fällen zu Fehldetektionen. Zum einen bleibt ein weit entferntes Ziel in Anwesenheit eines Ziels mit geringer Entfernung undetektiert und zum anderen bleibt ein kleines Ziel aufgrund eines nahegelegenen größeren Ziels unerkannt. Vor diesem Hintergrund werden zwei neue Konzepte zum Wellenform-Design vorgestellt und deren Leistung erfolgreich demonstriert. All die genannten Techniken führen letztendlich zu verbesserten Schätzgenauigkeiten, erhöhter Ressourceneffizienz sowie zu einer robusteren Detektionsfähigkeit und tragen damit zum Ziel der Weltraumlageerfassung bei. Auf Basis dieser Arbeit können neue Schätzverfahren und Betriebsmodi für einzelne Radar-Stationen, als auch für Radarnetzwerke, erforscht werden.

MEG and EEG source analysis is frequently used for the presurgical evaluation of pharma-coresistant epilepsy patients. The source localization of the epileptogenic zone depends, among other aspects, on the selected inverse and forward approaches and their respective parameter choices. In this validation study, we compare for the inverse problem the standard dipole scanning method with two beamformer approaches and we investigate the influence of the covariance estimation method and the strength of regularization on the localization performance for EEG, MEG and combined EEG and MEG. For forward modeling, we investigate the difference between calibrated six-compartment and standard three-compartment head modeling. In a retrospective study of two patients with focal epilepsy due to focal cortical dysplasia type IIb and seizure-freedom following lesionectomy or radiofrequency-guided thermocoagulation, we used the distance of the localization of interictal epileptic spikes to the resection cavity resp. rediofrequency lesion as reference for good localization. We found that beamformer localization can be sensitive to the choice of the regularization parameter, which has to be individually optimized. Estimation of the covariance matrix with averaged spike data yielded more robust results across the modalities. MEG was the dominant modality and provided a good localization in one case, while it was EEG for the other. When combining the modalities, the good results of the dominant modality were mostly not spoiled by the weaker modality. For appropriate regularization parameter choices, the beamformer localized better than the standard dipole scan. Compared to the importance of an appropriate regularization, the sensitivity of the localization to the head modeling was smaller, due to similar skull conductivity modeling and the fixed source space without orientation constraint.

Coherent plane-wave compound imaging (CPWCI) is used as alternative for conventional focused imaging (CFI) to increase frame rates linearly with the ratio number of imaging lines to steering angles. In this study, the image quality was compared between CPWCI and CFI, and the effect of steering angles (range and number) and beamforming strategies was evaluated in CPWCI. In automated breast volume scanners (ABVSs), which suffer from reduced volume rates, CPWCI might be an excellent candidate to replace CFI. Therefore, the image quality of CFI currently in ABVS and CPWCI was also compared in an in vivo breast lesion. Images were obtained by a Siemens Sequoia ultrasound system, and two transducers (14L5 and 10L4) in a CIRS multipurpose phantom (040GSE) and a breast lesion. Phantom results showed that contrast sensitivity and resolution, axial resolution, and generalized contrast-to-noise ratio (gCNR; imaging depths

Target source extraction is significant for improving human speech intelligibility and the speech recognition performance of computers. This study describes a method for target source extraction, called the similarity-and-independence-aware beamformer (SIBF). The SIBF extracts the target source using a rough magnitude spectrogram as the reference signal. The advantage of the SIBF is that it can obtain a more accurate signal than the spectrogram generated by target-enhancing methods such as speech enhancement based on deep neural networks. For the extraction, we extend the framework of deflationary independent component analysis (ICA) by considering the similarities between the reference and extracted target sources, in addition to the mutual independence of all the potential sources. To solve the extraction problem by maximum-likelihood estimation, we introduce three source models that can reflect the similarities. The major contributions of this study are as follows. First, the extraction performance is improved using two methods, namely boost start for faster convergence and iterative casting for generating a more accurate reference. The effectiveness of these methods is verified through experiments using the CHiME3 dataset. Second, a concept of a fixed point pertaining to accuracy is developed. This concept facilitates understanding the relationship between the reference and SIBF output in terms of accuracy. Third, a unified formulation of the SIBF and mask-based beamformer is realized to apply the expertise of conventional BFs to the SIBF. The findings of this study can also improve the performance of the SIBF and promote research on ICA and conventional beamformers. Index Terms: beamformer, independent component analysis, source separation, speech enhancement, target source extraction, Accepted for publication as a regular paper in the IEEE Open Journal of Signal Processing (2021)

Autonomous sensory meridian response (ASMR) describes an atypical multisensory experience of calming, tingling sensations in response to a specific subset of social audiovisual triggers. To date, the electrophysiological (EEG) correlates of ASMR remain largely unexplored. Here we sought to provide source-level signatures of oscillatory changes induced by this phenomenon and investigate potential decay effects—oscillatory changes in the absence of self-reported ASMR. We recorded brain activity using EEG as participants watched ASMR-inducing videos and self-reported changes in their state: no change (Baseline); enhanced relaxation (Relaxed); and ASMR sensations (ASMR). Statistical tests in the sensor-space were used to inform contrasts in the source-space, executed with beamformer reconstruction. ASMR modulated oscillatory power by decreasing high gamma (52–80 Hz) relative to Relaxed and by increasing alpha (8–13 Hz) and decreasing delta (1–4 Hz) relative to Baseline. At the source level, ASMR increased power in the low-mid frequency ranges (8–18 Hz) and decreased power in high frequency (21–80 Hz). ASMR decay effects reduced gamma (30–80 Hz) and in the source-space reduced high-beta/gamma power (21–80 Hz). The temporal profile of ASMR modulations in high-frequency power later shifts to lower frequencies (1–8 Hz), except for an enhanced alpha, which persists for up to 45 min post self-reported ASMR. Crucially, these results provide the first evidence that the cortical sources of ASMR tingling sensations may arise from decreases in higher frequency oscillations and that ASMR may induce a sustained relaxation state.

While substantial noise reduction and speech enhancement can be achieved with multiple microphones organized in an array, in some cases, such as when the microphone spacings are quite close, it can also be quite limited. This degradation can, however, be resolved by the introduction of one or more external microphones ( $\text{XM}$ s) into the same physical space as the local microphone array ( $\text{LMA}$ ). In this paper, three methods of extending an $\text{LMA}$ -based generalized sidelobe canceller ( $\text{GSC-LMA}$ ) with multiple $\text{XM}$ s are proposed in such a manner that the relative transfer function pertaining to the $\text{LMA}$ is treated as a priori knowledge. Two of these methods involve a procedure for completing an extended blocking matrix, whereas the third uses the speech estimate from the $\text{GSC-LMA}$ directly with an orthogonalized version of the $\text{XM}$ signals to obtain an improved speech estimate via a rank-1 generalized eigenvalue decomposition. All three methods were evaluated with recorded data from an office room and it was found that the third method could offer the most improvement. It was also shown that in using this method, the speech estimate from the $\text{GSC-LMA}$ was not compromised and would be available to the listener if so desired, along with the improved speech estimate that uses both the $\text{LMA}$ and $\text{XM}$ s.

This paper proposes a new technique for improving a generalized sidelobe canceller (GSC) for dual-microphone speech enhancement to be applied in an auditory device such as a hearing aid. Here, the GSC is implemented on a 32-channel uniform polyphase discrete Fourier transform filter bank, where the overall algorithm processing delay is 8 ms to meet hearing aid requirements. The proposed method can improve the fixed beamformer (FBF) and control the adaptive algorithm in the noise canceller (NC) using the phase difference obtained from dual-microphone signals. For this, spatial cues such as the phase differences are used to estimate the target-to-non-target directional signal ratio (TNR). A target-directional speech enhancing spectral gain-attenuator is calculated based on the estimated TNR, which is then incorporated to improve the FBF in the GSC. Furthermore, the weight update of the adaptive NC in the GSC is formulated using the phase difference-based TNR. The experimental results show that the auditory speech enhancement system that employs the proposed dual-microphone GSC algorithm provides better perceptual quality and intelligibility scores than conventional methods such as a beamformer, phase-error-based filter (PEF), GSC, or PEF-controlled GSC under multiple noise conditions of signal-to-noise ratio range 0-20 dB.

Optically pumped magnetometer-based magnetoencephalography (OP-MEG) can be used to measure neuromagnetic fields while participants move in a magnetically shielded room. Head movements in previous OP-MEG studies have been up to 20 cm translation and ∼30° rotation in a sitting position. While this represents a step-change over static MEG systems, naturalistic head movement is likely to exceed these limits, particularly when participants are standing up. In this proof-of-concept study, we sought to push the movement limits of OP-MEG even further. Using a 90 channel (45-sensor) whole-head OP-MEG system and concurrent motion capture, we recorded auditory evoked fields while participants were: (i) sitting still, (ii) standing up and still, and (iii) standing up and making large natural head movements continuously throughout the recording – maximum translation 120 cm, maximum rotation 198°. Following pre-processing, movement artefacts were substantially reduced but not eliminated. However, upon utilisation of a beamformer, the M100 event-related field localised to primary auditory regions. Furthermore, the event-related fields from auditory cortex were remarkably consistent across the three conditions. These results suggest that a wide range of movement is possible with current OP-MEG systems. This in turn underscores the exciting potential of OP-MEG for recording neural activity during naturalistic paradigms that involve movement (e.g. navigation), and for scanning populations who are difficult to study with static MEG (e.g. young children). Highlights Data were collected from a wearable, whole-head 45-sensor, 90 channel OP-MEG system Participants were standing up and continually moving their head Head movement exceeded 120cm translation and 190° rotation We successfully measured auditory evoked fields despite the continuous head movements This was facilitated by data pre-processing steps and beamforming

Significance: Coherence, a fundamental property of waves and fields, plays a key role in photoacoustic image reconstruction. Previously, techniques such as short-lag spatial coherence (SLSC) and filtered delay, multiply, and sum (FDMAS) have utilized spatial coherence to improve the reconstructed resolution and contrast with respect to delay-and-sum (DAS). While SLSC uses spatial coherence directly as the imaging contrast, FDMAS employs spatial coherence implicitly. Despite being more robust against noise, both techniques have their own drawbacks: SLSC does not preserve a relative signal magnitude, and FDMAS shows a reduced contrast-to-noise ratio. Aim: To overcome these limitations, our aim is to develop a beamforming algorithm—generalized spatial coherence (GSC)—that unifies SLSC and FDMAS into a single equation and outperforms both beamformers. Approach: We demonstrated the application of GSC in photoacoustic computed tomography (PACT) through simulation and experiments and compared it to previous beamformers: DAS, FDMAS, and SLSC. Results: GSC outperforms the imaging metrics of previous state-of-the-art coherence-based beamformers in both simulation and experiments. Conclusions: GSC is an innovative reconstruction algorithm for PACT, which combines the strengths of FDMAS and SLSC expanding PACT’s applications.

Orientador: Prof. Dr. Ricardo Suyama Co-orientador: Prof. Dr. Kenji Nose Filho Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia da Informação, Santo André, 2021.

This paper discusses orbital angular momentum (OAM) signal reception and alignment aspects using a Rotman lens based multimode circular patch antenna array. A 9-element planar circular array is connected to a 5 beam port Rotman lens which is capable of hosting 5 spatially orthogonal OAM modes namely $l = 0, \pm 1$ and ±2. The Rotman lens based circular array is paced at the receiver end when it is illuminated with OAM signals. It is shown that the OAM modes reception is separable at the Rotman lens stage, hence reducing the requirement of the OAM phase correction at the receiver’s signal processing block. It is also shown that a slight misalignment between transmitter and receiver circular arrays can substantially decrease the signal recovery chances for the transmitted data using the OAM modes $l = \pm1$ and ±2. This feature can enhance physical layer security to the communication link using Rotman lens based multimode circular array.

This paper reports a dual-wavelength photonic beamformer implementing optical true time delay (OTTD) to realize microwave beam steering. The beamformer is capable of providing independent delay tuning to two separate beams modulated on different optical carriers. The integrated TTD chip includes a multiplexer that combines the two input wavelengths, an optical sideband filter (OSBF) and optical ring resonators (ORRs) that induce different optical delays. The ORRs are thermo-optically tuned to change the coupling ratio and obtain an incremental delay in each optical path. The experimental demonstration includes a full-compliant WiFi channel (at 5 GHz or 18 GHz RF bands) transmitted in one optical carrier and a WiMAX channel (at 5.4 GHz or 19 GHz RF) in another optical carrier operating in the resonance slope of the ORRs. The different antenna elements are connected with 1-km of 7-core fiber, achieving EVM-compliant levels at the antennas with beam-steering angles ranging from -40° to +80°. The performance comparison considering single-carrier broadband RF signals at the same frequency bands is also reported in this work.

Hearing devices are becoming a more and more common solution for people with mild to profound hearing loss. The hearing instruments are, indeed, able to compensate for the individual hearing loss while trying to provide the best hearing experience possible. However, the acoustic environments which the average user experiences during the day are usually very different and complex. Most of the devices try to cope with these big variations in the surroundings by adjusting the settings based on some parameters senses by the microphones. One of the most common solutions, in this regards, is the sound classifier. The main objective of this tool is to blindly understand the acoustic scenario around the hearing aid user and enable the appropriate change in the settings based on the detected environment. Although the sound classifier is a precious tool in a hearing device, very often it does not consider a very important aspect of sound, i.e., sound is generated by sources placed in a 3D world. The spatial components in the acoustic scenarios are often discarded after being sensed by the microphones. In this work, a possible solution to integrate spatial components to the sound classifier in order to have a better understanding of the acoustic environment was investigated. The solution here proposed is to extend the inputs of the sound classifier with additional informations about the location of the sound sources present in the environment. To provide these additional informations, a localization algorithm tailored for hearing devices applications has been developed. The algorithm creation was inspired by the human auditory system which relies on the estimation of the binaural cues. In addition to the localization algorithm, a blind direct-to-reverberant energy ratio for speech signal has been developed. Moreover, an exploratory solution for head tracking based on a 3-axis accelerometer was investigated.

One of the primary technical challenges facing magnetoencephalography (MEG) is that the magnitude of neuromagnetic fields is several orders of magnitude lower than interfering signals. Recently, a new type of sensor has been developed - the optically pumped magnetometer (OPM). These sensors can be placed directly on the scalp and move with the head during participant movement, making them wearable. This opens up a range of exciting experimental and clinical opportunities for OPM-based MEG experiments, including paediatric studies, and the incorporation of naturalistic movements into neuroimaging paradigms. However, OPMs face some unique challenges in terms of interference suppression, especially in situations involving mobile participants, and when OPMs are integrated with electrical equipment required for naturalistic paradigms, such as motion capture systems. Here we briefly review various hardware solutions for OPM interference suppression. We then outline several signal processing strategies aimed at increasing the signal from neuromagnetic sources. These include regression-based strategies, temporal filtering and spatial filtering approaches. The focus is on the practical application of these signal processing algorithms to OPM data. In a similar vein, we include two worked-through experiments using OPM data collected from a whole-head sensor array. These tutorial-style examples illustrate how the steps for suppressing external interference can be implemented, including the associated data and code so that researchers can try the pipelines for themselves. With the popularity of OPM-based MEG rising, there will be an increasing need to deal with interference suppression. We hope this practical paper provides a resource for OPM-based MEG researchers to build upon., Comment: 56 pages, 19 figures, supplementary materials available on request

Bilateral hearing in early development protects auditory cortices from reorganizing to prefer the better ear. Yet, such protection could be disrupted by mismatched bilateral input in children with asymmetric hearing who require electric stimulation of the auditory nerve from a cochlear implant in their deaf ear and amplified acoustic sound from a hearing aid in their better ear (bimodal hearing). Cortical responses to bimodal stimulation were measured by electroencephalography in 34 bimodal users and 16 age-matched peers with normal hearing, and compared with the same measures previously reported for 28 age-matched bilateral implant users. Both auditory cortices increasingly favoured the better ear with delay to implanting the deaf ear; the time course mirrored that occurring with delay to bilateral implantation in unilateral implant users. Preference for the implanted ear tended to occur with ongoing implant use when hearing was poor in the non-implanted ear. Speech perception deteriorated with longer deprivation and poorer access to high-frequencies. Thus, cortical preference develops in children with asymmetric hearing but can be avoided by early provision of balanced bimodal stimulation. Although electric and acoustic stimulation differ, these inputs can work sympathetically when used bilaterally given sufficient hearing in the non-implanted ear., Graphical abstract Image 2, Highlights • Children with asymmetric hearing develop cortical preference for the better ear. • Cortical preference can be avoided by early cochlear implantation of the deaf ear. • Electrical implant stimulation can work sympathetically with acoustic hearing. • The implanted ear is preferred with poor acoustic hearing in the unimplanted ear.

The optically pumped magnetometer (OPM) is a viable means to detect magnetic fields generated by human brain activity. Compared to conventional detectors (superconducting quantum interference devices) OPMs are small, lightweight, flexible, and operate without cryogenics. This has led to a step change in instrumentation for magnetoencephalography (MEG), enabling a “wearable” scanner platform, adaptable to fit any head size, able to acquire data whilst subjects move, and offering improved data quality. Although many studies have shown the efficacy of ‘OPM-MEG’, one relatively untapped advantage relates to improved array design. Specifically, OPMs enable the simultaneous measurement of magnetic field components along multiple axes (distinct from a single radial orientation, as used in most conventional MEG systems). This enables characterisation of the magnetic field vector at all sensors, affording extra information which has the potential to improve source reconstruction. Here, we conduct a theoretical analysis of the critical parameters that should be optimised for effective source reconstruction. We show that these parameters can be optimised by judicious array design incorporating triaxial MEG measurements. Using simulations, we demonstrate how a triaxial array offers a dramatic improvement on our ability to differentiate real brain activity from sources of magnetic interference (external to the brain). Further, a triaxial system is shown to offer a marked improvement in the elimination of artefact caused by head movement. Theoretical results are supplemented by an experimental recording demonstrating improved interference reduction. These findings offer new insights into how future OPM-MEG arrays can be designed with improved performance.

High frequency oscillations (HFOs, 80–500 Hz) in invasive EEG are a biomarker for the epileptic focus. Ripples (80–250 Hz) have also been identified in non-invasive MEG, yet detection is impeded by noise, their low occurrence rates, and the workload of visual analysis. We propose a method that identifies ripples in MEG through noise reduction, beamforming and automatic detection with minimal user effort. We analysed 15 min of presurgical resting-state interictal MEG data of 25 patients with epilepsy. The MEG signal-to-noise was improved by using a cross-validation signal space separation method, and by calculating ~ 2400 beamformer-based virtual sensors in the grey matter. Ripples in these sensors were automatically detected by an algorithm optimized for MEG. A small subset of the identified ripples was visually checked. Ripple locations were compared with MEG spike dipole locations and the resection area if available. Running the automatic detection algorithm resulted in on average 905 ripples per patient, of which on average 148 ripples were visually reviewed. Reviewing took approximately 5 min per patient, and identified ripples in 16 out of 25 patients. In 14 patients the ripple locations showed good or moderate concordance with the MEG spikes. For six out of eight patients who had surgery, the ripple locations showed concordance with the resection area: 4/5 with good outcome and 2/3 with poor outcome. Automatic ripple detection in beamformer-based virtual sensors is a feasible non-invasive tool for the identification of ripples in MEG. Our method requires minimal user effort and is easily applicable in a clinical setting., Highlights • Cross-validation signal space separation and beamformer increase the SNR in MEG. • Automatic detection of MEG ripples in the time domain is feasible. • Our method identifies ripples with minimal user effort and is clinically applicable. • Automatically detected ripples are concordant with MEG spikes in 14/16 patients. • Automatically detected ripples are concordant with resection area in 6/8 patients.

Radio Frequency Interference (RFI) is a growing problem in Synthetic Aperture Radar (SAR) systems as scientific motivations push the radars to lower frequencies and as more wireless services share the frequency spectrum. New, advanced SAR instruments, such as NASA’s EcoSAR, DBSAR and DLR’s Tandem-L mission, employ a multichannel architecture capable of Digital Beamforming (DBF). Radars with DBF are capable of notching the antenna pattern in specific directions, which can be utilized to suppress RFI on board or in post-processing. A well-researched beamformer for this purpose is the Minimum Variance Distortionless Response (MVDR) Beamformer. However, the number of interferers that can be removed through notching is limited by the number of receive channels. It is therefore essential to adaptively change the antenna pattern notching throughout the image in time and frequency for the best results with a given number of receive channels. In this paper, we present several methods to achieve this notching by making use of the spatial SAR signal distribution in range time, range frequency, azimuth time and azimuth Doppler that is inherent to the SAR imaging geometry. Because this distribution is time-variable and yet predictable, it can be used to improve the angle of arrival estimation of the RFI and the adaptive notching. The presented methods can be applied to a Digital Beamforming (DBF) SAR signal with multiple channels in elevation and/or in azimuth. Simulations show that the proposed methods increase the ability to notch out-of-swath interference from multiple directions and lessen the impact on in-swath interference. The improvement of the interferometric coherence for a single-pass interferogram acquired by NASA’s EcoSAR system (capable of DBF in elevation) is demonstrated. The removal of periodic RFI artifacts is achieved.

International audience

International audience; In this paper, shaped continuous parallel plate waveguide delay lenses are proposed. The previous configurations introduced by the authors displayed a residual side lobe imbalance, showing the limitations of elliptical delay lens profiles, derived from a starting bifocal constrained lens. Polynomial profiles are proposed here as a way to enhance the scanning performance and the pattern shape. Optimized configurations demonstrate a reduction in the phase aberration levels over a large scanning range ([-30, 30]). The associated radiation patterns demonstrate lower and more balanced first side lobe levels (SLLs) ( $\cong -18$ dB), as compared to the previous elliptical approach ( $\cong -13.2$ dB). A validation has been proposed through the manufacturing and test of a prototype over the down-link Ka-band ([27.5-31] GHz). Excellent radiation performance [half-power beamwidth (HPBW), SLL] has been experimentally obtained over a wide angular range ([-31.5, 31.5]), including low scanning loss and high radiation stability over the entire frequency range. High radiation efficiencies are demonstrated with this fully metallic design, particularly suitable for space applications. The mechanical simplicity offered by the concept is also quite attractive for low-cost multi-beam platforms.

This paper presents a unified speech enhancement system to remove both background noise and interfering speech in serious noise environments by jointly utilizing the parabolic reflector model and neural beamformer. First, the amplification property of paraboloid is discussed, which significantly improves the Signal-to-Noise Ratio (SNR) of a desired signal. Therefore, an appropriate paraboloid channel is analyzed and designed through the boundary element method. On the other hand, a time-frequency masking approach and a mask-based beamforming approach are discussed and incorporated in an enhancement system. It is worth noticing that signals provided by the paraboloid and the beamformer are exactly complementary. Finally, these signals are employed in a learning-based fusion framework to further improve the system performance in low SNR environments. Experiments demonstrate that our system is effective and robust in five different noisy conditions (speech interfered with factory, pink, destroyer engine, volvo, and babble noise), as well as in different noise levels. Compared with the original noisy speech, significant average objective metrics improvements are about &Delta, STOI = 0.28, &Delta, PESQ = 1.31, &Delta, fwSegSNR = 11.9.

Objective: In presurgical evaluation of temporal lobe epilepsy (TLE), selection of the resection side is challenging when bilateral temporal epileptiform discharges or structural abnormalities are present. We aim to evaluate the lateralization value of beamformer analysis of magnetoencephalography (MEG) in TLE. Methods: MEG data from 14 TLE patients were analyzed through beamformer analysis. We measured the hemispherical power distribution of beamformer sources and calculated the lateralization index (LI). We calculated the LI at multiple frequencies to explore the frequency dependency and at the delta frequency to define laterality. LI values ranging from −1 to −0.05 indicated right hemispheric dominance. LI values ranging from 0.05 to 1 indicated left hemispheric dominance. LI values ranging from −0.05 to 0.05 defined bilaterality. We measured the power of beamformer sources with a 9-s duration to explore time dependency. Results: The beamformer analysis showed that 10/14 patients had power dominance ipsilateral to resection. The delta frequency band had a higher lateralization value than other frequency bands. A time-dependent power fluctuation was found in the delta frequency band. Conclusions: MEG beamformer analysis, especially in the delta band, might efficiently provide additional information regarding lateralization in TLE.

International audience; An analytical model based on geometrical optics is proposed to design and analyze continuous parallel plate waveguide (PPW) lens-like antennas. The proposed design is based on a transversal PPW section working as a lens-like beamformer. By simplifying the propagation inside this transversal section, a bifocal constrained lens model is first defined; it provides a relevant starting point to design the proposed beamformer. A refined model based on ray tracing and with an enhanced performance prediction is achieved by accounting the wave propagation inside the transversal cavity. The numerical analysis of phase aberrations and radiation demonstrate the performance of the proposed beamformer. The results of the ray-Tracing model are in a very good agreement with the corresponding full-wave model, while providing a significant reduction in the computational effort, making the proposed model more suitable for advanced optimization processes. © 1963-2012 IEEE.

The spatial topology of the human motor cortex has been well studied, particularly using functional Magnetic Resonance Imaging (fMRI) which allows spatial separation of haemodynamic responses arising from stimulation of different body parts, individual digits and even spatially separate areas of the same digit. However, the spatial organisation of electrophysiological responses, particularly neural oscillations (rhythmic changes in electrical potential across cellular assemblies) has been less well studied. Mapping the spatial signature of neural oscillations is possible using magnetoencephalography (MEG), however spatial differentiation of responses induced by movement of separate digits is a challenge, because the brain regions involved are separated by only a few millimetres. In this paper we first show, in simulation, how to optimise experimental design and beamformer spatial filtering techniques to increase the spatial specificity of MEG derived functional images. Combining this result with experimental data, we then capture the organisation of the post-movement beta band (13–30 Hz) oscillatory response to movement of digits 2 and 5 of the dominant hand, in individual subjects. By comparing these MEG results to ultra-high field (7T) fMRI, we also show significant spatial agreement between beta modulation and the blood oxygenation level dependent (BOLD) response. Our results show that, when using an optimised inverse solution and controlling subject movement (using custom fitted foam padding) the spatial resolution of MEG can be of order 3–5 mm. The method described offers exciting potential to understand better the cortical organisation of oscillations, and to probe such organisation in patient populations where those oscillations are known to be abnormal., Highlights • Aim is to map the topological organisation of neural oscillations in motor cortex. • MEG spatial resolution optimised by temporal separation of sources. • Subject motion controlled using foam headcasts. • Cortical representation of Digit 2 and Digit 5 separated spatially. • Post movement beta rebound maps motortopically in agreement with BOLD responses.

Background Point of care ultrasonography has been the focus of extensive research over the past few decades. Miniaturised, wireless systems have been envisaged for new application areas, such as capsule endoscopy, implantable ultrasound and wearable ultrasound. The hardware constraints of such small-scale systems are severe, and tradeoffs between power consumption, size, data bandwidth and cost must be carefully balanced. Methods In this work, two receiver architectures are proposed and compared to address these challenges. Both architectures uniquely combine low-rate sampling with synthetic aperture beamforming to reduce the data bandwidth and system complexity. The first architecture involves the use of quadrature sampling to minimise the signal bandwidth and computational load. Synthetic aperture beamforming (SAB) is carried out using a single-channel, pipelined protocol suitable for implementation on an FPGA/ASIC. The second architecture employs compressive sensing within the finite rate of innovation framework to further reduce the bandwidth. Low-rate signals are transmitted to a computational back-end (computer), which sequentially reconstructs each signal and carries out beamforming. Results Both architectures were tested using a custom hardware front-end and synthetic aperture database to yield B-mode images. The normalised root-mean-squared-error between the quadrature SAB image and the RF reference image was \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$13\%$$\end{document}13% while the compressive SAB error was \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$22\%$$\end{document}22% for the same degree of spatial compounding. The sampling rate is reduced by a factor of 2 (quadrature SAB) and 4.7 (compressive SAB), compared to the RF sampling rate. The quadrature method is implemented on FPGA, with a total power consumption of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$4.1 $$\end{document}4.1 mW, which is comparable to state-of-the-art hardware topologies, but with significantly reduced circuit area. Conclusions Through a novel combination of SAB and low-rate sampling techniques, the proposed architectures achieve a significant reduction in data transmission rate, system complexity and digital/analogue circuit area. This allows for aggressive miniaturisation of the imaging front-end in portable imaging applications.

Magnetoencephalography (MEG) captures the magnetic fields generated by neuronal current sources with sensors outside the head. In MEG analysis these current sources are estimated from the measured data to identify the locations and time courses of neural activity. Since there is no unique solution to this so-called inverse problem, multiple source estimation techniques have been developed. The nulling beamformer (NB), a modified form of the linearly constrained minimum variance (LCMV) beamformer, is specifically used in the process of inferring interregional interactions and is designed to eliminate shared signal contributions, or cross-talk, between regions of interest (ROIs) that would otherwise interfere with the connectivity analyses. The nulling beamformer applies the truncated singular value decomposition (TSVD) to remove small signal contributions from a ROI to the sensor signals. However, ROIs with strong crosstalk will have high separating power in the weaker components, which may be removed by the TSVD operation. To address this issue we propose a new method, the nulling beamformer with subspace suppression (NBSS). This method, controlled by a tuning parameter, reweights the singular values of the gain matrix mapping from source to sensor space such that components with high overlap are reduced. By doing so, we are able to measure signals between nearby source locations with limited cross-talk interference, allowing for reliable cortical connectivity analysis between them. In two simulations, we demonstrated that NBSS reduces cross-talk while retaining ROIs' signal power, and has higher separating power than both the minimum norm estimate (MNE) and the nulling beamformer without subspace suppression. We also showed that NBSS successfully localized the auditory M100 event-related field in primary auditory cortex, measured from a subject undergoing an auditory localizer task, and suppressed cross-talk in a nearby region in the superior temporal sulcus.

Linked pairs of hearing aids offer various possibilities for directional processing providing adjustable trade-off between improving signal-to-noise ratio and preserving binaural listening. The benefit depends on the processing scheme, the acoustic scenario, and the listener’s ability to exploit binaural cues. Neher et al. (2017) investigated candidacy for different bilateral processing schemes for 20 elderly listeners with symmetric and 19 age-matched listeners with asymmetric hearing thresholds below 2 kHz. The acoustic scenarios consisted of a frontal target talker presented against two intelligible or unintelligible speech maskers from ±60° azimuth. In this study, the SRT data were compared to predictions of the binaural speech intelligibility model (BSIM, Beutelmann et al., 2010), which was used to model pure better-ear-glimpsing as well as additional binaural unmasking. The speech intelligibility index (SII), which served as backend of BSIM, was calibrated to an individual reference value at the SRT for each listener. This reference value mirrors the amount of acoustical information needed by the listener to achieve the SRT and correlated with the listeners’ ability to process temporal fine structure. BSIM revealed a benefit due to binaural processing in well-performing listeners when processing provided low-frequency interaural timing cues.

International audience; This paper proposes a comparison between two optimization procedures for the design of continuous parallel plate waveguide multiple beam lens-like antennas. A phase-only approach is first considered and the design is analyzed in terms of angular scanning performances. A pattern-based optimization is then described, taking into account both phase and amplitude effects on the outer lens contour. Comparisons between the procedures are finally provided leading to conclusions on the potential of the proposed beamformer concept. © 2018 Institution of Engineering and Technology.All Rights Reserved.

Millimeter wave systems offer high date rate due to huge bandwidth but suffers from poor link budget. This is due to the blockage of the millimeter wave signal by the obstacles of size comparable to that of the wavelength of the signal. Various analysis in improving the signal strength is reported. One of them suggests use of directional antenna which guarantees signal delivery if line of sight communication between the transmitter and receiver exists. The other alternative scheme is Multi Input Multi Output (MIMO) beamforming that uses the channel statistics to steer the beam thereby improving the multiplexing gain and beamforming gain. In this paper, extensive research work carried out by us in MMW MIMO at 60 GHz covering aspects related to MIMO fixed-beam, adaptive beam and multibeam beamformers addressing line-of-sight and non-line-of-sight channel for MMW 60 GHz system is reviewed.

Beamformers are a widely-used tool in brain analysis with magnetoencephalography (MEG) and electroencephalography (EEG). For the construction of the beamformer filters realistic head volume conductor modeling is necessary for accurately computing the EEG and MEG leadfields, i.e., for solving the EEG and MEG forward problem. In this work, we investigate the influence of including realistic head tissue compartments into a finite element method (FEM) model on the beamformer's localization ability. Specifically, we investigate the effect of including cerebrospinal fluid, gray matter, and white matter distinction, as well as segmenting the skull bone into compacta and spongiosa, and modeling white matter anisotropy. We simulate an interictal epileptic measurement with white sensor noise. Beamformer filters are constructed with unit gain, unit array gain, and unit noise gain constraint. Beamformer source positions are determined by evaluating power and excess sample kurtosis (g2) of the source-waveforms at all source space nodes. For both modalities, we see a strong effect of modeling the cerebrospinal fluid and white and gray matter. Depending on the source position, both effects can each be in the magnitude of centimeters, rendering their modeling necessary for successful localization. Precise skull modeling mainly effected the EEG up to a few millimeters, while both modalities could profit from modeling white matter anisotropy to a smaller extent of 5–10 mm. The unit noise gain or neural activity index beamformer behaves similarly to the array gain beamformer when noise strength is sufficiently high. Variance localization seems more robust against modeling errors than kurtosis.

International audience; This paper presents the description and analysis of a continuous parallel plate waveguide (PPW) lens-like beamformer. The main design parameters of the continuous delay lens are defined starting from an ideal bifocal constrained lens. A dedicated ray tracing analysis tool is developed to better describe propagation effects in the delay lens and provide more insight on phase aberrations versus pointing angle. Numerical results of a specific design at Ku-band are reported by comparing radiation patterns obtained with the ray tracing tool and a full-wave method. These results are also compared to the ideal bifocal constrained lens design. © 2017 Euraap.

This study examined differences in benefit from bilateral directional processing. Groups of listeners with symmetric or asymmetric audiograms 2 dB profited more from low-frequency binaural cues than from greater SNR improvement, while for smaller BILDs the opposite was true. Audiometric asymmetry reduced the BILD influence. In spatially diffuse noise, the maximal SNR improvement was beneficial. Moreover, binaural tone-in-noise detection performance (N0Sπ threshold) at 500 Hz predicted the benefit from low-frequency binaural cues effectively. These results provide a basis for adapting bilateral directional processing to the user and the scenario.

We propose source-space independent component analysis (ICA) for separation, tomography, and time-course reconstruction of EEG and MEG source signals. Source-space ICA is based on the application of singular value decomposition and ICA on the neuroelectrical signals from all brain voxels obtained post minimum-variance beamforming of sensor-space EEG or MEG. We describe the theoretical background and equations, then evaluate the performance of this technique in several different situations, including weak sources, bilateral correlated sources, multiple sources, and cluster sources. In this approach, tomographic maps of sources are obtained by back-projection of the ICA mixing coefficients into the source-space (3-D brain template). The advantages of source-space ICA over the popular alternative approaches of sensor-space ICA together with dipole fitting and power mapping via minimum-variance beamforming are demonstrated. Simulated EEG data were produced by forward head modeling to project the simulated sources onto scalp sensors, then superimposed on real EEG background. To illustrate the application of source-space ICA to real EEG source reconstruction, we show the localization and time-course reconstruction of visual evoked potentials. Source-space ICA is superior to the minimum-variance beamforming in the reconstruction of multiple weak and strong sources, as ICA allows weak sources to be identified and reconstructed in the presence of stronger sources. Source-space ICA is also superior to sensor-space ICA on accuracy of localization of sources, as source-space ICA applies ICA to the time-courses of voxels reconstructed from minimum-variance beamforming on a 3D scanning grid and these time-courses are optimally unmixed via the beamformer. Each component identified by source-space ICA has its own tomographic map which shows the extent to which each voxel has contributed to that component.

A beamforming device for a 5×5-element subarray of receiving phased antenna array of new GURT radio telescope designed to operate within 10 − 70 MHz is presented. The device is composed of six identical units. Each unit contains equal-arm 5:1 combiner with connected to its arms discrete phase shifters based on time delay lines switching principle. Five of these units combine the signals of array elements inside rows of the subarray, whereas the sixth one assembles the combined signals of subarray rows. Operation principle of beamforming unit is described, the results of its computer modeling and performance measurement results are given. The time-delay lines manufacturing errors influence on subarray power parameters is estimated, as well as their fabrication tolerance found. Key words: phase changer, beamformer, phased array, radio-telescope Manuscript submitted 24.04.2014 Radio phys. radio astron. 2014, 19(3): 240-248 REFERENCES 1. KONOVALENKO, A. A., 2005. Low-Frequency Radio Astronomy Prospects. Radio Phys. Radio Astron . vol. 10, special issue, pp. S86–S114 (in Russian) 2. MYLOSTNA, K. Y. and ZAKHARENKO, V. V., 2013.Search and Study of Storm Activity on Saturn and Other Planets of the Solar System. Radio Phys. Radio Astron . vol. 18, no. 1, pp. 12–25 (in Russian). 3. DE VOS, M., GUNST, A. W., and NIJBOER, R., 2009.The LOFAR Telescope: System Architecture and Signal Processing. IEEE Proc. vol. 97, Is. 8, pp. 1431–1437. DOI: https://doi.org/10.1109/JPROC.2009.2020509Source 4. ELLINGSON, S. W., CLARKE, T. E., COHEN, A., CRAIG, J., KASSIM, N. E., PIHLSTROM, Y., RICKARD, L. J., and TAYLOR, G. B., 2009. The Long Wavelength Array. IEEE Proc . vol. 97, is. 8, pp. 1421–1430. DOI: https://doi.org/10.1109/JPROC.2009.2015683 5. GIRARD, J. N., ZARKA, P., TAGGER, M., DENIS, L., CHARRIER, D.,KONOVALENKO, A. A., and BOONE, F., 2012. Antenna design and distribution of the LOFAR super station. Comptes Rendus Physique . vol. 13, Is. 1, pp. 33–37. 6. DEWDNEY, P. E., HALL, P. J., SCHILIZZI, R. T., and LAZIO, T. J. L. W., 2009. The Square Kilometre Array. IEEE Proc . vol. 97, is. 8, pp. 1482–1496 7. KONOVALENKO, A. A., FALKOVICH, I. S., GRIDIN, A. A., TOKARSKY, P. L., and YERIN, S. N., 2012. UWB active antenna array for low frequency radio astronomy. In: Proc. of the VI-thIntern. Conf. on Ultrawide band and Ultrashort Impulse Signals (UWBUSIS'12). Sevastopol (Ukraine). pp. 39–43. DOI: https://doi.org/10.1109/UWBUSIS.2012.6379725 8. BRUCK, Y. M. and INYUTIN, G. A., 1978. Binary digital delay line (phase shifters) for electrically controlled broadband antenna. In: Anteny . Moscow, USSR: Svyaz' Publ., no. 26, pp. 107–121 (in Russian). 9. BRAUDE, S. Y., MEGN, A. V. and SODIN, L. G., 1978. Decameter wave band radio telescope UTR-2. In: Anteny . Moscow, USSR: Svyaz' Publ. no. 26, pp. 3–15 (in Russian). 10. FALKOVICH, I. S., KONOVALENKO, A. A., GRIDIN,A. A., SODIN, L. G., BUBNOV, I. N., KALINI CHENKO, N. N., RASHKOVSKII, S. L., MUKHA, D. V.and TOKARSKY, P. L., 2011. Wide-band high linearity active dipole for low frequency radio astronomy. Exp. Astron .vol. 32, is. 2, pp. 127–145. DOI: https://doi.org/10.1007/s10686-011-9256-z 11. VOSKRESENSKII, D. I., STEPANENKO, V. S., and FILIPPOV, V. S. Microwave devices and antennas. Designing phased arrays . Moscow: Radiotekhnika Publ. (in Russian). 12. Surface-mounting, 1-GHz-Band / 3-GHz-Band, Miniature, DPDT, High-frequency Relay datasheet [online]. Available from:www.omron.com/ecb/products/pdf/en-g6k_2f_rf.pdf. 13. Surface Mount Power Splitter/Combiner SCP-5-1 datasheet [online]. Available from: www.minicircuits.com/pdfs/SCP-5-1.pdf. 14. SHIFRIN, Ya. S., 1970. Questions of statistical antenna theory. Moscow: Sov. radio. Publ. (in Russian). 15. INDENBOM, M. V., 2008. Fluctuations of the directivity pattern of the antenna array for output. Anteny , no. 4, pp. 40–46. 16. MERKULOV, V. V., 1966. By the estimation of emitters CPV system with phase and amplitude distortion. Radiotechnika i elektronika , vol. 11, no. 11, pp. 2066–2069. 17. STEBLIN, V. I. and KLASSEN, V. I., 1981. The method of analysis of statistical characteristics of CPV phased array antenna with random amplitudes and phases of the location of radiators. Radiotechnika i elektronika , vol. 26, no. 3, pp. 524–531. 18. SHIFRIN, Ya. S. and KORNIENKO, L. G., 2000. Statistics field antenna arrays. Anteny , no. 1, pp. 3-26. 19. SAZONOV, D. M., GRIDIN, A. N., and MISHUSTIN, B. A., 1981. Microwave devices . Moscow: Vyshchaya shkola Publ. (in Russian).

In medical field, two-dimension ultrasound images are widely used in clinical diagnosis. Beamformer is critical in determining the complexity and performance of an ultrasound imaging system. Different from traditional means implemented with separated chips, a compact beamformer with 64 effective channels in a single moderate Field Programmable Gate Array has been presented in this paper. The compactness is acquired by employing receive synthetic aperture, harmonic imaging, time sharing and linear interpolation. Besides that, multi-beams method is used to improve the frame rate of the ultrasound imaging system. Online dynamic configuration is employed to expand system’s flexibility to two kinds of transducers with multi-scanning modes. The design is verified on a prototype scanner board. Simulation results have shown that on-chip memories can be saved and the frame rate can be improved on the case of 64 effective channels which will meet the requirement of real-time application.

We present a wavelength-dependent optical true time delay (TTD) for K-band radio beamformer targeting home-satellite communication. A proof-of-concept of optically-assisted radio beamformer with a TTD bandwidth of 2GHz is experimentally demonstrated. The beamformer is capable of generating multiple radio beams if multiple wavelengths are employed.

Contrast degradation is a critical problem in ultrasound plane wave imaging (PWI) resulting from signals leakage from the sidelobes. An ideal sidelobe reduction method may enhance the contrast without remarkably increasing computational load. To this end, we introduce a new singular value decomposition (SVD) sidelobe reduction beamformer for coherent plane wave compounding (CPWC) based on a previous work. The SVD takes advantage of the benefits of the different features of the mainlobe and sibelobe in terms of spatio-angular coherence and removes the sidelobes before the final coherent summation. This SVD-based method provides a three-dimensional approach (2D in the space and 1D in the angle) while the computation load is kept satisfactory by a dimension-reduced operation before the SVD. To directly observe the sidelobe level, we demonstrate the performance of our SVD method with a point spread function (PSF) simulation. Compared to CPWC, our method shows a 6.2 dB reduction in the peak sidelobe level (PSL). We also applied our method to the anechoic cyst inside the speckle for the imaging contrast. Both in the simulation and phantom studies, our method enhances the contrast-to-noise ratio (CNR) by more than 10%. Therefore, this new beamformer can be an efficient way to suppress sidelobes in PWI.