A robust sequential hypothesis testing method for brake squeal localisation

This contribution deals with the in situ detection and localisation of brake squeal in an automobile. As brake squeal is emitted from regions known a priori, i.e., near the wheels, the localisation is treated as a hypothesis testing problem. Distributed microphone arrays, situated under the automobile, are used to capture the directional properties of the sound field generated by a squealing brake. The spatial characteristics of the sampled sound field is then used to formulate the hypothesis tests. However, in contrast to standard hypothesis testing approaches of this kind, the propagation environment is complex and time-varying. Coupled with inaccuracies in the knowledge of the sensor and source positions as well as sensor gain mismatches, modelling the sound field is difficult and standard approaches fail in this case. A previously proposed approach implicitly tried to account for such incomplete system knowledge and was based on ad hoc likelihood formulations. The current paper builds upon this approach and proposes a second approach, based on more solid theoretical foundations, that can systematically account for the model uncertainties. Results from tests in a real setting show that the proposed approach is more consistent than the prior state-of-the-art. In both approaches, the tasks of detection and localisation are decoupled for complexity reasons. The localisation (hypothesis testing) is subject to a prior detection of brake squeal and identification of the squeal frequencies. The approaches used for the detection and identification of squeal frequencies are also presented. The paper, further, briefly addresses some practical issues related to array design and placement. (C) 2019 Author(s)

Use of the Wavelet Transform for Interference Detection and Mitigation in Global Navigation Satellite Systems

Radio frequency interference detection and mitigation are becoming of paramount importance due to the increasing number of services and applications based on the position obtained by means of Global Navigation Satellite Systems. A way to cope with such threats is the implementation in the receiver of advanced signal processing algorithm able to raise proper warning or improve the receiver performance. In this paper, we propose a method based on the Wavelet Transform able to split the useful signal from the interfering component in a transformed domain. The wavelet packet decomposition and proper statistical thresholds allow the algorithm to show very good performance in case of multiple pulse interference as well as in the case of narrowband interference, two scenarios in which traditional countermeasures might not be effective

EXPERIMENTAL EVALUATION OF MODIFIED PHASE TRANSFORM FOR SOUND SOURCE DETECTION

The detection of sound sources with microphone arrays can be enhanced through processing individual microphone signals prior to the delay and sum operation. One method in particular, the Phase Transform (PHAT) has demonstrated improvement in sound source location images, especially in reverberant and noisy environments. Recent work proposed a modification to the PHAT transform that allows varying degrees of spectral whitening through a single parameter, andamp;acirc;, which has shown positive improvement in target detection in simulation results. This work focuses on experimental evaluation of the modified SRP-PHAT algorithm. Performance results are computed from actual experimental setup of an 8-element perimeter array with a receiver operating characteristic (ROC) analysis for detecting sound sources. The results verified simulation results of PHAT- andamp;acirc; in improving target detection probabilities. The ROC analysis demonstrated the relationships between various target types (narrowband and broadband), room reverberation levels (high and low) and noise levels (different SNR) with respect to optimal andamp;acirc;. Results from experiment strongly agree with those of simulations on the effect of PHAT in significantly improving detection performance for narrowband and broadband signals especially at low SNR and in the presence of high levels of reverberation

Acoustic Solutions for Door Station

This thesis investigates how the audio quality in a door station can be improved by using multiple microphones and implementing beamforming. The concept of beamforming is explained, and two beamforming algorithms are implemented. These are tested with different microphone configurations in both simulated and real environments. Three already implemented solutions for single microphones are also tested. The performance of different microphone configurations is analysed, and the beamforming algorithms are compared to the single microphone solutions. Finally a solution for the application is proposed

Virtual PLC Lab Enabled Physical Layer Improvement Proposals for PRIME and G3-PLC Standards

Narrowband (NB) powerline communication (PLC) is extensively adopted by utilities for the communication in advanced metering infrastructure (AMI) systems. PLC technology needs to overcome channel disturbances present in certain grid segments. This study analyzes improvement proposals of the physical layer of the main narrowband PLC technologies approved by international communication organizations that are currently deployed in Europe: Powerline Intelligent Metering Evolution (PRIME) 1.3.6, PRIME 1.4, and G3-PLC, in order to improve PLC performance under channel disturbances. This thorough study is based on simulations carried out by an innovative ad hoc Virtual PLC Lab, developed by the authors, applied in replicable, fully-automated, and cost reduced test scenarios. The analysis is performed by applying standardized test methods and metrics, and by evaluating the influence of a set of representative channel disturbances defined by the European Telecommunications Standards Institute (ETSI) and selected noises generated by distributed energy resources (DER) in normal operation. PLC performance improvements in terms of equalizer curve fitting, error correction codes, and noisy subcarrier suppression mechanisms are presented. The performance gain due to each physical improvement proposal is accurately measured and compared under the same conditions in a replicable and automated test environment in order to evaluate the use of the proposals in the evolution of future PLC technologies.This work was financially supported in part by the Basque Government under the grant numbers Elkartek KK-2018/00037 and IT1234-19, and by the Spanish Government under the grant RTI2018-099162-B-I00 (MCIU/AEI/FEDER, UE)

Digitally-Enhanced Software-Defined Radio Receiver Robust to Out-of-Band Interference

A software-defined radio (SDR) receiver with improved robustness to out-of-band interference (OBI) is presented. Two main challenges are identified for an OBI-robust SDR receiver: out-of-band nonlinearity and harmonic mixing. Voltage gain at RF is avoided, and instead realized at baseband in combination with low-pass filtering to mitigate blockers and improve out-of-band IIP3. Two alternative “iterative” harmonic-rejection (HR) techniques are presented to achieve high HR robust to mismatch: a) an analog two-stage polyphase HR concept, which enhances the HR to more than 60 dB; b) a digital adaptive interference cancelling (AIC) technique, which can suppress one dominating harmonic by at least 80 dB. An accurate multiphase clock generator is presented for a mismatch-robust HR. A proof-of-concept receiver is implemented in 65 nm CMOS. Measurements show 34 dB gain, 4 dB NF, and 3.5 dBm in-band IIP3 while the out-of-band IIP3 is + 16 dBm without fine tuning. The measured RF bandwidth is up to 6 GHz and the 8-phase LO works up to 0.9 GHz (master clock up to 7.2 GHz). At 0.8 GHz LO, the analog two-stage polyphase HR achieves a second to sixth order HR > dB over 40 chips, while the digital AIC technique achieves HR > 80 dB for the dominating harmonic. The total power consumption is 50 mA from a 1.2 V supply

Ultra Wideband Communications: from Analog to Digital

Ultrabreitband-Signale (Ultra Wideband [UWB]) können einen signifikanten Nutzen im Bereich drahtloser Kommunikationssysteme haben. Es sind jedoch noch einige Probleme offen, die durch Systemdesigner und Wissenschaftler gelöst werden müssen. Ein Funknetzsystem mit einer derart großen Bandbreite ist normalerweise auch durch eine große Anzahl an Mehrwegekomponenten mit jeweils verschiedenen Pfadamplituden gekennzeichnet. Daher ist es schwierig, die zeitlich verteilte Energie effektiv zu erfassen. Außerdem ist in vielen Fällen der naheliegende Ansatz, ein kohärenter Empfänger im Sinne eines signalangepassten Filters oder eines Korrelators, nicht unbedingt die beste Wahl. In der vorliegenden Arbeit wird dabei auf die bestehende Problematik und weitere Lösungsmöglichkeiten eingegangen. Im ersten Abschnitt geht es um „Impulse Radio UWB”-Systeme mit niedriger Datenrate. Bei diesen Systemen kommt ein inkohärenter Empfänger zum Einsatz. Inkohärente Signaldetektion stellt insofern einen vielversprechenden Ansatz dar, als das damit aufwandsgünstige und robuste Implementierungen möglich sind. Dies trifft vor allem in Anwendungsfällen wie den von drahtlosen Sensornetzen zu, wo preiswerte Geräte mit langer Batterielaufzeit nötigsind. Dies verringert den für die Kanalschätzung und die Synchronisation nötigen Aufwand, was jedoch auf Kosten der Leistungseffizienz geht und eine erhöhte Störempfindlichkeit gegenüber Interferenz (z.B. Interferenz durch mehrere Nutzer oder schmalbandige Interferenz) zur Folge hat. Um die Bitfehlerrate der oben genannten Verfahren zu bestimmen, wurde zunächst ein inkohärenter Combining-Verlust spezifiziert, welcher auftritt im Gegensatz zu kohärenter Detektion mit Maximum Ratio Multipath Combining. Dieser Verlust hängt von dem Produkt aus der Länge des Integrationsfensters und der Signalbandbreite ab. Um den Verlust durch inkohärentes Combining zu reduzieren und somit die Leistungseffizienz des Empfängers zu steigern, werden verbesserte Combining-Methoden für Mehrwegeempfang vorgeschlagen. Ein analoger Empfänger, bei dem der Hauptteil des Mehrwege-Combinings durch einen „Integrate and Dump”-Filter implementiert ist, wird für UWB-Systeme mit Zeit-Hopping gezeigt. Dabei wurde die Einsatzmöglichkeit von dünn besetzten Codes in solchen System diskutiert und bewertet. Des Weiteren wird eine Regel für die Code-Auswahl vorgestellt, welche die Stabilität des Systems gegen Mehrnutzer-Störungen sicherstellt und gleichzeitig den Verlust durch inkohärentes Combining verringert. Danach liegt der Fokus auf digitalen Lösungen bei inkohärenter Demodulation. Im Vergleich zum Analogempfänger besitzt ein Digitalempfänger einen Analog-Digital-Wandler im Zeitbereich gefolgt von einem digitalen Optimalfilter. Der digitale Optimalfilter dekodiert den Mehrfachzugriffscode kohärent und beschränkt das inkohärente Combining auf die empfangenen Mehrwegekomponenten im Digitalbereich. Es kommt ein schneller Analog-Digital-Wandler mit geringer Auflösung zum Einsatz, um einen vertretbaren Energieverbrauch zu gewährleisten. Diese Digitaltechnik macht den Einsatz langer Analogverzögerungen bei differentieller Demodulation unnötig und ermöglicht viele Arten der digitalen Signalverarbeitung. Im Vergleich zur Analogtechnik reduziert sie nicht nur den inkohärenten Combining-Verlust, sonder zeigt auch eine stärkere Resistenz gegenüber Störungen. Dabei werden die Auswirkungen der Auflösung und der Abtastrate der Analog-Digital-Umsetzung analysiert. Die Resultate zeigen, dass die verminderte Effizienz solcher Analog-Digital-Wandler gering ausfällt. Weiterhin zeigt sich, dass im Falle starker Mehrnutzerinterferenz sogar eine Verbesserung der Ergebnisse zu beobachten ist. Die vorgeschlagenen Design-Regeln spezifizieren die Anwendung der Analog-Digital-Wandler und die Auswahl der Systemparameter in Abhängigkeit der verwendeten Mehrfachzugriffscodes und der Modulationsart. Wir zeigen, wie unter Anwendung erweiterter Modulationsverfahren die Leistungseffizienz verbessert werden kann und schlagen ein Verfahren zur Unterdrückung schmalbandiger Störer vor, welches auf Soft Limiting aufbaut. Durch die Untersuchungen und Ergebnissen zeigt sich, dass inkohärente Empfänger in UWB-Kommunikationssystemen mit niedriger Datenrate ein großes Potential aufweisen. Außerdem wird die Auswahl der benutzbaren Bandbreite untersucht, um einen Kompromiss zwischen inkohärentem Combining-Verlust und Stabilität gegenüber langsamen Schwund zu erreichen. Dadurch wurde ein neues Konzept für UWB-Systeme erarbeitet: wahlweise kohärente oder inkohärente Empfänger, welche als UWB-Systeme Frequenz-Hopping nutzen. Der wesentliche Vorteil hiervon liegt darin, dass die Bandbreite im Basisband sich deutlich verringert. Mithin ermöglicht dies einfach zu realisierende digitale Signalverarbeitungstechnik mit kostengünstigen Analog-Digital-Wandlern. Dies stellt eine neue Epoche in der Forschung im Bereich drahtloser Sensorfunknetze dar. Der Schwerpunkt des zweiten Abschnitts stellt adaptiven Signalverarbeitung für hohe Datenraten mit „Direct Sequence”-UWB-Systemen in den Vordergrund. In solchen Systemen entstehen, wegen der großen Anzahl der empfangenen Mehrwegekomponenten, starke Inter- bzw. Intrasymbolinterferenzen. Außerdem kann die Funktionalität des Systems durch Mehrnutzerinterferenz und Schmalbandstörungen deutlich beeinflusst werden. Um sie zu eliminieren, wird die „Widely Linear”-Rangreduzierung benutzt. Dabei verbessert die Rangreduzierungsmethode das Konvergenzverhalten, besonders wenn der gegebene Vektor eine sehr große Anzahl an Abtastwerten beinhaltet (in Folge hoher einer Abtastrate). Zusätzlich kann das System durch die Anwendung der R-linearen Verarbeitung die Statistik zweiter Ordnung des nicht-zirkularen Signals vollständig ausnutzen, was sich in verbesserten Schätzergebnissen widerspiegelt. Allgemeine kann die Methode der „Widely Linear”-Rangreduzierung auch in andern Bereichen angewendet werden, z.B. in „Direct Sequence”-Codemultiplexverfahren (DS-CDMA), im MIMO-Bereich, im Global System for Mobile Communications (GSM) und beim Beamforming.The aim of this thesis is to investigate key issues encountered in the design of transmission schemes and receiving techniques for Ultra Wideband (UWB) communication systems. Based on different data rate applications, this work is divided into two parts, where energy efficient and robust physical layer solutions are proposed, respectively. Due to a huge bandwidth of UWB signals, a considerable amount of multipath arrivals with various path gains is resolvable at the receiver. For low data rate impulse radio UWB systems, suboptimal non-coherent detection is a simple way to effectively capture the multipath energy. Feasible techniques that increase the power efficiency and the interference robustness of non-coherent detection need to be investigated. For high data rate direct sequence UWB systems, a large number of multipath arrivals results in severe inter-/intra-symbol interference. Additionally, the system performance may also be deteriorated by multi-user interference and narrowband interference. It is necessary to develop advanced signal processing techniques at the receiver to suppress these interferences. Part I of this thesis deals with the co-design of signaling schemes and receiver architectures in low data rate impulse radio UWB systems based on non-coherent detection.● We analyze the bit error rate performance of non-coherent detection and characterize a non-coherent combining loss, i.e., a performance penalty with respect to coherent detection with maximum ratio multipath combining. The thorough analysis of this loss is very helpful for the design of transmission schemes and receive techniques innon-coherent UWB communication systems.● We propose to use optical orthogonal codes in a time hopping impulse radio UWB system based on an analog non-coherent receiver. The “analog” means that the major part of the multipath combining is implemented by an integrate and dump filter. The introduced semi-analytical method can help us to easily select the time hopping codes to ensure the robustness against the multi-user interference and meanwhile to alleviate the non-coherent combining loss.● The main contribution of Part I is the proposal of applying fully digital solutions in non-coherent detection. The proposed digital non-coherent receiver is based on a time domain analog-to-digital converter, which has a high speed but a very low resolution to maintain a reasonable power consumption. Compared to its analog counterpart, itnot only significantly reduces the non-coherent combining loss but also offers a higher interference robustness. In particular, the one-bit receiver can effectively suppress strong multi-user interference and is thus advantageous in separating simultaneously operating piconets.The fully digital solutions overcome the difficulty of implementing long analog delay lines and make differential UWB detection possible. They also facilitate the development of various digital signal processing techniques such as multi-user detection and non-coherent multipath combining methods as well as the use of advanced modulationschemes (e.g., M-ary Walsh modulation).● Furthermore, we present a novel impulse radio UWB system based on frequency hopping, where both coherent and non-coherent receivers can be adopted. The key advantage is that the baseband bandwidth can be considerably reduced (e.g., lower than 500 MHz), which enables low-complexity implementation of the fully digital solutions. It opens up various research activities in the application field of wireless sensor networks. Part II of this thesis proposes adaptive widely linear reduced-rank techniques to suppress interferences for high data rate direct sequence UWB systems, where second-order non-circular signals are used. The reduced-rank techniques are designed to improve the convergence performance and the interference robustness especially when the received vector contains a large number of samples (due to a high sampling rate in UWB systems). The widely linear processing takes full advantage of the second-order statistics of the non-circular signals and enhances the estimation performance. The generic widely linear reduced-rank concept also has a great potential in the applications of other systems such as Direct Sequence Code Division Multiple Access (DS-CDMA), Multiple Input Multiple Output (MIMO) system, and Global System for Mobile Communications (GSM), or in other areas such as beamforming

Exploring, tailoring, and traversing the solution landscape of a phase-shaped CARS process

Pulse shaping techniques are used to improve the selectivity of broadband CARS experiments, and to reject the overwhelming background. Knowledge about the fitness landscape and the capability of tailoring it is crucial for both fundamental insight and performing an efficient optimization of phase shapes. We use an evolutionary algorithm to find the optimal spectral phase of the broadband pump and probe beams in a background-suppressed shaped CARS process. We then investigate the shapes, symmetries, and topologies of the landscape contour lines around the optimal solution and also around the point corresponding to zero phase. We demonstrate the significance of the employed phase bases in achieving convex contour lines, suppressed local optima, and high optimization fitness with a few (and even a single) optimization parameter

Interference Suppression for Spread Spectrum Signals Using Adaptive Beamforming and Adaptive Temporal Filter

Interference and jamming signals are a serious concern in an operational military communication environment. This thesis examines the utility and performance of combining adaptive temporal filtering with adaptive spatial filtering (i.e. adaptive beamforming) to improve the signal-to-jammer ratio (SJR) in the presence of narrowband and wideband interference. Adaptive temporal filters are used for narrowband interference suppression while adaptive beamforming is used to suppress wideband interference signals. A procedure is presented for the design and implementation of a linear constraints minimum variance generalized sidelobe canceler (LCMV-GSC) beamformer. The adaptive beamformer processes the desired signal with unity gain while simultaneously and adaptively minimizing the output due to any undesired signal. Using the LCMV-GSC beamformer with a least mean squares (LMS) adaptive algorithm, it was shown that the tapped delay line (TDL) adaptive antenna array is more effective for the suppression of wideband jammer suppression than the linear array sensors (LAS) adaptive antenna array. Also a new technique for adaptive beamforming is presented which improves wideband interference suppression in a frequency-hopped environment. The output SJR improvement for the new technique compared to the conventional technique is as much as 15dB. Sometimes, multipath signals and jammers generated by a smart enemy are correlated with the desired signal which destroys the traditional beamformer\u27s performance. After performing a spatial smoothing technique, adaptive beamforming can also be effective in suppressing the jamming signals that are highly correlated with the desired signal