Multi-point Security by a Multiplatform-compatible Multifunctional Authentication and Encryption Board

Securing the access in networks is a first-order concern that only gains importance with the advent of Internet of Things (IoT). In this paper, a security system is presented for password-free access over the secured link. It makes the connection faster than manual authentication and facilitates Machine-to-Machine (M2M) secure interactions, as required for IoT. The authentication procedure includes the exchange of certificate and challenge/response pairs, which are stored and computed in an external security coprocessor. The system enforces the authentication protocol, includes error detection, and handles multiple devices according to their Operating Systems (OS) through their connections/ disconnections. It also performs encryption, if necessary. It is applicable on application level for devices, including IoT based devices, sensors, Android, and iOS-based smartphones. The devices that have the correct certificate and can solve the challenge can connect to the network linked with the security system. The system security is hardened because the sensitive authentication elements such as keys, certificates, and challenge responses are invisible to users and are exchanged only using strong hashing algorithms that are irreversible. The proposed hardware security system can augment any supporting network, converting the entire insecure network into a secured one, as well as retrofit existing insecure Bluetooth devices for secure access. The system incurs low overhead in time and energy by performing security operations in an ASIC coprocessor, and can be shared to secure access to multiple devices, which reduces both energy and cost

Design, realisation and evaluation of a liquid hollow torso phantom appropriate for wearable antenna assessment

This paper examines the design, realization and evaluation of a lightweight and low cost hollow oval cross-section torso phantom appropriate for wearable antenna performance assessment. The phantom consists of an empty inner space (hollow) surrounded by a shell with double plastic walls between which there is a tissue simulating liquid. The phantom’s plastic shell is made of a low loss cast acrylic and the liquid is a commercially available one with properties calibrated for the frequency range of 2 - 6 GHz. The proposed phantom is compared, through simulations, with a full liquid torso phantom and a heterogeneous anthropomorphic voxel phantom. Additionally, the fabricated phantom is compared with human bodies and a homogeneous anthropomorphic solid phantom, through measurements. The phantom performance is tested in terms of electric field distribution of a wearable antenna on its surface and the path loss between two wearable antennas, on either side of the phantom. It is proved that the hollow phantom performance approximates the full liquid phantom when an RF absorbing material is placed in the central hollow region. The phantom performance in terms of S11 wearable antenna measurements is evaluated and found in good agreement with real human bodies in the examined frequency range (2 - 6 GHz). The far field wearable antenna performance of the proposed phantom shows deviation in gain less than 1.5 dB, compared with anthropomorphic phantom

Dual-Attention Neural Transducers for Efficient Wake Word Spotting in Speech Recognition

We present dual-attention neural biasing, an architecture designed to boost Wake Words (WW) recognition and improve inference time latency on speech recognition tasks. This architecture enables a dynamic switch for its runtime compute paths by exploiting WW spotting to select which branch of its attention networks to execute for an input audio frame. With this approach, we effectively improve WW spotting accuracy while saving runtime compute cost as defined by floating point operations (FLOPs). Using an in-house de-identified dataset, we demonstrate that the proposed dual-attention network can reduce the compute cost by $90\%$ for WW audio frames, with only $1\%$ increase in the number of parameters. This architecture improves WW F1 score by $16\%$ relative and improves generic rare word error rate by $3\%$ relative compared to the baselines.Comment: Accepted to Proc. IEEE ICASSP 202

Higher‐mode textile patch antenna with embroidered vias for on‐body communication

This paper is a preprint of a paper accepted by IET Microwaves, Antennas and Propagation, and is subject to Institution of Engineering and Technology Copyright. When the final version is published, the copy of record will be available at IET Digital Library.This study presents a wearable textile higher-mode microstrip patch antenna (HMMPA) that has been designed to radiate omni-directionally at 2.4 GHz Industrial Scientific and Medical (ISM) band. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that plays an important role in generating the optimal mode for on-body radiation. The embroidery technique enabled a side-fed low-profile antenna which could be placed directly against the body. The proposed textile HMMPA antenna performance is compared with a probe-fed HMMPA antenna fabricated with rigid copper radiating parts, for both free space and on-body conditions. The on-body antenna performance has been tested by performing near-field measurements of the antenna on a full-body specific anthropomorphic mannequin phantom in an anechoic chamber. Results show that the proposed textile HMMPA antenna with vias made from conductive thread can radiate on-body with good efficiency while minimising the radiation in the broadside direction

Design, realisation and evaluation of a liquid hollow torso phantom appropriate for wearable antenna assessment

This paper is a postprint of a paper submitted to and accepted for publication in IET Microwaves, Antennas & Propagation and is subject to Institution of Engineering and Technology Copyright. The copy of record will be available at the IET Digital Library.This paper examines the design, realization and evaluation of a lightweight and low cost hollow oval cross-section torso phantom appropriate for wearable antenna performance assessment. The phantom consists of an empty inner space (hollow) surrounded by a shell with double plastic walls between which there is a tissue simulating liquid. The phantom’s plastic shell is made of a low loss cast acrylic and the liquid is a commercially available one with properties calibrated for the frequency range of 2 - 6 GHz. The proposed phantom is compared, through simulations, with a full liquid torso phantom and a heterogeneous anthropomorphic voxel phantom. Additionally, the fabricated phantom is compared with human bodies and a homogeneous anthropomorphic solid phantom, through measurements. The phantom performance is tested in terms of electric field distribution of a wearable antenna on its surface and the path loss between two wearable antennas, on either side of the phantom. It is proved that the hollow phantom performance approximates the full liquid phantom when an RF absorbing material is placed in the central hollow region. The phantom performance in terms of S11 wearable antenna measurements is evaluated and found in good agreement with real human bodies in the examined frequency range (2 - 6 GHz). The far field wearable antenna performance of the proposed phantom shows deviation in gain less than 1.5 dB, compared with anthropomorphic phantom

Εκτίμηση θέσης και αριθμού πολλαπλών ηχητικών πηγών σε δίκτυα ακουστικών αισθητήρων

Wireless acoustic sensor networks (WASNs) represent a new paradigm for acoustic signal acquisition. Multiple acoustic nodes that feature processing and communication capabilities are distributed in the environment where typically multiple sound sources are active. In such a setup, inference of location information has always been an attractive research problem. Enabling machines to estimate the locations of the multiple simultaneously active sound sources from their acoustic emissions is crucial in many applications, such as wildlife monitoring and speech enhancement for robust signal acquisition. Throughout the years, different localization methods have been proposed with the everlasting goal to achieve the lowest possible localization error. Although significant steps have been made towards this direction, another unexplored field concerns the practical limitations posed by the sensor network that restrict the application of such methods to real-life WASNs. Such limitations include the limited processing power and battery life of the nodes, the communication bandwidth that has to be attained at low levels, the real-time requirements and synchronization issues. In this thesis, we consider the problem of multiple source localization and we investigate the development of methods that not only achieve high accuracy in realistic scenarios but also attain low communication bandwidth, tolerate unsynchronized input and are computationally efficient to facilitate their application in real-life WASNs. We consider a WASN where each node is a microphone array that estimates and transmits information related to the directions of arrival (DOAs) of the active sound sources. Such a scheme attains very low communication bandwidth, as only the DOAs need to be transmitted. Moreover, DOA-based localization methods can tolerate unsynchronized input, thus the acoustic signals need not be perfectly synchronized. We first focus on the single source case and propose a computationally efficient non-linear least squares estimator that can accurately estimate the source's location using an iterative grid-based approach. We then proceed to the multiple sources case, assuming that the number of sources is known. In this case, a core problem for DOA-based approaches is that the fusion center that receives the multiple DOA estimates from the nodes cannot know to which source each DOA belongs. This is known as the data-association problem. To address this problem we propose two solutions: the first concerns the extension of our grid-based approach to multiple sources and the second utilizes additional information, apart from the DOA estimates, in order to find the correct association of DOAs from the nodes to the sources. We then relax the assumption of known number of sources and propose another method that can jointly perform source counting and location estimation. Our method is based on clustering narrowband per-frequency location estimates which are inferred using narrowband per-frequency DOA estimates from the nodes. Since a determinant factor that affects localization performance is the accuracy in which the DOA estimates are obtained, we also investigate how we can improve DOA estimation performance and we propose a methodology to infer more accurate and reliable DOA estimates. Finally, we investigate the potential use of location information to audio processing applications. We provide two examples of how location information can be used for spatial audio capturing and for the design of beamformers that leverage location information in order to estimate the steering vector of the target source. Our preliminary results reveal the potential of location-based approaches to provide improved performance.Τα Ασύρματα Δίκτυα Ακουστικών Αισθητήρων αποτελούν μια νέα τεχνική λήψης ακουστικών σημάτων. Πολλαπλοί ακουστικοί αισθητήρες με επεξεργαστική ισχύ και ικανότητες μετάδοσης πληροφορίας διανέμονται σε ένα περιβάλλον όπου τυπικά πολλές ηχητικές πηγές είναι ενεργές. Σε τέτοιες περιπτώσεις, η εκτίμηση της θέσης των πηγών στο χώρο ήταν πάντα ένα ενδιαφέρον ερευνητικό πρόβλημα. Η πληροφορία της θέσης των πολλαπλών ενεργών ηχητικών πηγών είναι σημαντική σε μια πληθώρα εφαρμογών όπως η παρακολούθηση της άγριας πανίδας και η βελτίωση ποιότητας για την εύρωστη λήψη ηχητικών σημάτων. Με την πάροδο των χρόνων αναπτύχθηκαν διάφορες μέθοδοι εύρεσης θέσης με τελικό στόχο την επίτευξη του χαμηλότερου δυνατού σφάλματος. Ενώ έχει γίνει σημαντική πρόοδος προς αυτή την κατεύθυνση, ένας άλλος τομέας που δεν έχει ευρέως μελετηθεί αφορά τους πρακτικούς περιορισμούς που προκύπτουν από το δίκτυο αισθητήρων, οι οποίοι περιορίζουν την πρακτική εφαρμογή τέτοιων μεθόδων σε πραγματικά δίκτυα ακουστικών αισθητήρων. Τέτοιοι περιορισμοί αφορούν την περιορισμένη επεξεργαστική ισχύ των αισθητήρων, τις απαιτήσεις σε εύρος ζώνης που πρέπει να είναι χαμηλές, τις απαιτήσεις για εφαρμογές πραγματικού χρόνου και τα ζητήματα συγχρονισμού μεταξύ των ηχητικών σημάτων. Σε αυτή τη διατριβή, μελετάμε το πρόβλημα της εύρεσης θέσης πολλαπλών ταυτόχρονα ενεργών ηχητικών πηγών σε ένα δίκτυο ακουστικών αισθητήρων και ερευνούμε την ανάπτυξη μεθόδων εύρεσης θέσης που είναι ικανές όχι μόνο να επιτυγχάνουν υψηλή ακρίβεια σε ρεαλιστικά περιβάλλοντα, αλλά επίσης έχουν χαμηλές απαιτήσεις σε εύρος ζώνης, μπορούν να λειτουργήσουν με μη-συγχρονισμένη είσοδο και είναι υπολογιστικά αποτελεσματικές, ώστε να καθιστούν δυνατή την εφαρμογή τους σε πραγματικά δίκτυα ακουστικών αισθητήρων. Θεωρούμε ένα ασύρματο δίκτυο ακουστικών αισθητήρων όπου ο κάθε κόμβος είναι μια συστοιχία μικροφώνων η οποία εκτιμά και μεταδίδει πληροφορία σχετικά με την κατεύθυνση άφιξης των ηχητικών σημάτων των ενεργών ηχητικών πηγών στο περιβάλλον. Αυτή η προσέγγιση επιτυγχάνει χαμηλές απαιτήσεις σε εύρος ζώνης, αφού αρκεί μόνο η μετάδοση των εκτιμήσεων των κατευθύνσεων άφιξης. Επιπλέον, οι τεχνικές εύρεσης θέσης που βασίζονται σε εκτιμήσεις κατευθύνσεων άφιξης μπορούν να λειτουργήσουν όταν τα ηχητικά σήματα μεταξύ των διάφορων κόμβων του δικτύου δεν είναι τέλεια συγχρονισμένα. Αρχικά επικεντρωνόμαστε στο πρόβλημα εκτίμησης θέσης μιας ενεργής ηχητικής πηγής και προτείνουμε έναν υπολογιστικά αποτελεσματικό μη-γραμμικό εκτιμητή θέσης που είναι ικανός να εντοπίσει τη θέση της πηγής με ακρίβεια χρησιμοποιώντας μια επαναληπτική μέθοδο βασισμένη σε πλέγμα. Έπειτα, ασχολούμαστε με την περίπτωση όπου πολλαπλές ηχητικές πηγές είναι ταυτόχρονα ενεργές, θεωρώντας ότι ο αριθμός τους είναι γνωστός. Το βασικό πρόβλημα που προκύπτει στην περίπτωση των πολλαπλών πηγών είναι ότι ο κεντρικός κόμβος που λαμβάνει τις πολλαπλές εκτιμήσεις κατευθύνσεων άφιξης δεν γνωρίζει σε ποια πηγή αντιστοιχούν. Το πρόβλημα αυτό είναι γνωστό ως πρόβλημα αντιστοίχισης δεδομένων (data-association problem). Για να επιλύσουμε αυτό το πρόβλημα προτείνουμε δύο προσεγγίσεις: η πρώτη αφορά την επέκταση της βασισμένης σε πλέγμα τεχνικής σε πολλαπλές πηγές και η δεύτερη χρησιμοποιεί επιπλέον πληροφορία (εκτός των κατευθύνσεων άφιξης) από τους αισθητήρες με σκοπό να βρεθεί η σωστή αντιστοίχιση των κατευθύνσεων άφιξης από τους κόμβους στις ηχητικές πηγές. Έπειτα, θεωρούμε ότι ο αριθμός των πηγών είναι επίσης άγνωστος και προτείνουμε μια μέθοδο ικανή να εκτιμήσει τον αριθμό των πηγών που είναι ενεργές στο περιβάλλον και τις θέσεις τους. Η μέθοδος μας βασίζεται στην ομαδοποίηση εκτιμήσεων θέσης που προκύπτουν για κάθε συχνότητα των ηχητικών σημάτων και έχουν εκτιμηθεί χρησιμοποιώντας τις ανα-συχνότητα εκτιμήσεις κατευθύνσεων άφιξης. Στη συνέχεια μελετάμε το πώς μπορούμε να βελτιώσουμε την ακρίβεια στην εκτίμηση των κατευθύνσεων άφιξής, αφού αυτή αποτελεί έναν σημαντικό παράγοντα που επηρεάζει την ακρίβεια της εκτίμησης θέσης. Προτείνουμε μια τεχνική που μπορεί να συνδυαστεί με οποιαδήποτε μέθοδο εκτίμησης κατευθύνσεων άφιξης για πιο ακριβείς και αξιόπιστες εκτιμήσεις. Τέλος, ερευνούμε και περιγράφουμε δύο παραδείγματα για την δυνητική χρήση της πληροφορίας σχετικά με τη θέση των ηχητικών πηγών σε διάφορες εφαρμογές επεξεργασίας ήχου. Το πρώτο παράδειγμα αφορά τη χρήση της πληροφορίας της θέσης για την παραγωγή ήχου με χωρική πληροφορία και το δεύτερο αφορά τη σχεδίαση ενός σχηματιστή λοβού (beamformer) που χρησιμοποιεί την πληροφορία των θέσης για την ενίσχυση του σήματος μιας ηχητικής πηγής. Αρχικά αποτελέσματα στις δύο αυτές εφαρμογές δείχνουν ότι μέθοδοι που βασίζονται στη θέση των ηχητικών πηγών μπορούν δυνητικά να χρησιμοποιηθούν σε εφαρμογές διαχωρισμού πηγών και βελτίωσης της ποιότητας των λαμβανόμενων ηχητικών σημάτων

Multiple Sound Source Location Estimation in Wireless Acoustic Sensor Networks using DOA estimates: The Data-Association Problem

In this work, we consider the data-association problem for the localization of multiple sound sources in a wireless acoustic sensor network (WASN), where each node is a microphone array, using direction of arrival (DOA) estimates. The data-association problem arises because the central node that receives the multiple DOA estimates from the nodes cannot know to which source they belong. Hence, the DOAs from the different nodes that correspond to the same source must be found in order to perform accurate localization. We present a method to identify the correct association of DOAs to the sources and thus accurately estimate their locations. Our method results in high association and localization accuracy in realistic scenarios with missed detections, reverberation, noise, and moving sources and outperforms other recently proposed methods. It also incorporates a bitrate reduction scheme in order to keep the amount of information that needs to be transmitted in the network at low levels without affecting performance

Multiple sound source location estimation and counting in a wireless acoustic sensor network View Document

In this work, we consider the multiple sound source location estimation and counting problem in a wireless acoustic sensor network, where each sensor consists of a microphone array. Our method is based on inferring a location estimate for each frequency of the captured signals. A clustering approach---where the number of clusters (i.e., sound sources) is also an unknown parameter---is then employed to decide on the number of sources and their locations. The efficiency of our proposed method is evaluated through simulations in scenarios with up to three simultaneously active sound sources for different signal-to-noise ratios and reverberation times

A survey of sound source localization methods in wireless acoustic sensor networks

Wireless acoustic sensor networks (WASNs) are formed by a distributed group of acoustic-sensing devices featuring audio playing and recording capabilities. Current mobile computing platforms offer great possibilities for the design of audio-related applications involving acoustic-sensing nodes. In this context, acoustic source localization is one of the application domains that have attracted the most attention of the research community along the last decades. In general terms, the localization of acoustic sources can be achieved by studying energy and temporal and/or directional features from the incoming sound at different microphones and using a suitable model that relates those features with the spatial location of the source (or sources) of interest. This paper reviews common approaches for source localization in WASNs that are focused on different types of acoustic features, namely, the energy of the incoming signals, their time of arrival (TOA) or time difference of arrival (TDOA), the direction of arrival (DOA), and the steered response power (SRP) resulting from combining multiple microphone signals. Additionally, we discuss methods not only aimed at localizing acoustic sources but also designed to locate the nodes themselves in the network. Finally, we discuss current challenges and frontiers in this field