DolphinAtack: Inaudible Voice Commands

Speech recognition (SR) systems such as Siri or Google Now have become an increasingly popular human-computer interaction method, and have turned various systems into voice controllable systems(VCS). Prior work on attacking VCS shows that the hidden voice commands that are incomprehensible to people can control the systems. Hidden voice commands, though hidden, are nonetheless audible. In this work, we design a completely inaudible attack, DolphinAttack, that modulates voice commands on ultrasonic carriers (e.g., f > 20 kHz) to achieve inaudibility. By leveraging the nonlinearity of the microphone circuits, the modulated low frequency audio commands can be successfully demodulated, recovered, and more importantly interpreted by the speech recognition systems. We validate DolphinAttack on popular speech recognition systems, including Siri, Google Now, Samsung S Voice, Huawei HiVoice, Cortana and Alexa. By injecting a sequence of inaudible voice commands, we show a few proof-of-concept attacks, which include activating Siri to initiate a FaceTime call on iPhone, activating Google Now to switch the phone to the airplane mode, and even manipulating the navigation system in an Audi automobile. We propose hardware and software defense solutions. We validate that it is feasible to detect DolphinAttack by classifying the audios using supported vector machine (SVM), and suggest to re-design voice controllable systems to be resilient to inaudible voice command attacks.Comment: 15 pages, 17 figure

Over-The-Air Testing using Wave-Field Synthesis

Today's wireless communication devices, such as GNSS receivers, smart-phones, etc. aim at a high integration grade to save space, costs and energy consumption. Besides small devices, also very large communication devices, e.g. cars with integrated LTE antennas exist. To accelerate the development process and time-to-market, adequate test procedures are needed to ensure proper functioning of all device components. The goal of this thesis is to develop test processes that guarantee for reproducible test conditions and to allow for comparable performance measurements of communication systems of different sizes. This thesis consists of two parts, namely Wave Field Synthesis for electrically small, and Wireless Cable for electrically large devices.Moderne Kommunikationsgeräte, z. B. Smartphones und GPS-Empfänger streben einen hohen Integrationsgrad an, um Kosten, Platz und Energie zu sparen. Es existieren auch große Geräte, wie zum Beispiel Fahrzeuge mit integrierten Long Term Evolution-Antennen. Um den Entwicklungsprozess zu beschleunigen, werden adäquate Testverfahren benötigt, die eine korrekte Funktionsweise aller Gerätekomponenten sicherstellen. Das Ziel dieser Arbeit ist es, Testverfahren einschließlich Kalibrierverfahren zu entwickeln, die reproduzierbare Testbedingungen erlauben, um vergleichbare Leistungstests von Kommunikationssystemen zu ermöglichen. Diese Arbeit besteht aus zwei Teilen. Der erste Teil beschäftigt sich mit Wellenfeldsynthese (WFS) für elektrisch kleine Geräte. Der zweite Teil präsentiert ein alternatives Testverfahren für elektrisch große Geräte, welches Wireless Cable (WLC) bezeichnet wird. Im WFS-Teil werden Simulationen durchgeführt, um die Anwendbarkeit der WFS für Over-The-Air-Tests in 2D und 3D zur Erzeugung ebener elektromagnetischer Wellen zu untersuchen. Ein Kalibrierverfahren wird für die 2D-WFS vorgestellt, um den Frequenzgang analoger Systemkomponenten zu entzerren. Das Kalibrierverfahren wird mit Hilfe der Metriken Error Vector Magnitude und Poynting Vector Angular Deviation verifiziert. Es werden zur Verifikation des gesamten WFS-Systems Messungen auf Basis von GPS durchgeführt, die mit kabelgebundenen Tests verglichen werden. Zur Demonstration der Vollständigen Mess- und Testprozedur werden verschiedene Mehrelement-Antennen unter identischen Messbedingungen verglichen. Einflüsse auf ein reales System durch Rauschen, Drift und Temperatureinfluss werden untersucht. Für 3D-WFS wird ein optimierender Algorithmus wird entwickelt und verifiziert, um Emulationsantennen auf einer Sphäre oder Hemisphäre optimal zu verteilen. Im Wireless Cable-Teil wird das gleichnamige Testverfahren vorgestellt, das als alternative Over-The-Air-Testmethode die Untersuchung großer Geräte erlaubt. Die Anwendbarkeit in nicht-reflexionsfreien Umgebungen wird demonstriert. Wie alle Over-The-Air-basierten Testverfahren berücksichtigt Wireless Cable auch Selbstinterferenz. Eine Langzeitstabilitätsanalyse wird durchgeführt, außerdem eine Verifikation der Anwendbarkeit eines realistischen Funkkanals für den Anwendungsfall Long Term Evolution.Today's wireless communication devices, such as GNSS receivers, smart-phones, etc. aim at a high integration grade to save space, costs and energy consumption. Besides small devices, also very large communication devices, e.g. cars with integrated LTE antennas exist. To accelerate the development process and time-to-market, adequate test procedures are needed to ensure proper functioning of all device components. The goal of this thesis is to develop test processes that guarantee for reproducible test conditions and to allow for comparable performance measurements of communication systems of different sizes. This thesis consists of two parts, namely WFS for electrically small, and WLC for electrically large devices. In the WFS part, simulations are conducted to verify the applicability of OTA tests using WFS for two- and three-dimensional emulation of plane electromagnetic waves. A calibration procedure is developed for 2D-WFS to compensate for analog components' frequency responses that include contributions of amplifiers, cables and antennas. This calibration procedure is verified by grid measurements to allow visual inspection of the plane waves, and by analysis of the wave shape using appropriate metrics. Reflections inside the anechoic chamber are analyzed and discussed. A verification measurement is performed and compared to conducted measurements using a GPS use case to verify the whole WFS OTA system. Three different multi-element antennas are investigated by emulation of identical wave-fields in each test run to demonstrate the general test procedure. System imperfections such as noise, drift and the influence of temperature are investigated. For 3D WFS OTA testing, an optimizing sub-sphere algorithm is developed to distribute EA on a sphere or hemisphere adequately. Simulations are conducted to verify the derived distributions. In the WLC part, the homonymous test method is presented as an alternative OTA test method especially suited for large test devices. The applicability even in non-anechoic environments is shown. A long-term stability analysis is performed, and a verification of the application of a realistic measurement-based propagation channel for the use case LTE is made

Measurements, Models, Systems and Design

531 s.

Performance of RIS-Aided Nearfield Localization under Beams Approximation from Real Hardware Characterization

The technology of reconfigurable intelligent surfaces (RIS) has been showing promising potential in a variety of applications relying on Beyond-5G networks. Reconfigurable intelligent surface (RIS) can indeed provide fine channel flexibility to improve communication quality of service (QoS) or restore localization capabilities in challenging operating conditions, while conventional approaches fail (e.g., due to insufficient infrastructure, severe radio obstructions). In this paper, we tackle a general low-complexity approach for optimizing the precoders that control such reflective surfaces under hardware constraints. More specifically, it allows the approximation of any desired beam pattern using a pre-characterized look-up table of feasible complex reflection coefficients for each RIS element. The proposed method is first evaluated in terms of beam fidelity for several examples of RIS hardware prototypes. Then, by means of a theoretical bounds analysis, we examine the impact of RIS beams approximation on the performance of near-field downlink positioning in non-line-of-sight conditions, while considering several RIS phase profiles (incl. directional, random and localization-optimal designs). Simulation results in a canonical scenario illustrate how the introduced RIS profile optimization scheme can reliably produce the desired RIS beams under realistic hardware limitations. They also highlight its sensitivity to both the underlying hardware characteristics and the required beam kinds in relation to the specificity of RIS-aided localization applications.Comment: 27 pages, 8 figures, journa

Modelling Aspects of Planar Multi-Mode Antennas for Direction-of-Arrival Estimation

Multi-mode antennas are an alternative to classical antenna arrays, and hence a promising emerging sensor technology for a vast variety of applications in the areas of array signal processing and digital communications. An unsolved problem is to describe the radiation pattern of multi-mode antennas in closed analytic form based on calibration measurements or on electromagnetic field (EMF) simulation data. As a solution, we investigate two modeling methods: One is based on the array interpolation technique (AIT), the other one on wavefield modeling (WM). Both methods are able to accurately interpolate quantized EMF data of a given multi-mode antenna, in our case a planar four-port antenna developed for the 6-8.5 GHz range. Since the modeling methods inherently depend on parameter sets, we investigate the influence of the parameter choice on the accuracy of both models. Furthermore, we evaluate the impact of modeling errors for coherent maximum-likelihood direction-of-arrival (DoA) estimation given different model parameters. Numerical results are presented for a single polarization component. Simulations reveal that the estimation bias introduced by model errors is subject to the chosen model parameters. Finally, we provide optimized sets of AIT and WM parameters for the multi-mode antenna under investigation. With these parameter sets, EMF data samples can be reproduced in interpolated form with high angular resolution

Spatial Vector Microwave Measurement

V této práci je představena nová interferometrická měřicí metoda pro měření koeficientu přenosu mezi dvěma anténami. Jestliže je přenos mezi anténami realizován odrazem od nějakého předmětu, lze metodu využít např. pro mikrovlnné zobrazování. Navržený systém obsahuje referenční větev obsahující anténu, která přímo ozařuje přijímací anténu a testovací větev, kde anténa ozařuje testovaný objekt. Elektromagnetická vlna z testovacího kanálu je od testovacího objektu odražena do přijímací antény, kde interferuje s vlnou z referenční větve. Pro jednoznačné získání fázového posunu mezi referenční a testovací vlnou jsou provedena postupně minimálně dvě interferometrická měření, kdy je v referenčním kanálu nastaven vhodný fázový posun a amplituda přenosu. Při měření můžeme provést více nezávislých interferometrických měření a vzniklá redundance může být využita ke zmenšení nejistot měření. Dále byl popsán způsob geometrické representace měření, který umožňuje názorně odhadnout nejisty měření. Nejistoty měření byly určeny i na základě numerické Monte Carlo metody. Navržená konfigurace byla ověřena jak přesným měřením za použití vektorového analyzátoru pro ověření nejistot měření, tak původní konfigurací pro ověření funkčnosti celého konceptu. Navrženou metodou bylo provedeno mikrovlnné zobrazování metodou inverzní syntetické apertury a byla tak ověřena použitelnost navrženého systému.This work presents a new interferometric measuring method for measuring the transmission coefficient between two antennas. If the transmission between the antennas is realized by a reflection from an object, the method can be used, e.g., for microwave imaging. The proposed system contains a reference branch containing an antenna that directly irradiates the receiving antenna and a test branch where the antenna irradiates the object under test. The electromagnetic wave from the test channel is reflected from the test object into the receiving antenna where it interferes with the wave from the reference channel. To achieve a unambiguous phase shift between the reference and test waves, at least two interferometric measurements are performed sequentially, with a suitable phase shift and the amplitude of the transmission being set in the reference channel. We can perform more independent interferometric measurements while redundancy can be used to reduce measurement uncertainty. Furthermore, a method of geometric representation of the measurement has been described which makes it possible to clearly estimate the measurement uncertainty. Measurement uncertainties were determined by the numerical Monte Carlo method. The proposed configuration has been verified by accurate measurements using a vector analyzer to verify measurement uncertainties, and the original configuration to verify the functionality of the entire concept. Microwave imaging using the inverse synthetic aperture method was performed to verify the usability of the proposed system

Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin

Large deployable antenna program. Phase 1: Technology assessment and mission architecture

The program was initiated to investigate the availability of critical large deployable antenna technologies which would enable microwave remote sensing missions from geostationary orbits as required for Mission to Planet Earth. Program goals for the large antenna were: 40-meter diameter, offset-fed paraboloid, and surface precision of 0.1 mm rms. Phase 1 goals were: to review the state-of-the-art for large, precise, wide-scanning radiometers up to 60 GHz; to assess critical technologies necessary for selected concepts; to develop mission architecture for these concepts; and to evaluate generic technologies to support the large deployable reflectors necessary for these missions. Selected results of the study show that deployable reflectors using furlable segments are limited by surface precision goals to 12 meters in diameter, current launch vehicles can place in geostationary only a 20-meter class antenna, and conceptual designs using stiff reflectors are possible with areal densities of 2.4 deg/sq m