Thesis defence: Vertical III-V Nanowire Tunnel Field-Effect Transistors: A Circuit Perspective

Publicerad: 2023-11-27

The energy scaling of integrated circuits has reached its limit because the operating voltage of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFET) based switches has reached its minimum value. MOSFETs are limited by thermionic emission and cannot achieve a subthreshold swing (SS) below 60 mV/decade at room temperature. Tunnel Field-Effect Transistors (TFET), which operate on field modulation of band-to-band tunneling (BTBT), can deliver SS less than 60 mV/dec and are considered as a potential alternative for MOSFETs to further scale down the supply voltage.

This thesis work studied the capabilities and limitations of n-type TFETs based on III-V vertical nanowires and their circuit implementation. TFETs were fabricated using vertical InAs/GaSb or InAs/InGaAsSb/GaSb nanowires of high material
quality, and, switching from InAs/GaSb to InAs/InGaAsSb/GaSb allowed for optimization of the heterojunction, resulted in improvement of the device metrics. Along with heterostructure optimization, the dopant introduction and concentration were systematically varied to achieve devices with record performance. These devices achieved a minimum subthreshold swing of 42 mV/dec and a record high I₆₀ of 1.2 ?A/?m at a drive voltage of 0.5 V. The stability and high yield of the process allowed for statistical study of correlations between important device parameters such as I₆₀, on-current, subthreshold swing, and off-current. The implementation of circuits was also aided by sufficient process repeatability and yield.

To implement circuits based on these TFETs, the fabrication process was optimized with introduction of mesa and nonorganic spacers. Voltage based circuits in the following configurations were implemented: a current mirror, a diode connected inverter and a cascode buffer. Individual TFETs in the circuit operate well below 60 mV/dec operation with minimum achieved subthreshold swing (SS) of 30 mV/dec at drain voltage of 400 mV. In circuit operation, individual devices were connected via FEOL and are biased at 300 mV supply voltage, with an input frequency of 200 kHz. To explore current-mode based design principle, a current conveyor circuit was implemented, which exhibits large-signal voltage gain of 0.89 mV/mV, a current gain of 1 nA/nA and an operating frequency of 320 kHz.

Additionally, self-heating in a vertical nanowire device was examined using pulsed IV methodology. The results indicate that the intrinsic temperature rises to 385 K when the device is operated in DC at room temperature (300 K) with a thermal time constant of 1 ?s. We find that self-heating is a limiting factor for device performance.

Link to thesis i LU Research Portal:

https://portal.research.lu.se/en/publications/vertical-iii-v-nanowire-tunnel-field-effect-transistors-a-circuit

Zoom link:

https://lu-se.zoom.us/j/67084030192

Thesis defence: Taming Cloud Integrated Systems in the Wild

Publicerad: 2023-11-16

This thesis unfolds a journey into the realm of cloud integrated systems. More specifically, it explores the transformational role of diverse cloud infrastructure, be it public or private, centralized or edge-based, when integrated into traditional systems. In this transformation, the cloud assumes the vital role of controllers. Inevitably, this shift towards cloud integration also brings into play the expansive network that acts as the connective tissue between traditional systems and the cloud, adding another layer of complexity to the newly formed integrated system.

In this work, we shed light on the less-talked-about side of cloud integration. Beyond the evident benefits of this transition, we face an array of challenges that emerge along with the introduction of the cloud and its accompanying network. Adapting traditional system deployment to this new era of cloud-based computing is one such necessity. The advent of virtualization and container technologies introduces additional requirements for software management. Shared infrastructure mandates stricter control over incoming traffic. Furthermore, real-world networks often act unpredictably, straying from their simulated behaviours. Even the much-touted 5G technology has not completely lived up to the expectations set a decade ago.

However, the ambition of this thesis does not lie in the enhancement of existing infrastructure, the improvement of cloud technologies, or the acceleration of network speed. Rather, it aims to accept and work within the limitations and flaws inherent in both cloud and network infrastructures. The primary goal is to recognize the chal- lenges these systems introduce, embrace their imperfections, and adapt our systems to work effectively with the realities of our imperfect cloud and unpredictable network environments.

To accomplish this, the thesis undertake a comprehensive analysis of two types of cloud integrated systems?Cloud RAN and Cloud Control System. A central focus is the evaluation of the practicality of implementing these systems using existing infrastructure. This evaluation is based on rigorous simulation as well as hands-on testbed experiments. In response to the insights gained from these assessments, the thesis proposes an innovative framework, built on a microservice architecture, to de- ploy cloud services more effectively for these systems. This framework is designed to mitigate the network latency impact brought on by unpredictable, ?wild? environments. It does so by incorporating specialized prediction and estimation services, thereby enhancing the adaptability of these systems to real-world challenges.

Zoom link:
https://lu-se.zoom.us/j/68329380667

PhD thesis defence: Iman Ghotbi

Publicerad: 2023-11-02

This thesis primarily focuses on the design and implementation of a low-voltage, low-power RFFE tailored for direct sampling receivers in 5G FR1 applications. The RFFE consists of a balun low-noise amplifier (LNA), a Q-enhanced filter, and a programmable gain amplifier (PGA). The balun-LNA employs noise cancellation, current reuse, and gm boosting for wideband gain and input impedance matching. Leveraging FD-SOI technology allows for programmable gain and linearity via body biasing. The LNA's operational state ranges between high-performance and high-tolerance modes, which are apt for sensitivity and blocking tests, respectively. The Q-enhanced filter adopts noise-cancelling, current-reuse, and programmable Gm-cells to realize a fourth-order response using two resonators. The fourth-order filter response is achieved by subtracting the individual response of these resonators. Compared to cascaded and magnetically coupled fourth-order filters, this technique maintains the large dynamic range of second-order resonators. Fabricated in 22-nm FD-SOI technology, the RFFE achieves 1%-40% fractional bandwidth (FBW) adjustability from 1.7 GHz to 6.4 GHz, 4.6 dB noise figure (NF) and an OOB third-order intermodulation intercept point (IIP3) of 22 dBm. Furthermore, concerning the implementation uncertainties and potential variations of temperature and supply voltage, design margins have been considered and a hybrid calibration scheme is introduced. A combination of on-chip and off-chip calibration based on noise response is employed to effectively adjust the quality factors, Gm-cells, and resonance frequencies, ensuring desired bandpass response. To optimize and accelerate the calibration process, a reinforcement learning (RL) agent is used.
 

Link to thesis in LUCRIS:

https://portal.research.lu.se/en/publications/reconfigurable-receiver-front-ends-for-advanced-telecommunication

Zoom link:

https://lu-se.zoom.us/j/64532196838

Thesis defence: Zhongyunshen Zhu

Publicerad: 2023-10-02

Vertical III-V Nanowire Transistors for Low-Power Logic and Reconfigurable Applications

With rapid increase in energy consumption of electronics used in our daily life, the building blocks ? transistors ? need to work in a way that has high energy efficiency and functional density to meet the demand of further scaling. III-V channel combined with vertical nanowire gate-all-around (GAA) device architecture is a promising alternative to conventional Si transistors due to its excellent electrical properties in the channel and electrostatic control across the gate oxide in addition to reduced footprint. Based on this platform, two major objectives of this thesis are included: 1) to improve the performance of III-V p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) and tunnel FETs (TFETs) for low-power digital applications; 2) to integrate HfO2-based ferroelectric gate onto III-V FETs (FeFETs) and TFETs (ferro-TFETs) to enable reconfigurable operation for high functional density..

Link to thesis in LU Research Portal.

Zoom link. Zoom ID:  64195800022

Thesis defence: Navya Sri Garigapati

Publicerad: 2023-09-19

III-V-based Indium gallium arsenide is a promising channel material for high-frequency applications due to its superior electron mobility property. In this thesis, InGaAs/InP heterostructure radio frequency MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are designed, fabricated, and characterized. Various spacer technologies, from high dielectric spacers to air spacers, are implemented to reduce parasitic capacitances, and fT/fmax are evaluated. Three types of RF MOSFETs with different spacer technologies are fabricated in this work.

Link to thesis:

https://portal.research.lu.se/en/publications/radio-frequency-ingaas-mosfets

Zoom link:

https://lu-se.zoom.us/j/66856880417

PhD defence: Vertical III-V Nanowires For In-Memory Computing via Heterogeneous Integration-Rapid Melt Growth and Template Assi

Publicerad: 2023-08-24

Title: Vertical III-V Nanowires For In-Memory Computing

Author: Saketh Ram Mamidala, Department of Electrical and Information Technology, Lund University

Location: E:B E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Link to thesis.

Zoom:
https://lu-se.zoom.us/s/64202896244

Abstract

In recent times, deep neural networks (DNNs) have demonstrated great potential in various machine learning applications,
such as image classification and object detection for autonomous driving. However, increasing the accuracy of DNNs
requires scaled, faster, and more energy-efficient hardware, which is limited by the von Neumann architecture where
separate memory and computing units lead to a bottleneck in performance. A promising solution to address the von
Neumann bottleneck is in-memory computing, which can be achieved by integrating non-volatile memory cells such as
RRAMs into dense crossbar arrays. On the hardware side, the 1-transistor-1-resistor (1T1R) configuration has been central
to numerous demonstrations of reservoir, in-memory and neuromorphic computing.

In this thesis, to achieve a 1T1R cell with a minimal footprint of 4F², a technology platform has been developed to integrate a
vertical nanowire GAA MOSFET as a selector device for the RRAM. Firstly, the effect of the geometry (planar to vertical) of
the ITO/HfO₂/TiN RRAM cell was studied where low energy switching (0.49 pJ) and high endurance (10⁶) were achieved
in the vertical configuration. Furthermore, InAs was incorporated as the GAA MOSFET selector channel material to
leverage the beneficial transport properties of III-V materials desirable for supply voltage scaling. Finally, an approach was
developed wherein InAs is used as the selector channel as well as the RRAM electrode by carefully tuning the InAs native
oxides. This thesis also presents low-frequency noise characterization of the RRAM cell as well as the MOSFET to further
understand the semiconductor/oxide interface. The vertical 1T1R cell developed in this thesis enables the implementation
of Boolean logic operations using a single vertical nanowire while reducing the footprint by 51x when compared to its
traditional CMOS counterpart.

PhD defence: Beyond Massive MIMO: Trade-offs and Opportunities with Large Multi-Antenna Systems

Publicerad: 2023-05-24

Title: Beyond Massive MIMO: Trade-offs and Opportunities with Large Multi-Antenna Systems

Author: Juan Vidal Alegria, Department of Electrical and Information Technology, Lund University

Location: E1406 E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Link to thesis.

Zoom:
https://lu-se.zoom.us/s/64930479328

Abstract

After the commercial emergence of 5G, the research community is already putting its focus on proposing innovative solutions to enable the upcoming 6G. One important lesson put forth by 5G research was that scaling up the conventional multiple-input-multiple-output (MIMO) technology by increasing the number of antennas could be extremely beneficial for effectively multiplexing data streams in the spatial domain. This idea was embodied in massive MIMO, which constitutes one of the major technical advancements included in 5G. Consequently, 6G research efforts have been largely directed towards studying ways to further scale up wireless systems, as can be seen in some of the proposed 6G enabling technologies like large intelligent surface (LIS), cell-free massive MIMO, or even reconfigurable intelligent surface (RIS). This thesis studies the possibilities offered by some of these technologies, as well as the trade-offs that may naturally arise when scaling up such wireless systems.

An important part of this thesis deals with decentralized solutions for base station (BS) technologies including a large number of antennas. Already in the initial massive MIMO prototypes, the increased number of BS antennas led to scalability issues due to the high interconnection bandwidths required to send the received signals---as well as the channel state information (CSI)---to a central processing unit (CPU) in charge of the data processing. These issues can only be exacerbated if we consider novel system proposals like LIS, where the number of BS antennas may be increased by an order of magnitude with respect to massive MIMO, or cell-free massive MIMO, where the BS antennas may be located far from each other. We provide a number of decentralized schemes to process the received data while restricting the information that has to be shared with a CPU. We also provide a framework to study architectures with an arbitrary level of decentralization, showing that there exists a direct trade-off between the interconnection bandwidth to a CPU and the complexity of the decentralized processing required for fixed user rates.

Another part of this thesis studies RIS-based solutions to enhance the multiplexing performance of wireless communication systems. RIS constitutes one of the most attractive 6G enabling technologies since it provides a cost- and energy-efficient solution to improve the wireless propagation links by generating favorable reflections. We extend the concept of RIS by considering reconfigurable surfaces (RSs) with different processing capabilities, and we show how these surfaces may be employed for achieving perfect spatial multiplexing at reduced processing complexity in general multi-antenna communication settings. We also show that these surfaces can exploit the available degrees of freedom---e.g., due to excess of BS antennas---to embed their own data into the enhanced channel.

PhD defence: Antenna System Design for 5G and Beyond ? A Modal Approach

Publicerad: 2023-05-16

Title: Antenna System Design for 5G and Beyond ? A Modal Approach

Author: Hanieh Aliakbari, Department of Electrical and Information Technology, Lund University

Location: E:1406, E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Link to thesis.

Link to webinar (Zoom)

Summary

Today's society relies more and more on the communications of various contents, especially in the form of data, with wireless communications taking the center stage. The most common form of wireless communications, mobile communications, is changing people?s lives over the entire world. One example is the number of smartphone users that grows by hundreds of millions every year, many of whom do not previously have access to telephony or the many opportunities and conveniences it brings. Simultaneously, due to the popularity of bandwidth-hungry streaming video apps, the traffic generated by existing devices also increases by 30-40% annually. In addition, new wireless application areas are also emerging. For example, autonomous vehicles and drones must communicate with their surroundings to avoid collisions and other incidents. To support these different complex contents in wireless networks, higher data rates are needed.
Antenna is a critical component in wireless communications networks as it has the role of sending or receiving the aforementioned data as wireless signals over the air, which eliminates the need for wires. The wireless signals propagate through the medium or channel between the antennas at the transmitter and receiver in the form of electromagnetic waves. In my research, I utilized an antenna design paradigm based on modal methods to meet the antenna requirements for modern wireless systems and achieve higher data rates. Basically, in modal analysis, an antenna?s complex response is described by the weighted sum of multiple rather simpler responses called modes, with the modes being easier to characterize. This results in a more systematic design procedure, which is different from the traditional antenna design framework that mainly relies on intuition from past design experiences and blind numerical optimization of structural parameters.

Following the demand for ever increasing data rates, the antennas in mobile communication systems are required to provide more features and higher performance. One trend is to employ advanced multi-antenna technology to provide high data rates and link reliability. In this context, the first track of my research deals with some fundamental challenges of multi-antenna design for smartphones. The second trend to provide higher data rates for wireless communication is to move towards higher frequencies such as millimeter wave (mm-wave) bands in 5G due to the much larger bandwidths available in those bands than sub-6 GHz bands.  Therefore, the second track of my research investigates new concepts in integrated antennas for mm-wave wireless communications and/or radar systems using different modal theories.

PhD defence: Infrared Photodetectors based on InSb and InAs Nanostructures via Heterogeneous Integration-Rapid Melt Growth and

Publicerad: 2023-05-24

Title: Infrared Photodetectors based on InSb and InAs Nanostructures via Heterogeneous Integration-Rapid Melt Growth and Template Assisted Selective Epitaxy

Author: Heera Menon, Department of Electrical and Information Technology, Lund University

Location: E1406 E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Link to thesis.

Zoom:
https://lu-se.zoom.us/s/65807700869

Abstract

Monolithic heterogeneous integration of III-V semiconductors with the contemporary Si Complementary Metal Oxide Semiconductor (CMOS) technology has instigated a wide range of possibilities and functionalities in the semiconductor industry, in the field of digital circuits, optical sensors, light emitters, and high-frequency communication devices. However, the integration of III-V semiconductors is not trivial due to the differences in lattice parameters, polarity, and thermal expansion coefficient. This thesis explores two integration techniques to form III-V nanostructures with potential applications in the infrared detection field. The first technique implemented in this thesis work is the Rapid Melt Growth technique. InSb, which has a large lattice mismatch (19%) to Si, is used to demonstrate the RMG integration technique. A flash lamp with a millisecond annealing technique is utilized to melt and recrystallize amorphous InSb material to form a single crystalline material. The development of the fabrication process and the experimental results for obtaining a single crystalline InSb-on-insulator from a Si seed area through the RMG process are presented. Electron Back Scatter Diffraction (EBSD) technique was employed to understand the crystal quality, orientation, and defects in the RMG InSb nanostructures. The InSb nanostructures have a resistivity of 10 m? cm, similar to the VLS-grown InSb nanowires. Mobility ranging from 3490 - 877 cm2/ V sec was extracted through Hall and Van der Pauw measurements. Finally, we report the first monolithic integrated InSb nanostructure photodetector on Si through the RMG process. Detailed optical and electrical characterization of the device, including the spectrally resolved photocurrent and the temperature-dependent dark current, is studied. The thesis presents an InSb photodetector with a stable photodetector with a responsivity of 0.5 A/W at 16 nW illumination and millisecond time response. The second integration technique implemented in this thesis work is Template Assisted Selective Epitaxy. Here, the versatility of TASE technique to integrate InAs nanowires on W metal seed is demonstrated. This technique enables the feasibility of integrating III-V semiconductors to back -end of the line integration with Si CMOS technology. EBSD technique was utilized to study and obtain the statistics on the single crystalline InAs nanowires grown from different diameter templates. We also demonstrate the possibility of achieving an nBn InAs detector using TASE on W approach. This technique is a promising step towards developing high operating temperature (HOT) monolithic integrated mid-infrared detectors. Thus, the results of this thesis provide the perspective into two viable CMOS-compatible III-V integration techniques that could be utilized for photodetector applications at a reduced cost.

PhD defence: Vertical III-V Nanowire Transistors for Low-Power Electronics

Publicerad: 2023-05-24

Title: Vertical III-V Nanowire Transistors for Low-Power Electronics

Author: Abinaya Krishnaraja, Department of Electrical and Information Technology, Lund University

Location: E1406 E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Link to thesis.

Zoom:
https://lu-se.zoom.us/s/64156815501

Summary

In this thesis, we study the physical phenomena governing the current conduction in these devices through structural and electrical characterization and utilize the knowledge to improve their electrical performance to be competitive with the conventional transistors. The results from the project provide deeper insights into the material choice and device design considerations for these novel transistor technologies that can be tuned for specific applications. These understandings could help in the future developments within the research field.

LIC seminar: Enabling eMBB in 5G: Wireless Channel Characterization and Modeling

Publicerad: 2023-05-04

Title: Enabling eMBB in 5G: Wireless Channel Characterization and Modeling

Author: Chao Zhang, Department of Electrical and Information Technology, Lund University

Location: 2311, E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Summary

Today, fifth generation (5G) communication network is in its initial phase of commercialization and expected to penetrate every region by 2026. 5G New Radio (5G NR) is the new radio air interface being developed by 3rd Generation Partnership Project (3GPP) for 5G radio access technology. 3GPP introduces three major use cases, including Enhanced Mobile Broadband (eMBB), Massive Machine Type Communication (mMTC), and Ultra-Reliable and Low Latency Communication (uRLLC) for 5G NR. Among various enabling technologies for 5G, channel modeling, studied in release 14, is the key to understand the characteristics of the radio channel in 5G. Channel characteristics have a widerange impact on the system performance in terms of capacity, coverage, spectrum effciency and thus also affect the design of the radio, architecture, etc.

In this thesis, we focus on these enabling technologies for 5G, and mainly explore the channel characteristics for various scenarios as de ned in 5G NR with the frequency range from 2.58 GHz to 40 GHz. We aim to develop statistical channel models for the radio network and discuss how the channel characteristics will a ect the system performance. The thesis starts with a book chapter, i.e., a literature review which presents measurement-based propagation channel investigations for different scenarios. For each eMBB scenario, field measurements, antenna types, data processing, and channel characteristics are discussed. Then, the thesis explores a few interesting scenarios in this research field with several experimental results. We first focus on vegetation attenuation at high frequency bands, and study channel characteristics, e.g., path loss, dispersion, polarization, etc., by using our developed channel sounder for various types of vegetation. Further, we present dynamic channel characteristics of indoor scenarios with the frequency range from 28-30 GHz, and compare the cluster-level parameters between a hall scenario and a corridor scenario. At last, we study interference, detected cells number, handover rate, etc. for low-height air-to-ground channels in two suburban scenarios.

PhD defence: Integration of Ferroelectric HfO2 onto a III-V Nanowire Platform

Publicerad: 2023-04-26

Thesis title: Integration of Ferroelectric HfO2 onto a III-V Nanowire Platform

Author: Anton E. O. Persson, Department of Electrical and Information Technology, Lund University

Faculty opponent:  tbd

Location: E:A, E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Streamed at:  https://lu-se.zoom.us/s/61108835189

Thesis at LU Research Portal

Abstract

The discovery of ferroelectricity in CMOS-compatible oxides, such as doped hafnium oxide, has opened new possibilities for electronics by reviving the use of ferroelectric implementations on modern technology platforms. This thesis presents the ground-up integration of ferroelectric HfO2 on a thermally sensitive III-V nanowire platform leading to the successful implementation of ferroelectric transistors (FeFETs), tunnel junctions (FTJs), and varactors for mm-wave applications. As ferroelectric HfO2 on III-V semiconductors is a nascent technology, a special emphasis is put on the fundamental integration issues and the various engineering challenges facing the technology.

The fabrication of metal-oxide-semiconductor (MOS) capacitors is treated as well as the measurement methods developed to investigate the interfacial quality to the narrow bandgap III-V materials using both electrical and operando synchrotron light source techniques. After optimizing both the films and the top electrode, the gate stack is integrated onto vertical InAs nanowires on Si in order to successfully implement FeFETs. Their performance and reliability can be explained from the deeper physical understanding obtained from the capacitor structures.

By introducing an InAs/(In)GaAsSb/GaSb heterostructure in the nanowire, a ferroelectric tunnel field effect transistor (ferro-TFET) is fabricated. Based on the ultra-short effective channel created by the band-to-band tunneling process, the localized potential variations induced by single ultra-scaled ferroelectric domains and individual defects are sensed and investigated. By intentionally introducing a gate-source overlap in the ferro-TFET, a non-volatile reconfigurable single-transistor solution for modulating an input signal with diverse modes including signal transmission, phase shift, frequency doubling, and mixing is implemented.

Finally, by fabricating scaled ferroelectric MOS capacitors in the front-end with a dedicated and adopted RF and mm-wave backend-of-line (BEOL) implementation, the ferroelectric behavior is captured at RF and mm-wave frequencies.

PhD defence: Decryption Failure Attacks on Post Quantum Cryptography

Publicerad: 2023-04-13

Thesis title: Decryption Failure Attacks on Post Quantum Cryptography

Author: Alexander Nilsson, Department of Electrical and Information Technology, Lund University

Faculty opponent:  Professor Markku-Juhani Saarinen, Finland

Location: E:A, E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Streamed at:  https://lu-se.zoom.us/s/67941251689

Thesis at LU Research Portal

Abstract

The evaluation of next generation of public-key encryption and digital signature algorithms are ongoing, with much at stake. The hope is that these algorithms will be secure for many, many years after their initial deployment. In fact they are expected to remain secure even in the face of fully developed and functional Quantum Computers (QCs). It is well known within the research community that QCs will break some of the most important and widespread algorithms that we otherwise use today. Replacements must be standardized well before QCs are realized. This field is called Post-Quantum Cryptography (PQC). The research included in this dissertation relates to cryptanalysis of several candidate PQC schemes. In one case a proposed alternative decoder is proposed for one of the schemes. Other results pertain to implementation issues of some of the new proposed schemes. Some attacks found in literature have been improved upon with new techniques. And some attacks are novel and affects the source code implementation of the schemes. We argue that our novel attacks are general and affect many different schemes and we show the applicability of the attacks by implementing them against some of them.

PhD defence: Low-Complexity Multiband and Beam-Reconfigurable Antennas for Beyond 5G Communications

Publicerad: 2023-03-14

Thesis title: Low-Complexity Multiband and Beam-Reconfigurable Antennas for Beyond 5G Communications

Author: Qiuyan Liang, Department of Electrical and Information Technology, Lund university

Faculty opponent:  Professor Sean Victor Hum - Canada.

Location: E:1406 E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Streamed at: https://lu-se.zoom.us/s/64926871940

Thesis at LU Research Portal

Abstract

Antennas with large frequency bandwidth, high gain, and beam steering capability are very importance for future wireless communication systems. However, it is very challenging to design antennas with low-complexity structures and high space utilization that can achieve these desired features. Base stations with fixed installations and non-stationary mobile terminals play critical roles in wireless communication networks. The research in this thesis focuses on the low-complexity multiband and beam-reconfigurable antenna design for the two applications.

The first topic of this thesis is about partially reflective surfaces (PRS) antennas, which have significant potential for application in future base stations. In the first part (Part I) of this thesis, existing PRS antennas and challenges to be addressed in PRS antenna design are introduced with respect to beam steering capability and shared-aperture antenna design. To give a clearer insight into the working principle of PRS antenna as well as several observed phenomena involving PRS, the existing theory for PRS antenna is extended. Ray-tracing models as well as the theory of PRS unit cells are utilized to explain the operation of PRS antennas that generate broadside and/or deflected beams. Using these tools, two practical PRS antennas are designed for beam reconfigurability and shared-aperture implementation, respectively. In the first work, we compare the beam deflection capability of different types of PRSs using ray-tracing analysis, with the aim of providing a guideline for selecting a suitable PRS type that would yield a larger beam steering range. In addition, the role of a feeding source in enhancing beam deflection of PRS is explained using ray-tracing analysis, and a beam-reconfigurable feeding source with low-complexity structure is presented. In the second work, we derive the frequency ratio gap for traditional dual-band shared-aperture Fabry-Pérot cavity (DS-FPC) antennas with single-layer PRS and subsequently present a shared-aperture antenna design method with flexible frequency ratio to fill the gap.

The second topic of this thesis is on the co-design of mobile terminal antennas that can cover a wide range of frequency bands. Such antennas are of significant current interest due to the current trend of utilizing higher frequency spectra in wireless communication. A co-designed millimeter-wave (mm-wave) and sub-6GHz antenna system is conceived, where the mm-wave antennas that offer reconfigurable beams for beam steering are integrated into the capacitive coupling elements (CCEs) of the sub-6GHz antenna. Such an implementation aims to achieve a compact and low-complexity antenna structure. In addition, several techniques have been investigated by simulation to achieve further performance improvements in the proposed antenna system with respect to mm-wave antenna gain and bandwidth as well as sub-6GHz antenna tunability and bandwidth.

PhD defence: Efficient Security Protocols for Constrained Devices

Publicerad: 2023-03-14

Thesis title: Efficient Security Protocols for Constrained Devices

Author: Martin Gunnarsson, Department of Electrical and Information Technology, Lund university

Faculty opponent:  Professor Jerker Delsing - Luleå University of Technology.

Location: E:1406 E-huset, Ole Römers väg 3, LTH, Lund University, Lund.

Streamed at: https://lu-se.zoom.us/s/69278738433

Thesis at LU Research Portal

Abstract

During the last decades, more and more devices have been connected to the Internet. Today, there are more devices connected to the Internet than humans. An increasingly more common type of devices are cyber-physical devices. A device that interacts with its environment is called a cyber-physical device. Sensors that measure their environment and actuators that alter the physical environment are both cyber-physical devices.

Devices connected to the Internet risk being compromised by threat actors such as hackers. Cyber-physical devices  have become a preferred target for threat actors since the consequence of an intrusion disrupting or destroying a cyber-physical system can be severe. Cyber attacks against power and energy infrastructure have caused significant disruptions in recent years.

Many cyber-physical devices are categorized as constrained devices. A constrained device is characterized by one or more of the following limitations: limited memory, a less powerful CPU, or a limited communication interface. Many constrained devices are also powered by a battery or energy harvesting, which limits the available energy budget. Devices must be efficient to make the most of the limited resources.

Mitigating cyber attacks is a complex task, requiring technical and organizational measures. Constrained cyber-physical devices require efficient security mechanisms to avoid overloading the systems limited resources. In this thesis, we present research on efficient security protocols for constrained cyber-physical devices.

We have implemented and evaluated two state-of-the-art protocols, OSCORE and Group OSCORE. These protocols allow end-to-end protection of CoAP messages in the presence of untrusted proxies.

Next, we have performed a formal protocol verification of WirelessHART, a protocol for communications in an industrial control systems setting. In our work, we present a novel attack against the protocol.

We have developed a novel architecture for industrial control systems utilizing the Digital Twin concept. Using a state synchronization protocol, we propagate state changes between the digital and physical twins. The Digital Twin can then monitor and manage devices.

We have also designed a protocol for secure ownership transfer of constrained wireless devices. Our protocol allows the owner of a wireless sensor network to transfer control of the devices to a new owner. With a formal protocol verification, we can guarantee the security of both the old and new owners.

Lastly, we have developed an efficient Private Stream Aggregation (PSA) protocol. PSA allows devices to send encrypted measurements to an aggregator. The aggregator can combine the encrypted measurements and calculate the decrypted sum of the measurements. No party will learn the measurement except the device that generated it.

Cake seminar by Jakob Nordström: The Computational Challenge of Combinations

Publicerad: 2023-01-23

The Computational Challenge of Combinations

Prof. Jakob Nordström, Dept of Computer Science, Lund University

Abstract:

Combinatorial solving deals with problems that are solved by combining objects, but where these objects cannot be subdivided to make it easier to find solutions. To see what this means, note that in a power grid we can fine-tune voltages and currents to get the right power distribution, but if we want to distribute packages between delivery trucks, there is no way we can fine-tune the load balance by assigning 90% of a package to one truck and the remaining 10% to another. This fact makes combinatorial problems computationally very challenging. In this talk, I will discuss three aspects of my research on combinatorial problems:

1. Are we lacking good general-purpose algorithms for combinatorial problems because we just haven't been smart enough, or can one prove mathematically that these problems are somehow inherently hard to solve for computers?
2. For the type of combinatorial problems that can be solved in practice, can we leverage more sophisticated mathematical tools to get even better performance?
3. For problems with life-or-death consequences, is there any way we can guarantee that what the computer outputs is in fact a correct solution?

Design for security, privacy, and trust I - ELLIIT tech talk 7

Publicerad: 2023-01-09

AI-enabled digitalization of both good and evil intentions challenges how we handle justice, integrity, security, transparency and the division of responsibilities. We give examples of problems and explain principles for how they can be tackled - but also show that we sometimes have to choose what we mean by justice, convenience and security before we move on.

• Christian Gehrmann, professor in computer security
• Elena Pagnin, Assistant professor, Networks and security,
• Ulrika Evertsson, Chief Information Security Officer, LFV
• Johan Wester, Programledare, Host

You can watch this and more ELLIIT tech talks at Youtube.

Introduction to the theme Design for security, privacy, and trust

Participants: Fredrik Tufvesson, Johan Wester

Watch: https://youtu.be/gMjhzIj4064

Why don't the hackers leave our systems alone, and what can we do about it?

Every leap in the history of technology usually leads to consequential problems. Digitalization opens up fantastic opportunities but unfortunately also for the hackers who do not leave our systems alone. Professor Christian Gehrmann explains the paths to a safer digital future where we plan very carefully before creating a new digital service, where we use the latest protection mechanisms and also have a plan for how problems that nevertheless arise will be handled.

Speaker: Christian Gehrmann, professor in computer security

Watch: https://youtu.be/VEnS_NgbeoI

Enhancing Data Authentication

We live in a digital era where almost everybody owns and uses a couple of digital devices. Every time we send some digital information we take for granted that it  will be received precisely as it was sent, but how can we be sure of that? Assistant Professor Elena Pagnin brings us to the world of digital signatures and explains how they can be used to prevent hackers from changing the data we all are sending around.

Speaker: Elena Pagnin, Assistant professor, Networks and security

Watch: https://youtu.be/F7A6mQx5OVc

Conversation about design for security, privacy, and trust

Panelists

• Christian Gehrmann, professor in computer security
• Elena Pagnin, Assistant professor, Networks and security,
• Ulrika Evertsson, Chief Information Security Officer, LFV
• Johan Wester, Programledare, Host

Watch: https://youtu.be/7sx8CSHGl4w

Access

You can watch this and more ELLIIT tech talks at Youtube.

Read about ELLIIT tech talk at elliit.se