| 1. |
- Nedic, Mitja, et al.
(författare)
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Herglotz functions and applications in electromagnetics
- 2020
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Ingår i: Advances in Mathematical Methods for Electromagnetics. - : Institution of Engineering and Technology. - 9781785613845 - 9781785613852 ; , s. 491-514
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Herglotz functions inevitably appear in pure mathematics, mathematical physics, and engineering with a wide range of applications. In particular, they are the pertinent functions to model passive systems, and thus appear in modeling of electromagnetic phenomena in circuits, antennas, materials, and scattering. In this chapter, we review the basic theory of Herglotz functions and its applications to determine sum rules and physical bounds for passive systems.
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| 2. |
- Björklund, Svante, et al.
(författare)
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Measurement of Rank and Other Properties of Direct and Scattered Signals
- 2016
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Ingår i: International Journal of Antennas and Propagation. - : Hindawi Publishing Corporation. - 1687-5869 .- 1687-5877. ; 2016
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Tidskriftsartikel (refereegranskat)abstract
- We have designed an experiment for low-cost indoor measurements of rank and other properties of direct and scattered signals with radar interference suppression in mind. The signal rank is important also in many other applications, for example, DOA (Direction of Arrival) estimation, estimation of the number of and location of transmitters in electronic warfare, and increasing the capacity in wireless communications. In real radar applications, such measurements can be very expensive, for example, involving airborne radars with array antennas. We have performed the measurements in an anechoic chamber with several transmitters, a receiving array antenna, and a moving reflector. Our experiment takes several aspects into account: transmitted signals with different correlation, decorrelation of the signals during the acquisition interval, covariance matrix estimation, noise eigenvalue spread, calibration, near-field compensation, scattering in a rough surface, and good control of the influencing factors. With our measurements we have observed rank, DOA spectrum, and eigenpatterns of direct and scattered signals. The agreement of our measured properties with theoretic and simulated results in the literature shows that our experiment is realistic and sound. The detailed description of our experiment could serve as help for conducting other well-controlled experiments. © Copyright 2016 Svante Björklund et al.
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| 3. |
- Vu, Viet Thuy, et al.
(författare)
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A hybrid GMTI method for reliable detection results in SAR images
- 2018
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Ingår i: Proceedings - 2018 2nd International Conference on Recent Advances in Signal Processing, Telecommunications and Computing, SIGTELCOM 2018. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538629765 ; , s. 73-78
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Konferensbidrag (refereegranskat)abstract
- Stand-alone synthetic aperture radar (SAR) ground moving target indication (GMTI) methods have both advantages and disadvantages. This paper introduces a hybrid SAR GMTI method that is based on two well-known methods: space time adaptive processing (STAP) and moving target detection by focusing (MTDF). The input of the proposed hybrid method is two time separated complex radar images. The output is detected ground moving targets, the target normalized relative speeds (NRS), and focused images of the detected targets. In the paper, we provide the mathematical background behind the hybrid SAR GMTI method in details. We also provide some experimental results for validating the proposed method. The data for the experiments was acquired in early 2015 by TanDEM-X and TerraSAR-X operating in monostatic pursuit mode. The ground scene where the measurements were conducted is around Mantorp, west of Linköping, Sweden. © 2018 IEEE.
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| 4. |
- Khan, Muhammad Gufran, et al.
(författare)
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Measurements and Analysis of UWB Channels in Industrial Environments
- 2005
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Konferensbidrag (refereegranskat)abstract
- Communication in industrial environments is an important scenario for ultra wideband (UWB) systems. The characteristics of this environment differ considerably from office environments, where most of the channel measurements reported in the literature are performed. In this paper, we present the results and analysis of UWB channel measurements in an industrial environment. We investigate both peer-to-peer non-line-of-sight (P-P NLOS) and base station NLOS (BS NLOS) scenarios. The measurements are performed in the frequency range 3.1 to 8 GHz, at distances 2-16 m, using a vector network analyzer in conjunction with virtual antenna arrays. From these measurements, we extract channel model parameters such as power delay profiles, pathloss exponents, rms delay spread and the percentage of energy captured by RAKE receivers with a finite number of fingers. In addition, Saleh- Valenzuela parameters such as ray and cluster power decay constants and distribution of cluster interarrival times are extracted.
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| 5. |
- Jiang, Yuning, 1993-, et al.
(författare)
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Multi-Level Vulnerability Modeling of Cyber-Physical Systems
- 2018
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Konferensbidrag (refereegranskat)abstract
- Vulnerability is defined as ”weakness of an asset or control that can be exploited by a threat” according to ISO/IEC 27000:2009, and it is a vital cyber-security issue to protect cyber-physical systems (CPSs) employed in a range of critical infrastructures (CIs). However, how to quantify both individual and system vulnerability are still not clear. In our proposed poster, we suggest a new procedure to evaluate CPS vulnerability. We reveal a vulnerability-tree model to support the evaluation of CPS-wide vulnerability index, driven by a hierarchy of vulnerability-scenarios resulting synchronously or propagated by tandem vulnerabilities throughout CPS architecture, and that could be exploited by threat agents. Multiple vulnerabilities are linked by boolean operations at each level of the tree. Lower-level vulnerabilities in the tree structure can be exploited by threat agents in order to reach parent vulnerabilities with increasing CPS criticality impacts. At the asset-level, we suggest a novel fuzzy-logic based valuation of vulnerability along standard metrics. Both the procedure and fuzzy-based approach are discussed and illustrated through SCADA-based smart power-grid system as a case study in the poster, with our goal to streamline the process of vulnerability computation at both asset and CPS levels.
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| 6. |
- Bjorklund, Svante, et al.
(författare)
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Features for micro-Doppler based activity classification
- 2015
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Ingår i: IET radar, sonar & navigation. - : Institution of Engineering and Technology (IET). - 1751-8784 .- 1751-8792. ; 9:9, s. 1181-1187
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Tidskriftsartikel (refereegranskat)abstract
- Safety and security applications benefit from better situational awareness. Radar micro-Doppler signatures from an observed target carry information about the target's activity, and have potential to improve situational awareness. This article describes, compares, and discusses two methods to classify human activity based on radar micro-Doppler data. The first method extracts physically interpretable features from the time-velocity domain such as the main cycle time and properties of the envelope of the micro-Doppler spectra and use these in the classification. The second method derives its features based on the components with the most energy in the cadence-velocity domain (obtained as the Fourier transform of the time-velocity domain). Measurements from a field trial show that the two methods have similar activity classification performance. It is suggested that target base velocity and main limb cadence frequency are indirect features of both methods, and that they do often alone suffice to discriminate between the studied activities. This is corroborated by experiments with a reduced feature set. This opens up for designing new more compact feature sets. Moreover, weaknesses of the methods and the impact of non-radial motion are discussed.
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| 7. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
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Reconstruction of Clipped Signals in Quantized Uplink Massive MIMO Systems
- 2020
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers Inc.. - 0090-6778 .- 1558-0857. ; 68:5, s. 2891-2905
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the uplink of a single-cell multiuser massive multiple-input multiple-output system. Each receiver antenna of the base station (BS) is assumed to be equipped with a pair of analog-to-digital converters to quantize the real and imaginary part of the received signal. We propose a novel clipping-aware receiver (CA-MMSE), which performs minimum mean square error (MMSE) reconstruction only on the clipped received samples, while the granular samples are left unchanged after the quantization. On this basis, we present an iterative algorithm to implement the CA-MMSE receiver and derive a sufficient condition for its geometrical convergence to a fixed point. We show that as long as the number of BS antennas or the quantization resolution is sufficiently high, then, the performance of the CA-MMSE is as good as the optimal MMSE receiver which reconstructs all quantized received symbols. Additionally, we propose a novel Bussgang-based weighted zero-forcing (B-WZF) receiver which distinguishes the clipping and granular distortion and it is shown that as long as the received training symbols per antenna are correlated, the CA-MMSE brings significant improvements compared to conventional receivers in the literature while for users that do not experience deep large-scale fading the simpler B-WZF is near to the CA-MMSE for sufficiently high signal-to-noise ratio and quantization resolution. © 1972-2012 IEEE.
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| 8. |
- Paladi, Nicolae, et al.
(författare)
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Protecting OpenFlow Flow Tables with Intel SGX
- 2019
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Ingår i: ACM SIGCOMM 2019 Conference on Posters and Demos. - Beijing : ACM. - 9781450368865 ; , s. 146-147
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- OpenFlow flow tables in Open vSwitch contain valuable information about installed flows, priorities, packet actions and routing policies. Their importance is emphasized when collocated tenants compete for the limited entries available to install flow rules. From a security point of view, OpenFlow flow tables are a valuable asset that requires both confidentiality and integrity guarantees. However, commodity software switch implementations - such as Open vSwitch - do not implement protection mechanisms capable to prevent attackers from either obtaining information about the installed flows or modifying the contents of flow tables. In this work, we adopt a radical approach to enabling OpenFlow flow table protection through decomposition. Based on a careful analysis of the architecture and implementation of Open vSwitch, we identify core assets requiring security guarantees, design an approach to isolating OpenFlow flow tables, and implement a prototype using Open vSwitch and Software Guard Extensions enclaves.
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| 9. |
- Søgaard, Jacob, et al.
(författare)
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On subjective quality assessment of adaptive video streaming via crowdsourcing and laboratory based experiments
- 2017
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Ingår i: Multimedia tools and applications. - : Springer Science and Business Media LLC. - 1380-7501 .- 1573-7721. ; 76:15, s. 16727-16748
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Tidskriftsartikel (refereegranskat)abstract
- Video streaming services are offered over the Internet and since the service providers do not have full control over the network conditions all the way to the end user, streaming technologies have been developed to maintain the quality of service in these varying network conditions i.e. so called adaptive video streaming. In order to cater for users’ Quality of Experience (QoE) requirements, HTTP based adaptive streaming solutions of video services have become popular. However, the keys to ensure the users a good QoE with this technology is still not completely understood. User QoE feedback is therefore instrumental in improving this understanding. Controlled laboratory based perceptual quality experiments that involve a panel of human viewers are considered to be the most valid method of the assessment of QoE. Besides laboratory based subjective experiments, crowdsourcing based subjective assessment of video quality is gaining popularity as an alternative method. This article presents insights into a study that investigates perceptual preferences of various adaptive video streaming scenarios through crowdsourcing based and laboratory based subjective assessment. The major novel contribution of this study is the application of Paired Comparison based subjective assessment in a crowdsourcing environment. The obtained results provide some novel indications, besides confirming the earlier published trends, of perceptual preferences for adaptive scenarios of video streaming. Our study suggests that in a network environment with fluctuations in the bandwidth, a medium or low video bitrate which can be kept constant is the best approach. Moreover, if there are only a few drops in bandwidth, one can choose a medium or high bitrate with a single or few buffering events.
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| 10. |
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