| 1. |
- Zhang, Kewei, et al.
(författare)
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Protecting GNSS Open Service-Navigation Message Authentication against Distance-Decreasing Attacks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- As the security of global navigation satellite systems (GNSS) for civilian usage is increasingly important, navigation message authentication (NMA) significantly improves resilience to spoofing attacks. However, not all attacks can be effectively countered: a strong variant of replay/relay attacks, distance-decreasing (DD) attacks, can shorten pseudorange measurements, without manipulating the cryptographically protected navigation message, thus manipulating the position, velocity, and time solution undetected. First, we discuss how DD attacks can tamper with GNSS signals, demonstrating the attack effectiveness on a recorded Galileo signal. DD attacks might introduce bit errors to the forged signals, but the adversary can keep this error rate very low with proper attack parameter settings. Then, based on our mathematical model of the prompt correlator output of the tracking phase at the victim receiver, we find that the correlator output distribution changes in the presence of DD attacks. This leads us to apply hypothesis testing to detect DD attacks, notably a Goodness of Fit (GoF) test and a generalized likelihood ratio test (GLRT), depending on the victim’s knowledge on the DD attacks. Monte Carlo simulations are used to evaluate the detection probability and the receiver operating characteristic (ROC) curves for two tests, for different adversary configuration and noise settings. Then, we evaluate the effectiveness of the GoF and GLRT tests with a synthesized DD signal. Both tests can detect DD attacks with similar performance in high signal-to-noise ratio (SNR) environments. The GLRT detection probability is approximately 20% higher than that of the GoF test in low SNR environments.
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| 2. |
- Ivanov, Mikhail, 1986, et al.
(författare)
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Unequal Error Protection in Coded Slotted ALOHA
- 2016
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Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2345 .- 2162-2337. ; 5:5, s. 536-539
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the performance of coded slotted ALOHA systems for a scenario where users have different error protection requirements and correspondingly can be divided into user classes. The main goal is to design the system so that the requirements for each class are satisfied. To that end, we derive analytical error floor approximations of the packet loss rate for each class in the finite frame length regime, as well as the density evolution in the asymptotic case. Based on this analysis, we propose a heuristic approach for the optimization of the degree distributions to provide the required unequal error protection. In addition, we analyze the decoding delay for users in different classes and show that better protected users experience a smaller average decoding delay.
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| 3. |
- Yanggratoke, Rerngvit, 1983-
(författare)
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Data-driven Performance Prediction and Resource Allocation for Cloud Services
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cloud services, which provide online entertainment, enterprise resource management, tax filing, etc., are becoming essential for consumers, businesses, and governments. The key functionalities of such services are provided by backend systems in data centers. This thesis focuses on three fundamental problems related to management of backend systems. We address these problems using data-driven approaches: triggering dynamic allocation by changes in the environment, obtaining configuration parameters from measurements, and learning from observations. The first problem relates to resource allocation for large clouds with potentially hundreds of thousands of machines and services. We developed and evaluated a generic gossip protocol for distributed resource allocation. Extensive simulation studies suggest that the quality of the allocation is independent of the system size for the management objectives considered.The second problem focuses on performance modeling of a distributed key-value store, and we study specifically the Spotify backend for streaming music. We developed analytical models for system capacity under different data allocation policies and for response time distribution. We evaluated the models by comparing model predictions with measurements from our lab testbed and from the Spotify operational environment. We found the prediction error to be below 12% for all investigated scenarios.The third problem relates to real-time prediction of service metrics, which we address through statistical learning. Service metrics are learned from observing device and network statistics. We performed experiments on a server cluster running video streaming and key-value store services. We showed that feature set reduction significantly improves the prediction accuracy, while simultaneously reducing model computation time. Finally, we designed and implemented a real-time analytics engine, which produces model predictions through online learning.
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| 4. |
- Lian, Mengke, et al.
(författare)
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What Can Machine Learning Teach Us about Communications
- 2018
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Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. ; 15 January 2019
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Konferensbidrag (refereegranskat)abstract
- Rapid improvements in machine learning over the past decade are beginning to have far-reaching effects. For communications, engineers with limited domain expertise can now use off-the-shelf learning packages to design high-performance systems based on simulations. Prior to the current revolution in machine learning, the majority of communication engineers were quite aware that system parameters (such as filter coefficients) could be learned using stochastic gradient descent. It was not at all clear, however, that more complicated parts of the system architecture could be learned as well. In this paper, we discuss the application of machine-learning techniques to two communications problems and focus on what can be learned from the resulting systems. We were pleasantly surprised that the observed gains in one example have a simple explanation that only became clear in hindsight. In essence, deep learning discovered a simple and effective strategy that had not been considered earlier.
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| 5. |
- Khanzadi, M Reza, 1983, et al.
(författare)
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Calculation of the Performance of Communication Systems from Measured Oscillator Phase Noise
- 2014
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Ingår i: IEEE Transactions on Circuits and Systems I: Regular Papers. - 1549-8328 .- 1558-0806. ; 61:5, s. 1553-1565
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Tidskriftsartikel (refereegranskat)abstract
- Oscillator phase noise (PN) is one of the major problems that affect the performance of communication systems. In this paper, a direct connection between oscillator measurements, in terms of measured single-side band PN spectrum, and the optimal communication system performance, in terms of the resulting error vector magnitude (EVM) due to PN, is mathematically derived and analyzed. First, a statistical model of the PN, considering the effect of white and colored noise sources, is derived. Then, we utilize this model to derive the modified Bayesian Cramer-Rao bound on PN estimation, and use it to find an EVM bound for the system performance. Based on our analysis, it is found that the influence from different noise regions strongly depends on the communication bandwidth, i.e., the symbol rate. For high symbol rate communication systems, cumulative PN that appears near carrier is of relatively low importance compared to the white PN far from carrier. Our results also show that 1/f^3 noise is more predictable compared to 1/f^2 noise and in a fair comparison it affects the performance less.
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| 6. |
- Khanzadi, M Reza, 1983
(författare)
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Modeling and Estimation of Phase Noise in Oscillators with Colored Noise Sources
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The continuous increase in demand for higher data rates due to applications with massive number of users motivates the design of faster and more spectrum efficient communication systems. In theory, the current communication systems must be able to operate close to Shannon capacity bounds. However, the real systems perform below capacity limits, mainly due to channel estimation error and hardware impairments that have been neglected by idealistic or simplistic assumptions on the imperfections. Oscillator phase noise is one of the hardware impairments that is becoming a limiting factor in high data rate digital communication systems. Phase noise severely limits the performance of systems that employ dense constellations. Moreover, the level of phase noise (at a given off-set frequency) increases with carrier frequency which means that the problem of phase noise may be even more severe in systems with high carrier frequency.The focus of this thesis is on finding accurate statistical models of phase noise, as well as the design of efficient algorithms to mitigate the effect of this phenomenon on the performance of modern communication systems. First we derive the statistics of phase noise with white and colored noise sources in free-running and phase-locked-loop-stabilized oscillators. We investigate the relation between real oscillator phase noise measurements and the performance of communication systems by means of the proposed model. Our findings can be used by hardware and frequency generator designers to better understand the effect of phase noise with different sources on the system performance and optimize their design criteria respectively. Then, we study the design of algorithms for estimation of phase noise with colored noise sources. A soft-input maximum a posteriori phase noise estimator and a modified soft-input extended Kalman smoother are proposed. The performance of the proposed algorithms is compared against that of those studied in the literature, in terms of mean square error of phase noise estimation, and symbol error rate of the considered communication system. The comparisons show that considerable performance gains can be achieved by designing estimators that employ correct knowledge of the phase noise statistics. The performance improvement is more significant in low-SNR or low-pilot density scenarios.
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| 7. |
- Nopchinda, Dhecha, 1991
(författare)
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mm-Wave Data Transmission and Measurement Techniques: A Holistic Approach
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ever-increasing demand on data services places unprecedented technical requirements on networks capacity. With wireless systems having significant roles in broadband delivery, innovative approaches to their development are imperative. By leveraging new spectral resources available at millimeter-wave (mm-wave) frequencies, future systems can utilize new signal structures and new system architectures in order to achieve long-term sustainable solutions. This thesis proposes the holistic development of efficient and cost-effective techniques and systems which make high-speed data transmission at mm-wave feasible. In this paradigm, system designs, signal processing, and measurement techniques work toward a single goal; to achieve satisfactory system level key performance indicators (KPIs). Two intimately-related objectives are simultaneously addressed: the realization of efficient mm-wave data transmission and the development of measurement techniques to enable and assist the design and evaluation of mm-wave circuits. The standard approach to increase spectral efficiency is to increase the modulation order at the cost of higher transmission power. To improve upon this, a signal structure called spectrally efficient frequency division multiplexing (SEFDM) is utilized. SEFDM adds an additional dimension of continuously tunable spectral efficiency enhancement. Two new variants of SEFDM are implemented and experimentally demonstrated, where both variants are shown to outperform standard signals. A low-cost low-complexity mm-wave transmitter architecture is proposed and experimentally demonstrated. A simple phase retarder predistorter and a frequency multiplier are utilized to successfully generate spectrally efficient mm-wave signals while simultaneously mitigating various issues found in conventional mm-wave systems. A measurement technique to characterize circuits and components under antenna array mutual coupling effects is proposed and demonstrated. With minimal setup requirement, the technique effectively and conveniently maps prescribed transmission scenarios to the measurement environment and offers evaluations of the components in terms of relevant KPIs in addition to conventional metrics. Finally, a technique to estimate transmission and reflection coefficients is proposed and demonstrated. In one variant, the technique enables the coefficients to be estimated using wideband modulated signals, suitable for implementation in measurements performed under real usage scenarios. In another variant, the technique enhances the precision of noisy S-parameter measurements, suitable for characterizations of wideband mm-wave components.
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| 8. |
- Stigwall, Johan, 1977, et al.
(författare)
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Photonic GHz to THz tunable signal generation by chirped-pulse mixing
- 2006
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Ingår i: 2006 European ISIS Workshop, Emerging Optical Broadband Technologies, Boppard am Rhein, Germany, May 29 - June 1, 2006.
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Konferensbidrag (refereegranskat)abstract
- Frequency-tunable generation of pulsed tones in the millimeter to sub-millimeter range was demonstrated by mixing of two chromatically dispersing femtosecond laser pulses split up in time by an adjustable differential group delay (DGD) and a polarizer. The signal frequency was set by adjusting the amount of DGD and the amount of dispersion, and was here tuned from below 1 GHz to 0.9 THz. Time-domain measurements were conducted using a sampling oscilloscope for the lower frequencies and an auto-correlator for the higher frequencies. Near 100% modulation depth was obtained, and the signal phase was very stable, being locked to the pulses from the femtosecond laser. The line-width of the mm-wave waveform was found to be transform-limited if the signal chirp induced by higher order dispersion was compensated for. Suggested applications for this system are for instance THz spectroscopy, characterization of high performance photo-diodes and real-time dispersion measurements.
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| 9. |
- Ivashina, Marianna, 1975, et al.
(författare)
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Antenna Technologies for Beyond-5G Wireless Communication : Challenges and Opportunities
- 2021
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Ingår i: 2021 International Symposium on Antennas and Propagation, ISAP 2021. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- This paper provides an overview of the Sweden-Taiwan collaborative research framework project 'Antenna Technologies for Beyond-5G Wireless Communication' that has been recently established to develop robust and energy-efficient integrated antenna solutions for frequencies beyond 100 GHz as future enabling technologies for the 5G+ applications. Technological challenges in manufacturing and integration with electronics as well as available opportunities are discussed.
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| 10. |
- Grabowski, Alexander, 1993
(författare)
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VCSEL Equivalent Circuits and Silicon Photonics Integration
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The vertical-cavity surface-emitting laser (VCSEL) is a light source of great importance for numerous industrial and consumer products. The main application areas are datacom and sensing. The datacom industry uses GaAs-based VCSELs for optical interconnects, the short-reach fiber optical communication links used to transfer large amounts of data at high rates between units within data centers and supercomputers. In the area of sensing, VCSELs are largely used in consumer products such as smart phones (e.g. face ID and camera auto focus), computer mice, and automobiles (e.g. gesture recognition and LIDAR for autonomous driving). In this work, an advanced physics-based equivalent circuit model for datacom VCSELs has been developed. The model lends itself to co-design and co-optimization with driver and receiver ICs, thereby enabling higher data rate transceivers with bandwidth limited VCSELs and photodiodes. The model also facilitates an understanding of how each physical process within the VCSEL affects the VCSEL static and dynamic performance. It has been applied to study the impact of carrier transport and capture on VCSEL dynamics. The work also includes micro-transfer-printing of GaAs-based single-mode VCSELs on silicon nitride photonic integrated circuits (PICs). Such PICs are increasingly used for e.g. compact and highly functional bio-photonic sensors. Transfer printing of VCSELs enables the much-needed on-PIC integration of power efficient light sources. The bottom-emitting VCSELs are printed above grating couplers on the PIC and optical feedback is used to control the polarization for efficient coupling to the silicon nitride waveguide. Wavelength tuning, as required by the bio-sensing application, is achieved by direct current modulation.
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