| 1. |
- Lyamin, Nikita, 1989-
(författare)
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Performance evaluation of safety critical ITS-G5 V2V communications for cooperative driving applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intelligent Transport Systems (ITS) are aiming to provide innovative services related to different modes of transport and traffic management, and enable various users to be better informed and make safer, more coordinated and smarter use of transport networks. Cooperative-ITS (C-ITS) support connectivity between vehicles, vehicles and roadside infrastructure, traffic signals as well as with other road users. In order to enable vehicular communications European Telecommunication Standards Institute (ETSI) delivered ITS-G5 -- a of set of C-ITS standards. Considering the goals of C-ITS, inter-vehicle communications should be reliable and efficient.The subject of this thesis is evaluation of the performance, efficiency, and dependability of ITS-G5 communications for cooperative driving applications support. This thesis includes eight scientific papers and extends the research area in three directions: evaluation of the performance of ITS-G5 beaconing protocols; studying the performance of ITS-G5 congestion control mechanisms; and studying the radio jamming Denial-of-Service (DoS) attacks and their detection methods.First, an overview of currently available and ongoing standardization targeting communications in C-ACC/platooning cooperative driving applications is provided. Then, as part of the first research direction, we demonstrate via a number of studies, that the adaptive beaconing approach where message generation is coupled to the speed variation of the originating ITS-s may lead to a message synchronization effect in the time domain when vehicles follow mobility scenarios that involve cooperative speed variation. We explain in detail the cause of this phenomenon and test it for a wide range of parameters. In relation to the second problem, we, first, study the influence of different available ITS-G5 legitimate setups on the C-ACC/platooning fuel efficiency and demonstrate that proper communication setup may enhance fuel savings. Then we thoroughly study the standardization of the congestion control mechanism for ITS-G5, which will affect the operation of all cooperative driving C-ITS applications as a mandatory component. We study the influence of congestion control on application performance and give recommendations for improvement to make the congestion control to target at optimizing the applications performance metrics. In the scope of the last research direction, we propose two real-time jamming DoS detection methods. The main advantage of our detection techniques is their short learning phase that not exceed a few seconds and low detection delay of a few hundreds of milliseconds. Under some assumptions, the proposed algorithms demonstrates the ability to detect certain types of attacks with high detection probability.
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| 2. |
- Hoang, Le-Nam, 1984-
(författare)
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Relaying for Timely and Reliable Applications in Wireless Networks
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many emerging applications based on wireless networks involve distributed control. This implies high requirements on reliability, but also on predictable maximum delay. Further, for applications, it is vital to use off-the-shelf components, both due to cost constraints and requirements on interoperability with existing networks. This, in turn, implies that concurrent transmissions and multiuser detection are seldom possible. Instead, half-duplex time-division multiple access (TDMA) is typically used. Aiming to reduce the packet error rate given a deadline (a set of TDMA time-slots), this thesis proposes a relaying scheme, which can be implemented on top of off-the-shelf components. The relaying scheme selects the best sequence of relayers, given the number of time-slots allowed by the deadline, such that the resulting error probability is minimized at the targeted receiver(s). The scheme differs from existing work in that it considers both unicast as well as broadcast and assumes that all nodes can overhear each other, as opposed to separating source nodes, relay nodes and destination nodes into three disjoint sets. A full analysis of the resulting error probability is provided and complementary numerical results show that the proposed relay sequencing strategy significantly improves reliability given a certain maximum delay, or alternatively, reduces the delay, given a certain target reliability requirement. To illustrate the performance improvements of relay sequencing, it is incorporated in a platooning application. If the decision regarding which relayer to assign in each time-slot can be taken online, just before the transmission, much can be gained. To this end, a low-complexity algorithm is developed, which is shown to be highly likely to find the optimal combination of relaying nodes that minimizes the resulting error probability at the targeted receiver(s). Data packets in wireless automation networks is typically small. To enable timely and reliable all-to-all broadcast in such systems, relay sequencing using packet aggregation is proposed. The strategy assigns relayers to time slots, as well as determines which packets to aggregate in each slot, using the proposed low-complexity algorithm. To further increase the reliability, a clustering scheme is proposed. When a relayer in the sequence fails to overhear a correct copy, a backup relayer in the cluster takes over. This work thereby enables ultra-reliable communications with maintained end-toend delay using low-complexity techniques and off-the-shelf components.
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| 3. |
- Ramazanali, Hawar, 1979-
(författare)
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Managing Radio and Energy Resources in LTE-Based Military Training Networks
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The number of wireless connected devices are growing exponentially and the importance of this research area is growing as well to meet the known and looming challenges and expectations. The 5:th Generation telecommunications standard is partly embodied by the Machine-to-Machine (M2M) and Internet of Things (IoT) technologies and standards to handle a big part of these devices and connections. An example within the IoT paradigm is military training systems where each system can consist of thousands of battery operated mobile devices and their shifting requirements shall be fullled in an energy-aware manner to increase battery operating times.Military training radio networks enables realistic combat training. The services and features provided in commercial telecommunications networks are desirable in these often proprietary and task specic networks, increasing capabilities and functionalities. To facilitate the current and future R&D of LTE based networks for adoption in military training networks and services this doctoral thesis intends to provide the starting ground for the energy-aware LTE based wireless communications. The thesis first presents general solutions on how to meet traffic deadlines in wireless networks for large number of nodes, and then continues with solutions for energy-aware LTE-based communications for the User Equipments (UEs).The work builds on the problem formulation how to provide energy-aware resource handling for LTE-based military training networks from where three research questions are derived. From the research questions we derive different hypotheses and then test these within the investigated area to answer the research questions.The contributions of this work are within areas of resource handling and power saving for mobile devices. In the first area an admission control using deterministic analysis is proposed fullling traffic requirements for military training mobile nodes. This admission control is enhanced for multiple-channel base stations, and evaluated using mobile nodes with different heterogeneous traffic requirements. In the second part energy-awareness is in focus for LTE/LTE-A based networks. The main power saving method for LTE/LTE-A UEs, Discontinuous Reception (DRX) mechanism, is evaluated and models for DRX in Idle and Connected state are proposed including metrics for wake-up delay and power saving. Additionally a mean queuing delay analysis is proposed for a variant of the Connected state DRX. Using these models and metrics, practical design guidelines for tuning of DRX parameters are proposed, including optimization of DRX parameters for either minimizing delay or maximizing power saving.
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| 4. |
- Dabrowski, Konrad K., et al.
(författare)
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Almost Consistent Systems of Linear Equations
- 2023
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Ingår i: Proceedings of the 2023 Annual ACM-SIAM Symposium on Discrete Algorithms (SODA). - Philadelphia, PA : Society for Industrial and Applied Mathematics. - 9781611977554 ; , s. 3179-3217
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Konferensbidrag (refereegranskat)abstract
- Checking whether a system of linear equations is consistent is a basic computational problem with ubiquitous applications. When dealing with inconsistent systems, one may seek an assignment that minimizes the number of unsatisfied equations. This problem is NP-hard and UGC-hard to approximate within any constant even for two-variable equations over the two-element field. We study this problem from the point of view of parameterized complexity, with the parameter being the number of unsatisfied equations. We consider equations defined over Euclidean domains—a family of commutative rings that generalize finite and infinite fields including the rationals, the ring of integers and many other structures. We show that if every equation contains at most two variables, the problem is fixed-parameter tractable. This generalizes many eminent graph separation problems such as Bipartization, Multiway Cut and Multicut parameterized by the size of the cutset. To complement this, we show that the problem is W[1]-hard when three or more variables are allowed in an equation, as well as for many commutative rings that are not Euclidean domains. On the technical side, we introduce the notion of important balanced subgraphs, generalizing important separators of Marx [Theor. Comput. Sci. 2006] to the setting of biased graphs. Furthermore, we use recent results on parameterized MinCSP [Kim et al., SODA 2021] to efficiently solve a generalization of Multicut with disjunctive cut requests.
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| 5. |
- Jonsson, Cathrine, 1969-
(författare)
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Advances in quantitative emission tomography : development and analysis of methods for validation and correction
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The nuclear medicine imaging techniques SPECT and PET are sensitive tools in mapping various physiological and biochemical processes in vivo. This work was devoted to investigations of methodological and physical properties of the SPECT technique as well as developing methods for validation and correction. Brain imaging was the major focus in this work, but the results are applicable to other examination areas. In the first part regional cerebral blood flow (rCBF) as measured by PET - the golden standard - and by SPECT was compared using a computerised brain atlas. Overall the differences were surprisingly small but revealed an apparent reduced grey-to-white matter ratio for SPECT, mainly due to the lack of scatter correction in SPECT, a lower spatial resolution and a non-linear extraction of the SPECT radiopharmaceutical. Furthermore, the reproducibility of resting state rCBF with SPECT was investigated, imperative information whenever scans are being repeated, as in activation studies, or when comparing an individual scan to a database of scans from healthy individuals. The results indicate that normalised flow data show high intra- and inter-individual reproducibility, expressed as standard deviations, ±1.3% and ±2.9%, respectively. The major error was addressed to the methodology, i.e. the scanning procedure and the atlas adaptation.At that stage of the study, using a clinical protocol, without scatter correction and proper attenuation correction there was no possibility to extract quantitative information from the SPECT images. Therefore, in the subsequent work, a phantom concept (the stack phantom) was designed aiming at experimental validation of the SPECT methodology, including effects of photon interactions. Extracting information where the primary (unscattered) photons are separated from the ones undergoing scattering or attenuation before detection, was, until now, only possible using Monte Carlo simulations. The basis of the novel phantom concept is to sample various 3D-activity distributions from a set of 2D samples. The 2D samples are ordinary paper sheets where the cross sectional radioactivity distribution is printed out using radioactive ink. Mounting the samples together with a certain equidistant axial spacing, using either tissue equivalent material or some low-density material, give possibilities to mimick the very same activity distribution clinically (with degrading photon interactions) as well as almost "pure" primary photon images. The phantom concept is very flexible, any activity distribution may be constructed, pathological patterns can easily be introduced and varied. Moreover, correction methods and software evaluation tools may be assessed and validated with the phantom. However, the phantom has not only applicability in research areas - recurrent quality assurance programs can as well make use of dedicated stack phantoms.In the last phase of this work a scatter correction algorithm was developed, making use of the stack phantom. The correction was developed using a multi-spectral acquisition system. This allowed for spectral acquisitions in each pixel in the projection images. After correcting for the scatter contribution in the upper half of the photo-peak using the shape of the scatter distribution from the Klein-Nishina cross section the resulting estimate of primary photons was mirrored (folded) over to estimate the primary photons in the lower half of the photo-peak. The scatter correction works in each spectrum and hence corrects for the scatter contribution locally. The correction method was validated both with Monte Carlo simulations and the stack-phantom, both indicating accurate results.
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| 6. |
- Jonsson, Magnus, 1969-
(författare)
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High performance fiber-optic interconnection networks for real-time computing systems
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Parallel and distributed computing systems become more and more powerful and hence place increasingly higher demands on the networks that interconnect their processors or processing nodes. Many of the applications running on such systems, especially embedded systems applications, have real-time requirements and, with increasing application demands, high-performance networks are the hearts of these systems. Fiber-optic networks are good candidates for use in such systems in the future. This thesis contributes to the relatively unexplored area of fiber-optic networks for parallel and distributed real-time computer systems and suggests and evaluates several fiber-optic networks and protocols. Two different technologies are used in the networks, WDM (Wavelength Division Multiplexing) and fiber-ribbon point-to-point links. WDM offers multiple channels, each with a capacity of several Gbit/s. A WDM star network in which protocols and services are efficiently integrated to support different kinds of real-time demands, especially hard ones, has been developed. The star-of-stars topology can be chosen to offer better network scalability. The WDM star architecture is attractive but its future success depends on components becoming more commercially mature. Fiber-ribbon links, offering instead an aggregated bandwidth of several Gbit/s, have already reached the market with a promising price/performance ratio. This has motivated the development and investigation of two new ring networks based on fiber-ribbon links. The networks take advantage of spatial bandwidth reuse, which can greatly enhance performance in applications with a significant amount of nearest downstream neighbor communication. One of the ring networks is control channel based and not only has support for real-time services like the WDM star network but also low level support for, e.g., group communication. The approach has been to develop network protocols with support for dynamic real-time services, out of time-deterministic static TDMA systems. The focus has been on functionality more than pure performance figures, mostly on real-time features but also on other types of functionality for parallel and distributed systems. Worst-case analyses, some simulations, and case studies are reported for the networks. The focus has been on embedded supercomputer applications, where each node itself can be a parallel computer, and it is shown that the networks are well suited for use in the radar signal processing systems studied. Other application examples in which these kinds of networks are valuable are distributed multimedia systems, satellite imaging and other image processing applications.
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| 7. |
- Jonsson, Åsa, 1969-
(författare)
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How to create and analyze a Heart Failure Registry with emphasis on Anemia and Quality of Life
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background and aimsHeart failure (HF) is a major cause of serious morbidity and death in the population and one of the leading medical causes of hospitalization among people older than 60 years. The aim of this thesis was to describe how to create and how to analyze a Heart Failure Registry with emphasis on Anemia and Quality of Life. (Paper I) We described the creation of the Swedish Heart Failure Registry (SwedeHF) as an instrument, which may help to optimize the handling of HF patients and show how the registry can be used to improve the management of patients with HF. (Paper II) In order to show how to analyze a HF registry we investigated the prevalence of anemia, its predictors, and its association with mortality and morbidity in a large cohort of unselected patients with HFrEF included in the SwedeHF, and to explore if there are subgroups of HF patients identifying high--‐risk patients in need of treatment. (Paper III) In order to show another way of analyzing a HF registry we assessed the prevalence of, associations with, and prognostic impact of anemia in patients with HFmrEF and HFpEF. (Paper IV) Finally we examined the usefulness of EQ--‐ 5D as a measure of patient--‐reported outcomes among HF patients using different analytical models and data from the SwedeHF, and comparing results about HRQoL for patients with HFpEF and HFrEF.Methods An observational study based on the SwedeHF database, consisting of about 70 variables, was undertaken to describe how a registry is created and can be used (Paper I). One comorbidity (anemia) was applied to different types of HF patients, HFrEF (EF <40%) (II) and HFmrEF (EF 40--‐49% ) or HFpEF (> 50%) (III) analyzing the data with different statistical methods. The usefulness of EQ--‐5D as measure of patient--‐ reported outcomes was studied and the results about HRQoL were compared for patients with HFpEF and HFrEF (IV).ResultsIn the first paper (Paper I) we showed how to create a HF registry and presented some characteristics of the patients included, however not adjusted since this was not the purpose of the study. In the second paper (Paper II) we studied anemia in patients with HFrEF and found that the prevalence of anemia in HFrEF were 34 % and the most important independent predictors were higher age, male gender and renal dysfunction. One--‐year survival was 75 % with anemia vs. 81 % without (p<0,001). In the matched cohort after propensity score the hazard ratio associated with anemia was for all--‐cause death 1.34. Anemia was associated with greater risk with lower age, male gender, EF 30--‐39%, and NYHA--‐class I--‐II. In the third paper (Paper III) we studied anemia in other types of HF patients and found that the prevalence in the overall cohort in patients with EF > 40% was 42 %, in HFmrEF 38 % and in HFpEF (45%). Independent associations with anemia were HFpEF, male sex, higher age, worse New York Heart Association class and renal function, systolic blood pressure <100 mmHg, heart rate ≥70 bpm, diabetes, and absence of atrial fibrillation. One--‐year survival with vs. without anemia was 74% vs. 89% in HFmrEF and 71% vs. 84% in HFpEF (p<0.001 for all). Thus very similar results in paper II and III but in different types of HF patients. In the fourth paper (Paper IV) we studied the usefulness of EQ--‐5D in two groups of patients with HF (HFpEF and HFrEF)) and found that the mean EQ--‐5D index showed small reductions in both groups at follow--‐up. The patients in the HFpEF group reported worsening in all five dimensions, while those in the HFrEF group reported worsening in only three. The Paretian classification showed that 24% of the patients in the HFpEF group and 34% of those in the HFrEF group reported overall improvement while 43% and 39% reported overall worsening. Multiple logistic regressions showed that treatment in a cardiology clinic affected outcome in the HFrEF group but not in the HFpEF group (Paper IV).Conclusions The SwedeHF is a valuable tool for improving the management of patients with HF, since it enables participating centers to focus on their own potential for improving diagnoses and medical treatment, through the online reports (Paper I). Anemia is associated with higher age, male gender and renal dysfunction and increased risk of mortality and morbidity (II, III). The influence of anemia on mortality was significantly greater in younger patients in men and in those with more stable HF (Paper II, III). The usefulness of EQ--‐5D is dependent on the analytical method used. While the index showed minor differences between groups, analyses of specific dimensions showed different patterns of change in the two groups of patients (HFpEF and HFrEF). The Paretian classification identified subgroups that improved or worsened, and can therefore help to identify needs for improvement in health services (Paper IV).
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| 8. |
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| 9. |
- Rezk, Nesma, 1987-
(författare)
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Deep Learning on the Edge : A Flexible Multi-level Optimization Approach
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent advances in Deep Learning (DL) research have been adopted in a wide variety of applications, including autonomous driving, AI in health care, and smart homes. In parallel, research in high-performance embedded computing has resulted in advanced hardware platforms that offer enhanced performance and energy efficiency for demanding computations. However, the high demands of DL models for computational and memory resources are still a challenge for embedded computing. Algorithmic optimizations can be used to reduce the computational and memory requirements of DL models. Hardware implementations and architectures can also be tuned to support DL applications’ requirements. This thesis identifies that insufficient coordination between hardware implementations and models’ optimizations limits the efficiency of the resulting implementations. In addition, the implementation methods themselves suffer from poor flexibility in adapting to changes in the model and application constraints. The overarching theme of this thesis is to study and propose methods for the efficient and flexible implementation of DL models on embedded platforms. The work in this thesis bridges the gap between DL models’ algorithmic optimizations and embedded platforms’ hardware-specific optimizations, and investigates the features that need support from DL domain-specific architectures. In addition, a method for multi-objective quantization of DL models is proposed to address both the model error and platform performance metrics. Post-training optimization techniques are employed to facilitate the multiobjective optimization of the models because they do not require retraining after model optimization. This thesis also reviews the optimization methods that are known to have been applied to improve the implementation efficiency of DL models. It highlights the most fruitful optimizations found in existing, highly efficient implementations, and applies them in the proposed methods. A method for mapping Convolution Neural Networks (CNN) on Epiphany, a manycore architecture, is proposed and evaluated. A method for quantization and approximation for RNN models in a post-training fashion is also proposed, and evaluated on four RNN models. The proposed quantization method is used in a hardware-aware multi-objective optimization for RNN models to be deployed on SiLago and Bit fusion architectures.
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