| 1. |
- Eng, Frida, 1977-, et al.
(författare)
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Frequency Analysis using Non-Uniform Sampling with Application to Active Queue Management
- 2004
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Ingår i: Proceedings of the 2004 IEEE International Conference on Acoustics, Speech and Signal Processing. - Linköping : Linköping University Electronic Press. - 0780384849 ; , s. 581-584
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Konferensbidrag (refereegranskat)abstract
- In many real-time applications, sample values and time stamps are delivered in pairs, where sampling times are non-uniform. Frequency analysis using non-uniform data occurs in various real life problems and embedded systems, such as vibrational analysis in cars and control of packet network queue lengths. Our contribution is to first overview different ways to approximate the Fourier transform, and secondly to give analytical expressions for how non-uniform sampling affects these approximations. The results are expressed in terms of frequency windows describing how a single frequency in the continuous time signal is smeared out in the frequency domain, or, more precisely, in the expected value of the Fourier transform approximation.
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| 2. |
- Gunnarsson, Frida, et al.
(författare)
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Issues on Performance Measurements of TCP
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Due to the rapid growth of the Internet and the use of packet data traffic, the communication world has to find ways of improving performance of this traffic. New areas of use include, e.g., radio transmissions and real time data. This work discusses some issues of performance when using TCP and also present some of the measures that are used today. Furthermore we discuss this matter from the perspective of a bottleneck queue and present a measure that can be used from that viewpoint in the network. This measure is illustrated by comparing two versions of TCP and form the basis for a discussion of what models will be needed to actually achieve the goals that we have. A control structure is presented and using simulations and a control interpretation we note that RED introduces an implicit wanted steady state value of the queue length. We use the dropping of packets as a control signal and the output signal is the queue length.
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| 3. |
- Gunnarsson, Fredrik, et al.
(författare)
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Signal processing : exercises
- 2010. - 1
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- This book provides signal processing exercises and can with advantage be used together with the text book Signal Processing by Fredrik Gustafsson, Lennart Ljung and Mille Millnert. The chapters of the books are aligned, which means that there are matching exercises to each theory chapter. The first part of the book treats classical digital signal processing based on transforms and filters, while model based digital processing is in focus in the second part. Some exercises are more theoretical and solved by hand, while others are intended for Matlab on a computer. The book material is inspired by real problems, and so are the exercises. This is emphasized by the use of data sets, both simulated and real. Most exercises have complete solutions, and a section with hints provides guidance to some exercises. Selected exercises also result in a Matlab function corresponding to specific signal processing algorithms. These functions are used to solve other exercises. Thereby, the reader gradually build up a signal processing toolbox during the studies of the material. The book homepage contains more information and links to access the matlab functions, data sets and examples used in the book. Main book Signal Processing
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| 4. |
- Gustafsson, Fredrik, et al.
(författare)
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Aspects on Performance Measurements of TCP Traffic and Its Reflection into Control Theory
- 2002
-
Ingår i: Proceedings of Reglermöte 2002.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One of the challenges of the communication world today is to improve the performance of Internet traffic for the changing traffic scenarios of today, e.g., radio transmissions. This leaves us with the question of what good performance is and how we measure it. This work will discuss some issues of performance when using TCP and also present some of the measures that are used today. We will then discuss this matter from the perspective of a bottleneck queue and present a measure that can be used from that view point in the network. This measure is illustrated by comparing two versions of TCP and is used as a base for a discussion of what models will be needed to actually achieve the goals that we have. A control structure is presented that currently is used as a base for the development of a mathematical description of the system. We use the dropping of packets as a control signal, as is done by e.g. ~ RED, and the output signal is the queue length.
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| 5. |
- Gustafsson, Fredrik, et al.
(författare)
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Issues on Performance Measurements of TCP
- 2002
-
Ingår i: Proceedings of Radiovetenskap och Kommunikation 2002.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to the rapid growth of the Internet and the use of packet data traffic, the communication world has to find ways of improving performance of this traffic. New areas of use include, e.g., radio transmissions and real time data. This work discusses some issues of performance when using TCP and also present some of the measures that are used today. Furthermore we discuss this matter from the perspective of a bottleneck queue and present a measure that can be used from that viewpoint in the network. This measure is illustrated by comparing two versions of TCP and form the basis for a discussion of what models will be needed to actually achieve the goals that we have. A control structure is presented and using simulations and a control interpretation we note that RED introduces an implicit wanted steady state value of the queue length. We use the dropping of packets as a control signal and the output signal is the queue length.
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| 6. |
- Gustafsson, Fredrik, et al.
(författare)
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Radio Access Network (UTRAN) Modeling for Heterogenous Network Simulations, A Brief Description
- 2003
-
Ingår i: Proceedings of the 1st Swedish National Computer Networking Workshop. - Linköping : Linköping University Electronic Press.
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Konferensbidrag (refereegranskat)abstract
- The vision of mobile Internet comprises heterogeneous networks with both wired and wireless infrastructures. The network parts are typically radio access network, core network, service network, Internet, etc. Due to the multitude of nodes and users in such networks and the complicated nature of layered communications protocols, performance analysis through simulations is crucial. The open source network simulation tool, ns-2, is widely used for simulating the behavior of wired, routed networks. This work adds modules to model radio access network nodes that emulate typical behavior of UTRAN (UMTS Terrestrial Radio Access Network) - the 3G standard opted for in Europe and Japan. Furthermore, data communication examples illustrate typical behavior of such a heterogenous network.
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| 7. |
- Gustafsson, Fredrik, et al.
(författare)
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TCP Performance based on Queue Occupation
- 2001
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Ingår i: Proceedings of the 2001 Nordic Radio Symposium. - Linköping : Linköping University Electronic Press.
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Konferensbidrag (refereegranskat)abstract
- The main protocol for flow and congestion control on the Internet is the Transmission Control Protocol, TCP. This protocol was constructed and developed based on heuristic arguments, and its main purpose is to prevent network congestion. Because of changes in the character of the Internet traffic, TCP does not work as well as when it was designed - a problem that has been addressed by researchers in different ways. In this contribution, the bad performance of TCP will be illustrated using queue occupation. Simulations have been made using a simple simulation testbed implemented in the Matlab tools Simulink and StateFlow, as well as a more complex environment in a simulator developed at Berkeley called ns-2. It is seen that a modified TCP implementation yields significant performance improvements.
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| 8. |
- Gustafsson, Fredrik, et al.
(författare)
-
TCP Performance based on Queue Occupation
- 2001
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Ingår i: Proceedings of the Third Conference on Computer Science and Systems Engineering. ; , s. 127-134
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Konferensbidrag (refereegranskat)abstract
- The main protocol for flow and congestion control on the Internet is the Transmission Control Protocol, TCP. This protocol was constructed and developed based on heuristic arguments, and its main purpose is to prevent network congestion. Because of shifts in the Internet traffic, TCP does not work as well as when it was designed - a problem that has been addressed by researchers in different ways. We will illustrate the bad performance using the queue occupancy and also show that a proposed feedback scheme improves the performance, in a simulation environment.
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| 9. |
- Bergström, Andreas, 1978-
(författare)
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Timing-Based Localization using Multipath Information
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The measurements of radio signals are commonly used for localization purposes where the goal is to determine the spatial position of one or multiple objects. In realistic scenarios, any transmitted radio signal will be affected by the environment through reflections, diffraction at edges and corners etc. This causes a phenomenon known as multipath propagation, by which multiple instances of the transmitted signal having traversed different paths are heard by the receiver. These are known as Multi-Path Components (MPCs). The direct path (DP) between transmitter and receiver may also be occluded, causing what is referred to as non-Line-of-Sight (non-LOS) conditions. As a consequence of these effects, the estimated position of the object(s) may often be erroneous.This thesis focuses on how to achieve better localization accuracy by accounting for the above-mentioned multipath propagation and non-LOS effects. It is proposed how to mitigate these in the context of positioning based on estimation of the DP between transmitter and receiver. It is also proposed how to constructively utilize the additional information about the environment which they implicitly provide. This is all done in a framework wherein a given signal model and a map of the surroundings are used to build a mathematical model of the radio environment, from which the resulting MPCs are estimated.First, methods to mitigate the adverse effects of multipath propagation and non-LOS conditions for positioning based on estimation of the DP between transmitter and receiver are presented. This is initially done by using robust statistical measurement error models based on aggregated error statistics, where significant improvements are obtained without the need to provide detailed received signal information. The gains are seen to be even larger with up-to-date real-time information based on the estimated MPCs.Second, the association of the estimated MPCs with the signal paths predicted by the environmental model is addressed. This leads to a combinatorial problem which is approached with tools from multi-target tracking theory. A rich radio environment in terms of many MPCs gives better localization accuracy but causes the problem size to grow large—something which can be remedied by excluding less probable paths. Simulations indicate that in such environments, the single best association hypothesis may be a reasonable approximation which avoids the calculation of a vast number of possible hypotheses. Accounting for erroneous measurements is crucial but may have drawbacks if no such are occurring.Finally, theoretical localization performance bounds when utilizing all or a subset of the available MPCs are derived. A rich radio environment allows for good positioning accuracy using only a few transmitters/receivers, assuming that these are used in the localization process. In contrast, in a less rich environment where basically only the DP/LOS components are measurable, more transmitters/receivers and/or the combination of downlink and uplink measurements are required to achieve the same accuracy. The receiver’s capability of distinguishing between multiple MPCs arriving approximately at the same time also affects the localization accuracy.
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| 10. |
- Bergström, Andreas, 1978-, et al.
(författare)
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TOA Estimation Improvements in Multipath Environments by Measurement Error Models
- 2017
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Ingår i: Proceedings of the 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538635315 - 9781538635308 ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- Many positioning systems rely on accuratetime of arrival measurements. In this paper, we addressnot only the accuracy but also the relevance of Time ofArrival (TOA) measurement error modeling. We discusshow better knowledge of these errors can improve relativedistance estimation, and compare the impact of differentlydetailed measurement error information. These models arecompared in simulations based on models derived froman Ultra Wideband (UWB) measurement campaign. Theconclusion is that significant improvements can be madewithout providing detailed received signal information butwith a generic and relevant measurement error model.
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