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1.	Gunnarsson, Fredrik, et al. (författare) Signal processing : exercises 2010. - 1 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
2.	Gustafsson, Harald, et al. (författare) Den dubbla blicken. En inledning 2007 Ingår i: Den dubbla blicken. Historia i de nordiska samhällena. - 9789185767007 ; , s. 7-26 Bokkapitel (övrigt vetenskapligt/konstnärligt)
3.	Willgren, David, et al. (författare) Adventsuppropet problematiskt 2012 Ingår i: Dagen. - 1652-5264. Tidskriftsartikel (populärvet., debatt m.m.)abstract "Vi har problem med Adventsuppropet och den privilegierade ställning som den kristna tron förutsätts ha i det, skriver 18 pastorer och församlingsledare."
4.	Willgren, David, et al. (författare) Ett annat sätt att se på makt 2013 Ingår i: Dagen. - 1652-5264. Tidskriftsartikel (populärvet., debatt m.m.)
5.	Willgren, David, et al. (författare) Vi har inga problem att stöta oss med staten 2012 Ingår i: Dagen. - 1652-5264. Tidskriftsartikel (populärvet., debatt m.m.)
6.	Alimohammadi, Mohammad, et al. (författare) Pulmonary Autoimmunity as a Feature of Autoimmune Polyendocrine Syndrome Type 1 and Identification of KCNRG as a Bronchial Autoantigen 2009 Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:11, s. 4396-4401 Tidskriftsartikel (refereegranskat)abstract Patients with autoimmune polyendocrine syndrome type 1 (APS-1) suffer from multiple organ-specific autoimmunity with autoantibodies against target tissue-specific autoantigens. Endocrine and nonendocrine organs such as skin, hair follicles, and liver are targeted by the immune system. Despite sporadic observations of pulmonary symptoms among APS-1 patients, an autoimmune mechanism for pulmonary involvement has not been elucidated. We report here on a subset of APS-1 patients with respiratory symptoms. Eight patients with pulmonary involvement were identified. Severe airway obstruction was found in 4 patients, leading to death in 2. Immunoscreening of a cDNA library using serum samples from a patient with APS-1 and obstructive respiratory symptoms identified a putative potassium channel regulator (KCNRG) as a pulmonary autoantigen. Reactivity to recombinant KCNRG was assessed in 110 APS-1 patients by using immunoprecipitation. Autoantibodies to KCNRG were present in 7 of the 8 patients with respiratory symptoms, but in only 1 of 102 APS-1 patients without respiratory symptoms. Expression of KCNRG messenger RNA and protein was found to be predominantly restricted to the epithelial cells of terminal bronchioles. Autoantibodies to KCNRG, a protein mainly expressed in bronchial epithelium, are strongly associated with pulmonary involvement in APS-1. These findings may facilitate the recognition, diagnosis, characterization, and understanding of the pulmonary manifestations of APS-1.
7.	Ardeshiri, Tohid, et al. (författare) Bicycle Tracking Using Ellipse Extraction 2011 Ingår i: Proceedings of the 14thInternational Conference on Information Fusion, 2011. - : IEEE. - 9781457702679 ; , s. 1-8 Konferensbidrag (refereegranskat)abstract A new approach to track bicycles from imagery sensor data is proposed. It is based on detecting ellipsoids in the images, and treat these pair-wise using a dynamic bicycle model. One important application area is in automotive collision avoidance systems, where no dedicated systems for bicyclists yet exist and where very few theoretical studies have been published. Possible conflicts can be predicted from the position and velocity state in the model, but also from the steering wheel articulation and roll angle that indicate yaw changes before the velocity vector changes. An algorithm is proposed which consists of an ellipsoid detection and estimation algorithm and a particle filter. A simulation study of three critical single target scenarios is presented, and the algorithm is shown to produce excellent state estimates. An experiment using a stationary camera and the particle filter for state estimation is performed and has shown encouraging results.
8.	Bergström, Andreas, 1978- (författare) Timing-Based Localization using Multipath Information 2020 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.
9.	Bergström, Andreas, 1978-, et al. (författare) TOA Estimation Improvements in Multipath Environments by Measurement Error Models 2017 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 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.
10.	Blom, Jonas, et al. (författare) A New Concept of Power Control in Cellular Systems Reflecting Challenges of Today's Systems 1999 Rapport (övrigt vetenskapligt/konstnärligt)abstract When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.
11.	Blom, Jonas, et al. (författare) Method and System for Quality-Based Power Control in Cellular Communications Systems 2002 Patent (populärvet., debatt m.m.)abstract A method and system for quality-based transmission power control in a cellular communications system (100) are disclosed, whereby a network operator can specify the transmission quality requirements using a measurement that better reflects the actual quality perceived by the users. All transmitter power levels in the network can be controlled by identical power regulators (200), each of which can adapt to individual traffic situations in order to achieve the specified quality. For example, in a GSM frequency-hopping network, the FER together with the parameters estimated from the current traffic situation (54), are mapped onto a target C/I (56), which in turn, the power control algorithm strives (16) to achieve (58, 60). Consequently, the power regulators can adapt to the traffic situation experienced by each receiver.
12.	Blom, Jonas, et al. (författare) Pole Placement Design of Power Control Algorithms 1999 Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780355652 Konferensbidrag (refereegranskat)abstract Time delays reduces the performance of any controlled system. If neglected in the design phase, the system may even become unstable when using the designed controller. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, it is shown that the problems can be handled by considering the time delays in the design phase in order to choose the appropriate parameter values. Most popular algorithms can be seen as special cases of an integrating controller. This structure is extended first to a proportional integrating (PI)-controller and then further on to a general linear controller of higher orders. Corresponding design procedures are outlined based on techniques, such as pole placement, from the field of automatic control. The PI-controller is a very appealing choice of structure, with better performance compared to an I-controller and less complex than a higher order controller. The benefits are further illuminated by network simulations.
13.	Bonagas, Nadilly, et al. (författare) Pharmacological targeting of MTHFD2 suppresses acute myeloid leukemia by inducing thymidine depletion and replication stress 2022 Ingår i: NATURE CANCER. - : Springer Science and Business Media LLC. - 2662-1347. ; 3:2, s. 156- Tidskriftsartikel (refereegranskat)abstract The folate metabolism enzyme MTHFD2 (methylenetetrahydrofolate dehydrogenase/cyclohydrolase) is consistently overexpressed in cancer but its roles are not fully characterized, and current candidate inhibitors have limited potency for clinical development. In the present study, we demonstrate a role for MTHFD2 in DNA replication and genomic stability in cancer cells, and perform a drug screen to identify potent and selective nanomolar MTHFD2 inhibitors; protein cocrystal structures demonstrated binding to the active site of MTHFD2 and target engagement. MTHFD2 inhibitors reduced replication fork speed and induced replication stress followed by S-phase arrest and apoptosis of acute myeloid leukemia cells in vitro and in vivo, with a therapeutic window spanning four orders of magnitude compared with nontumorigenic cells. Mechanistically, MTHFD2 inhibitors prevented thymidine production leading to misincorporation of uracil into DNA and replication stress. Overall, these results demonstrate a functional link between MTHFD2-dependent cancer metabolism and replication stress that can be exploited therapeutically with this new class of inhibitors. Helleday and colleagues describe a nanomolar MTHFD2 inhibitor that causes replication stress and DNA damage accumulation in cancer cells via thymidine depletion, demonstrating a potential therapeutic strategy in AML tumors in vivo.
14.	Eng, Frida, 1977-, et al. (författare) Frequency Analysis using Non-Uniform Sampling with Application to Active Queue Management 2004 Ingår i: Proceedings of the 2004 IEEE International Conference on Acoustics, Speech and Signal Processing. - Linköping : Linköping University Electronic Press. - 0780384849 ; , s. 581-584 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.
15.	Eng, Frida, et al. (författare) Frequency Domain Analysis of Signals with Stochastic Sampling Times 2007 Rapport (övrigt vetenskapligt/konstnärligt)abstract In nonuniform sampling (NUS), signal amplitudes and time stamps are delivered in pairs. Several methods to compute an approximate Fourier transform (AFT) have appeared in literature, and their posterior properties in terms of alias suppression and leakage have been addressed. In this paper, the sampling times are assumed to be generated by a stochastic process. The main result gives the prior distribution of several AFTs expressed in terms of the true Fourier transform and variants of the characteristic function of the sampling time distribution. The result extends leakage and alias suppression with bias and variance terms due to NUS. Specific sampling processes as described in literature are analyzed in detail. The results are illustrated on simulated signals, with particular focus to the implications for spectral estimation.
16.	Eng, Frida, et al. (författare) Frequency Domain Analysis of Signals with Stochastic Sampling Times 2008 Ingår i: IEEE Transactions on Signal Processing. - : IEEE Signal Processing Society. - 1053-587X .- 1941-0476. ; 56:7, s. 3089-3099 Tidskriftsartikel (refereegranskat)abstract In nonuniform sampling (NUS), signal amplitudes and time stamps are delivered in pairs. Several methods to compute an approximate Fourier transform (AFT) have appeared in literature, and their posterior properties in terms of alias suppression and leakage have been addressed. In this paper, the sampling times are assumed to be generated by a stochastic process. The main result gives the prior distribution of several AFTs expressed in terms of the true Fourier transform and variants of the characteristic function of the sampling time distribution. The result extends leakage and alias suppression with bias and variance terms due to NUS. Specific sampling processes as described in literature are analyzed in detail. The results are illustrated on simulated signals, with particular focus to the implications for spectral estimation.
17.	Gad, Helge, et al. (författare) MTH1 inhibition eradicates cancer by preventing sanitation of the dNTP pool 2014 Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 508:7495, s. 215-221 Tidskriftsartikel (refereegranskat)abstract Cancers have dysfunctional redox regulation resulting in reactive oxygen species production, damaging both DNA and free dNTPs. The MTH1 protein sanitizes oxidized dNTP pools to prevent incorporation of damaged bases during DNA replication. Although MTH1 is non-essential in normal cells, we show that cancer cells require MTH1 activity to avoid incorporation of oxidized dNTPs, resulting in DNA damage and cell death. We validate MTH1 as an anticancer target in vivo and describe small molecules TH287 and TH588 as first-in-class nudix hydrolase family inhibitors that potently and selectively engage and inhibit the MTH1 protein in cells. Protein co-crystal structures demonstrate that the inhibitors bindin the active site of MTH1. The inhibitors cause incorporation of oxidized dNTPs in cancer cells, leading to DNA damage, cytotoxicity and therapeutic responses in patient-derived mouse xenografts. This study exemplifies the non-oncogene addiction concept for anticancer treatment and validates MTH1 as being cancer phenotypic lethal.
18.	Geijer Lundin, Erik, et al. (författare) Adaptive Filtering Applied to an Uplink Load Estimate in WCDMA 2003 Ingår i: Proceedings of the 57th IEEE Semiannual Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780377575 ; , s. 452-456 Konferensbidrag (refereegranskat)abstract In the uplink of a WCDMA system, a natural choice of resource quantity is the uplink noise rise, i.e., total received power over noise power. Unfortunately this quantity is hard to measure and estimates are often noisy. This paper focuses on relative load which is closely related to the noise rise. Model-based signal processing with change detection techniques is herein used to suppress noise and minor oscillations while being alert on fast load changes. The time varying model identified in the process can also be used for prediction of future values, something which resource management algorithms can benefit from.
19.	Geijer Lundin, Erik, et al. (författare) Robust Uplink Resource Allocation in CDMA Cellular Radio Systems 2005 Ingår i: Proceedings of the 44th IEEE Conference on Decision and Control and European Control Conference 2005. - Linköping : Linköping University Electronic Press. - 0780395670 ; , s. 1848-1853 Konferensbidrag (refereegranskat)abstract Radio resource management (RRM) in cellular radio system is an example of automatic control. The system performance may be increased by introducing decentralization, shorter delays and increased adaptation to local demands. However, it is hard to guarantee system stability without being, too conservative while using decentralized resource management. In this paper, two algorithms that both guarantee system stability and use local resource control are proposed for the uplink (mobile to base station). While one of the algorithms uses only local decisions, the other uses a central node to coordinate resources among different local nodes. In the chosen design approach, a feasible solution to the optimization problems corresponds to a stable system. Therefore, the algorithms will never assign resources that lead to an unstable system. Simulations indicate that the proposed algorithms also provide high capacity at any given uplink load level.
20.	Geijer Lundin, Erik, et al. (författare) Uplink Load Estimates in WCDMA with Different Availability of Measurements 2003 Ingår i: Proceedings of the 57th IEEE Semiannual Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780377575 ; , s. 1198-1202 vol.2 Konferensbidrag (refereegranskat)abstract In the uplink of a WCDMA system, a natural choice of resource management control quantity is the uplink noise rise, i.e., total received power over noise power. Unfortunately this quantity is hard to measure. In this paper, we propose and evaluate a number of noise rise estimates which all rely on path gain measurements. These measurements can be made available either periodically or event-driven as described in 3GPP (Release 99). Simulations show that event-driven measurements yield comparable performance to periodic measurements, but with much fewer measurement reports. Despite severely limited path gain knowledge due to that some users report to another RNC, we still manage to estimate the uplink noise rise reasonably well.
21.	Geijer Lundin, Erik, et al. (författare) Uplink Load Estimation in WCDMA 2003 Ingår i: Proceedings of the 2003 IEEE Wireless Communications and Networking. - 0780377001 ; , s. 1669-1674 vol.3 Konferensbidrag (refereegranskat)abstract All cellular radio systems have radio resource management algorithms which rely on some sort of resource quantity. In the uplink of a WCDMA system, a natural choice of such a quantity is the uplink noise rise, i.e., total received power over noise power. Unfortunately this quantity is hard to measure. In this paper, we propose and evaluate four different noise rise 711 estimates. The best performing estimate provides an average error of less than 1 dB for practical load levels. Due to low standard deviation of single estimates it is possible to apply a simple error correction algorithm.
22.	Geijer Lundin, Erik (författare) Uplink Load in CDMA Cellular Systems 2003 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Cellular mobile systems designed to handle multimedia services are currently being developed. The primary goal for any mobile system is to provide a satisfactory quality of service, both to operators and customers. Providing good quality of service while maintaining system stability requires accurate knowledge of the system load. In particular, it is important to be able to predict how a resource management decision will affect the stability of the network. This thesis addresses the problem of characterizing and estimating the uplink load in a cellular system using CDMA (Code Division Multiple Access) in the radio interface.Uplink load can be related directly to the uplink power control problem of finding transmitter powers to support the users' quality of service requirements. This yields a rather theoretical view. Another way of looking at uplink load is to relate it to the total received power users induce in the base station antennas. Both of these views are handled and relations between them are established in this thesis.The literature survey on uplink load provided in this work concludes that practical estimates of the uplink load are generally what can be referred to as decentralized estimates; they use information gathered only in the immediate vicinity of the estimates' host node. As an alternative to these estimates, a number of centralized estimates based on information readilyavailable to the system are proposed. The usage of information from several cells makes them more sensitive to the soft capacity inherent in all CDMA cellular systems.Extensive simulations in an advanced WCDMA (Wideband Code Division Multiple Access) simulator show that the estimates statistically perform well and the performance is insensitive to non uniform traffic load.In the time domain, the load approximation can be described as oscillations superimposed on a slowly varying bias. If occasional high loads can be accepted, a non-oscillative signal representing the uplink load can be used to further increase the utilization of the resources. An algorithm is proposed to estimate the bias and a prediction of it.
23.	Georgii, Carl Fredrik, 1715-1795 (författare) Dissertatio historica de regione metallica Carlskoga, quam, venia ampl. fac. philos. Ups. praeside mag. Carolo Freder. Georgii, ... Pro gradu philosophico, publice ventilandam exhibet Nicolaus Gustavi Kjellin, Vermelandus. In audit. Gust. maj. d. 5 Maji 1779. H. A. M. C. 1779 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)
24.	Gunnarsson, Fredrik, et al. (författare) A Concept of Power Control in Cellular Radio Systems 1999 Ingår i: Proceedings of the 14th World Congress. - Linköping : Linköping University Electronic Press. - 9780080432137 Konferensbidrag (refereegranskat)abstract Due to the rapid expansion of the cellular radio systems market, and the need for wireless multimedia services, the available resources have to be utilized efficently. A common strategy is to control the transmitter powers of the mobiles and base stations. However, when applying power control to real systems, a number of challenges are prevalent. The performance is limited by time delays, nonlinearities and the availability of measurements and adequate quality measures. In this paper we present a Power Regulator concept, which comprises an Unknown Input Observer, a Quality Mapper and a Power Control Algorithm. The applicability of the concept is exemplified using frequency hopping GSM, and simulations indicate benefits of employing the proposed concept.
25.	Gunnarsson, Fredrik, et al. (författare) Control Theory Aspects of Power Control in UMTS 2003 Ingår i: Control Engineering Practice. - : Elsevier. - 0967-0661 .- 1873-6939. ; 11:10, s. 1113-1125 Tidskriftsartikel (refereegranskat)abstract The global communication systems critically rely on control algorithms of various kinds. In universal mobile telephony system (UMTS)-the third generation mobile telephony system just being launched-power control algorithms play an important role for efficient resource utilization. This survey article describes and discusses relevant aspects of UMTS power control with emphasis on practical issues, using an automatic control framework. Generally, power control of each connection is distributedly implemented as cascade control, with an inner loop to compensate for fast variations and an outer loop focusing on longer term statistics. These control loops are interrelated via complex connections, which affect important issues such as capacity, load and stability. Therefore, both local and global properties are important. The concepts and algorithms are illustrated by simple examples and simulations.
26.	Gunnarsson, Fredrik, et al. (författare) Controlling Internet Queue Dynamics using Recursively Identified Models 2003 Ingår i: Proceedings of the 42nd IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 0780379241 ; , s. 593-597 vol.1 Konferensbidrag (refereegranskat)abstract Data traffic on the Internet of today is controlled by a non-linear controller (TCP) at each sender node, which increases packet transmission rate each time an acknowledgment is received in due time, and decreases otherwise. The routers may co-operate with TCP by deliberately dropping packets, so called early drops. The idea is to decrease packet arrival rate before the queue becomes full and hard drops of packets are necessary. State of the art is to compute the probability of an early drop as a static function of the (filtered) queue length. We propose to use an auto-regressive model for the oscillative behavior of the queue length that can be observed in practice. With this model, the queue length can be predicted and a dynamic algorithm for computing the early drop probability can be used. We suggest a very simple modification of existing algorithms, where a short-time prediction is used instead of the current queue value, and demonstrate using ns-2 simulations that the overall throughput increases.
27.	Gunnarsson, Fredrik, et al. (författare) Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled DS-CDMA 2001 Ingår i: IEEE Journal on Selected Areas in Communications. - Linköping : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 19:1, s. 141-151 Tidskriftsartikel (refereegranskat)abstract Transmission power control is essential in systems of the third-generation (3G) in order to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers, due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete time-describing functions, which are introduced and applied. More importantly, time-delay compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm exhibits greater stability, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved, and thus, less fading margin is needed. The results apply not only to wideband code division multiple access (WCDMA), but to other direct-sequence (DS) CDMA systems power controlled in a similar manner as well.
28.	Gunnarsson, Fredrik, et al. (författare) Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled WCDMA 1999 Rapport (övrigt vetenskapligt/konstnärligt)abstract Transmission power control is essential in WCDMA in order to optimize the bandwidth utilization which is critical when variable data ratesare used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. When employing TDC, the power control algorithm operates more stable, which is important from a network perspective. Simulations illustrate the oscillations and the benefits of TDC. Moreover, the fading tracking capability is improved and thus less fading margin is needed. The latest news from standardization is to try to operate without additional delay when close to a base station. Nevertheless, there will still be more distant mobile stations for which TDC will be beneficial.
29.	Gunnarsson, Fredrik, et al. (författare) Estimation and Outer Loop Power Control in Cellular Radio Systems 2001 Rapport (övrigt vetenskapligt/konstnärligt)abstract A common strategy to utilize available resources in cellular radio systems is to control the transmitter powers. However, when applying power control to real systems, a number of challenges are prevalent. Available information in measurement reports are crude and highly quantized. This paper utilizes point-mass approximations of probability density functions to implement nonlinear estimation of relevant parameters. Most popular power control algorithms track specified target signal-to-interference ratios (SIR:s), but the challenge is to control target values in an outer control loop. Here target SIR:s are provided by utilizing models of the relation between a relevant quality measure, such as frame erasure rate (FER), and the estimated parameters. This is an interesting alternative to outer loop strategies based on relatively infrequent frame error measurements. The discussed outer loop can also include handling of different priorities. The methods proposed in this work are applicable to a general system, but FH-GSM is used as the example throughout the paper. Illuminating simulations of a FH-GSM system illustrate the behavior and performance, which are considered acceptable. By using the proposed outer loop, capacity gains of up to 30% have been observed.
30.	Gunnarsson, Fredrik, et al. (författare) Estimation of the Carrier-to-Interference Ratio in Cellular Radio Systems 1999 Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780355652 ; , s. 1312-1316 vol.2 Rapport (övrigt vetenskapligt/konstnärligt)abstract The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work has demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a maximum likelihood estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fast varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.
31.	Gunnarsson, Fredrik, et al. (författare) Improved Performance Using Nonlinear Components in Power Control Algorithms 1999 Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference. - Linköping : Linköping University Electronic Press. - 0780355652 ; , s. 1276-1280 vol.2 Konferensbidrag (refereegranskat)abstract When employing power control algorithms in real systems there are anumber of problems that have to be considered, of which some are addressed in this work. It is probably impossible to solve the problems using a linear controller, and as an extension, various nonlinear components and their applicability are discussed. Problems due to hardware and external constraints have been identified in previous work, and here anti-reset windup techniques are reviewed and employed. Previous proposals can be seen as special cases. Sometimes it is desirable to employ several algorithms in parallel, and then use a device to state priorities, i.e., to switch between the algorithms. The applicability of switches and selectors are described and exemplified as proposed solutions to the low interference problem, where a C/I balancing algorithm causes a user to use a too low a power. The benefits of using the proposed nonlinear components are further illustrated by network simulations.
32.	Gunnarsson, Frida, et al. (författare) Issues on Performance Measurements of TCP 2003 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.
33.	Gunnarsson, Fredrik, et al. (författare) MOSE - A Simulation Environment for Mobile Communications Systems 1998 Rapport (övrigt vetenskapligt/konstnärligt)abstract Thorough analytical analysis of cellular radio networks is difficult in general. Therefore simulation environments are adequate tools to gain understanding about the behaviour of algorithms used in cellular radio networks. In this report MOSE (MObile communications System Emulator) is described. The objective has been to develop an intuitive and user-friendly environment supported by a graphical user-interface. The implemented models include time-varying communication channels, co-channel interference, time delays and constraints. Several filtering and power control algorithms are implemented, and dedicated tests facilitate comparison with respect to different aspects.
34.	Gunnarsson, Fredrik, et al. (författare) Parameter Estimation in Cellular Radio Systems 1999 Ingår i: Proceedings of the Second Conference on Computer Science and Systems Engineering. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The problem to track time-varying parameters in cellular radio systems is studied. The focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance relying on analog measurement. In a real system most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). Therefore a different approach is required and for that matter a Maximum Likelihood Estimator has been designed and exemplified in the case of GSM. The needed probability functions of the measurements cannot be described analytically. Instead point-mass approximations can be obtained from Monte-Carlo simulations for each point in a grid covering the interesting parameter space. The proposed algorithm can be tuned to track both slowly and fastly varying parameters individually. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.
35.	Gunnarsson, Fredrik, et al. (författare) Post-processing of drive test measurements using spatial filtering 2004 Ingår i: IEEE Vehicular Technology Conference (VTC) Proceedings. - : IEEE. - 1550-2252. ; 1, s. 79-83 Tidskriftsartikel (refereegranskat)abstract Drive tests are important means to evaluate critical properties of a wireless network in operation. The network coverage is vital, and therefore, the received power of pilot signals from the base stations are monitored to estimate the spatial distributions and variations of the power gain. With uniform time-sampling and a varying velocity, the typical temporal filter fails to extract the interesting information. In this paper we apply convolutional spatial filtering, both causal and non-causal, to resolve the problem. Relations to spatial data analysis methods are also commented upon. Simulations indicate significant improvements.
36.	Gunnarsson, Fredrik, et al. (författare) Power Control in Cellular Radio Systems : Analysis and Design 1999 Ingår i: Proceedings of the 1999 Radiovetenskap och Kommunikation. - 9789163081569 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Many algorithms in communications systems can be considered as control loops, where the computed quantities depend on feedback information. A common scheme is to use increase/decrease signaling for bandwidth efficiency. Furthermore, the feedback information is delayed. The time delay itself, and even more pronounced in combination with nonlinearities, such as the increase/decrease mechanism, may cause oscillations and instabilities in the system. In this work, analysis methods based on root locus and describing functions are discussed. Design and tuning of algorithms are employed using pole placement techniques. Particular examples include clock synchronization in ADSL modems, control of available bit rate in data networks and, as studied in this project, distributed implementation of power control in cellular radio systems. The relevance of the methods is further illuminated by simulations.
37.	Gunnarsson, Fredrik, et al. (författare) Power Control in Cellular Radio Systems 2000 Ingår i: Proceedings of Reglermöte 2000. Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The primary goal of cellular radio systems is to provide communications services to a large number of mobile users. Due to the dramatic increase of this market, the available resources have to be utilized efficiently. Closed-loop power control is considered as an important component in these resource management algorithms. Here, relevant aspects on power control are discussed, using an automatic control framework. Generally, power control strategies are implemented as cascade control, with an inner loop to compensate for fast variations and an outer loop focusing on longer term statistics. Issues as capacity, load and stability are discussed and related to whether it is possible to accommodate the requirements of all users or not. The operation of such algorithms are illustrated by simulations.
38.	Gunnarsson, Fredrik (författare) Power Control in Cellular Radio Systems : Analysis, Design and Estimation 2000 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The primary goal of cellular radio systems is to provide communications services to a large number of mobile users. Due to the dramatic increase in number ofusers and their demand for more advanced services, the available resources haveto be utilized efficiently. Closed-loop power control is considered as an important component in this resource management.For practical reasons, the powers have to be computed locally for each connection, though performance and stability depend on how the different connections interact. We consider the power control problem as a decentralized control system, consisting of interconnected local control loops. Methods from control theory are used to analyze existing algorithms locally and to design controllers with improved performance. Thereby, performance degradation due to time delays and nonlinearities, can be handled by careful controller design. On a global level, we provide results on stability and convergence of the designed controllers. The results are illustrated by simulations using both small and large-scale simulation environments.
39.	Gunnarsson, Fredrik, et al. (författare) Power Control in Cellular Systems Subject to Constraints and Time Delays 1999 Rapport (övrigt vetenskapligt/konstnärligt)abstract Stability is a fundamental property desirable for any controlled system. We briefly review the root locus and describing function techniques, which are tools for stability analysis, and show how they can be applied to power control algorithms in cellular radio networks. The root locus method is used to find stability limits on controller parameters, and describing functions for predicting the presence of oscillations in the system. Thus these methods can be used to support the design phase, when deciding upon the appropriate controller parameters. These tools are demonstrated for various control algorithms and when different smoothing filters are applied. The analysis reveals that the distributed power control (DPC) algorithm, which works fine under ideal circumstances, yields an unstable system when subject to a small time delay. Furthermore, it is concluded that the performance with respect to stability is better when the measurements are averaged by an exponential forgetting filter than by the moving average filter.
40.	Gunnarsson, Fredrik, et al. (författare) Power Control with Time Delay Compensation 2000 Ingår i: Proceedings of the 52nd IEEE Vehicular Technology Conference. - Linköping : IEEE. - 0780365070 ; , s. 646-653 Konferensbidrag (refereegranskat)abstract Closed-loop power control is considered as an important component in the management of radio resources in cellular radio systems. The algorithms are typically based on feedback information, which for practical reasons is outdated. These time delays in the system, hamper the performance and might even result in unstable systems. Several power control strategies have been proposed in order to improve the capacity of cellular radio systems, but time delays are usually neglected. Here, time delay compensation is introduced as a means to improve the dynamical behavior of power controlled cellular systems, despite time delays. The improvements are validated both in theory with respect to global convergence and stability and in some illuminating simulations.
41.	Gunnarsson, Fredrik, et al. (författare) Time Delay Compensation for CDMA Power Control 2000 Ingår i: Proceedings of the 2000 IEEE Global Telecommunications Conference. - Linköping : IEEE. - 0780364511 ; , s. 1504-1508 Konferensbidrag (refereegranskat)abstract Transmission power control is essential in CDMA systems in order to reduce the near-far effect and to optimize the bandwidth utilization, which is critical when variable data rates are used. One remaining problem is oscillations in the output powers due to round-trip delays in the power control loops together with the power up-down command device. The oscillations are naturally quantified using discrete-time describing functions, which are introduced and applied. More importantly, Time Delay Compensation (TDC) is proposed to mitigate the oscillations. It is also formally proven that TDC result in a stable overall system, with power control errors that converges to a defined bounded region. These bounds are tighter, compared to when not employing TDC. Simulations illustrate the oscillations and the significant performance gains using TDC.
42.	Gunnarsson, Fredrik, et al. (författare) Time Delay Compensation in Power Controlled Cellular Radio Systems 2001 Ingår i: IEEE Communications Letters. - Linköping : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 5:7, s. 295-297 Tidskriftsartikel (refereegranskat)abstract Transmission power control is an important means to manage the radio resources in wireless communications. The performance, however, may be reduced due to time delays as in any controlled system. Most controllers to date are designed without considering time delays, which may result in oscillatory or unstable systems. To overcome these problems, time delay compensation (TDC) is introduced. The main idea is to adjust the measurements [e.g., signal-to-interference ratio (SIR)] to include the effects of issued but not yet applied power control commands. TDC thereby improves the stability and performance of an arbitrary power control algorithm. The benefits are illustrated by simulations using some popular power control algorithms.
43.	Gunnarsson, Fredrik, et al. (författare) Transmit Power Control Time Delay Compensation in a Wireless Communications System 2002 Patent (populärvet., debatt m.m.)abstract The present invention compensates for transmit power control time delays between a radio transmitter and receiver that adversely affect the transmit power control process. A time delay associated with a power control loop is compensated for by adjusting a detected signal quality value of a received signal, e.g., signal-to-interference ratio (SIR), based on one or more previous power control commands already sent but whose effect has not yet been experienced. Because the determined signal quality value of the received signal is adjusted based on one or more power control commands already sent but yet to take effect, the transmit power level control command is appropriately determined so that it also takes into account a power control loop time delay. The delay compensation value may be determined based on the output power of a single, previously generated transmit power control command, or on plural previously generated transmit power control commands, depending upon the length of the time delay. If the adjusted signal quality parameter exceeds the target signal quality parametery the generated power control command directs a decrease in transmit power, and the compensation factor causes a decrease in the subsequently determined signal quality parameter. If the adjusted signal quality parameter is less than the target signal quality parameter, the generated power control command directs an increase in transmit power, and the compensation factor causes an increase in the subsequently determined signal quality parameter.
44.	Gunnarsson, Fredrik, et al. (författare) Uplink Load and Link Budget with Stochastic Noise Rise Levels in CDMA Cellular Systems 2005 Ingår i: Proceedings of Radiovetenskap och Kommunikation 2005. ; , s. 491- Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract The limiting factor in the uplink of all CDMA cellular systems is the relation between uplink noise rise and intended coverage. In link budgets, noise rise is usually simply handled as a constant contribution to the background noise in logarithmic scale, often referred to as interference margin. In practice, however, it is not constant. We model the uplink noise rise as a lognormal distribution, and investigate the impact to link budgets. Simulations and numerical calculations show that the uplink noise rise variance does not critically affect the uplink capacity and coverage. System feasibility and its relation to the uplink load is also discussed. It is shown that approximative load expressions provides an upper bound on the uplink load and therefore they can be used to imply system feasibility. Furthermore, the uplink load expressions provide accurate approximations of the load given that the load is within the practical limits given by the link budgets.
45.	Gustafsson, Fredrik, et al. (författare) A New Concept of Power Control in Cellular Systems Reflecting Challenges of Today's Systems 1998 Ingår i: Proceedings of the 1998 IEEE Global Telecommunications Conference. - 0780349849 ; , s. 2097-2102 vol.4 Konferensbidrag (refereegranskat)abstract When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We will use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.
46.	Gustafsson, Fredrik, et al. (författare) Aspects on Performance Measurements of TCP Traffic and Its Reflection into Control Theory 2002 Ingår i: Proceedings of Reglermöte 2002. 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.
47.	Gustafsson, Fredrik, et al. (författare) Constrained Power Control in Cellular Systems Subject to Time Delays 1998 Ingår i: Proceedings of Reglermöte 1998. Konferensbidrag (övrigt vetenskapligt/konstnärligt)
48.	Gustafsson, Fredrik, et al. (författare) Constrained Power Control Subject to Time Delays 1998 Ingår i: Proceedings of the 1998 International Conference on Communication Technology. Konferensbidrag (refereegranskat)
49.	Gustafsson, Fredrik, et al. (författare) Estimation in Cellular Radio Systems 1999 Ingår i: Proceedings of the 1999 IEEE International Conference on Acoustics, Speech, and Signal Processing. - Linköping : Linköping University Electronic Press. - 0780350413 ; , s. 2551-2554 vol.5 Konferensbidrag (refereegranskat)abstract The problem to track time-varying parameters in cellular radio systems is studied, and the focus is on estimation based only on the signals that are readily available. Previous work have demonstrated very good performance, but were relying on analog measurement that are not available. Most of the information is lost due to quantization and sampling at a rate that might be as low as 2 Hz (GSM case). For that matter a maximum likelihood estimator have been designed and exemplified in the case of GSM. Simulations indicate good performance both when most parameters are varying slowly, and when subject to fast variations as in realistic cases. Since most computations take place in the base stations, the estimator is ready for implementation in a second generation wireless system. No update of the software in the mobile stations is needed.
50.	Gustafsson, Fredrik, et al. (författare) Forskare: ”Se upp med komplexa coronamodeller – de kan överträffa verkligheten” 2020 Ingår i: Ny teknik. - 0550-8754. Tidskriftsartikel (populärvet., debatt m.m.)

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