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  • 151.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Time Delay Compensation for CDMA Power Control2000Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 152.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Time Delay Compensation in Power Controlled Cellular Radio Systems2001Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 153.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Time Delay Compensation in Power Controlled Cellular Radio Systems2001Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 5, nr 7, s. 295-297Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 154.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled DS-CDMA2001Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 155.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled DS-CDMA2001Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 19, nr 1, s. 141-151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 156.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Dynamical Effects of Time Delays and Time Delay Compensation in Power Controlled WCDMA1999Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 157.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Estimation and Outer Loop Power Control in Cellular Radio Systems2001Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 158.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Improved Performance Using Nonlinear Components in Power Control Algorithms1999Ingår i: Proceedings of the 49th IEEE Vehicular Technology Conference, 1999, s. 1276-1280 vol.2Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 159.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Improved Performance Using Nonlinear Components in Power Control Algorithms1999Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 160.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Blom, Jonas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Pole Placement Design of Power Control Algorithms1999Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 161.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gunnarson, Frida
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Controlling Internet Queue Dynamics using Recursively Identified Models2003Ingår i: Proceedings of the 42nd IEEE Conference on Decision and Control, 2003, Vol. 1, s. 593-597 vol.1Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 162.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Tjärnström, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Signal processing: exercises2010 (uppl. 1)Bok (Övrigt vetenskapligt)
    Abstract [en]

    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

  • 163.
    Gunnarsson, Fredrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Wiberg, Niclas
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Transmit Power Control Time Delay Compensation in a Wireless Communications System2002Patent (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    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.

  • 164.
    Gunnarsson, Frida
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Björsson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Knutsson, Björn
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Gunarsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
    Radio Access Network (UTRAN) Modeling for Heterogenous Network Simulations2003Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 165.
    Gunnarsson, Frida
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gunnarsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Issues on Performance Measurements of TCP2003Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 166.
    Gunnarsson, Frida
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gunnarsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    TCP Performance based on Queue Occupation2001Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 167.
    Gunnarsson, Frida
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Gunnarsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Frequency Analysis using Non-Uniform Sampling with Application to Active Queue Management2004Rapport (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 168.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Change Detection and Segmentation Toolbox for Matlab1994Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This report describes the algorithms implemented in a Matlab toolbox for change detection and data segmentation. Functions are provided for simulating changes, choosing design parameters and detecting abrupt changes in signals.

  • 169.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Comparative Study on Change Detection for some Automotive Applications1997Ingår i: Proceedings of the 1997 European Control Conference, 1997Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a comparison of some different change detection methods for three automotive applications. The applications are tire-road friction estimation, fuel consumption monitoring and navigation using wheel velocities. In simulation studies on real data, measures of performance are given. Experience of real-time implementations in a Volvo is also presented.

  • 170.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Generalization of MDL for Choosing Adaptation Mechanism and Design Parameters in Identification1997Ingår i: Proceedings of the 11th IFAC Symposium on System Identification, 1997, Vol. 2, s. 487-492Konferensbidrag (Refereegranskat)
    Abstract [en]

    The minimum description length (MDL) has for some decades been known to be an efficient tool for choosing model structure. We will in this contribution generalize MDL to adaptive algorithms in system and signal identification. The parameter vector in these problems can either be considered as piecewise constant using segmentation and change detection algorithms or as time-varying estimated by recursive identification algorithms. MDL is derived as a measure of code length needed to transmit or store a signal. With the generalization we can compute not only the best model structure for the signal, but also when it pays off to use recursive identification and transmit the parameter updates together with the residuals, or if it is better to segment the signal and transmit the change points and the parameters. The approach opens an auto-tuning possibility, where the design parameters in the recursive identification and change detection methods can be optimized with respect to the code length.

  • 171.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Two-filter Approach to Optimal Detection of Jumps in Linear Systems1992Ingår i: Proceedings of the 4th IFAC Symposium on Adaptive Systems in Control and Signal Processing, 1992, s. 681-686Konferensbidrag (Refereegranskat)
  • 172.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Two-Filter Approach to Optimal Detection of Jumps in Linear Systems1992Rapport (Övrigt vetenskapligt)
  • 173.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    A Two-Filter Off-Line Solution to Optimal Detection1991Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The problem of detecting abrupt changes of the dynamics in linear systems is addressed. First the generalized likelihood ratio test for detection in a state space model is examined. This test can be interpreted as a simultaneous maximum likelihood (ML) estimator of the jump time and jump magnitude. The problem is that this test requires a large number of matched filters which increases linearly with time. This is shown by simulations to be very time consuming. Therefore, a two-filter implementation of the ML estimator of the jump time is derived, which is very efficient in off-line detection. It consists of two Kalman filters, one running forwards and one backwards in time. The algorithm gives a considerable improvement on-line as well, if a batchwise data processing is allowed. A major problem in detection is the sensivity to incorrect values of the noise variance. This is solved by treating the noise variance as a stochastic variable, possibly changing at the jump time. A modified algorithm is given, which is still optimal for this case.

  • 174.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Automotive Safety Systems2009Ingår i: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 26, nr 4, s. 32-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, we have surveyed the main needs for signal processing development and argued for a sensor fusion approach where all tasks are considered jointly. First, the section "automotive safety systems" summarized a number of safety systems, and it was pointed out that a limited number of sensors can be sufficient to implement a variety of safety systems. Second, the active development of improved communication networks enables new sensor fusion strategies.

  • 175.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Challenges in Signal Processing for Automotive Safety Systems2005Ingår i: Proceedings of the 13th IEEE/SP Workshop on Statistical Signal Processing, 2005, s. 1-8Konferensbidrag (Refereegranskat)
    Abstract [en]

    The amount of software in general and safety systems inparticular increases rapidly in the automotive industry. The trend is that functionality is decentralized, so new safety functions are distributed to common shared computer hardware, sensors and actuators using central data buses. This paper overviews recent and future safety systems, and highlights the big challenges for researchers in the signal processing area.

  • 176.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Change Detection and Adaptive Filtering Toolbox2001Övrigt (Övrigt vetenskapligt)
  • 177.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Consistent Low-Complexity Estimation of Active Parameters in Large Linear Regressions1997Ingår i: Proceedings of the 11th IFAC Symposium on System Identification, 1997, Vol. 3, s. 1419-1424Konferensbidrag (Refereegranskat)
    Abstract [en]

    Some important practical signals and systems can be modeled by very large linear regression models where it is reasonable that most of the parameters are zero. We give an efficient method to solve this combined estimation and structure determination problem. It is related to Akaike-like criteria, and is based on one LMS filter and thus it is of low complexity. Asymptotic analysis shows that the method is consistent for finite impulse response models. A recursive algorithm is derived, which can be applied to time-varying systems as well. An example shows the efficiency of the approach.

  • 178.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Determining the Initial States in Forward-Backward Filtering1994Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Forward-backward filtering is a common tool in off-line filtering for implementing noncausal filters. Filtering first forward and then backward or the other way around does not generally give the same result. Here, we propose a method to choose the initial state to obtain uniqueness and to remove transients at both ends.

  • 179.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Determining the Initial States in Forward-Backward Filtering1996Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 46, nr 4, s. 988-992Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Forward-backward filtering is a common tool in off-line filtering for implementing noncausal filters. Filtering first forward and then backward or the other way around does not generally give the same result. Here, we propose a method to choose the initial state to obtain uniqueness and to remove transients at both ends.

  • 180.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation and Change Detection of Tire -- Road Friction using Wheel Slip1996Ingår i: Proceedings of the 1996 IEEE International Symposium on Computer-Aided Control System Design, 1996Konferensbidrag (Refereegranskat)
    Abstract [en]

    An estimation approach and a comparison of some change detection algorithms for surveillance of vehicle tire--road friction are presented. The over-all method is aimed to provide the driver with tire--road friction information during normal driving conditions, using only standard sensors. A Kalman filter is applied to a physical model of tire-road friction based on the so called wheel slip. To get a simultaneous accurate estimate and fast response to friction changes, different change detectors are examined and evaluated. From a real-time implementation in a Volvo 850 and extensive field tests, we conclude that a low complexity change detector, the CUSUM test, gives fast alarms after friction changes, while giving a very low false alarm rate.

  • 181.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation of Discrete Parameters in Linear Systems1992Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Linear models are the by far most commonly used approach for describing physical signals and systems. As a result, the theory of linear models is quite extensive in areas like control theory and signal processing. However, in many applications a linear model is adequate only if some information of discrete nature is available. This thesis addresses the problem of how to treat and estimate this discrete information. Several applications on the problem of estimating discrete parameters in linear systems from measurements of its output are covered in the literature. Typically, the problem is treated separately in each context without overlapping. Orre objective of the present work is to discuss this problem in a general framework, relating proposed methods at a higher leve! of abstraction for revealing the main ideas.

    Estimators for discrete parameters are quite complex to compute, due to the fact that essentially every possible value of the discrete parameter has to be examined separately. The key question in applications is to find feasible expressions for the estimators, either exact or approximate. Besides the general discussion of the problem, the thesis contains more detailed treatments of four applications: mode! structure selection, detection, segmentation and blind equalization. The main topics covered in the applications consider the computation of optimal estimates, analysis and practical recursive schemes. Several statistical optimality criteria are examined, and a number of efficient computation schemes are presented. In the analysis, questions such as detectability, identifiability and efficiency are addressed. It is also investigated how different prior assumptions infiuence the estimates, and how their effects can be reduced by giving as non-informative priors as possible. This leads to estimation algorithms which contain almost no design variables.

  • 182.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation of Discrete Parameters in Linear Systems1992Rapport (Övrigt vetenskapligt)
  • 183.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Estimation of Discrete Parameters in Linear Systems1992Rapport (Övrigt vetenskapligt)
  • 184.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Geolocation: Maps, measurements and methods2012Ingår i: IET Conference Publications, 2012, Vol. 2012, nr 595 CP, s. 1-48Konferensbidrag (Refereegranskat)
    Abstract [en]

    [No abstract available]

  • 185.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Identification of sparse linear regression1995Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Some important practical signals and systems can be modeled by very large linear regression models where it is reasonable that most of the parameters are zero We give an ecient method to solve this combined estimation and struc ture determination problem and relate the result to Akaikes information criteria for structure selection and criteria based on hypothesis testing A recursive algorithm is derived which can be applied to timevarying systems as well Two practical examples show the eciency of the approach

  • 186.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Identification of Sparse Linear Regressions1996Ingår i: Proceedings of the 13th IFAC World Congress, 1996, Vol. J, s. 203-208Konferensbidrag (Refereegranskat)
  • 187.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Identification of Time-Varying Systems from a Bayesian Viewpoint1989Rapport (Övrigt vetenskapligt)
  • 188.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Monitoring Tire-Road Friction using the Wheel Slip1998Ingår i: IEEE Control System, ISSN 1066-033X, Vol. 18, nr 4, s. 42-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Tire-road friction estimation has become an intense research area as the interest of information technology in vehicles increases. In this work, we follow a model-based approach where the difference in wheel velocities of driven and non-driven wheels is used. The perhaps most important feature is that only existing sensors are needed if the car is supplied with ABS brakes. The goal is to compute certain parameters from available standard sensors in the car, which depend directly or indirectly on the friction, and to find rules regarding how to evaluate the maximal friction forces that can be used for braking or cornering.

  • 189.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    On Simultaneous System and Input Sequence Estimation1992Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Equalization is concerned with estimation of the input sequence of a linear system given noisy measurements of the output signal. In case the system description is unknown we have the problem of blind equalization. A scheme for blind equalization which is based on the assumption that the input signal belongs to a finite alphabet is proposed. A finite impulse response model can be directly estimated by the least-squares method if the input sequence is known. Since we know that the number of possible input sequences is limited, we can associate one system estimate to each possible input sequence. This allows us to determine the a posteriori probability of an input sequence given output observations. The maximum a posteriori (MAP) input sequence estimate is then taken as the most probable input sequence. Sufficient conditions for identifiability of the input signal and the system are given. The complexity of this scheme increases exponentially with time. A recursive approximate MAP estimator of fixed complexity is obtained by, at each time update, only keeping the K most probable input sequences. This method is evaluated on a Rayleigh fading communication channel.

  • 190.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    On the Estimation of Discrete Parameters in Linear Systems1993Ingår i: Proceedings of the 12th IFAC World Congress, 1993, s. 351-Konferensbidrag (Refereegranskat)
  • 191.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    On the Estimation of Discrete Parameters in Linear Systems1993Rapport (Övrigt vetenskapligt)
  • 192.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Optimal Segmentation in a Linear Regression Framework1991Ingår i: Proceedings of the 1991 International Conference on Acoustics, Speech and Signal Processing, 1991, s. 1677-1680 vol.3Konferensbidrag (Refereegranskat)
    Abstract [en]

    The problem of estimating the time instants when the dynamical properties of a signal make abrupt changes is studied. This segmentation problem is usually considered as exponential in time. The author presents a specific but natural signal mode-called a changing regression model-and points out a method to compute an optimal estimate of the segmentation problem linearly in time. The linear constant is always less than one and decreases to zero as the measurement noise decreases to zero. The method is thus asymptotically efficient in the measurement noise.

  • 193.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Optimal Segmentation of Linear Regression Parameters1991Ingår i: Proceedings of the 9th IFAC Symposium on System Identification and System Parameter Estimation, 1991, s. 225-229Konferensbidrag (Refereegranskat)
  • 194.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Optimal Segmentation of Linear Regression Parameters1990Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The problem of detecting multiple changes in the dynamical properties of a measured signal, which we call segmentation, is studied. A Bayesian model-based approach is used. The signal is supposed to be described by a linear regression. The posterior distribution for the change instants is first derived for a quite general signal model. Three special choices of signal model are then proposed for segmentation. The maximum a posteriori (MAP) estimate is studied. It is shown that it contains the estimates from the maximum likelihood method and the generalized likelihood ratio test as special cases.

    This posterior distribution contains a number of components which increases exponentially in the number of measurements, t. Nevertheless, it is shown that under certain assumptions on the parameter variation structure, the number of components that really ha veto be examined increases considerably less than t. This exact pruning possibility is shown to be asymptotically efficient in the ratio between the jump magnitude and the noise variance.

    For the general signal model a recursive search scheme is proposed to approximate the MAP estimate. Segmentation examples and other possible applications of the search scheme are given.

  • 195.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Optimal Segmentation of Linear Regression Parameters1991Rapport (Övrigt vetenskapligt)
  • 196.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Optimal Segmentation of Signals in a Linear Regression Framework1991Ingår i: Proceedings of the 1991 International Conference on Acoustics, Speech and Signal Processing, 1991, s. 1677-1680 vol.3Konferensbidrag (Refereegranskat)
    Abstract [en]

    The problem of estimating the time instants when the dynamical properties of a signal make abrupt changes is studied. This segmentation problem is usually considered as exponential in time. The author presents a specific but natural signal mode-called a changing regression model-and points out a method to compute an optimal estimate of the segmentation problem linearly in time. The linear constant is always less than one and decreases to zero as the measurement noise decreases to zero. The method is thus asymptotically efficient in the measurement noise.

  • 197.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Optimal Segmentation of Signals in a Linear Regression Framework1991Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The problem of estimating the time instants when the dynamical properties of a signal make abrupt changes is studied. This segmentation problem is usually considered as exponential in time. The author presents a specific but natural signal mode-called a changing regression model-and points out a method to compute an optimal estimate of the segmentation problem linearly in time. The linear constant is always less than one and decreases to zero as the measurement noise decreases to zero. The method is thus asymptotically efficient in the measurement noise.

  • 198.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Particle Filter Theory and Practice with Positioning Applications2010Ingår i: IEEE Aerospace and Electronic Systems Magazine, ISSN 0885-8985, E-ISSN 1557-959X, Vol. 25, nr 7, s. 53-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The particle filter (PF) was introduced in 1993 as a numerical approximation to the nonlinear Bayesian filtering problem, and there is today a rather mature theory as well as a number of successful applications described in literature. This tutorial serves two purposes: to survey the part of the theory that is most important for applications and to survey a number of illustrative positioning applications from which conclusions relevant for the theory can be drawn. The theory part first surveys the nonlinear filtering problem and then describes the general PF algorithm in relation to classical solutions based on the extended Kalman filter (EKF) and the point mass filter (PMF). Tuning options, design alternatives, and user guidelines are described, and potential computational bottlenecks are identified and remedies suggested. Finally, the marginalized (or Rao-Blackwellized) PF is overviewed as a general framework for applying the PF to complex systems. The application part is more or less a stand-alone tutorial without equations that does not require any background knowledge in statistics or nonlinear filtering. It describes a number of related positioning applications where geographical information systems provide a nonlinear measurement and where it should be obvious that classical approaches based on Kalman filters (KFs) would have poor performance. All applications are based on real data and several of them come from real-time implementations. This part also provides complete code examples.

  • 199.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Rotational Speed Sensors: Limitations, Pre-processing and Automotive Applications2010Ingår i: IEEE Instrumentation & Measurement Magazine, ISSN 1094-6969, E-ISSN 1941-0123, Vol. 13, nr 2, s. 16-23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rotational speed sensors are critical for all vehicular driver assistance systems and other applications such as engine control and robotics. For many embedded control systems, the accuracy of the computed speed needs to be high, and this puts special demands on the pre-processing of the sensor signal. In a wired centralized solution, the computational unit can get access to the raw square wave signal from the sensor. Without a dedicated wire, the sensor must include a timer, and the cog times tk can be communicated to the processor. These cog times are the input to the algorithms described here, whose purpose is to calibrate manufacturing errors in the cog wheel and to interpolate the speed signal to the (usually time) domain of the application. A further purpose was to derive rules of thumb for how the sampling and quantization processes influence the bias and variance of the computed speed signal. Examples of applications to imbalance monitoring, frequency analysis applications, and fault detection were provided.

  • 200.
    Gustafsson, Fredrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Segmentation of Signals Using Piecewise Constant Linear Regression Models1994Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The signal segmentation approach described herein assumes that the signal can be accurately modelled by a linear regression with piece-wise constant parameters. A simultaneous estimate of the change times is considered. The maximum likelihood and maximum a posteriori probability estimates are derived after marginalization of the linear regression parameters and the measurement noise variance, which are considered as nuisance parameters. A well-known problem is that the complexity of segmentation increases exponentially in the number of data. Therefore, two inequalities are derived enabling the exact estimate to be computed with quadratic complexity. A linear in time complexity recursive approximation is proposed as well, based on these inequalities. The method is evaluated on a speech signal previously analyzed in literature, showing that a comparable result is obtained directly without the usual tuning effort. It is also detailed how it successfully has been applied in a car for online segmentation of the driven path for supporting guidance systems.

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