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  • 1.
    af Ekenstam, Love
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Modellering av signalbehandlingen i ett cochleaimplantat och utvärdering av modellen.2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A program that simulates the signal processing in a cochlear implant using the signal processing strategy ACE (Advanced Combination Encoder) was constructed. Its main purpose is to, in advance, predict and test different implant settings with the purpose to be able to predict individual patient's differences in implant settings.

     

    The program was validated using output signals processed by Cochlear Limited using their own Matlab Toolbox for implant research, NMT (Nucleus Matlab Toolbox). Identical signals were processed by the program and then compared with NMT:s output. The outputs, produced with several different identical settings matched each other well.

     

    The amplitude compression function, a vital part of the signal processing, also matched well, apart from a relative loss of strength at high input amplitudes. The program will now be used by the cochlear implant section at Uppsala University Hospital to try out individual settings for cochlear implant users. The hope for the future is that better implant settings will lead to improved speech and sound experience, especially, in the long run, with regards to music.

  • 2.
    Agrawal, Piyush
    et al.
    United Technologies Research Center, Cork, Irland.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Olofsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Gidlund, M
    Characterization of long term channel variations in industrial wireless sensor networks2014Conference paper (Refereed)
  • 3.
    Agrawal, Piyush
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlén, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Olofsson, Tomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Gidlund, Mikael
    Long Term Channel Characterization for Energy Efficient Transmission in Industrial Environments2014In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, no 8, p. 3004-3014Article in journal (Refereed)
    Abstract [en]

    One of the challenges for a successful use of wireless sensor networks in process industries is to design networks with energy efficient transmission, to increase the lifetime of the deployed network while maintaining the required latency and bit-error rate. The design of such transmission schemes depend on the radio channel characteristics of the region. This paper presents an investigation of the statistical properties of the radio channel in a typical process industry, particularly when the network is meant to be deployed for a long time duration, e. g., days, weeks, and even months. Using 17-20-h-long extensive measurement campaigns in a rolling mill and a paper mill, we highlight the non-stationarity in the environment and quantify the ability of various distributions, given in the literature, to describe the variations on the links. Finally, we analyze the design of an optimal received signal-to-noise ratio (SNR) for the deployed nodes and show that improper selection of the distribution for modeling of the variations in the channel can lead to an overuse of energy by a factor of four or even higher.

  • 4.
    Ahlén, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Ahlgren, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Grönroos, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Katardjiev, Ilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Rohner, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rydberg, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Presentation of the VINN Excellence Center for Wireless Sensor Networks (WISENET)2008In: Conference on Radio Science (RVK08), Växjö, 2008Conference paper (Refereed)
  • 5.
    Ahlén, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. Univ Newcastle, Dept Elect & Comp Engn, Callaghan, NSW, Australia.
    Åkerberg, Johan
    ABB Corp, Vasteras, Sweden.
    Eriksson, Markus
    Scania CV, Sodertalje, Sweden.
    Isaksson, Alf J.
    Linkoping Univ, Linkoping, Sweden;Univ Newcastle, Callaghan, NSW, Australia;Royal Inst Technol, Stockholm, Sweden;ABB Corp Res, Vasteras, Sweden.
    Iwaki, Takuya
    JGC Corp, Yokohama, Kanagawa, Japan;KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Stockholm, Sweden.
    Johansson, Karl Henrik
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Stockholm, Sweden.
    Knorn, Steffi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. Univ Newcastle, Ctr Complex Dynam Syst & Control, Callaghan, NSW, Australia.
    Lindh, Thomas
    Iggesund Mill, Maintenance Technol Dev, Iggesund Paperboard, Sweden.
    Sandberg, Henrik
    KTH Royal Inst Technol, Div Decis & Control Syst, Stockholm, Sweden;CALTECH, Pasadena, CA 91125 USA;MIT, Lab Informat & Decis Syst, 77 Massachusetts Ave, Cambridge, MA 02139 USA.
    Toward Wireless Control in Industrial Process Automation: A Case Study at a Paper Mill2019In: IEEE CONTROL SYSTEMS MAGAZINE, ISSN 1066-033X, Vol. 39, no 5, p. 36-57Article in journal (Refereed)
    Abstract [en]

    Wireless sensors and networks are used only occasionally in current control loops in the process industry. With rapid developments in embedded and highperformance computing, wireless communication, and cloud technology, drastic changes in the architecture and operation of industrial automation systems seem more likely than ever. These changes are driven by ever-growing demands on production quality and flexibility. However, as discussed in "Summary," there are several research obstacles to overcome. The radio communication environment in the process industry is often troublesome, as the environment is frequently cluttered with large metal objects, moving machines and vehicles, and processes emitting radio disturbances [1], [2]. The successful deployment of a wireless control system in such an environment requires careful design of communication links and network protocols as well as robust and reconfigurable control algorithms.

  • 6. Alfredsson, Stefan
    et al.
    Brunström, Anna
    Karlstad universitet.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group. Signals and systems.
    Analysis of a 4G system performance from a link- and transport layer perspective2007Conference paper (Refereed)
  • 7.
    Alfredsson, Stefan
    et al.
    Karlstad universitet.
    Brunström, Anna
    Karlstad universitet.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Impact of 4G wireless link configurations on VoIP network performance2008In: IEEE International Symposium on Wireless Communication Systems 2008, ISWCS2008, Reykjavik, Iceland, 2008Conference paper (Refereed)
  • 8.
    Al-Husseiny, Zeid
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Energy Efficient LTE Site Operation: with Antenna Muting and dynamic Psi-Omni2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To allow access to the network at all times a base station has to continuously stay active. While being active, a base station does not usually transmit data constantly. Typically, the base stations either send out lots of data or barely anything at all, yet, the network is actively drawing power the whole time. Succeeding in lowering the power consumed when the data rate is often so low would therefore lead to great benefits, both economically and environmentally, as well as new prospects of innovation in engineering. The process of how to dynamically change from a capacity optimized mode to an energy optimized mode as well as when to do this change is studied in this thesis for LTE.

    By using methods such as antenna muting and psi-omni coverage, the power consumption can decrease. These solutions however also decreases performance, and has to be activated with great care in mind not to cause any major impact on user performance. The dynamic configuration is dependent on the load of the system, changing to an energy efficient mode when traffic is low and to a capacity optimized mode when the network needs to supply high data rates.

    Simulations show that most energy savings can be found in rural and urban environments. Dynamic antenna muting achieved, summarizing macro environments, 24.9% energy savings with 95.27% downlink data rates compared to the reference case of using sector mode continuously i.e MIMO. In the same environments, dynamic psi-omni coverage together with antenna muting achieved energy savings of 43.8% with 89.3% downlink data rates compared to typical sector mode. Traffic rates are based on future demands in Europe by 2015, assuming that 20% of the subscribers are downloading 900 MB/h and the other 80% subscribers, at 112.5 MB/h. 

  • 9.
    Alpcan, Tansu
    et al.
    Department of Electrical and Electronic Engineering, The University of Melbourne, Australien.
    Dey, Subhrakanti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    An information-theoretic analysis of distributed resource allocation2013In: Proceedings, 2013, p. 7327-7332Conference paper (Refereed)
  • 10.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Magda, P
    AGH University of Science and Technology, Kraków, Polen.
    Dragan, K
    Air Force Institute of Technology, Warsawa, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Temperature compensation based on Hilbert transform and instantaneous phase for Lamb waves-based SHM systems of aircraft structures2013In: Proceedings of the 9th International Workshop on Structural Heath Monitoring 2013 / [ed] Fu-Kuo Chang, 2013, Vol. sept, p. 1259-1266Conference paper (Refereed)
  • 11.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Packo, Pawel
    AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Experimental comparison of 2D arrays topologies for SHM of planar structures2012In: SPIE Conference Smart Structures and Materials & NDE and Health Monitoring, 2012, San Diego, CA, USA, Proceedings SPIE 8347, SPIE - International Society for Optical Engineering, 2012, p. 834717-Conference paper (Refereed)
  • 12.
    Ambrozinski, Lukasz
    et al.
    Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Kraków, Polen.
    Packo, Pawel
    Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    Department of Robotics and Mechatronics, Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, Kraków, Polen.
    Ultrasonic guided waves based method for SHM: Simulations and an experimental test2011In: 5th World Conference on Structural Control and Monitoring, Tokyo, Japan, 2011Conference paper (Refereed)
  • 13.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Piwakowski, Bogdan
    Ecole Centrale de Lille, Villeneuve d'Ascq, Frankrike.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Application of air-coupled ultrasonic transducers for damage assessment of composite panels2012In: 6th European Workshop on Structural Health Monitoring, Dresden, Tyskland, 2012Conference paper (Refereed)
  • 14.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Packo, Pawel
    AGH University of Science and Technology, Kraków, Polen.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Self-focusing Lamb waves based on the decomposition of the time-reversal operator using time-frequency representation2012In: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 27, p. 337-349Article in journal (Refereed)
    Abstract [en]

    Active ultrasonic arrays are very useful for structural health monitoring (SHM) of large plate-like structures. Large areas of a plate can be monitored from a fixed position but it normally requires precise information on material properties. Self-focusing methods can perform well without the exact knowledge of a medium and array parameters. In this paper a method for selective focusing of Lamb waves will be presented. The algorithm is an extension of the DORT method (French acronym for decomposition of time-reversal operator) where the continuous wavelet transform (CWT) is used for the time-frequency representation (TFR) of nonstationary signals instead of the discrete Fourier transform. The performance of the methods is compared and verified in the paper using both simulated and experimental data. It is shown that the extension of the DORT method with the use of TFR considerably improved its resolving ability. To experimentally evaluate the performance of the proposed method, a linear array of small piezoelectric transducers attached to an aluminum plate was used to obtain interelement responses, required for beam self-focusing on targets present in the plate. The array was used for the transmission of signals calculated with the DORT-CWT algorithm. To verify the self-focusing effect the backpropagated field generated in the experiment was sensed using laser scanning vibrometer.

  • 15.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Design of 2D phased array for monitoring isotropic plate-like structures using Lamb waves2012In: 6th European Workshop on Structural Health Monitoring, Dresden, Tyskland, 2012Conference paper (Refereed)
  • 16.
    Ambrozinski, Lukasz
    et al.
    AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    AGH University of Science and Technology, Kraków, Polen.
    Self focusing of 2D arrays for SHM of plate-like structures using time reversal operator2011In: 8th Workshop on SHM, Stanford, CA, 2011, 2011Conference paper (Refereed)
  • 17.
    Ambrozinski, Lukasz
    et al.
    Faculty of Mechanical Engineering and Robotics, Dept of Robotics and Mechatronics,AGH University of Science and Technology, Kraków, Polen.
    Stepinski, Tadeusz
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Uhl, Tadeusz
    Faculty of Mechanical Engineering and Robotics, Dept of Robotics and Mechatronics,AGH University of Science and Technology, Kraków, Polen.
    Ochonski, Janusz
    Faculty of Mechanical Engineering and Robotics, Dept of Robotics and Mechatronics,AGH University of Science and Technology, Kraków, Polen.
    Klepka, Andrzej
    Faculty of Mechanical Engineering and Robotics, Dept of Robotics and Mechatronics,AGH University of Science and Technology, Kraków, Polen.
    Development of Lamb waves-based SHM systems2012In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 518, p. 87-94Article in journal (Refereed)
  • 18.
    Andersson, Claes R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Fryknäs, Mårten
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Genetics and Pathology.
    Rickardson, Linda
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Larsson, Rolf
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Isaksson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology.
    Gustafsson, Mats G.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    In vitro drug sensitivity-gene expression correlations involve a tissue of origin dependency2007In: Journal of chemical information and modeling, ISSN 1549-9596, Vol. 47, no 1, p. 239-248Article in journal (Refereed)
    Abstract [en]

    A major concern of chemogenomics is to associate drug activity with biological variables. Several reports have clustered cell line drug activity profiles as well as drug activity-gene expression correlation profiles and noted that the resulting groupings differ but still reflect mechanism of action. The present paper shows that these discrepancies can be viewed as a weighting of drug-drug distances, the weights depending on which cell lines the two drugs differ in.

  • 19.
    Andersson, Claes R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics.
    Hvidsten, Torgeir R.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics.
    Isaksson, Anders
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences.
    Gustafsson, Mats G.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Clinical Pharmacology. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Komorowski, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, The Linnaeus Centre for Bioinformatics.
    Revealing cell cycle control by combining model-based detection of periodic expression with novel cis-regulatory descriptors2007In: BMC Systems Biology, ISSN 1752-0509, Vol. 1, p. 45-Article in journal (Refereed)
    Abstract [en]

    Background: We address the issue of explaining the presence or absence of phase-specific transcription in budding yeast cultures under different conditions. To this end we use a model-based detector of gene expression periodicity to divide genes into classes depending on their behavior in experiments using different synchronization methods. While computational inference of gene regulatory circuits typically relies on expression similarity (clustering) in order to find classes of potentially co-regulated genes, this method instead takes advantage of known time profile signatures related to the studied process. Results: We explain the regulatory mechanisms of the inferred periodic classes with cis-regulatory descriptors that combine upstream sequence motifs with experimentally determined binding of transcription factors. By systematic statistical analysis we show that periodic classes are best explained by combinations of descriptors rather than single descriptors, and that different combinations correspond to periodic expression in different classes. We also find evidence for additive regulation in that the combinations of cis-regulatory descriptors associated with genes periodically expressed in fewer conditions are frequently subsets of combinations associated with genes periodically expression in more conditions. Finally, we demonstrate that our approach retrieves combinations that are more specific towards known cell-cycle related regulators than the frequently used clustering approach. Conclusion: The results illustrate how a model-based approach to expression analysis may be particularly well suited to detect biologically relevant mechanisms. Our new approach makes it possible to provide more refined hypotheses about regulatory mechanisms of the cell cycle and it can easily be adjusted to reveal regulation of other, non-periodic, cellular processes.

  • 20.
    Apelfröjd, Rikke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Channel Estimation and Prediction for 5G Applications2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Accurate channel state information (CSI) is important for many candidate techniques of future wireless communication systems. However, acquiring CSI can sometimes be difficult, especially if the user equipment is mobile in which case the future channel realisations must be estimated/predicted. In realistic settings the predictability of radio channels is limited due to measurement noise, limited model orders and since the fading statistics must be modelled based on a set of limited and noisy training data.

    In this thesis, the limits of predictability for the radio channel are investigated. Results show that the predictability is limited primarily due to limitations in the training data, while the model order provides a second order limitation effect and the measurement noise comes in as a third order effect.

    Then, a Kalman-based linear filter is studied for potential 5G technologies:

    Coherent coordinated multipoint joint transmission, where channel predictions and the covariance matrix of the prediction error are used to design a robust linear precoder, evaluated in a three base station system. Results show that prediction improves the CSI for the pedestrian users such that system delays of 10 ms are acceptable. The use of the covariance matrix is important for difficult user groups, but of less importance with a simple user grouping system proposed.

    Massive multiple-input multiple-output (MIMO) in frequency division duplex (FDD) systems were a reduced, suboptimal, Kalman filter is suggested to estimate channels based on non-orthogonal pilots. By introducing a fixed grid of beams, the system generates sparsity in the channel vectors seen by each user, which then estimates its most relevant channels based on unique pilot codes for each beam. Results show that there is a 5 dB loss compared to orthogonal pilots.

    Downlink time division duplex (TDD) channels are estimated based on uplink pilots. By using a predictor antenna, which scouts the channel in advance, the desired downlink channel can be estimated using pilot-based estimates of the channels before and after it (in space). Results indicate that, with the help of Kalman smoothing, predictor antennas can enable accurate CSI for TDD downlinks at vehicular velocities of 80 km/h.

    List of papers
    1. Kalman predictions for multipoint OFDM downlink channels
    Open this publication in new window or tab >>Kalman predictions for multipoint OFDM downlink channels
    2014 (English)Report (Other academic)
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-235010 (URN)
    Available from: 2014-10-28 Created: 2014-10-28 Last updated: 2018-03-07
    2. Design and measurement based evaluations of coherent JT CoMP: A study of precoding, user grouping and resource allocation using predicted CSI
    Open this publication in new window or tab >>Design and measurement based evaluations of coherent JT CoMP: A study of precoding, user grouping and resource allocation using predicted CSI
    2014 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499Article in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-235014 (URN)DOI:10.1186/1687-1499-2014-100 (DOI)
    Available from: 2014-10-28 Created: 2014-10-28 Last updated: 2018-11-08
    3. Robust linear precoder for coordinated multipoint joint transmission under limited backhaul with imperfect CSI
    Open this publication in new window or tab >>Robust linear precoder for coordinated multipoint joint transmission under limited backhaul with imperfect CSI
    2014 (English)In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), 2014, p. 138-143Conference paper, Published paper (Refereed)
    Abstract [en]

    Coordinated Multipoint (COMP) transmission provides high theoretic gains in spectral efficiency, in particular with coherent linear Joint Transmission (JT) to multiple users. However, this requires high backhaul capacity. If the backhaul requirement cannot be met by the system, then CoNIP gains decrease as the linear precoder matrix must be adjusted to include zeros. To minimize the loss of CoMP gains, all elements in the precoder should be adjusted as zeros are added to the precoder. We here propose a low complexity method for adjusting a precoder matrix when some elements are required to be zero, with respect to a robust MSE criterion. This is done by introducing penalties on specific precoder matrix elements. This generalized MSE criterion can then be used as a low complexity tool for optimizing e.g. with respect to sum-rate. Results show that this does indeed provide a better solution than if zeros are added separately. It is especially beneficial for cell edge users, i.e. for the same users that can gain the most from JT CoNIP.

    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-235007 (URN)000363906500027 ()978-1-4799-5863-4 (ISBN)
    Conference
    International Symposium on Wireless Communication Systems ISWCS, Barcelona, Spanien, 25-29 Augusti
    Available from: 2014-10-28 Created: 2014-10-28 Last updated: 2018-03-07Bibliographically approved
    4. Joint reference signal design and Kalman/Wiener channel estimation for FDD massive MIMO. Extended Report Version.
    Open this publication in new window or tab >>Joint reference signal design and Kalman/Wiener channel estimation for FDD massive MIMO. Extended Report Version.
    2017 (English)Report (Other academic)
    Place, publisher, year, edition, pages
    Uppsala: Signals and Systems, Uppsala University, 2017
    Series
    Report r1701
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-330705 (URN)
    Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2018-03-07
    5. Kalman smoothing for irregular pilot patterns; A case study for predictor antennas in TDD systems
    Open this publication in new window or tab >>Kalman smoothing for irregular pilot patterns; A case study for predictor antennas in TDD systems
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    For future large-scale multi-antenna systems, channel orthogonal downlink pilots are not feasible due to extensive overhead requirements. Instead, channel reciprocity can be utilized in time division duplex (TDD) systems so that the downlink channel estimates can be based on pilots transmitted during the uplink. User mobility affects the reciprocity and makes the channel state information outdated for high velocities and/or long downlink subframe durations. Channel extrapolation, e.g. through Kalman prediction, can reduce the problem but is also limited by high velocities and long downlink subframes. An alternative solution has been proposed where channel predictions are made with the help of an extra antenna, e.g. on the roof of a car, so called predictor antenna, with the primary objective to measure the channel at a position that is later encountered by the rearward antenna(s). The predictor antenna is not directly limited by high velocities and allows the channel in the downlinks to be interpolated rather than extrapolated. One remaining challenge here is to obtain a good interpolation of the uplink channel estimate, since a sequence of uplink reference signals (pilots) will be interrupted by downlink subframes. We here evaluate a Kalman smoothing estimate of the downlink channels and compare it to a cubic spline interpolation. These results are compared to results where uplink channels are estimated through Kalman filters and predictors. Results are based on measured channels and show that with Kalman smoothing, predictor antennas can enable accurate channel estimates for a longer downlink period at vehicular velocities.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-344267 (URN)
    Available from: 2018-03-06 Created: 2018-03-06 Last updated: 2018-03-07
  • 21.
    Apelfröjd, Rikke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Design Aspects of Coordinated Multipoint Transmission: A Study of Channel Predictions, Resource Allocation, User Grouping and Robust Linear Precoding for Coherent Joint Transmission2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Shadowed areas and interference at cell borders pose great challenges for future wireless broadband systems. Coordinated Multipoint (CoMP) coherent joint transmission has shown the potential to overcome these challenges by turning harmful interference into useful signal power. However, there are obstacles to overcome before coherent joint transmission CoMP can be deployed. Some of these are the investigated in this thesis.

    First, coherent joint transmission requires very accurate Channel State Information (CSI), but unfortunately long system latencies cause outdating of the CSI. This can to some extend be counteracted by channel predictions. Two schemes are here investigated for predicting downlink Frequency Division Duplex (FDD) Orthogonal Frequency Division Multiplexing (OFDM) channels; Kalman filters and “predictor antennas”. The first is well suited for slow moving users, e.g. pedestrians or cyclists, as it does not require any special antenna setup. The second, which utilizes an extra antenna, located in front of the main receive antennas, is well suited for vehicular users, such as buses or trams, as these require long spatial prediction horizon.

    Second, a user grouping and resource allocation scheme is investigated. This scheme forms CoMP groups by local resource allocations and provides multi-user diversity gains very close to the optimal gains, found through an extensive combinatorial search. It has very low complexity, requires less feedback capacity than other schemes and places no demands on backhaul capacity.

    Finally, a linear precoder, which is robust to errors in the CSI, is investigated. This precoder takes the covariances of the channel errors into account while optimizing a Mean Squared Error (MSE) criterion. The MSE criterion includes design parameters that can be used as flexible tools for low dimensional searches with respect to an arbitrary optimization criterion, e.g. a weighted sum-rate criterion. The precoder design is also extended to handle backhaul constraints.

    Results show that with the combination of these three schemes: channel predictions, the proposed user grouping and resource allocation scheme and the robust linear precoder, then coherent joint transmission will indeed provide large capacity gains.

    List of papers
    1. Measurement-based evaluation of robust linear precoding for downlink CoMP
    Open this publication in new window or tab >>Measurement-based evaluation of robust linear precoding for downlink CoMP
    2012 (English)In: IEEE International Conference on Communications, ICC, Ottawa, Canada, 2012Conference paper, Published paper (Refereed)
    Abstract [en]

    We study the design and evaluation of joint processing coordinated multipoint (CoMP) downlink transmission. Precoders will then be designed based on outdated channel state information (CSI), so interference cannot be eliminated completely as by an ideal zero-forcing (ZF) solution. We here strive to design and evaluate realistic linear transmit schemes. Kalman predictors are used for orthogonal frequency-division multiplexing (OFDM) channels. They provide optimal linear predictions and also estimates of their uncertainty. Robust linear precoders are designed based on these uncertainty estimates. We introduce and use robust linear quadratic optimal feedforward control, with the criterion averaged (marginalized) over the CSI uncertainty. This flexible solution performs minimum mean square error (MSE) minimization. It can also iteratively optimize other criteria, such as sum-rate. The prediction- and transmission performance is evaluated using measured data on 20 MHz OFDM downlinks from three base stations, for users at fast pedestrian velocities. Downlink CoMP is here also compared to cellular transmission, that uses orthogonal resources within cells but allows uncontrolled interference between cells.

    National Category
    Signal Processing
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-181051 (URN)
    Conference
    IEEE International Conference on Communications, ICC, June 10 - 15, Ottawa, Canada.
    Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2014-06-04Bibliographically approved
    2. Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI
    Open this publication in new window or tab >>Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI
    2014 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, p. 100-Article in journal (Refereed) Published
    Abstract [en]

    Coordinated multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent joint transmission (JT) to multiple users. However, this requires accurate channel state information at the transmitter (CSIT) and also user groups with spatially compatible users. The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques. We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (> 20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities. A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding. Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.

    Keywords
    Coordinated Multipoint, channel predictions, user grouping, resource allocation, robust precoding
    National Category
    Signal Processing
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224254 (URN)10.1186/1687-1499-2014-100 (DOI)000347399300001 ()
    Available from: 2014-05-07 Created: 2014-05-07 Last updated: 2018-11-08Bibliographically approved
    3. Robust Linear Precoder for Coordinated Multipoint Joint Transmission under Limited Backhaul with Imperfect CSI
    Open this publication in new window or tab >>Robust Linear Precoder for Coordinated Multipoint Joint Transmission under Limited Backhaul with Imperfect CSI
    (English)Manuscript (preprint) (Other academic)
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224255 (URN)
    Available from: 2014-05-07 Created: 2014-05-07 Last updated: 2014-06-04
    4. Analysis and Measurement of Multiple Antenna Systems for Fading Channel Prediction in Moving Relays
    Open this publication in new window or tab >>Analysis and Measurement of Multiple Antenna Systems for Fading Channel Prediction in Moving Relays
    Show others...
    2014 (English)In: 2014 8TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP), 2014, p. 2015-2019Conference paper, Published paper (Other academic)
    Abstract [en]

    The performance of wireless data transmission to mobile vehicles is improved if channel state information is available at the transmitter but movement of vehicles causes outdating of channel estimates. The concept of a predictor antenna has recently been proposed, where an antenna is placed in front of other antennas on the roof of the vehicle to sense the radio environment in advance. This can comparatively provide an order-of-magnitude improvement in channel prediction performance. A potential problem with this idea is that closely placed antennas will experience mutual electromagnetic couplings. These may reduce the efficiency of the predictor antenna concept if they are not taken into account. In this paper, we discuss about how to treat the forgoing issue and eventually evaluate a promising candidate on measured channels. We argue that only open-circuit voltage method would be realistic for the present application. The usefulness of the proposed decoupling method is demonstrated on field measurements obtained in downtown Dresden, Germany. We also partly address the sensitivity of the open-circuit decoupling method to the accuracy of the utilized network parameters.

    Series
    Proceedings of the European Conference on Antennas and Propagation, ISSN 2164-3342
    Keywords
    Multi-element antennas; channel state prediction; moving relays; multipath measurement
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224256 (URN)978-88-907018-4-9 (ISBN)
    Conference
    The 8th European Conference on Antennas and Propagation (EuCAP), to be held at the World Forum in The Hague, The Netherlands, on 6-11 April 2014.
    Note

    This paper has been presented as a poster on: the 8th European Conference on Antennas and Propagation (EuCAP), in The Hague, The Netherlands, on 6-11 April 2014, and will appear in the proceedings

    Available from: 2014-05-08 Created: 2014-05-07 Last updated: 2015-11-06Bibliographically approved
    5. Kalman Predictions for Multipoint OFDM Downlink Channels
    Open this publication in new window or tab >>Kalman Predictions for Multipoint OFDM Downlink Channels
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Coordinated Multipoint (CoMP) transmission provides high theoreticgains in spectral eciency with coherent Joint Transmission (JT) to mul-tiple users. However, this requires accurate Channel State Information atthe Transmitter (CSIT). Unfortunately, coherent JT CoMP often is accom-panied by long system delays, due to e.g. data sharing over backhaul links.Therefore, the CSIT will be outdated.This report provides a detailed description on how to increase the accu-racy of the CSIT by utilizing Kalman lters to predict Orthogonal FrequencyDivision Multiplexing (OFDM) downlink channels. The small scale fading ofthese channels are modeled by Auto Regressive (AR) models of nite order.The report includes descriptions on how to estimate these models basedon past knowledge of the channel as well as analytical result on the pre-dictability of such models. Dierent technical design aspects for deployingthe Kalman lters in communication, such as pilot patterns, AR model esti-mations and the location of Kalman lters that predict downlink FrequencyDivision Duplex (FDD) channels, are also discussed.The aim of the report is to in detail describe the prediction procedureused in previous work. Some of the results from this previous work arehere presented and extended to provide a complete overview. All simulationresults are based on measured channels.The report also includes a description on how to model block-fading chan-nels with a specied channel accuracy that would have been obtained withKalman predictions. This model can then be used for system simulations.V:

    Keywords
    Linear predictions of OFDM channels, outdated channel state information (CSI), Coordinated Multipoint (CoMP), Predictability of radio channles, AR modelling of radio channels
    National Category
    Engineering and Technology
    Research subject
    Electrical Engineering with specialization in Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-224263 (URN)
    Available from: 2014-05-08 Created: 2014-05-08 Last updated: 2014-06-04
  • 22.
    Apelfröjd, Rikke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Kalman predictions for multipoint OFDM downlink channels2014Conference paper (Refereed)
  • 23.
    Apelfröjd, Rikke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Kalman Predictions for Multipoint OFDM Downlink ChannelsManuscript (preprint) (Other academic)
    Abstract [en]

    Coordinated Multipoint (CoMP) transmission provides high theoreticgains in spectral eciency with coherent Joint Transmission (JT) to mul-tiple users. However, this requires accurate Channel State Information atthe Transmitter (CSIT). Unfortunately, coherent JT CoMP often is accom-panied by long system delays, due to e.g. data sharing over backhaul links.Therefore, the CSIT will be outdated.This report provides a detailed description on how to increase the accu-racy of the CSIT by utilizing Kalman lters to predict Orthogonal FrequencyDivision Multiplexing (OFDM) downlink channels. The small scale fading ofthese channels are modeled by Auto Regressive (AR) models of nite order.The report includes descriptions on how to estimate these models basedon past knowledge of the channel as well as analytical result on the pre-dictability of such models. Dierent technical design aspects for deployingthe Kalman lters in communication, such as pilot patterns, AR model esti-mations and the location of Kalman lters that predict downlink FrequencyDivision Duplex (FDD) channels, are also discussed.The aim of the report is to in detail describe the prediction procedureused in previous work. Some of the results from this previous work arehere presented and extended to provide a complete overview. All simulationresults are based on measured channels.The report also includes a description on how to model block-fading chan-nels with a specied channel accuracy that would have been obtained withKalman predictions. This model can then be used for system simulations.V:

  • 24.
    Apelfröjd, Rikke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Kalman predictions for multipoint OFDM downlink channels2014Report (Other academic)
  • 25. Apelfröjd, Rikke
    et al.
    Björsell, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Phan Huy, Dinh Thuy
    Orange.
    Kalman smoothing for irregular pilot patterns; A case study for predictor antennas in TDD systemsManuscript (preprint) (Other academic)
    Abstract [en]

    For future large-scale multi-antenna systems, channel orthogonal downlink pilots are not feasible due to extensive overhead requirements. Instead, channel reciprocity can be utilized in time division duplex (TDD) systems so that the downlink channel estimates can be based on pilots transmitted during the uplink. User mobility affects the reciprocity and makes the channel state information outdated for high velocities and/or long downlink subframe durations. Channel extrapolation, e.g. through Kalman prediction, can reduce the problem but is also limited by high velocities and long downlink subframes. An alternative solution has been proposed where channel predictions are made with the help of an extra antenna, e.g. on the roof of a car, so called predictor antenna, with the primary objective to measure the channel at a position that is later encountered by the rearward antenna(s). The predictor antenna is not directly limited by high velocities and allows the channel in the downlinks to be interpolated rather than extrapolated. One remaining challenge here is to obtain a good interpolation of the uplink channel estimate, since a sequence of uplink reference signals (pilots) will be interrupted by downlink subframes. We here evaluate a Kalman smoothing estimate of the downlink channels and compare it to a cubic spline interpolation. These results are compared to results where uplink channels are estimated through Kalman filters and predictors. Results are based on measured channels and show that with Kalman smoothing, predictor antennas can enable accurate channel estimates for a longer downlink period at vehicular velocities.

  • 26.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Björsell, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Phan Huy, D-T
    Kalman smoothing for irregular pilot patterns: A case study for predictor antennas in TDD systems2018In: 2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2018Conference paper (Refereed)
    Abstract [en]

    For future large-scale multi-antenna systems, channel orthogonal downlink pilots are not feasible due to extensive overhead requirements. Instead, channel reciprocity can be utilized in time division duplex (TDD) systems so that the downlink channel estimates can be based on pilots transmitted during the uplink. User mobility affects the reciprocity and makes the channel state information outdated for high velocities and/or long downlink subframe durations. Channel extrapolation, e.g. through Kalman prediction, can reduce the problem but is also limited by high velocities and long downlink subframes. An alternative solution has been proposed where channel predictions are made with the help of an extra antenna, e.g. on the roof of a car, so called predictor antenna, with the primary objective to measure the channel at a position that is later encountered by the rearward antenna(s). The predictor antenna is not directly limited by high velocities and allows the channel in the downlinks to be interpolated rather than extrapolated. One remaining challenge here is to obtain a good interpolation of the uplink channel estimate, since a sequence of uplink reference signals (pilots) will be interrupted by downlink subframes. We here evaluate a Kalman smoothing estimate of the downlink channels and compare it to a cubic spline interpolation. These results are also compared to results where uplink channels are estimated through Kalman filters and predictors. Results are based on measured channels and show that with Kalman smoothing, predictor antennas can enable accurate channel estimates for a longer downlink period at vehicular velocities. The gaps in the uplink pilot stream, due to downlink subframes, can have durations that correspond to a vehicle movement of up to 0.75 carrier wavelengths in space, for Rayleigh-like non-line-of-sight fading.

  • 27.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Design and measurement based evaluations of coherent JT CoMP: A study of precoding, user grouping and resource allocation using predicted CSI2014In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499Article in journal (Refereed)
  • 28.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI2014In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, p. 100-Article in journal (Refereed)
    Abstract [en]

    Coordinated multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent joint transmission (JT) to multiple users. However, this requires accurate channel state information at the transmitter (CSIT) and also user groups with spatially compatible users. The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques. We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (> 20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities. A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding. Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.

  • 29.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Robust Linear Precoder for Coordinated Multipoint Joint Transmission under Limited Backhaul with Imperfect CSIManuscript (preprint) (Other academic)
  • 30.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Robust linear precoder for coordinated multipoint joint transmission under limited backhaul with imperfect CSI2014In: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), 2014, p. 138-143Conference paper (Refereed)
    Abstract [en]

    Coordinated Multipoint (COMP) transmission provides high theoretic gains in spectral efficiency, in particular with coherent linear Joint Transmission (JT) to multiple users. However, this requires high backhaul capacity. If the backhaul requirement cannot be met by the system, then CoNIP gains decrease as the linear precoder matrix must be adjusted to include zeros. To minimize the loss of CoMP gains, all elements in the precoder should be adjusted as zeros are added to the precoder. We here propose a low complexity method for adjusting a precoder matrix when some elements are required to be zero, with respect to a robust MSE criterion. This is done by introducing penalties on specific precoder matrix elements. This generalized MSE criterion can then be used as a low complexity tool for optimizing e.g. with respect to sum-rate. Results show that this does indeed provide a better solution than if zeros are added separately. It is especially beneficial for cell edge users, i.e. for the same users that can gain the most from JT CoNIP.

  • 31.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Aronsson, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Measurement-based evaluation of robust linear precoding for downlink CoMP2012In: IEEE International Conference on Communications, ICC, Ottawa, Canada, 2012Conference paper (Refereed)
    Abstract [en]

    We study the design and evaluation of joint processing coordinated multipoint (CoMP) downlink transmission. Precoders will then be designed based on outdated channel state information (CSI), so interference cannot be eliminated completely as by an ideal zero-forcing (ZF) solution. We here strive to design and evaluate realistic linear transmit schemes. Kalman predictors are used for orthogonal frequency-division multiplexing (OFDM) channels. They provide optimal linear predictions and also estimates of their uncertainty. Robust linear precoders are designed based on these uncertainty estimates. We introduce and use robust linear quadratic optimal feedforward control, with the criterion averaged (marginalized) over the CSI uncertainty. This flexible solution performs minimum mean square error (MSE) minimization. It can also iteratively optimize other criteria, such as sum-rate. The prediction- and transmission performance is evaluated using measured data on 20 MHz OFDM downlinks from three base stations, for users at fast pedestrian velocities. Downlink CoMP is here also compared to cellular transmission, that uses orthogonal resources within cells but allows uncontrolled interference between cells.

  • 32.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Zirwas, Wolfgang
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Joint reference signal design and Kalman/Wiener channel estimation for FDD massive MIMO. Extended Report Version.2017Report (Other academic)
  • 33.
    Apelfröjd, Rikke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Zirwas, Wolfgang
    Nokia Bell Labs, D-81541 Munich, Germany.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Low-Overhead Cyclic Reference Signals for Channel Estimation in FDD Massive MIMO2019In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 67, no 5, p. 3279-3291Article in journal (Refereed)
    Abstract [en]

    Massive multiple input multiple output (MIMO) transmission and coordinated multipoint transmission are candidate technologies for increasing data throughput in evolving 5G standards. Frequency division duplex (FDD) is likely to remain predominant in large parts of the spectrum below 6 GHz for future 5G systems. Therefore, it is important to estimate the downlink FDD channels from a very large number of antennas, while avoiding an excessive downlink reference signal overhead. We here propose and investigate a three part solution. First, massive MIMO downlinks use a fixed grid of beams. For each user, only a subset of beams will then be relevant, and require estimation. Second, sets of coded reference signal sequences, with cyclic patterns over time, are used. Third, each terminal estimates its most relevant channels. We here propose and compare a linear mean square estimation and a Kalman estimation. Both utilize frequency and antenna correlation, and the later also utilizes temporal correlation. In extensive simulations, this scheme provides channel estimates that lead to an insignificant beamforming performance degradation as compared to full channel knowledge. The cyclic pattern of coded reference signals is found to be important for reliable channel estimation, without having to adjust the reference signals to specific users.

  • 34.
    Arfwedson, Pontus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Creating a usable analysis application built on an existing visualization platform2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The advances in research on wireless communications has lead up to the current success of 4G mobile broadband and is currently focusing on designing the upcoming even more advanced fifth generation (5G) networks. The type of research behind this typically generates large quantities of data and requires efficient analysis in order to achieve tangible results. To enable this analysis, visualization of the data is used to give the researchers the needed insights. For this master thesis project an existing platform will be analyzed with the goal of, by utilizing the platform, creating a powerful, useful analysis application with the necessary and desired tools. The platform can access data produced from research simulations and visualize them through different types of useful charts. However, it has up until now lacked some important functionality, mainly letting the user modify and alter the visualization to aid in the analysis. It furthermore requires knowledge and experience before being useful. To solve this, there existed a need of extending the platform with new tools and functionality to give the user more control and possibilities and to simplify the usage. The thesis resulted in a functioning analysis application that gives the user many necessary features to effectively analyze data. The result fulfilled the set requirements with improved and added views, extended tools and optimized performance.

  • 35.
    Arfwedson, Viktor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Improving eciency of EMC ImmunityMonitoring of RBS using a FPGA basedinstrument2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A test system for Immunity testing of Ericsson's LTE radiobase station (RBS) was built using a National Instruments(NI) PXI chassis tted with a vector signal transceiver (VST)module and a PC controller module. A program made in Lab-VIEW and MATLAB was run on the controller module in thePXI chassis. The tasks of the program was, on one hand, tocontrol the VST which was used to record the signal emittedfrom the RBS and on the other hand, to process the signal anddetermine its quality by acquiring the bits transmitted. Functionalityenabling the VST to transmit a given signal was alsoincluded in the program. The built system performed up toninety times faster than the old system but lacked turbo decodingnecessary to correctly determine bit error ratio (BER)and block error ratio (BLER). The performance of the systemleaves room for adding time consuming processes such as turbodecoding later on and by examining the undecoded bits the signalquality can still be measured. The program handles both1tx and 2tx signals.

  • 36.
    Aronsson, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Channel Estimation and Prediction for MIMO OFDM Systems: Key Design and Performance Aspects of Kalman-based Algorithms2011Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Wireless broadband systems based on Orthogonal Frequency Division Multiplexing (OFDM) are being introduced to meet demands for high data transfer rates. In multiple users systems, the available bandwidth has to be shared efficiently by several users. The radio channel quality will fluctuate, or fade, as users move. Fading complicates the resource allocation, but channel prediction may alleviate this problem. A flexible and computationally inexpensive state space representation of fading channels is here used in conjunction with a Kalman filter, operating on special-purpose reference signals, to track and predict fading OFDM channels. The thesis investigates key design and performance aspects of such estimators. Taking a probabilistic approach, we interpret the output of the Kalman filter as a full representation of a state of knowledge about the fading channels, given whatever information is at hand. For systems analysis, this permits conclusions to be drawn about channel estimation and prediction performance based on only vague information about the fading characteristics of the channel rather than on actual channel measurements. This is an alternative to conducting classic simulation studies. Various reference signal designs are studied and good design choices are recommended. Superimposed reference signal schemes are also proposed for and evaluated in cases where multiple signals are received, e.g. in multi-user (MU), multi-input multi-output (MIMO), or coordinated multi-point (CoMP) settings. By using time-varying reference signals, channel estimation and prediction performance is shown to be improved considerably in crowded frequency bands. The variation of prediction performance with prediction range and Doppler spectrum characteristics is investigated. For link adaptation, we derive the appropriate metric on which adaptation decisions should be used. The probability density function for this metric is derived for general MIMO channels. Link adaptation is studied for a single link system when channel prediction and estimation errors are present, both for uncoded systems and systems using large block codes with soft decoders. Various aspects of channel model acquisition are addressed by conducting studies on measured channels. Owing to the use of special matrix structures and fast convergence to time-invariant or periodic solutions, we find the Kalman filter complexity to be reasonable for future implementation. Finally, expressions for the impact of modelling errors are derived and used to study the impact of modelling errors on channel prediction performance in some example cases.

  • 37.
    Aronsson, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Svensson, Tommy
    Chalmers University of Technology, Dept of Signals and Systems.
    Sternad, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Performance evaluation of memory-less and Kalman-based channel estimation for OFDMA2009In: IEEE Vehicular Technology Conference, Barcelona, Spanien, April 26-29, 2009, 2009, p. 2314-2318Conference paper (Refereed)
    Abstract [en]

    The next generation wireless systems based on Orthogonal Frequency Division Multiple Access (OFDMA) need to operate in widely different deployment and usage scenarios. Thus, support for flexible resource allocation is important. In this paper we investigate the performance or different memory-less and memory-based channel estimators for different OFDMA subcarrier allocation schemes and different pilot patterns. We evaluate the performance in various fading environments and for different user terminal velocities. The results show that channel estimation can perform well enough for time-frequency localized resources as small as 22 channel symbols with two pilots in many important scenarios. The results provided can be used to identify appropriate subcarrier allocations for the next generation OFDMA based wireless systems.

  • 38.
    Asraf, Daniel
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Optimal Detectors for Transient Signal Families and Nonlinear Sensors: Derivations and Applications2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is concerned with detection of transient signal families and detectors in nonlinear static sensor systems. The detection problems are treated within the framework of likelihood ratio based binary hypothesis testing.

    An analytical solution to the noncoherent detection problem is derived, which in contrast to the classical noncoherent detector, is optimal for wideband signals. An optimal detector for multiple transient signals with unknown arrival times is also derived and shown to yield higher detection performance compared to the classical approach based on the generalized likelihood ratio test.

    An application that is treated in some detail is that of ultrasonic nondestructive testing, particularly pulse-echo detection of defects in elastic solids. The defect detection problem is cast as a composite hypothesis test and a methodology, based on physical models, for designing statistically optimal detectors for cracks in elastic solids is presented. Detectors for defects with low computational complexity are also formulated based on a simple phenomenological model of the defect echoes. The performance of these detectors are compared with the physical model-based optimal detector and is shown to yield moderate performance degradation.

    Various aspects of optimal detection in static nonlinear sensor systems are also treated, in particular the stochastic resonance (SR) phenomenon which, in this context, implies noise enhanced detectability. Traditionally, SR has been quantified by means of the signal-to-noise ratio (SNR) and interpreted as an increase of a system's information processing capability. Instead of the SNR, rigorous information theoretic distance measures, which truly can support the claim of noise enhanced information processing capability, are proposed as quantifiers for SR. Optimal detectors are formulated for two static nonlinear sensor systems and shown to exhibit noise enhanced detectability.

    List of papers
    1. An analytical series expansion solution to the problem of noncoherent detection
    Open this publication in new window or tab >>An analytical series expansion solution to the problem of noncoherent detection
    2004 (English)In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 50, no 12, p. 3369-3375Article in journal (Refereed) Published
    Abstract [en]

    The well-known noncoherent detection problem concerns optimal detection of an amplitude-modulated sinusoid, with an unknown phase angle, corrupted by additive Gaussian noise. The classical solution to this problem is the noncoherent detector which is known to be optimal if the envelope belongs to a specific set of functions or satisfies the narrow-band approximation i.e., that the bandwidth of the envelope is narrow in comparison with the (carrier) frequency of the sinusoid. In this work, an analytical series expansion solution to the likelihood ratio for the noncoherent detection problem is derived. This solution offers a generalization of the noncoherent detector in which the conditions imposed on the envelope stated above have been relaxed. Analytical expressions for the joint probability density functions (pdfs) of the in-phase and quadrature components, jointly expressed in polar coordinates, are also derived under the signal-plus-noise and the noise-only hypotheses, respectively. Numerical simulations of the detector performance are presented in the form of receiver operating characteristics (ROC) and minimum probability of error curves. The results from a comparison of the general analytical solution with the classical noncoherent detector show significant differences between the two detectors when the narrow-band approximation does not hold.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-90173 (URN)10.1109/TIT.2004.838396 (DOI)
    Available from: 2003-03-17 Created: 2003-03-17 Last updated: 2017-12-14Bibliographically approved
    2. Detection of Multiple Transient Signals with Unknown Arrival Times
    Open this publication in new window or tab >>Detection of Multiple Transient Signals with Unknown Arrival Times