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  • 1.
    Alayon Glazunov, Andres
    et al.
    TeliaSonera.
    Wang, Ying
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Experimental Evaluation of CW MIMO Channel Capacity in Urban Multicell Environment2006Conference paper (Refereed)
  • 2.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Martin, Cristoff
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ben Slimane, Slimane
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Recent Advances on MIMO Processing in the SATURN Project2002In: Proc. IST Mobile Communications Summit, 2002, p. 309-313Conference paper (Other academic)
    Abstract [en]

    We highlight some recent results on the theory and algorithms for  MIMO systems, obtained at the Royal Institute of  Technology (KTH) within the SATURN project.   The paper includes a a new approximate expression for the ergodic  channel capacity of a MIMO system with correlated fading, algorithms  for MIMO beamforming under EIRP (equivalent isotropic radiated  power) constraints and a low-complexity algorithm for MIMO channel  estimation in OFDM systems. Also, we show how transmit and  beamformers can be determined in a decentralized fashion without  explicitly estimating the channel response.

  • 3.
    Bengtsson, Mats
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Martin, Cristoff
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Slimane, Ben
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Recent Advances on MIMO Processing in the SATURN Project2002In: Proc. IST Mobile Communications Summit, 2002Conference paper (Refereed)
    Abstract [en]

    We highlight some recent results on the theory and algorithmsfor MIMO systems, obtained at the Royal Instituteof Technology (KTH) within the SATURN project.The paper includes a a new approximate expression forthe ergodic channel capacity of a MIMO system with correlatedfading, algorithms for MIMO beamforming underEIRP (equivalent isotropic radiated power) constraintsand a low-complexity algorithm for MIMO channel estimationin OFDM systems. Also, we show how transmitand beamformers can be determined in a decentralizedfashion without explicitly estimating the channel response.

  • 4.
    Bengtsson, Mats
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Svedman, Patrick
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Comparison and Cost Analysis of Smart and Opportunistic MIMO OFDM Schemes2006In: IST Mobile & Wireless Communications Summit 2006, 2006Conference paper (Refereed)
    Abstract [en]

    This paper attempts to compare the system downlinkperformance of a smart antenna scheme for OFDMA thatutilizes channel covariance information with an opportunisticmulti-antenna scheme for OFDMA that uses fast limited feedbackof the instantaneous channel condition. The schemes areevaluated by means of simulations in a low load scenario andalso compared to a simple HSDPA-like scheme. The smartantenna method manages to utilize the multiple antennas betterthan the opportunistic scheme. Furthermore, the performanceof the schemes is inserted into a cost model that assumes thatthe receivers are relays that use short-range technologies tocommunicate with user equipments. Also in terms of cost peruser equipment, the smart antenna scheme proves to be moresuitable for the studied scenario.

  • 5.
    Bengtsson, Mats
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Svedman, Patrick
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zhang, Xi
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    System comparison of smart and dumb antennas2005In: VTC2005-SPRING: 2005 IEEE 61ST VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, PROCEEDINGS, 2005, p. 230-233Conference paper (Refereed)
    Abstract [en]

    Different approaches have been proposed to utilize multiple antennas at both transmitters and receivers of wireless systems. Herein, we provide a system comparison between covariance feedback schemes where a large amount of information is fed back at a low rate and opportunistic beamforming schemes where a small amount of information is fed back at a high rate.

  • 6. Berardinelli, G.
    et al.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tonelli, O.
    Cattoni, A. F.
    Sørensen, T. B.
    Mogensen, P.
    An SDR architecture for OFDM transmission over USRP2 boards2011In: Conference Record: Asilomar Conference on Signals, Systems and Computers, 2011, p. 965-969Conference paper (Refereed)
    Abstract [en]

    The Universal Software Radio Peripheral (USRP) developed by Ettus research is emerging as one of the most promising hardware solution for building a Software Defined Radio (SDR) platform. Originally designed for supporting GNU radio, it can also be interfaced to customized C++ code, thus allowing a higher degree of flexibility in the design of the transceiver chain. In this paper we describe the implementation of a coded Orthogonal Frequency Division Multiplexing (OFDM) transceiver running over USRP2 boards. The baseband processing and the radio-frequency settings are designed for coping with a local area scenario as well as with the physical capabilities of the USRP2 boards. Moreover, a simple subcarrier blinding algorithm is proposed with the aim of compensating the common phase error in the symbol constellation due to the limited nominal accuracy of the local oscillators. Performance results show the effectiveness of the proposed architecture and settings for achieving Block Error Rate (BLER) results below 1% at 12 dB of Signal-to-Noise Ratio (SNR) without requiring a high precision reference clock.

  • 7.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal Coordinated Beamforming in the Multicell Downlink with Transceiver Impairments2012In: 2012 IEEE Global Telecommunications Conference (GLOBECOM), New York: IEEE conference proceedings, 2012, p. 4775-4780Conference paper (Refereed)
    Abstract [en]

    Physical wireless transceivers suffer from a variety of impairments that distort the transmitted and received signals. Their degrading impact is particularly evident in modern systems with multiuser transmission, high transmit power, and low-cost devices, but their existence is routinely ignored in the optimization literature for multicell transmission. This paper provides a detailed analysis of coordinated beamforming in the multicell downlink. We solve two optimization problems under a transceiver impairment model and derive the structure of the optimal solutions. We show numerically that these solutions greatly reduce the impact of impairments, compared with beamforming developed for ideal transceivers. Although the so-called multiplexing gain is zero under transceiver impairments, we show that the gain of multiplexing can be large at practical SNRs.

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  • 8.
    Björnson, Emil
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Capacity Limits and Multiplexing Gains of MIMO Channels with Transceiver Impairments2013In: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, no 1, p. 91-94Article in journal (Refereed)
    Abstract [en]

    The capacity of ideal MIMO channels has a high-SNR slope that equals the minimum of the number of transmit and receive antennas. This letter analyzes if this result holds when there are distortions from physical transceiver impairments. We prove analytically that such physical MIMO channels have a finite upper capacity limit, for any channel distribution and SNR. The high-SNR slope thus collapses to zero. This appears discouraging, but we prove the encouraging result that the relative capacity gain of employing MIMO is at least as large as with ideal transceivers.

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    fulltext
  • 9.
    Brandt, Rasmus
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Interference Alignment over a Combination of Space and Frequency2013In: 2013 IEEE International Conference on Communications Workshops, ICC 2013, IEEE Communications Society, 2013, p. 149-153Conference paper (Refereed)
    Abstract [en]

    Time or frequency extensions are integral in most information theoretic studies of interference alignment (IA), but a large majority of the more practically oriented studies have focused on narrowband space-only schemes. As wideband systems are now common, it is natural to investigate IA for frequency extended multiple antenna systems where precoding is performed over a combination of space and frequency dimensions. For this setting, we derive a necessary condition on IA feasibility using the properness framework and investigate the sum rate performance using simulations. Applying frequency extensions to multiple antenna systems allows for some additional users to be served interference-free, but our numerical results with synthetic channels indicate a practically more important improvement in terms of a power gain. Emulating a particular scenario using channel measurements, with real-world path losses and channel correlations, we see similar performance gains.

    Download full text (pdf)
    fulltext
  • 10. Dordlofva, Bengt
    et al.
    Karlsson, Magnus
    Larsson, Per
    Larsson, Thomas
    Zetterberg, Per
    KTH.
    Arrangement for Frequency Planning in Cellular Systems1999Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention relates to an arrangement for frequency planning in cellular systems using a mix of wide and narrow antenna beams. The arrangement employs a dual frequency reuse for the respective wide and narrow antenna beams. According to the invention, a first frequency group is allocated to a cluster with a reuse distance sufficient for narrow beam channels and a second frequency group is allocated to a larger cluster with a reuse distance sufficent for wide beam channels. The second frequency group is a subdivision of and contained in the first frequency group. The second frequency group is the only frequency group available for wide beam channels, while all the frequencies of the two groups are available for the narrow beams channels. Generally, the wide beams are used for control channels and the narrow beams are used for traffic channels. A frequency planning in accordance with the invention makes it possible to use narrow beam traffic channels more efficiently compared to known state of the art methods which results in improved trunking efficiency.

  • 11. El-Sallabi, H.
    et al.
    Baum, D. S.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Kyosti, P.
    Rautiainen, T.
    Schneider, C.
    Wideband spatial channel model for MIMO systems at 5 GHz in indoor and outdoor environments2006In: IEEE Vehicular Technology Conference, 2006, Vol. 6, p. 2916-2921Conference paper (Refereed)
    Abstract [en]

    This work presents a spatial channel model developed within the EC WINNER1 project. The channel model is mainly based on double-directional measurement campaigns carried out in the 5 GHz ISM 2 band with bandwidths of up to 120 MHz. The model is based on a unified structure for indoor and outdoor environment. It covers 6 different propagation scenarios, namely indoor small office, indoor hall, urban microcell, urban macrocell, suburban macrocell, and rural environment. Both line-of-sight (LOS) and non-line-of-sight (NLOS) propagation conditions are modeled.

  • 12. Falconer, D.
    et al.
    Alexiou, A.
    Kaiser, S.
    Haardt, M.
    Jämsä, T.
    Thomä, R. S.
    Milojevic, M.
    Fleury, B. H.
    Andersen, J. B.
    Eggers, P. C. F.
    Nielsen, J. Ø
    Kovács, I. Z.
    Ylitalo, J.
    Kyösti, P.
    Nuutinen, J.
    Zhao, X.
    Baum, D.
    Ettefagh, A.
    Ran, M.
    Kalliola, K.
    Rautiainen, T.
    Kitchener, D.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Katz, M.
    Hämäläinen, M.
    Juntti, M.
    Matsumoto, T.
    Czink, N.
    New Air-interface Technologies and Deployment Concepts2006In: Technologies for the Wireless Future: Wireless World Research Forum (WWRF), John Wiley & Sons, 2006, Vol. 2, p. 131-226Chapter in book (Other academic)
  • 13. Garcia-Garcia, L.
    et al.
    Jaldén, Niklas
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Lindmark, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    De Haro, L.
    Measurements of MIMO capacity at 1800 MHZ with in- and outdoor transmitter locations2006In: European Space Agency, 2006, no Special Publication) ESA SP, 626 SP, 6 p.Conference paper (Refereed)
    Abstract [en]

    A measurement campaign was carried out to analyse several possible transmitter locations for a 4x4 MIMO system. The receiver modules were moved along indoor routes, and both indoor and outdoor locations were considered for the transmitters. The spatial correlation, path loss and capacity were analysed. Also several options regarding signal combination at system level were studied, assuming two base stations with 2 antennas each. As a result, it is shown that the 2x4 configuration with base station selection and waterfilling scheme provides almost as good performance as a 4x4 full waterfilling scheme when the 2 base stations are spatially separated. This solution may be very interesting to reduce system complexity without significant loss of performance.

  • 14.
    Garcia-Garcia, Laura
    et al.
    Dept. of Signals, Systems and Radiocommunications Universidad Politécnica de Madrid (UPM), 28040 Madrid (Spain) .
    Jaldén, Niklas
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Lindmark, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    de Haro, Leandro
    Dept. of Signals, Systems and Radiocommunications Universidad Politécnica de Madrid (UPM), 28040 Madrid (Spain) .
    Measurements of MIMO indoor channels at 1800 MHz with multiple indoor and outdoor base stations2007In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499Article in journal (Refereed)
    Abstract [en]

    This paper proposes several configurations for multiple base stations in indoor MIMO systems and compares their performance. The results are based on channel measurements realized with a MIMO testbed. The receiver was moved along several routes and floors on an office building. Both outdoor and indoor locations are considered for the transmitters or base stations, which allow the analysis of not only indoor but also outdoor-to-indoor environment. The use of 2 base stations with different system level combinations of the two is analyzed. We show that the 2 x 4 configuration with base station selection provides almost as good performance as a 4 x 4 full water-filling scheme when the 2 base stations are placed at different locations. Also the spatial correlation properties for the different configurations are analyzed and the importance of considering path loss when evaluating capacity is highlighted.

  • 15.
    Giles, Tim
    et al.
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Markendahl, Jan
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Zander, Jens
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Karlsson, P
    Cost drivers and deployment scenarios for future broadband wireless networks: Key research problems and directions for research2004In: VTC2004-SPRING: 2004 IEEE 59TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, PROCEEDINGS, NEW YORK: IEEE , 2004, p. 2042-2046Conference paper (Refereed)
    Abstract [en]

    The most prominent problem in providing anywhere, anytime wideband mobile access is the towering infrastructure cost as it is basically proportional to the bandwidth provided. In this paper, we provide a simple, initial, analysis of the various infrastructure cost factors. This analysis shows that, contrary to what one may expect, the infrastructure cost is not dominated by electronic equipment, but rather by other deployment related costs (towers, wiring,, building, network connections) and maintenance costs. In the paper some novel architectural approaches for future wideband mobile access focusing on these dominant cost factors are described and the related key research issues are discussed.

  • 16.
    Giles, Tim
    et al.
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Markendahl, Jan
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Zander, Jens
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Wireless at KTH.
    Karlsson, Peter
    TeliaSonera Sweden.
    Lind, Jonas
    Stockholm School of Economics.
    Malmgren, Göran
    Ericsson Research.
    Nilsson, Jan
    Swedish Defense Research Agency.
    Cost Drivers and Deployment Scenarios for Future Braodband Wireless Networks - Key research problems and directions for research2004Conference paper (Refereed)
    Abstract [en]

    The most prominent problem in providing anywhere, anytime wideband mobile access is the towering infrastructure cost as it is basically proportional to the bandwidth provided. In this paper, we provide a simple, initial, analysis of the various infrastructure cost factors. This analysis shows that, contrary to what one may expect, the infrastructure cost is not dominated by electronic equipment, but rather by other deployment related costs (towers, wiring, building, network connections) and maintenance costs. In the paper some novel architectural approaches for future wideband mobile access focusing on these dominant cost factors are described and the related key research issues are discussed.

  • 17. Glazunov, Andres Alayon
    et al.
    Wang, Y.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Decorrelation distance characterization of long term fading of CW MIMO channels in urban multicell environment2005In: ICECom 2005: 18th International Conference on Applied Electromagnetics and Communications, Conference Proceedings / [ed] Bonefacic, D., IEEE , 2005, p. 75-78Conference paper (Refereed)
  • 18.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Investigating the USRP: I/Q imbalance2009Conference paper (Other academic)
  • 19.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Measuring demodulator imbalance in radio frequency receivers by tone test2009In: 19th IMEKO World Congress 2009, 2009, p. 462-465Conference paper (Refereed)
    Abstract [en]

    The measurement of in-phase/quadrature (IQ) imbalance parameters of radio frequency direct downconversion receivers by tone test is considered. The receiver is excited by a radio frequency sinewave, and the digital baseband output is used as the sole basis for the determination of the IQ imbalance parameters, which are the gain imbalance, quadrature skew and local oscillator leakage. A set of parameters is estimated from the baseband output of the direct downconversion receiver and the required parameters are then calculated by a transformation. The universal software radio peripheral (USRP) is a widespread hardware for research, education, and development regarding future wireless communication receivers. A set of USRPs are tested. It is shown that for the receivers studied, gain imbalance and quadrature skew may be predicted accurately (that is, < 0.1 dB and < 1 deg, respectively) by employing baseband data covering a handful of full periods of the excitation stimuli. The work also shows that local oscillator leakage may suffer from systematic bias error of the order of 15 dB. To obtain leakage estimates with an uncertainty in the order of one dB, the measurement time has to be increased by two orders of magnitude.

  • 20.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Receiver I/Q Imbalance: Tone Test, Sensitivity Analysis, and the Universal Software Radio Peripheral2010In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 59, no 3, p. 704-714Article in journal (Refereed)
    Abstract [en]

    The problem of determining the gain imbalance, quadrature skew, and local oscillator leakage of contemporary radio frequency receivers by tone test is considered. A least squares approach for indirect estimation of the sought-for parameters is proposed, which is linear in six out of its seven parameters. The performance of the method, particularly its accuracy as a function of measurement time, imbalance parameters, and signal-to-noise ratios, is investigated. The theoretical predictions of the performance are illustrated by Monte Carlo simulations and experimental data that are obtained from testing several universal software radio peripheral (USRP) receivers. This paper shows that, for the studied off-the-shelf receivers, gain imbalance and quadrature skew may accurately be predicted (i.e., < 0.1 dB and < 1 degrees, respectively) by employing baseband data covering only a handful of full periods of the excitation stimuli. Using short records of data, this paper also shows that local oscillator leakage adding a bias term in the receiver baseband data may suffer from a systematic bias error on the order of 15 dB in the estimate. To obtain local oscillator leakage estimates with an uncertainty on the order of 1 dB, the measurement time has to be increased by two orders of magnitude.

  • 21.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bergman, Svante
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Werner, Karl
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cross layer implementation of a multi-user MIMO test-bed2010Conference paper (Refereed)
    Abstract [en]

    This paper describes an implementation of a realtime multi-user multiple-input multiple-output (MU-MIMO) communication system, with cross-layer channel-aware scheduling. The system is implemented using software reconfigurable nodes that may be configured as either user terminals, or as base stations, communicating in the GSM 1800 uplink band. Three different commonly used scheduling algorithms (based on channel state information fed back by the receiver nodes) are studied and compared experimentally for three different signal to noise ratios in an indoor non line of sight environment. It is shown that channel-aware scheduling increases not only the system throughput, but also the fairness. Further, using the possibility of changing antenna polarization through software controlled switches, the multiuser gains may be increased even further, both in total throughput as well as fairness.

  • 22.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Directional dependence of large scale parameters in wireless channel models2008Conference paper (Refereed)
    Abstract [en]

    In this paper the autocorrelation properties of shadow fading and angle spread at both the base station (BS) and at the mobile station (MS) are analyzed using urban macro cellular measurement data. The shadow fading parameter is shown to have a longer decorrelation distance than the angle spread at both the BS and at the MS. Furthermore, we observe variations in the shadow fading that depend on the direction of the MS movement due to street canyons. The same dependence is not observed in the angle spreads. These results indicate that the origin of the angle spread is local to the transmitter and receiver, while the shadow fading depends on the intermediate environment.

  • 23.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Modelling angle spread autocorrelations and the impact on multi-user diversity gains2010In: IEEE Wireless Communications and Networking Conference, 2010, Vol. WCNC, p. 1-6Conference paper (Refereed)
    Abstract [en]

    One way of modelling the wireless channel is in a statistical manner, based on a few parameters describing the characteristics of the environment. In most current wireless channel models, these key parameters are assumed independent between separate links, i.e. on the channels modelling the propagation between one base station and several mobile stations, or one mobile station and several base stations. In practice, dependencies between these wireless channels is expected and as a consequence, system performance evaluations based on models with independent links may be inaccurate. Herein, we consider simulations of a system that depend on the spatial nature of the channel. In particular, we study a system with multi-user scheduling using a single carrier. We investigate the impact of angle spread correlations on multi-user diversity gains using opportunistic scheduling. To facilitate this, a novel method of modelling the angle spread correlations for multi-user system simulations is developed. It is shown that in systems with multiple user scheduling, modelling the angle spread autocorrelation is necessary to obtain reliable system performance results, especially as the number of simultaneous scheduled users increases.

  • 24.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Garcia, Laura
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Inter-and Intrasite Correlation of Large Scale Parameters from Macro Cellular Measurements at 1800MHz2007In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2007Article in journal (Refereed)
    Abstract [en]

    Herein, the inter- and intra-site correlation propertiesof shadow fading and power-weighted angular spreadat both the mobile station and the base station are studiedutilizing narrow band multi-site MIMO measurements in the1800MHz band. The influence of the distance between two basestations on the correlation is studied in an urban environment.Measurements have been conducted for two different situations,widely separated as well as closely positioned base stations. Novelresults regarding the correlation of the power-weighted anglespread between base station sites with different separations arepresented. Furthermore, the measurements and analysis presentedherein confirm the autocorrelation and cross-correlationproperties of the shadow fading and the angle spread that havebeen observed in previous studies.

  • 25.
    Jaldén, Niklas
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hong, Aihua
    Institute for Information Technology Technische Universit¨at Ilmenau PSF 100 565, D-98684 Ilmenau, Germany.
    Thomae, Reiner
    Institute for Information Technology Technische Universit¨at Ilmenau PSF 100 565, D-98684 Ilmenau, Germany.
    Correlation properties of large scale fading based on indoor measurements2007In: 2007 IEEE WIRELESS COMMUNICATIONS & NETWORKING CONFERENCE, VOLS 1-9, NEW YORK: IEEE , 2007, p. 1894-1899Conference paper (Refereed)
    Abstract [en]

    Statistical channel models are attractive for their simplicity but sometimes lack in precision. In order to improve modelling accuracy, statistical model parameters, which are dependent on the environment, are extended to include spatial and temporal correlation. In outdoor scenarios these parameters are assumed constant over '' large '' areas of several wavelengths hence the name large scale parameters. This paper studies the large scale fading (LSF) and the applicability of bringing this previously used outdoor variable to the indoor case. The impacts of the model of the LSF on the outdoor system-performance have been studied and several relevant models have been proposed for outdoor cases. We present the intra-site autocorrelation as well as the inter-site cross correlation of the LSF for an indoor channel. The results are based on two separate measurement campaigns conducted at KTH, Stockholm and TUI, Ilmenau, using a single mobile station (MS) and multiple base stations (BSs) to investigate such models. We observe that the areas under which the LSF could be assumed constant are, in indoor scenarios, so small that it can be assumed independent from one local area to another. Furthermore, we find results that point towards the existence of inter-site correlation in some specific scenarios.

  • 26.
    Johansson, Klas
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Markendahl, Jan
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    A vertical split of the air interface - an architecture for future low-cost infrastructure2004In: Austin Mobility Roundtable, 2004Conference paper (Refereed)
  • 27.
    Johansson, Klas
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Markendahl, Jan
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Relaying access points and related business models for low cost mobile systems.2004Conference paper (Refereed)
    Abstract [en]

    In this paper we consider provisioning of high bit rate mobile services without the need of complex user terminals or deployment of a full coverage network with a very large number of traditional cellular base stations (access points) Existing broadband, Wireless Local Area Network (WLAN) and cellular solutions are combined with novel technologies such as ad-hoc network and Multiple-Input-Multiple-Output (MIMO) antenna systems in order to obtain high capacity links, highly flexible solutions and support for mobilityt. In the proposed solution we introduce an intermediate access point, or relay, that connects the end-user terminals to either a wireless or fixed network. Thus, a direct high bit rate connection between base stations and user terminals is not required, which would be beneficial both technically and cost wise. The proposed solution enables flexible rollout strategies and small-scale deployment for both traditional mobile operators and local access providers. The new type of equipment can also be owned and deployed by local actors like facility owners, hotels and private persons that imply possibilities for more flexible business models.

  • 28. Kanatas, A.
    et al.
    Kyritsis, K.
    Karamalis, P.
    Skentos, N.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Reduced hardware complexity MIMO systems with enhanced capacity performance2005In: IST Mobile and Wireless Communications Summit 2005, 2005Conference paper (Refereed)
  • 29. Le Dortz, N.
    et al.
    Gain, Florian
    KTH, School of Electrical Engineering (EES).
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    WiFi fingerprint indoor positioning system using probability distribution comparison2012In: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on, IEEE , 2012, p. 2301-2304Conference paper (Refereed)
    Abstract [en]

    Positioning services are increasingly used for applications such as navigation, advertising and social media. While outdoor navigation based on GPS and/or cellular systems works well, indoor navigation is a much tougher challenge. This paper presents a new indoor positioning method based on Wi-Fi fingerprints, i.e. RSSI measurements from multiple Wi-Fi access points. During an offline phase, fingerprints are collected at known positions in the building. This database of locations and the associated fingerprints are called the radio map. In the online mode, the current Wi-Fi fingerprint probability distributions are compared with those of the radio map. The user location is estimated by calculating a weighted average of the three offline positions that best match the online measurements. Experiments show that our technique is superior to other proposed methods and reaches a median error of 2.4m.

  • 30.
    Lindmark, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Garcia-Garcia, L.
    Macro-cellular MIMO with dual polarized base station antennas and different spacing2007In: IET Seminar Digest, 2007, Vol. 2007, no 11961), .Conference paper (Refereed)
    Abstract [en]

    We present a theoretical analysis of the joint effect of azimuth spread, base station antenna spacing, and environment cross-polar discrimination on the capacity of a 4 x 4 MIMO system using dual polarized antennas. The results indicate that a spatial separation of 3 wavelengths is sufficient for near-optimal MIMO operation. We also present analysis of channel measurements from urban Stockholm which shows that two dual polarized base station antennas with a spacing of only 1.12 wavelengths at 1747 MHz increases the capacity by 50% compared to a single dual polarized antenna.

  • 31.
    Logothetis, Andrew
    et al.
    Ericsson Research, Ericsson AB, Stockholm, Sweden.
    Osseiran, Afif
    Ericsson Research, Ericsson AB, Stockholm, Sweden.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Single Carrier Frequency Domain Equalization on a Real-Time DSP-Based MIMO Test-Bed2005Conference paper (Refereed)
    Abstract [en]

    In this paper, single carrier frequency domain equalization with space time transmit diversity was implemented and evaluated in real-time using a DSP-based wireless MIMO test-bed. The implemented schemes supported a large set of modulations, from BPSK up to QAM64. Zero padding is introduced to mitigate inter-block interference. Robust time and frequency synchronization together with channel estimation based on Kalman filtering is used to address the adverse intersymbol interference and the severe carrier frequency offset due to hardware impairments.

  • 32.
    Lundin, Henrik
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Svedman, Patrick
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Zhang, Xi
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Skoglund, Mikael
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Händel, Peter
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    ADC imperfections in multiple antenna wireless systems - An experimental study2004In: 9th IMEKO Workshop on ADC Modeling and Testing, IWADC 2004, Held Together with the 13th IMEKO TC4 Symposium on Measurements for Research and Industrial Applications, IMEKO-International Measurement Federation Secretariat , 2004, p. 84-89Conference paper (Refereed)
    Abstract [en]

    This paper investigates some of the effects that ADC imperfections may have on wireless communication systems. First, an experimental communication system for wireless multiple-input multiple-output (MIMO) is described. In this test bed, an ADC behavioural model has been implemented. The resulting performance of the communication system, in terms of bit error rate, is assessed when the parameters of the ADC model are altered. The results show that, for this system, the ADC resolution is the key parameter while the non-linearity errors are of minor importance.

  • 33.
    Medawar, Samer
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Approximate Maximum Likelihood Estimation of Rician K-Factor and Investigation of Urban Wireless Measurements2013In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 12, no 6, p. 2545-2555Article in journal (Refereed)
    Abstract [en]

    We consider the problem of estimating the K-factor of a Rician fading wireless channel based on observations of the envelope only, i.e., without phase-information. An approximate Rician power density function (pdf) is introduced to overcome the complexity of the exact pdf. A closed-form maximum-likelihood estimator is derived based on this approximate Rician pdf, while a maximum-likelihood estimator based on the exact Rician pdf appears to be infeasible. An improved estimator is also proposed that features less bias and less variance than the first estimator. The performance of the latter estimator is compared to moment-based estimators that were previously proposed in the literature and is found to have superior performance to closed-form moment estimators, especially for low sample numbers and/or large K-values. The estimator is applied to real wireless macro-cell urban-area measurements. The results show generally low K-factors (below 3dB), with occasional higher values in particular circumstances.

  • 34.
    Medawar, Samer
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ricean K-factor estimation and investigation of urban wireless measurements2012In: 2012 IEEE International Conference on Wireless Information Technology and Systems, ICWITS 2012, IEEE , 2012, p. 6417686-Conference paper (Refereed)
    Abstract [en]

    We consider the problem of estimating the K-factor of a Ricean fading wireless channel based on observations of the envelope only. An approximate Ricean power density function (pdf) is introduced to enable the derivation of a closed-form maximum-likelihood K-factor estimator. A further improved estimator is also proposed, featuring less bias and variance than the first one. The latter estimator outperforms closed form estimators found in the literature especially for low number of samples and/or large K-values. The estimator is applied to real wireless macro-cell urban-area measurements.

  • 35. Mogenssen, Preben E.
    et al.
    Espensen, Poul-Leth
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Pedersen, Klaus I.
    Frederiksen, Frank
    Performance of Adaptive Antennas in FH-GSM using Conventional Beamforming2000In: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 14, no 3, p. 255-274Article in journal (Refereed)
  • 36.
    Moghadam, N. N.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Farhadi, Hamed
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal Power Allocation for Pilot-Assisted Interference Alignment in MIMO Interference Networks: Test-bed Results2015Conference paper (Refereed)
    Abstract [en]

    This paper addresses channel training and data communication over multi-input multi-input (MIMO) interference networks. We consider a pilot-assisted interference alignment scheme in which part of radio resources are allocated to channel training and the remaining resources are used for data transmission. A more accurate channel estimation can be obtained by increasing pilot transmission power. Since each transmitter has limited energy budget, this implies that less power is available for data transmission. Clearly, there is a trade off between the allocated power for channel training and the one for data communication. In order to investigate this trade off, first we compute an achievable sum-rate, and next we find the optimum power allocation to pilot transmission and data transmission. Finally, we verify these theoretical results with experimental measurements on USRP-based test-bed.

  • 37.
    Moghadam, Nima N.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Farhadi, Hamed
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Test-Bed Implementation of Iterative Interference Alignment and Power Control for Wireless MIMO Interference Networks2014In: 2014 IEEE 15th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE , 2014, p. 239-243Conference paper (Refereed)
    Abstract [en]

    This paper presents for the first time the testbed implementation of an iterative interference alignment and power control algorithm for downlink transmission in a multiple-input multiple-output (MIMO) cellular network. The network is composed of three cells where within each cell one base station (BS) communicates with one mobile station (MS). Each terminal is equipped with two antennas. All the BSs transmit at the same time and the same frequency band. Transmitter beamforming vectors and receiver filtering vectors are computed according to the interference alignment concept, and power control is performed to guarantee successful communication of each BS-MS pair at a desired fixed rate. The indoor measurements performed on an universal software radio peripheral (USRP) based test-bed, show that the power can be reduced by at least 4 dB, 90% of the time, while at the same time reducing the bit-error-rate (BER).

  • 38.
    Moghadam, Nima N.
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Correlation of distortion noise between the branches of MIMO transmit antennas2012In: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on, IEEE , 2012, p. 2079-2084Conference paper (Refereed)
    Abstract [en]

    Despite the tremendous research effort spent on MIMO systems - very few papers address the impact of hardware imperfections. In this paper we analyze the distortion noise of the transmitter branches of a MIMO transmitter. In particular we analyze the cross-correlation of the distortion noises for the case that the transmitted signals are correlated. This case arises when there is just a single stream being transmitted with beamforming or in the case of multiple streams and linear precoding. We analyze the problem in two ways: using analytical derivations and using measurements on our testbed. In the analytical case we assume a transmitter impaired by a 3rd order non-linearity. For this scenario we find that the absolute correlation coefficient of the distortion noises is given by the absolute value of the correlation coefficients of the input signals to the power of three, while the phase is the same as that of the input signal. Our measurements also show good agreement between measurements and analytical results. It seems to suggest that the distortion noises can be regarded as practically independent whenever there are two or more modulation streams being transmitted (spatial multiplexing). In a single-stream scenario, the distortion noise will tend to have the same spatial distribution as the desired signal.

  • 39.
    Najari Moghadam, Nima
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Farhadi, Hamed
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nasiri Khormuji, Majid
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Interference Alignment — Practical Challenges and Test-bed Implementation2014In: Contemporary Issues in Wireless Communications / [ed] Dr. Mutamed Khatib, INTECH, 2014, p. 51-77Chapter in book (Refereed)
    Abstract [en]

    Data traffic over wireless communication networks has experienced a tremendous growth in the last decade, and it is predicted to exponentially increase in the next decades. Enabling future wireless networks to fulfill this expectation is a challenging task both due to the scarcity of radio resources (e.g. spectrum and energy), and also the inherent characteristics of the wireless transmission medium. Wireless transmission is in general subject to two phenomena: fading and interference. The elegant interference alignment concept reveals that with proper transmission signalling design, different interference signals can in fact be aligned together, such that more radio resources can be assigned to the desired transmission. Although interference alignment can achieve a larger data rate compared to orthogonal transmission strategies, several challenges should be addressed to enable the deployment of this technique in future wireless networks For instance, to perform interference alignment, normally, global channel state information (CSI) is required to be perfectly known at all terminals. Clearly, acquiring such channel knowledge is a challenging problem in practice and proper channel training and channel state feedback techniques need to be deployed. In addition, since the channels are time-varying proper adaptive transmission is needed. This chapter review recent advances in practical aspects of interference alignment. It also presents recent test-bed implementations of signal processing algorithms for the realization of interference alignment.

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  • 40.
    Negusse, Senay
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    IEEE-STD-1057 Three Parameter Sine Wave Fit for SNR Estimation: Performance Analysis and Alternative Estimators2014In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 63, no 6, p. 1514-1523Article in journal (Refereed)
    Abstract [en]

    This paper considers the three-parameter-fit sine wave model. Under a Gaussian noise assumption, it is known that the three-parameter fit given in IEEE Standards 1057 and 1241 coincides with the method of maximum likelihood (ML), which is known for its favorable properties in large samples. Under coherent sampling assumption, the Cramér--Rao Bound of an unbiased estimator (UE) of the signal-to-noise ratio (SNR) is derived followed by an exact finite-sample analysis of the ML estimator of SNR derived from the three-parameter fit, revealing its nonsymmetric F-distribution. Exact expressions for the bias, variance, and the mean squared error (MSE) of the ML estimator are then derived, revealing that the ML estimator in finite samples is far from optimal in terms of precision and accuracy. With the ML estimator as a starting point, several alternative estimators are derived, which outperform the method of ML. In particular, a UE is derived, with lower variance compared with the ML for small sample size. In addition, estimators are derived based on constrained minimization of the MSE. The theoretical findings are illustrated by simulations, showing an excellent agreement between theory and practice. Simulations using quantized data are also used to show the performance of the derived estimators mimicking an analog-to-digital converter (ADC) testing scenario. Furthermore, the derived estimators are applied to coherently and noncoherently sampled measurement data from a 12-bit ADC and, for small number of samples, all are shown to outperform the original estimate, showing the practical relevance of the theoretical findings.

  • 41.
    Negusse, Senay
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On SNR estimation using IEEE-STD-1057 three-parameter sine wave fit2013In: IEEE International Instrumentation and Measurement Technology Conference (I2MTC), 2013, IEEE conference proceedings, 2013, p. 658-661Conference paper (Refereed)
    Abstract [en]

    In this paper, theoretical properties of a maximum-likelihood (ML) estimator of signal-to-noise ratio (SNR) is discussed. The three-parameter sine fit algorithm is employed on a finite and coherently sampled measurement set corrupted by additive white Gaussian noise. Under the Gaussian noise model, the least squares solution provided by the three-parameter sine fit is also ML estimator. Exact distribution and finite sample properties of the SNR estimate are derived. Moreover, an explicit expression for the mean squared error (MSE) of the estimator is given. Simulation results are shown to verify the underlying theoretical results.

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  • 42.
    Negusse, Senay
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cost reference particle filter in data aided channel estimation and phase noise tracking for OFDM systems2012In: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on, IEEE , 2012, p. 3153-3156Conference paper (Refereed)
    Abstract [en]

    In this paper, we present a robust technique based on cost reference particle filter (CRPF) for combined channel impulse response (CIR) estimation and phase noise (PN) tracking in OFDM systems without any priori information regarding the noise in the state and measurement equation. Contrary to previous works, we hold no assumption regarding the magnitude of the PN variance and hence no approximation is made to simplify the model. The algorithm employs CRPF along with a Rao-Blackwellization technique for CIR estimation assuming static channel state over a number of OFDM symbols. Numerical results are given to demonstrate the performance of the algorithm based on mean squared error (MSE).

  • 43.
    Negusse, Senay
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Phase-noise mitigation in OFDM by best match trajectories2015In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 5, p. 1712-1725Article in journal (Refereed)
    Abstract [en]

    This paper proposes a novel approach to phasenoise compensation. The basic idea is to approximate the phasenoise statistics by a finite number of realizations, i.e., a phasenoise codebook. The receiver then uses an augmented received signal model, where the codebook index is estimated along with other parameters. The realization of the basic idea depends on the details of the air interface, the phase-noise statistics, the propagation scenario and the computational constraints. In this paper, we will focus on a MQAM-OFDM system with pilot subcarriers within each OFDM symbol. The channel is frequency selective, fading and unknown. A decision-feedback method is employed to further enhance performance of the system. Simulation results are shown for uncoded and coded systems to illustrate the performance of the algorithm, which is als o compared with previously employed methods. Our simulation s show that for a 16-QAM coded OFDM system over a frequency selective Rayleigh fading channel affected by phase noise with root-mean-square (RMS) of 14.4 degrees per OFDM symbol, the proposed algorithm is 1.5dB from the ideal phase-noise free case at a BER of 10 − 4 . The performance of the best reference scheme is 2.5dB from the ideal case at BER of 10 − 4 . The proposed scheme is also computationally attractive.

  • 44.
    Ottersten, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Base-station antenna arrays in mobile communications1995In: Transactions of the 7th Tyrrhenian International Workshop on Digital Communications, 1995Conference paper (Refereed)
  • 45.
    Rojas, Cristian R.
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Transceiver Inphase/Quadrature Imbalance, Ellipse Fitting, and the Universal Software Radio Peripheral2011In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 60, no 11, p. 3629-3639Article in journal (Refereed)
    Abstract [en]

    In this paper, we introduce a method for inphase/quadrature imbalance parameter estimation based on ellipse fitting. The performance of the method is analytically derived. In particular, it is shown that the method exhibits a small bias (which can be negligible under some standard practical conditions) and a variance slightly above the Cramer-Rao bound. The method is then applied to measurements from a contemporary BiCMOS transceiver which is used on one of the most popular daughterboards of the universal software radio peripheral. In our measurements, the phase skew varies up to 5 degrees with the baseband frequency, while the amplitude imbalance varies between 0 and 0.3 dB over carrier frequencies and across hardware units. The time variation, however, is only 0.004 dB in amplitude and 0.06 degrees in phase. This indicates that the units could either be calibrated online when there is no transmission (in a two-antenna MIMO system, one antenna could transmit a calibration signal to the other), or they could be calibrated during production, in which case a table with different carrier and baseband frequencies would be needed. However, there is no need to estimate the parameters on every burst.

  • 46.
    Samuelsson, David
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jaldén, Joakim
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Realization of a spatially multiplexed MIMO system2006In: EURASTP journal an applied signal processing, ISSN 1110-8657, E-ISSN 1687-0433, Vol. 2006, p. 78349-Article in journal (Refereed)
    Abstract [en]

    Multi-antenna systems can provide improvements in wireless systems increasing spectral efficiency, reliability, range, and system capacity. Herein we show how some of the potentials of MIMO systems can be realized on a simple radio hardware platform by utilizing advanced real-time signal processing and coding. We present a real-time implementation of a 2 by 2 MIMO system employing spatial multiplexing to achieve high spectral efficiency in an indoor non-line-of-sight environment operating in the 1800 MHz range. Well-known processing and coding techniques are employed and our contributions lie in: discussing implementational aspects and solutions often overlooked but critical for high-performance operation; demonstrating the degree to which the simple baseband AWGN model can be used to accurately model/predict the MIMO system on the current hardware; and demonstrating the feasibility of real-time spatial multiplexing achieving up to 15 bps/Hz on a 2 by 2 system in a realistic indoor environment with off-the-shelf radio hardware.

  • 47.
    Zetterberg, Per
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    A Smart Antenna Concept for 4G and Transceiver Cost2004In: Proceedings of Nordic Radio Symposium, 2004Conference paper (Other academic)
  • 48.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Comparison of angle-spread in outdoor-to-outdoor and outdoor-to-indoor cases in an urban macro-cesll2005In: Wireless Personal Multimedia Communications (WPMC), Aalborg, Denmark, 2005Conference paper (Refereed)
  • 49.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Experimental Investigation of TDD Reciprocity-Based Zero-Forcing Transmit Precoding2011In: EURASIP J ADV SIGNAL PROCESS, ISSN 1687-6172, p. 137541-Article in journal (Refereed)
    Abstract [en]

    We describe an implementation of TDD reciprocity based zero-forcing linear precoding on a wireless testbed. A calibration technique which self-calibrates the base-station without the need for help from other nodes is described. Performance results in terms of downlink channel estimation error as well as bit error rate (BER) and signal to interference noise and distortion ratio (SINDR) are presented for a scenario with two base-stations and two mobile stations, with two antennas at the base-stations and a single antenna at the mobile-station. The results show considerable performance improvements over reference schemes (such as maximum ratio transmission). However, our analysis also reveals that the hardware impairments significantly limit the performance achieved. We further investigate how to model these impairments and attempt to predict the SINDR, such as what would be needed in a coordinated multipoint (CoMP) scenario where scheduling is performed jointly over the two cells. Although the results are obtained for a MISO scenario the general conclusions are relevant also for MIMO scenarios.

  • 50.
    Zetterberg, Per
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Interference alignment (IA) and coordinated multi-point (CoMP) overheads and RF impairments: Testbed results2014In: 2014 IEEE 80th Vehicular Technology Conference (VTC Fall), 2014, p. 1-7Conference paper (Refereed)
    Abstract [en]

    In this work we investigate the network MIMO techniques of interference alignment (IA) and joint transmission coordinated multipoint (CoMP) in an indoor very small cell environment. Our focus is on the overheads in a system with quantized channel state feedback from the receiver to the transmitter (based on the 802.11ac standard) and on the impact of non-ideal hardware. The indoor office scenario should be the most favorable case in terms of the required feedback rates due to the large coherence bandwidth and coherence time of the channel.The evaluations are done using a real-world wireless testbed with three BSs and three MSs all having two antennas. The signal to noise ratio in the measurements is very high, 35-60dB, due to the short transmission range. Under such conditions radio hardware impairments becomes a major limitation on the performance. We quantify the impact of these impairments. For a 23ms update interval the overhead is 2.5% and IA and CoMP improves the sum throughput 25% and 50% in average (over the reference schemes e.g. TDMA MIMO), under stationary conditions. When two people are walking in the measurement area the throughput improvements drops to 17% and 45%, respectively.

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