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  • 251.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bergman, Svante
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spatial loading based on channel covariance feedback and channel estimates2004In: Proceedings European Signal Processing Conference, 2004Conference paper (Refereed)
    Abstract [en]

    Techniques for communication over flat multi-input, multi-output (MIMO) channels are well established when either perfect channel state information or no channel state information is available at the transmitter. However, communication over channels where the transmitter has access to partial or imperfect information has received less attention. If explored, such information could improve system performance and reduce the demand on feedback channels or the quality of channel estimates. In this paper, a simple design scheme is introduced, that approximately maximizes the data rates of MIMO communication systems where the transmiter have access to partial channel state information in the form of covariance feedback or erroneous channel estimates. The presented algorithm is computationally attractive and gains compared with systems not exploring this information are demonstrated.

  • 252. Martin, Cristoff
    et al.
    Geurtz, A
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    File based mobile satellite broadcast systems: Error rate computation and QoS based design2004In: VTC2004-FALL: 2004 IEEE 60TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-7 - WIRELESS TECHNOLOGIES FOR GLOBAL SECURITY, NEW YORK: IEEE , 2004, p. 4017-4021Conference paper (Refereed)
    Abstract [en]

    Mobile satellite broadcast systems have the potential of delivering entertainment, information and other data services with outstanding coverage and reliability. However, the long signal interruptions due to obstacles in the terminal environment that characterizes the land mobile satellite channel make the design of efficient air interfaces challenging. In this paper, a file based mobile satellite broadcast system is studied where, to overcome the signal blockages, packet time diversity is applied. Based on some simple assumptions, an analytical expression for the file error rate of the system is derived. Using this result, a design scheme is proposed that, for a given channel and file, minimizes the total number of transmitted symbols required to satisfy quality of service (QoS) constraints in terms of acceptable delay and file receive probability. The results can also be used to estimate the reduction in bandwidth requirements that can be achieved if users in demanding environments can be served using terrestrial repeaters or other means.

  • 253. Martin, Cristoff
    et al.
    Geurtz, A
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spectrally efficient mobile satellite real-time broadcast with transmit diversity2004In: VTC2004-FALL, NEW YORK: IEEE , 2004, p. 4079-4083Conference paper (Refereed)
    Abstract [en]

    Mobile broadcast services from satellites require the terminals to constantly be in near line of sight conditions with the transmitting satellite in order to efficiently provide real-time services. To satisfy this constraint in practice, satellite diversity as well as terrestrial repeaters are used. By separating the various transmissions in frequency, exploiting this spatial diversity at the receiver is straightforward. However, transmitting the same information at different frequencies also reduces the limited and expensive spectrum available for these types of services. By configuring the different transmissions as a single frequency network. in principle a more efficient usage of the spectrum can be achieved. Due to the vast distances involved in satellite diversity systems, practical design of such a system is challenging. In this paper we propose the use of a small adaptive antenna at the receiver in order to separate the different transmissions and improve the spectral efficiency. System architectures are outlined, an example illustrates the potential gain and implementation issues are discussed.

  • 254.
    Martin, Cristoff
    et al.
    Luxembourg International Advanced Studies in Information Technologies (LIASIT) 211, route d’Esch L-1471 Luxembourg, Luxembourg.
    Geurtz, Alexander
    SES GLOBAL S.A. L-6815 Chˆateau de Betzdorf Luxembourg.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Packet Coded Mobile Satellite Broadcast Systems: Error Rate Computations and Quality of Service Based Design2004In: ESA ASMS/EMPS, 2004Conference paper (Refereed)
  • 255.
    Martin, Cristoff
    et al.
    Luxembourg International Advanced Studies in Information Technologies, 1471 Luxembourg, Luxembourg.
    Geurtz, Alexander
    SES GLOBAL S.A., 6815 Betzdorf, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Statistical analysis and optimal design for efficient mobile satellite broadcast with diversity2008In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 57, no 2, p. 986-1000Article in journal (Refereed)
    Abstract [en]

    The design of mobile satellite broadcast architectures requires complex tradeoffs involving technical, economical, and regulatory aspects. A satisfactory quality of service in terms of the number of receivers successfully receiving the broadcasted cervices can be ensured using space, terrestrial, and time diversity techniques. The amount of applied diversity affects the system's spectral efficiency and performance. In addition, dedicated satellite and terrestrial networks represent significant investments, and regulatory limitations on terrestrial deployment may further complicate the system design. Herein, we provide insights into the technical aspects of the aforementioned tradeoffs by deriving an efficient method to estimate what system resources in terms of spectrum and delay are required to provide a satisfactory number of end users with mobile broadcast services using space, terrestrial, and time diversity techniques. The presented results are based on statistical models of the mobile satellite channel for which efficient analytical design and error rate estimation methods are derived. To provide a coded space and time diversity, a generalized approach is taken that includes most transmission schemes in use, or considered for use, for mobile satellite broadcast as special cases. As a side result, it is shown that for optimal error rate performance, the provided time diversity should be designed by taking into account channel statistics. An efficient yet simple method of enumerating time-varying Markov chains is also included. The proposed techniques and results are illustrated with numerical examples using temporal Ku-band channel statistics. The examples include a wide range of possible transmission schemes in system configurations with and without space and terrestrial diversity and, thus, demonstrate how different transmission schemes and infrastructure configurations can be compared.

  • 256.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Analytic Approximations of Eigenvalue Moments and Mean Channel Capacity for MIMO Channels2002In: Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2002, p. 2389-2392Conference paper (Refereed)
    Abstract [en]

    Approximate second order moments of the squared singular values of the channel matrix of a multiple input multiple output (MIMO) system are derived. Correlation at both the receiver and the transmitter antenna arrays is allowed. The approximation converges to the true moments as either the number of transmit or receive antennas increases. Simulations indicate that the derived moments may provide a good approximation of the true moments even for realistic array sizes. As an application, an expression for the mean channel capacity is derived. The expression is simple enough to provide insight while offering promising performance when compared with simulated channel capacities.

  • 257.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Analytic approximations of eigenvalue moments and mean channel capacity for MIMO channels2002In: 2002 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING, 2002, p. 2389-2392Conference paper (Refereed)
    Abstract [en]

    Approximate second order moments of the squared singular values of the channel matrix of a multiple input multiple output (MIMO) system are derived. Correlation at both the receiver and the transmitter antenna arrays is allowed, The approximation converges to the true moments as either the number of transmit or receive antennas increases. Simulations indicate that the derived moments may provide a good approximation of the true moments even for realistic array sizes. As an application, an expression for the mean channel capacity is derived. The expression is simple enough to provide insight while offering promising performance when compared with simulated channel capacities.

  • 258.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Approximate Transmit Covariance Optimization of MIMO Systems with Covariance Feedback2003In: Proceedings Asilomar Conference on Signals, Systems & Computers, IEEE , 2003, p. 1047-1051Conference paper (Refereed)
    Abstract [en]

    The data rate of a multiple input, multiple output (MIMO) communication link can be improved if knowledge about the channel statistics is exploited at the transmitter. However, many realistic system scenarios require computationally prohibitive Monte Carlo methods in order to optimize the transmit covariance for maximization of the exact mutual information. This paper instead considers an approximative approach to maximize the performance of a communication link where covariance feedback is available at the transmitter. The algorithm presented is based on an asymptotic expression of the mutual information that allows for correlation at both the transmit and the receive side of the system. From simulations we demonstrate significant gain over beamforming and pure divversity schemes in many realistic system scenarios.

  • 259.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Approximate transmit covariance optimization of MIMO systems with covariance feedback2003In: CONFERENCE RECORD OF THE THIRTY-SEVENTH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, 2003, p. 1047-1051Conference paper (Refereed)
    Abstract [en]

    The data rate of a multiple input, multiple output (MIMO) communication link can be improved if knowledge about the channel statistics is exploited at the transmitter. However, many realistic system scenarios require computationally prohibitive Monte Carlo methods in order to optimize the transmit covariance for maximization of the exact mutual information. This paper instead considers an approximative approach to maximize the performance of a communication link where covariance feedback is available at the transmitter. The algorithm presented is based on an asymptotic expression of the mutual information that allows for correlation at both the transmit and the receive side of the system. From simulations we demonstrate significant gain over beamforming and pure diversity schemes in many realistic system scenarios.

  • 260.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Asymptotic eigenvalue distributions and capacity for MIMO channels under correlated fading2004In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 3, no 4, p. 1350-1359Article in journal (Refereed)
    Abstract [en]

    Closed form approximations of the outage capacity and the mutual information between the in- and outputs of a multi-input, multi-output (MIMO) narrowband system in the presence of correlated fading are considered. First, the limiting distribution of the squared singular values of the channel matrix is derived as the number of antennas at either the transmit or receive site increases. Spatial correlation is allowed according to a realistic stochastic channel model and correlation is allowed between the transmitted signals. The derived limiting distribution has the advantage of being closed form while simulations indicate that it provides a reasonable approximation of the true distribution also for realistic antenna array sizes. Second, the channel outage capacity is derived from the limiting distribution above for the case when the number of transmit antennas is large. The resulting outage capacity has a simple form and allows for spatially correlated channel elements as well as correlation among the transmitted signals. Results from simulations and channel measurements are presented that indicate that the derived expression provides an accurate approximation of the true channel outage capacity for a wide range of realistic system conditions.

  • 261.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Joint Channel Estimation and Detection for Interference Cancellation in Multi-Channel Systems2000In: The 10th IEEE Workshop on Statistical Signal and Array Processing, IEEE , 2000, p. 186-190Conference paper (Refereed)
    Abstract [en]

    Interference from other users and interference due to multipath propagation limit the capacity of wireless communication networks. As the number of users and the demand for new services in the networks increases, co-channel interference will be a limiting factor. This paper proposes an iterative structured multichannel receiver algorithm that jointly estimates the communication channels and desired data while cancelinginterference. A general way of adding training redundancy to a data frame is also introduced. From simulations the proposed method is shown to achieve low bit error rates also in the presence of strong interference. These simulations also show that by distributing the training information in a data burst elaborately further improvements in performance are achievable.

  • 262.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On robustness against burst unsynchronized co-channel interference in semi-blind detection2000In: Conference Record of the Asilomar Conference on Signals, Systems and Computers, 2000, Vol. 2, p. 946-950Conference paper (Refereed)
    Abstract [en]

    Interference from other users and interference due to multipath propagation limit the capacity of wireless communication networks. As the number of users and the demand for new services in the networks increases, co-channel interference will be a limiting factor. This paper investigates the effects of burst unsynchronized co-channel interference on the performance of a joint channel estimation and detection algorithm. Further, the paper tries to give some insight in how to add training redundancy to a data frame in order to provide robustness against unsynchronized co-channel interference. From simulations and Cramer-Rao bound calculation we find that by using distributing training information elaborately it is possible to increase the robustness against unsynchronized co-channel interferers.

  • 263.
    Martin, Cristoff
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On Robustness Against Burst Unsynchronized Co-Channel Interference in Semi-Blind Detection2000In: Proceedings Asilomar Conference on Signals, Systems & Computers, IEEE , 2000, p. 946-950Conference paper (Refereed)
    Abstract [en]

    Interference from other users and interference due to multi-path propagation limit the capacity of wireless communication networks. As the number of users and the demand for new services in the networks increases, co-channel interference will be a limiting factor. This paper investigates the effects of burst unsynchronized co-channel interference on the performance of a joint channel estimation and detection algorithm. Further, the paper tries to give some insight in how to add training redundancy to a data frame in order to provide robustness against unsynchronized co-channel interference. From simulations and Cramér-Rao bound calculation we find that by using distributing training information elaborately it is possible to increase the robustness against unsynchronized co-channel interferers.

  • 264. Meng, Qingmin
    et al.
    Feng, Wei
    Zheng, Gan
    Chatzinotas, Symeon
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fixed Full Duplex Relaying for Wireless Broadband Communication2012Conference paper (Other academic)
  • 265.
    Mowlér, Marc
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Khalid, Bilal
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lindmark, Björn
    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.
    Capacity and Gain Analysis of a Reconfigurable MEMS Antenna2008In: Nordic Conference on Radio Science and Communications (RVK), 2008Conference paper (Other academic)
    Abstract [en]

    This paper presents the investigation results on therecon¯gurable properties of an antenna array compris-ing of four feed elements and four parasitic elementsplaced on a ¯nite ground plane. This antenna is in-tended to improve the diversity gain for a Multiple In-put Multiple Output (MIMO) communication system.We intend to use a recon¯gurable antenna to com-bat the problem of signal deterioration in a handhelddevice so that it can get optimum signal strength inany orientation. With our presented antenna, we canachieve up to sixteen di®erent con¯gurations depend-ing on the requirement. The di®erent con¯gurationsare controlled with the help of RF switches which areimplemented using micro-electromechanical systems(MEMS). The recon¯gurable antenna was fabricatedand tested for its impedance and radiation character-istics and the results were found to be in reasonable agreement with the simulations. Channel measure-ments were made with the help of a MIMO test setup.

  • 266.
    Mowlér, Marc
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Khalid, Bilal
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lindmark, Björn
    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.
    Switched MEMS Antenna for Handheld Devices2008In: ICT-MobileSummit 2008, 2008Conference paper (Refereed)
    Abstract [en]

    This paper presents the investigation results on the reconfigurableproperties of a monopole antenna array. The antenna array comprises of four feedelements and four parasitic elements on a finite ground plane. This antenna isintended to improve the diversity gain for a Multiple Input Multiple Output (MIMO)communication system. We intend to combat the problem of signal deterioration inhandheld devices by the use of reconfigurable antenna. A common communicationproblem seen in the handheld devices is the change in strength of radio signal whenthe orientation of the device is changed. Reconfigurable antennas can be used get ridof this nuisance so that what ever be the orientation, the handheld device still gets thebest possible signal level. With our presented antenna, we can achieve up to sixteendifferent configurations depending upon the requirement. The differentconfigurations are controlled with the help of RF switches which are implementedusing micro-electromechanical systems (MEMS). The reconfigurable antenna wasfabricated and tested for its impedance and radiation characteristics and the resultswere found to be in reasonable agreement with the simulations.

  • 267.
    Mowlér, Marc
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Larsson, Erik G.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lindmark, Björn
    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.
    Methods and bounds for antenna array coupling matrix estimation2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, p. 881-884Conference paper (Refereed)
    Abstract [en]

    A novel method is proposed for estimation of the mutual coupling matrix of an antenna array. The method extends previous work by incorporating an unknown phase center and the element factor (antenna radiation pattern) in the model, and treating these as nuisance parameters during the estimation of coupling. To facilitate this, a parametrization of the element factor based on a truncated Fourier series is proposed. The Cramer-Rao bound (CRB) for the estimation problem is derived and used to analyze how the required amount of measurement data increases when introducing a more and more flexible model for the element factor. Finally, the performance of the proposed estimator is illustrated using data from measurements on an 8-element antenna array.

  • 268.
    Mowlér, Marc
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lindmark, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    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.
    Joint estimation of mutual coupling, element factor, and phase center in antenna arrays2007In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2007, no 1, p. 030684-Article in journal (Refereed)
    Abstract [en]

    A novel method is proposed for estimation of the mutual coupling matrix of an antenna array. The method extends previous work by incorporating an unknown phase center and the element factor (antenna radiation pattern) in the model, and treating them as nuisance parameters during the estimation of coupling. To facilitate this, a parametrization of the element factor based on a truncated Fourier series is proposed. The performance of the proposed estimator is illustrated and compared to other methods using data from simulations and measurements, respectively. The Cramer-Rao bound (CRB) for the estimation problem is derived and used to analyze how the required amount of measurement data increases when introducing additional degrees of freedom in the element factor model. We find that the penalty in SNR is 2.5 dB when introducing a model with two degrees of freedom relative to having zero degrees of freedom. Finally, the tradeoff between the number of degrees of freedom and the accuracy of the estimate is studied. A linear array is treated in more detail and the analysis provides a specific design tradeoff.

  • 269. Mysore Rama Rao, B. S.
    et al.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Detection of sparse random signals using compressive measurements2012In: Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on, IEEE , 2012, p. 3257-3260Conference paper (Refereed)
    Abstract [en]

    We consider the problem of detecting a sparse random signal from the compressive measurements without reconstructing the signal. Using a subspace model for the sparse signal where the signal parameters are drawn according to Gaussian law, we obtain the detector based on Neyman-Pearson criterion and analytically determine its operating characteristics when the signal covariance is known. These results are extended to situations where the covariance cannot be estimated. The results can be used to determine the number of measurements needed for a particular detector performance and also illustrate the presence of an optimal support for a given number of measurements.

  • 270. Naghsh, M. M.
    et al.
    Soltanalian, M.
    Stoica, P.
    Masjedi, M.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg City, 2721, Luxembourg.
    Efficient Sum-Rate Maximization for Medium-Scale MIMO AF-Relay Networks2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 9, p. 6400-6411Article in journal (Refereed)
    Abstract [en]

    We consider the problem of sum-rate maximization in multiple-input multiple-output (MIMO) amplify-and-forward relay networks with multi-operator. The aim is to design the MIMO relay amplification matrix (i.e., the relay beamformer) to maximize the achievable communication sum rate through the relay. The design problem for the case of single-antenna users can be cast as a non-convex optimization problem, which, in general, belongs to a class of NP-hard problems. We devise a method based on the minorization-maximization technique to obtain quality solutions to the problem. Each iteration of the proposed method consists of solving a strictly convex unconstrained quadratic program. This task can be done quite efficiently, such that the suggested algorithm can handle the beamformer design for relays with up to similar to 70 antennas within a few minutes on an ordinary personal computer. Such a performance lays the ground for the proposed method to be employed in medium-scale (or lower regime massive) MIMO scenarios.

  • 271. Nasir, A. A.
    et al.
    Mehrpouyan, H.
    Durrani, S.
    Blostein, S. D.
    Kennedy, R. A.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    DSTBC based DF cooperative networks in the presence of timing and frequency offsets2013In: Signal Processing Advances in Wireless Communications (SPAWC), 2013 IEEE 14th Workshop on, 2013, p. 86-90Conference paper (Refereed)
    Abstract [en]

    n decode-and-forward (DF) relaying networks, the received signal at the destination may be affected by multiple impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple carrier frequency offsets (MCFOs). This paper proposes novel optimal and sub-optimal minimum mean-square error (MMSE) receiver designs at the destination node to detect the signal in the presence of these impairments. Distributed space-time block codes (DSTBCs) are used at the relays to achieve spatial diversity. The proposed sub-optimal receiver uses the estimated values of multiple channel gains, MTOs, and MCFOs, while the optimal receiver assumes perfect knowledge of these impairments at the destination and serves as a benchmark performance measure. To achieve robustness to estimation errors, the estimates statistical properties are exploited at the destination. Simulation results show that the proposed optimal and sub-optimal MMSE compensation receivers achieve full diversity gain in the presence of channel and synchronization impairments in DSTBC based DF cooperative networks

  • 272. Nasir, A. A.
    et al.
    Mehrpouyan, H.
    Durrani, S.
    Blostein, S. D.
    Kennedy, R. A.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Optimal Training Sequences for Joint Timing Synchronization and Channel Estimation in Distributed Communication Networks2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 7, p. 3002-3015Article in journal (Refereed)
    Abstract [en]

    For distributed multi-user and multi-relay cooperative networks, the received signal may be affected by multiple timing offsets (MTOs) and multiple channels that need to be jointly estimated for successful decoding at the receiver. This paper addresses the design of optimal training sequences for efficient estimation of MTOs and multiple channel parameters. A new hybrid Cramer-Rao lower bound (HCRB) for joint estimation of MTOs and channels is derived. Subsequently, by minimizing the derived HCRB as a function of training sequences, three training sequence design guidelines are derived and according to these guidelines, two training sequences are proposed. In order to show that the proposed design guidelines also improve estimation accuracy, the conditional Cramer-Rao lower bound (ECRB), which is a tighter lower bound on the estimation accuracy compared to the HCRB, is also derived. Numerical results show that the proposed training sequence design guidelines not only lower the HCRB, but they also lower the ECRB and the mean-square error of the proposed maximum a posteriori estimator. Moreover, extensive simulations demonstrate that application of the proposed training sequences significantly lowers the bit-error rate performance of multi-relay cooperative networks when compared to training sequences that violate these design guidelines.

  • 273. Nasir, A. A.
    et al.
    Mehrpouyan, H.
    Durrani, S.
    Blostein, S. D.
    Kennedy, R. A.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Transceiver Design for Distributed STBC Based AF Cooperative Networks in the Presence of Timing and Frequency Offsets2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 12, p. 3143-3158Article in journal (Refereed)
    Abstract [en]

    In multi-relay cooperative systems, the signal at the destination is affected by impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple carrier frequency offsets (MCFOs). In this paper we account for all these impairments and propose a new transceiver structure at the relays and a novel receiver design at the destination in distributed space-time block code (DSTBC) based amplify-and-forward (AF) cooperative networks. The Cramer-Rao lower bounds and a least squares (LS) estimator for the multi-parameter estimation problem are derived. In order to significantly reduce the receiver complexity at the destination, a differential evolution (DE) based estimation algorithm is applied and the initialization and constraints for the convergence of the proposed DE algorithm are investigated. In order to detect the signal from multiple relays in the presence of unknown channels, MTOs, and MCFOs, novel optimal and sub-optimal minimum mean-square error receiver designs at the destination node are proposed. Simulation results show that the proposed estimation and compensation methods achieve full diversity gain in the presence of channel and synchronization impairments in multi-relay AF cooperative networks.

  • 274.
    Nilsson, Martin
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Völcker, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    A Cluster Approach to Spatio-Temporal Channel Estimation2000In: IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2000, p. 2757-2760Conference paper (Refereed)
    Abstract [en]

    In a severe multipath environment the antenna receives multiple copies of the same transmitted signal. To solve for all waves is difficult if possible at all. In this paper we use the approach of grouping the spatio-temporalreflections into clusters. We study how the aperture and bandwidth affects the cluster resolution using experimental data. The measurements were obtained by transmitting linear FM (chirp) signals of 150 MHz bandwidth, in the 1800 MHz band. An antenna array of 16 elements was used as a receiver.

  • 275.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Adaptive Antennas in Wideband Radio Access Networks2002Other (Other academic)
  • 276.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Affordable Wireless Infrastructures and Services2001Other (Other academic)
  • 277.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Antenna Arrays for Wireless Communications Models and Algorithms1999Other (Other academic)
  • 278.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Antenna Arrays for Wireless Communications Models and Algorithms from a Systems Perspective1999Conference paper (Other academic)
  • 279.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    “Antenna Arrays in Mobile Communications”1995In: Communications, Computing, Control, and Signal Processing: 2000, 1995Conference paper (Refereed)
  • 280.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Array Processing for Wireless Communications1996Other (Other (popular science, discussion, etc.))
  • 281.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Array Processing for Wireless Communications1998Conference paper (Refereed)
  • 282.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Asymptotic Analysis of SVD-Based Array Processing Algorithms1990In: SIAM Conference on Linear Algebra in Signals, Systems and Contro, San Francisco, CA, 1990Conference paper (Refereed)
  • 283.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    MIMO Channel Modeling and Multi-User MIMO Systems2002Other (Other academic)
  • 284.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Robust Direction Estimation from Hydroacoustic Array Data1993In: Hydroakustik 93, 1993Conference paper (Refereed)
    Abstract [en]

    In hydro-acoustic array signal processing we are often concerned with accurate determination of signal parameters from array measurements. To obtain accurate direction estimates, knowledge of the array response is required. Most estimation techniques are sensitive to errors in the array response model. Thus, reliable array calibration schemes are of great importance. In practice, calibration is done by measuring the array response when only one emitter is present and the signal parameters of which are allowed to vary in a known way. Herein, methods for generating an array model from noise corrupted calibration vectors is developed. The performance of the technique is examined on data collected from a full-scale hydro-acoustic array.

  • 285.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spatial channel modeling for wireless systems2001Other (Other academic)
  • 286.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Spatial Division Multiple Access (SDMA) in Wireless Communications1995In: Proceedings of Nordic Radio Symposium, 1995Conference paper (Other academic)
    Abstract [en]

    This paper describes the utilization of antenna arrays at the base stations of wireless communication systems. Multiple antennas can provide a processing gain to increase the base station range and improve coverage. Also, by exploiting the angular selectivity of an antenna array at the base stations of a wireless system, users may be spatially multiplexed to increase system capacity. We address several aspects of the reception and transmission problems that arise when the spatial dimension is considered. Both the forward and reverse channels are discussed and an overview of related research conducted at the signal processing group, KTH is presented.

  • 287.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Astély, David
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kristensson, Martin
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Parkvall, Stefan
    KTH, Superseded Departments, Signals, Sensors and Systems.
    A Statistical Approach to Subspace Based Estimation with Applications in Telecommunications1996Conference paper (Other academic)
  • 288.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Astély, David
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kristensson, Martin
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Parkvall, Stefan
    KTH, School of Electrical Engineering (EES), Signal Processing.
    A Statistical Approach to Subspace Based Estimation with Applications in Telecommunications1997In: 2nd International Workshop on TLS and Errors-in-Variables Modeling / [ed] Huffel, S. Van, SIAM , 1997, p. 285-294Chapter in book (Other academic)
  • 289.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Barratt, Craig H.
    Parish, David M.
    Roy, Richard H.
    Spectrally efficient high capacity wireless communication systems with spatio-temporal processing1998Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A wireless system includes a network of base stations for receiving uplink signals transmitted from a plurality of remote terminals and for transmitting downlink signals to said plurality of remote terminals using a plurality of channels. A plurality of antenna elements at each base station receives uplink signals, and a plurality of antenna elements at each base station for transmits downlink signals. A signal processor at each base station is connected to the receiving antenna elements and to the transmitting antenna elements for determining spatio-temporal signatures. Spatio-temporal multiplexing and demultiplexing functions are provided for each remote terminal antennae for each channel, and a multiple base station network controller optimizies network performance, whereby communication between the base stations and the plurality of remote terminals in each of the channels can occur simultaneously.

  • 290.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Jöngren, George
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Space-Time Processing and Coding in Wireless Communications2003Other (Other academic)
  • 291.
    Ottersten, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    KAILATH, T
    DIRECTION-OF-ARRIVAL ESTIMATION FOR WIDE-BAND SIGNALS USING THE ESPRIT ALGORITHM1990In: IEEE TRANSACTIONS ON ACOUSTICS SPEECH AND SIGNAL PROCESSING, ISSN 0096-3518, Vol. 38, no 2, p. 317-327Article in journal (Refereed)
  • 292.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kailath, T.
    ESPRIT for Wideband Signals1987In: Proceedings 21st Asilomar Conf. Sig., Syst., Comput., Monterey, CA, 1987Conference paper (Refereed)
  • 293.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Roy, R.
    “Subspace Algorithms in Systems Identification and Telecommunication Applications”1994In: 3rd International Workshop on SVD and Signal Processing, 1994Conference paper (Refereed)
  • 294.
    Ottersten, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    ROY, R
    KAILATH, T
    SIGNAL WAVE-FORM ESTIMATION IN SENSOR ARRAY-PROCESSING1989In: TWENTY-THIRD ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, VOLS 1 AND 2: CONFERENCE RECORD, p. 787-791Article in journal (Refereed)
  • 295.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Stoica, Petre
    Department of Systems and Control, Uppsala University, Uppsala, Sweden.
    Astély, David
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Jakobsson, Andreas
    Department of Systems and Control, Uppsala University, Uppsala, Sweden.
    Spatio-Temporal Processing in Wireless Communications1999In: RadioVetenskap och Kommunikation (RVK), 1999, p. 402-406Conference paper (Other academic)
    Abstract [en]

    Herein, we provide an overview of the research conducted in the project "Spatio-Temporal Processing in Wireless Communications" supported by NUTEK's telecommunications program. Spatio-temporal processing at the base stations of a wireless system can provide processing gain which may be used to extend range and improve coverage of the network and/or improve signal quality and lower terminal power requirements. Furthermore, with spatially selective reception and transmission, the capacity in wireless communication systems can be increased without exploiting additional bandwidth. We will give an overview of the results of this research project to date. 

  • 296.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Stoica, Petre
    Department of Systems and Control, Uppsala University, Uppsala, Sweden.
    Roy, R.
    ArrayComm Inc.
    Covariance matching estimation techniques for array signal processing applications1998In: Digital signal processing (Print), ISSN 1051-2004, E-ISSN 1095-4333, Vol. 8, no 3, p. 185-210Article in journal (Refereed)
    Abstract [en]

    A class of covariance matching estimation techniques (COMET) has recently attracted interest in the signal processing community. These techniques have their roots in the statistical literature where they are sometimes referred to as generalized least squares methods. Covariance matching is an alternative to maximum likelihood estimation, providing the same large sample properties often at a lower computational cost. Herein, we present a general framework. for covariance matching techniques and show that they are well suited to solve several problems arising in array signal processing. A straightforward derivation of the COMET criterion from first principles is presented, which also establishes the large sample properties of the estimator. Closed form compact expressions for the asymptotic covariance of the estimates of the parameters of interest are also derived. Some detection schemes are reviewed and two COMET-based detection schemes are proposed. The main part of the paper treats three applications where the COMET approach proves interesting. First, we consider the localization of underwater sources using a hydro-acoustic array. The background noise is often spatially correlated in such an application and this must be taken into account in the estimation procedure. Second, the problem of channel estimation in wireless communications is treated. In digital communications, an estimate of the channel is often required to perform accurate demodulation as well as spatially selective transmission. Finally, a radar detection problem is formulated and the proposed detection schemes are evaluated.

  • 297.
    Ottersten, Björn
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Söderström, Torsten
    Wahlberg, Bo
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Statistical signal processing and control1994In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 30, no 1, p. 9-Article in journal (Refereed)
  • 298.
    Ottersten, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    VIBERG, M
    ASYMPTOTIC ROBUSTNESS OF SENSOR ARRAY-PROCESSING METHODS1990Conference proceedings (editor) (Refereed)
  • 299.
    Ottersten, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    VIBERG, M
    KAILATH, T
    ANALYSIS OF SUBSPACE FITTING AND ML TECHNIQUES FOR PARAMETER-ESTIMATION FROM SENSOR ARRAY DATA1992In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 40, no 3, p. 590-600Article in journal (Refereed)
    Abstract [en]

    Signal parameter estimation from sensor array data is a problem that is encountered in many engineering applications. Under the assumption of Gaussian distributed emitter signals, the so-called stochastic maximum likelihood (ML) technique is known to be statistically efficient, i.e., the estimation error covariance attains the Cramer-Rao bound (CRB) asymptotically. Herein, it is shown that also the multi-dimensional signal subspace method, termed weighted subspace fitting (WSF), is asymptotically efficient. This also results in a novel, compact matrix expression for the CRB on the estimation error variance. The asymptotic analysis of the ML and WSF methods is extended to deterministic emitter signals. The asymptotic properties of the estimates for this case are shown to be identical to the Gaussian emitter signal case, i.e., independent of the actual signal waveforms. Conclusions, concerning the modeling aspect of the sensor array problem are drawn.

  • 300.
    Ottersten, Björn
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    VIBERG, MKAILATH, T
    ASYMPTOTIC ANALYSIS OF THE TOTAL LEAST-SQUARES ESPRIT ALGORITHM1989Conference proceedings (editor) (Other academic)
3456789 251 - 300 of 495
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