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  • 1.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Koslicki, David
    Dept of Mathematics, Oregon State University, Corvallis, USA.
    Dong, Siyuan
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Innocenti, Nicolas
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Cheng, Lu
    Dept of Mathematics and Statistics, University of Helsinki, Finland.
    Lan, Yueheng
    Dept of Physics, Tsinghua University, Beijing, China.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Communication Theory.
    K. Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Corander, Jukka
    Dept of Signal Processing, Aalto University, Finland.
    SEK: Sparsity exploiting k-mer-based estimation of bacterial community composition2014In: Bioinformatics, ISSN 1460-2059, Vol. 30, no 17, p. 2423-2431Article in journal (Refereed)
    Abstract [en]

    Motivation: Estimation of bacterial community composition from a high-throughput sequenced sample is an important task in metagenomics applications. As the sample sequence data typically harbors reads of variable lengths and different levels of biological and technical noise, accurate statistical analysis of such data is challenging. Currently popular estimation methods are typically time-consuming in a desktop computing environment.

    Results: Using sparsity enforcing methods from the general sparse signal processing field (such as compressed sensing), we derive a solution to the community composition estimation problem by a simultaneous assignment of all sample reads to a pre-processed reference database. A general statistical model based on kernel density estimation techniques is introduced for the assignment task, and the model solution is obtained using convex optimization tools. Further, we design a greedy algorithm solution for a fast solution. Our approach offers a reasonably fast community composition estimation method, which is shown to be more robust to input data variation than a recently introduced related method.

    Availability and implementation: A platform-independent Matlab implementation of the method is freely available at http://www.ee.kth.se/ctsoftware; source code that does not require access to Matlab is currently being tested and will be made available later through the above Web site.

  • 2.
    Chatterjee, Saikat
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Sundman, Dennis
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Skolglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Projection-based and look ahead strategies for atom selection2012In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, no 2, p. 634-647Article in journal (Refereed)
    Abstract [en]

    In this paper, we improve iterative greedy search algorithms in which atoms are selected serially over iterations, i.e., one-by-one over iterations. For serial atom selection, we devise two new schemes to select an atom from a set of potential atoms in each iteration. The two new schemes lead to two new algorithms. For both the algorithms, in each iteration, the set of potential atoms is found using a standard matched filter. In case of the first scheme, we propose an orthogonal projection strategy that selects an atom from the set of potential atoms. Then, for the second scheme, we propose a look-ahead strategy such that the selection of an atom in the current iteration has an effect on the future iterations. The use of look-ahead strategy requires a higher computational resource. To achieve a tradeoff between performance and complexity, we use the two new schemes in cascade and develop a third new algorithm. Through experimental evaluations, we compare the proposed algorithms with existing greedy search and convex relaxation algorithms.

  • 3.
    Cottatellucci, Laura
    et al.
    EURECOM.
    Müller, Ralf R.
    University Erlangen-Nürnberg.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Analysis of Pilot Decontamination Based on Power Control2013In: IEEE Vehicular Technology Conference (VTC Spring), 2013, 2013Conference paper (Refereed)
    Abstract [en]

    A subspace method for channel estimation is pro- posed for asymmetric antenna array systems. The so-called pilot contamination problem reported in [1] is found to be due to the linearity of channel estimation in [2]. We show that it does not occur in cellular systems with power control and power-controlled handoff when the nonlinear channel estimation method proposed in this paper is used. Power-control hand-off is needed to guarantee separability between signal and interference subspaces. We derive the transmission conditions for subspace separability based on free probability and perturbation theory.

  • 4. Flam, J. T.
    et al.
    Zachariah, Dave
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The linear model under mixed gaussian inputs: Designing the transfer matrix2013In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 61, no 21, p. 5247-5259Article in journal (Refereed)
    Abstract [en]

    Suppose a linear model Y = Hx+n, where inputs x, n are independent Gaussian mixtures. The problem is to design the transfer matrix so as to minimize the mean square error (MSE) when estimating x from . This problem has important applications, but faces at least three hurdles. Firstly, even for a fixed H, the minimum MSE (MMSE) has no analytical form. Secondly, theMMSE is generally not convex in . Thirdly, derivatives of the MMSEw.r.t. are hard to obtain. This paper casts theproblemas a stochastic program and invokes gradient methods. The study is motivated by two applications in signal processing. One concerns the choice of error-reducing precoders; the other deals with selection of pilot matrices for channel estimation. In either setting, our numerical results indicate improved estimation accuracy-markedly better than those obtained by optimal design based on standard linear estimators. Some implications of the non-convexities of the MMSE are noteworthy, yet, to our knowledge, not well known. For example, there are cases in which more pilot power is detrimental for channel estimation. This paper explains why.

  • 5. Flåm, John
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zachariah, Dave
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Tsakonas, Efthymios
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mean square error reduction by precoding of mixed Gaussian input2012In: 2012 International Symposium on Information Theory and Its Applications, ISITA 2012, 2012, p. 81-85Conference paper (Refereed)
    Abstract [en]

    Suppose a vector of observations y = Hx + n stems from independent inputs x and n, both of which are Gaussian Mixture (GM) distributed, and that H is a fixed and known matrix. This work focuses on the design of a precoding matrix, F, such that the model modifies to z = HFx + n. The goal is to design F such that the mean square error (MSE) when estimating x from z is smaller than when estimating x from y. We do this under the restriction E[(Fx)TFx] ≤ PT, that is, the precoder cannot exceed an average power constraint. Although the minimum mean square error (MMSE) estimator, for any fixed F, has a closed form, the MMSE does not under these settings. This complicates the design of F. We investigate the effect of two different precoders, when used in conjunction with the MMSE estimator. The first is the linear MMSE (LMMSE) precoder. This precoder will be mismatched to the MMSE estimator, unless x and n are purely Gaussian variates. We find that it may provide MMSE gains in some setting, but be harmful in others. Because the LMMSE precoder is particularly simple to obtain, it should nevertheless be considered. The second precoder we investigate, is derived as the solution to a stochastic optimization problem, where the objective is to minimize the MMSE. As such, this precoder is matched to the MMSE estimator. It is derived using the KieferWolfowitz algorithm, which moves iteratively from an initially chosen F0 to a local minimizer F*. Simulations indicate that the resulting precoder has promising performance.

  • 6.
    Girnyk, Maksym A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Vehkapera, Mikko
    Rasmussen, Lars Kildehoj
    Christakou, Athanasia
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Wiklund, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Onfelt, Bjorn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Orange, Jordan
    Lytic granule convergence is essential for NK cells to promote targeted killing while preventing collateral damage2016In: Journal of Immunology, ISSN 0022-1767, E-ISSN 1550-6606, Vol. 196Article in journal (Other academic)
  • 7.
    Girnyk, Maksym A.
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars Kildehoj
    Asymptotic Performance Analysis of a K-Hop Amplify-and-Forward Relay MIMO Channel2016In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 62, no 6, p. 3532-3546Article in journal (Refereed)
    Abstract [en]

    This paper studies the asymptotic performance of multi-hop amplify-and-forward relay multiple-antenna communication channels. Each multi-antenna relay terminal in the considered network amplifies the received signal, sent by a source, and retransmits it upstream toward a destination. Achievable ergodic rates of the relay channel with both jointly optimal detection and decoding and practical separate-decoding receiver architectures for arbitrary signaling schemes, along with average bit error rates for various types of detectors are derived in the regime where the number of antennas at each terminal grows large without a bound. To overcome the difficulty of averaging over channel realizations, we apply a large-system analysis based on the replica method from statistical physics. The validity of the large-system analysis is further verified through Monte Carlo simulations of realistic finite-sized systems.

  • 8.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gabry, Frédéric
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lars, Rasmussen
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mikael, Skoglund
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the transmit beamforming for MIMO wiretap channels: Large-system analysis2013In: Information Theoretic Security: 7th International Conference, ICITS 2013, Singapore, November 28-30, 2013, Proceedings, Springer Publishing Company, 2013, p. 90-102Conference paper (Refereed)
    Abstract [en]

    With the growth of wireless networks, security has become a fundamental issue in wireless communications due to the broadcast nature of these networks. In this work, we consider MIMO wiretap channels in a fast fading environment, for which the overall performance is characterized by the ergodic MIMO secrecy rate. Unfortunately, the direct solution to finding ergodic secrecy rates is prohibitive due to the expectations in the rates expressions in this setting. To overcome this difficulty, we invoke the large-system assumption, which allows a deterministic approximation to the ergodic mutual information. Leveraging results from random matrix theory, we are able to characterize the achievable ergodic secrecy rates. Based on this characterization, we address the problem of covariance optimization at the transmitter. Our numerical results demonstrate a good match between the large-system approximation and the actual simulated secrecy rates, as well as some interesting features of the precoder optimization.

  • 9.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gabry, Frédéric
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. 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.
    Large-System Analysis of MIMO Wire-Tap Channels with Randomly Located Eavesdroppers2013In: Proceedings of the Tenth International Symposium on Wireless Communication Systems (ISWCS 2013), VDE Verlag GmbH, 2013, p. 380-384Conference paper (Refereed)
    Abstract [en]

    Wireless security has become a subject of growinginterest in wireless communications due to the broadcast natureof wireless channels. In the present paper, we consider a multiantennawire-tap channel with randomly distributed eavesdroppers.In the fast fading environment, the overall performance ofsuch channel is characterized by the ergodic secrecy capacity,which, in general, cannot be characterized explicitly. Nevertheless,based on the assumption that the numbers of antennasat legitimate terminals and the number of eavesdroppers growlarge without bound, we derive a deterministic approximation forthe achievable ergodic secrecy rate. The obtained large-systemapproximation matches well with the actual simulated secrecyrates, revealing some interesting behavior of the secrecy rates inthe given scenario.

  • 10.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the asymptotic sum-rate of the relay-assisted amplify-and-forward cognitive MIMO channel2012In: Personal Indoor and Mobile Radio Communications (PIMRC), 2012 IEEE 23rd International Symposium on, IEEE , 2012, p. 709-714Conference paper (Refereed)
    Abstract [en]

    This paper studies the asymptotic sum-rate of the primary network within the relay-assisted multi-antenna cognitive radio system performing amplify-and-forward relaying. The achievable sum-rates are derived in the large-system limit by means of the replica method. A closed-form expression for the sum-rate of the primary network is obtained for large antenna arrays as a function of parameters obtained by solving a set of fixed-point equations. Numerical simulations confirm the validity of the results even for systems with only a few antennas at each terminal.

  • 11.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the Asymptotic Sum-Rate of Uplink MIMO Cellular Systems in the Presence of Non-Gaussian Inter-Cell Interference2012In: 2012 IEEE Global Communications Conference (GLOBECOM 2012), New York: IEEE , 2012, p. 2475-2480Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a scenario, where several mobile multi-antenna terminals communicate with the multi- antenna base station within a cellular communication system over the flat Rayleigh fading channel. In addition, several terminals from the neighboring cell cause interference. For such a scenario, we derive, using the replica method, the asymptotic sum-rate of the communication in the large-system limit for arbitrary signal constellations. Moreover, we show via numerical results that when the interfering terminals use a QPSK constellation, the resulting interference becomes easier to handle. In effect, we may be able to accumulate more interfering transmitter-receiver pairs within the same area as compared to the case of Gaussian signals. Monte- Carlo simulations show that the derived asymptotic expression matches well with the simulated values even for small numbers of antennas.

  • 12.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Large-System Analysis of Correlated MIMO Multiple Access Channels with Arbitrary Signaling in the Presence of Interference2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 4, p. 2060-2073Article in journal (Refereed)
    Abstract [en]

    Presence of multiple antennas on both sides of a communication channel promises significant improvements in system throughput and power efficiency. In effect, a new class of large multiple-input multiple-output (MIMO) communication systems has recently emerged and attracted both scientific and industrial attention. To analyze these systems in realistic scenarios one has to include such aspects as co-channel interference, multiple access and spatial correlation. In this paper, we study the properties of correlated MIMO multiple-access channels in the presence of external interference. Using the replica method from statistical physics, we derive the ergodic sum-rate of the communication for arbitrary signal constellations when the numbers of antennas at both ends of the channel grow large. Based on these asymptotic expressions, we also address the problem of sum-rate maximization using statistical channel state information and linear precoding. The numerical results demonstrate that when the interfering terminals use discrete constellations, the resulting interference becomes easier to handle compared to Gaussian signals. Thus, it may be possible to accommodate more interfering transmitter-receiver pairs within the same area as compared to the case of Gaussian signals. In addition, we demonstrate numerically for the Gaussian and QPSK signaling schemes that it is possible to design precoder matrices that significantly improve the achievable rates at low-to-mid range of signal-to-noise ratios when compared to isotropic precoding.

  • 13.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Large-System Analysis of the K-Hop AF MIMO Relay Channel with Arbitrary Inputs2013In: IEEE International Symposium on Information Theory: Proceedings, IEEE conference proceedings, 2013, p. 439-443Conference paper (Refereed)
    Abstract [en]

    The present paper investigates the achievable data rates of multi-hop amplify-and-forward multi-antenna relay channels with arbitrary number of hops K. Each multi-antenna terminal in the system amplifies the received signal and retransmits it upstream. To analyze the ergodic end-to-end mutual information of the system, one has to perform averaging over the fading coefficients. To overcome this difficulty we apply large-system analysis, based on the assumption that the number of antennas grows without bound at every terminal. Using the replica method, we derive an explicit asymptotic expression for the ergodic mutual information between the input and output of the K-hop channel with no restrictions on the channel inputs. Numerical results support the validity of the replica analysis and show that the result is tight even for small antenna arrays.

  • 14.
    Girnyk, Maksym
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Multi-Cell Cooperation with Random User Locations under Arbitrary Signaling2013In: 2013 IEEE Information Theory Workshop (ITW), IEEE , 2013, p. 6691326-Conference paper (Refereed)
    Abstract [en]

    Base station cooperation in cellular networks has been recently recognized as a key technology for mitigating interference, providing thus significant improvements in the system performance. In this paper, we consider a simple scenario consisting of two one-dimensional cells, where the base stations have fixed locations, while the user terminals are randomly distributed on a line. Exploiting the replica method from statistical physics, we derive the ergodic sum-rate under arbitrary signaling for both cooperative and non-cooperative scenarios, when the system size grows large. The obtained results are analytically tractable and can be used to optimize the system parameters in a simple manner. The numerical examples show that the analysis provides good approximations for finite-sized systems.

  • 15.
    Juntti, Markku
    et al.
    Department of Electrical and Information Engineering, University of Oulu.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Leinonen, Jouko
    Li, Zexian
    Tujkovic, Djordje
    Tsumura, Shigehiko
    Hara, Shinsuke
    Graduate School of Engineering, Osaka City University .
    MIMO MC-CDMA communications for future cellular systems2005In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 43, no 2, p. 118-124Article in journal (Refereed)
  • 16.
    Kabashima, Yoshiyuki
    et al.
    Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Typical l(1)-recovery limit of sparse vectors represented by concatenations of random orthogonal matrices2012In: Journal of Statistical Mechanics: Theory and Experiment, ISSN 1742-5468, E-ISSN 1742-5468, Vol. 2012, no 12, p. P12003-Article in journal (Refereed)
    Abstract [en]

    We consider the problem of recovering an N-dimensional sparse vector x from its linear transformation y = Dx of M (<N) dimensions. Minimization of the l(1)-norm of x under the constraint y = Dx is a standard approach for the recovery problem, and earlier studies report that the critical condition for typically successful l(1)-recovery is universal over a variety of randomly constructed matrices D. To examine the extent of the universality, we focus on the case in which D is provided by concatenating T = N/M matrices O-1, O-2,O- ... ,O-T drawn uniformly according to the Haar measure on the M x M orthogonal matrices. By using the replica method in conjunction with the development of an integral formula to handle the random orthogonal matrices, we show that the concatenated matrices can result in better recovery performance than that predicted by the universality when the density of non-zero signals is not uniform among the T matrix modules. The universal condition is reproduced for the special case of uniform non-zero signal densities. Extensive numerical experiments support the theoretical predictions.

  • 17.
    Khabbazibasmenj, Arash
    et al.
    University of Alberta.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Vorobyov, Sergiy
    Aalto Univeristy.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rasmussen, Lars K.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On the Optimal Precoding for MIMO Gaussian Wire-Tap Channels2013In: Proc. Int. Symp. Wireless Commun. (ISWCS) 2013, VDE Verlag GmbH, 2013, p. 356-359Conference paper (Refereed)
    Abstract [en]

    We consider the problem of finding secrecy rate ofa multiple-input multiple-output (MIMO) wire-tap channel. Atransmitter, a legitimate receiver, and an eavesdropper are allequipped with multiple antennas. The channel states from thetransmitter to the legitimate user and to the eavesdropper areassumed to be known at the transmitter. In this contribution,we address the problem of finding the optimal precoder/transmitcovariance matrix maximizing the secrecy rate of the given wiretapchannel. The problem formulation is shown to be equivalentto a difference of convex functions programming problem andan efficient algorithm for addressing this problem is developed.

  • 18. Mahmood, Kashif
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jiang, Yuming
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Delay constrained throughput analysis of a correlated MIMO wireless channel2011In: 20th International Conference on Computer Communications and Networks (ICCCN), 2011, 2011, p. 1-7Conference paper (Refereed)
    Abstract [en]

    The maximum traffic arrival rate at the network for a given delay guarantee (delay constrained throughput) has been well studied for wired channels. However, few results are available for wireless channels, especially when multiple antennas are employed at the transmitter and receiver. In this work, we analyze the network delay constrained throughput of a multiple input multiple output (MIMO) wireless channel with time-varying spatial correlation. The MIMO channel is modeled via its virtual representation, where the individual spatial paths between the antenna pairs are Gilbert-Elliot channels. The whole system is then described by a K-State Markov chain, where K depends upon the degree of freedom (DOF) of the channel. We prove that the DOF based modeling is indeed accurate. Furthermore, we study the impact of the delay requirements at the network layer, violation probability and the number of antennas on the throughput under different fading speeds and signal strength.

  • 19. Mahmood, Kashif
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jiang, Yuming
    Delay Constrained Throughput Analysis of CDMA Using Stochastic Network Calculus2011In: 17th IEEE International Conference on Networks (ICON2011), 2011Conference paper (Refereed)
    Abstract [en]

    Code-division multiple-access (CDMA) has the potentialto support traffic sources with a wide range of qualityof service (QoS) requirements. The traffic carrying capacity ofCDMA channels under QoS constraints (such as delay guarantee)is, however, less well-understood. In this work, we propose amethod based on stochastic network calculus and large systemanalysis to quantify the maximum traffic that can be carriedby a multiuser CDMA network under the QoS constraints. Atthe physical layer, we have linear minimum-mean square errorreceivers and adaptive modulation and coding, while the channelservice process is modeled by using a finite-state Markov chain.We study the impact of delay requirements, violation probabilityand the user load on the traffic carrying capacity under differentsignal strengths. A key insight provided by the numerical resultsis as to how much one has to back-off from capacity under thedifferent delay requirements.

  • 20. Mahmood, Kashif
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jiang, Yuming
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Delay constrained throughput analysis of SISO2012In: Proceedings - 2012 3rd IEEE International Conference on Network Infrastructure and Digital Content, IC-NIDC 2012, IEEE , 2012, p. 116-121Conference paper (Refereed)
    Abstract [en]

    We analyze the traffic carrying capacity of a single-input single-output system for a given delay guarantee at the flow level. A continuous time ON/OFF data source is considered as the traffic model while the wireless channel is modeled using the Gilbert-Elliot model. We study the impact of the delay bound violation probability, traffic burstiness, channel memory and the delay requirements at the network layer on the throughput under different signal strength.

  • 21. Mahmood, Kashif
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jiang, Yuming
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Performance of Multiuser CDMA Receivers With Bursty Traffic and Delay Constraints2012In: 2012 International Conference on Computing, Networking and Communications, ICNC'12, 2012, p. 428-433Conference paper (Refereed)
    Abstract [en]

    In this work, we analyze the performance of linear multiuser CDMA receivers under bursty traffic and queuing delay constraints. An ON/OFF source is used to model the traffic burstiness and stochastic network calculus incorporates the queuing delay constraints in the analysis. At the physical layer, adaptive modulation and coding scheme is adopted and the channel service process is modeled by using a finite-state Markov chain. The following receivers are considered for performance evaluation: single-user matched filter, decorrelator, and linear minimum mean square error detector. We quantify the effect of these multiuser receivers on the traffic carrying capacity of uplink CDMA channels in the large system limit.

  • 22. Mueller, Ralf R.
    et al.
    Cottatellucci, Laura
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. Aalto University, Finland .
    Blind Pilot Decontamination2014In: IEEE Journal on Selected Topics in Signal Processing, ISSN 1932-4553, E-ISSN 1941-0484, Vol. 8, no 5, p. 773-786Article in journal (Refereed)
    Abstract [en]

    A subspace projection to improve channel estimation in massive multi-antenna systems is proposed and analyzed. Together with power-controlled hand-off, it can mitigate the pilot contamination problem without the need for coordination among cells. The proposed method is blind in the sense that it does not require pilot data to find the appropriate subspace. It is based on the theory of large random matrices that predicts that the eigenvalue spectra of large sample covariance matrices can asymptotically decompose into disjoint bulks as the matrix size grows large. Random matrix and free probability theory are utilized to predict under which system parameters such a bulk decomposition takes place. Simulation results are provided to confirm that the proposed method outperforms conventional linear channel estimation if bulk separation occurs.

  • 23.
    Müller, Ralf R.
    et al.
    University Erlangen-Nürnberg.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cottatellucci, Laura
    EURECOM.
    Analysis of Blind Pilot Decontamination2013In: Proceedings of the 47th Annual Asilomar Conference on Signals, Systems, and Computers, 2013Conference paper (Refereed)
  • 24.
    Müller, Ralf R.
    et al.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cottatellucci, Laura
    Institute Eurecom, Mobile Communications department .
    Blind Pilot Decontamination2013In: International ITG Workshop on Smart Antennas (WSA 2013), VDE Verlag GmbH, 2013Conference paper (Refereed)
    Abstract [en]

    We propose a nonlinear channel estimation method based on a subspace projection that is suitable for asymmetric antenna array systems. We show that the so-called pilot contamination problem reported in [1], is an artefact of (inappropriate) linear channel estimation and does not occur in cellular systems with power-controlled handoff when the channel estimation method proposed in this paper is used. We intuitively explain our result by establishing an isomorphism between a massive MIMO system and a spread-spectrum system with unknown signature sequences.

  • 25.
    Riihonen, Taneli
    et al.
    Aalto University, Department of Signal Processing and Acoustics.
    Vehkaperä, Mikko
    Department of Signal Processing and Acoustics Aalto University School of Electrical Engineering.
    Wichman, Risto
    Aalto University, Department of Signal Processing and Acoustics.
    Large-System Analysis of Rate Regions in Bidirectional Full-Duplex MIMO Link: Suppression versus Cancellation2013In: 2013 47th Annual Conference on Information Sciences and Systems (CISS), 2013Conference paper (Refereed)
    Abstract [en]

    We analyze the performance of bidirectionalcommunication links between two multi-antenna full-duplextransceivers, explicitly taking into account the effect of un-avoidable self-interference. The main theme of this paper is tocomparespatial-domainsuppression (implemented in the form of null-space projection) and subtractive time-domain cancellation: both schemes can eliminate the self-interference but the former consumes spatial degrees of freedom unlike the latter. We perform large-system analysis based on the replica method, while refer-ence simulations show that the asymptotic results are applicable also for practical systems with low number of antennas. Inparticular, we evaluate rate regions achieved by controllingthe spatial multiplexing order in each node and time sharingbetween different stream configurations. Consequently, we cancharacterize the rate loss of suppression versus cancellation.

  • 26.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Construction of Turbo-Like Codes for Iterative Channel Estimation Based on Probabilistic Bias2011In: IEEE Global Telecommunications Conference (GLOBECOM 2011), 2011, 2011, p. 1-5Conference paper (Refereed)
    Abstract [en]

    A novel signaling scheme for iterative channel estimation and data decoding is proposed. In the proposed scheme, the occurrence probability of transmitted symbols is biased. A priori information about the bias is utilized for the initial channel estimation. The proposed scheme is based on parallel concatenation of two biased convolutional codes (BCCs), which are constructed as systematic recursive convolutional codes with state-dependent puncturing. The BCCs can be regarded as a joint coding scheme that determines the insertion positions of pilot symbols according to information bits. The proposed scheme is numerically shown to outperform conventional pilot-based schemes in the waterfall region, while it is inferior to the conventional schemes in the error-floor region.

  • 27.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Bias-Based Training for Iterative Channel Estimation and Data Decoding in Fast Fading Channels2011In: IEICE transactions on communications, ISSN 0916-8516, E-ISSN 1745-1345, Vol. E94B, no 7, p. 2161-2165Article in journal (Refereed)
  • 28.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    University Erlangen-Nürnberg.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Iterative LMMSE Channel Estimation and Decoding Based on Probabilistic Bias2013In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, no 7, p. 2853-2863Article in journal (Refereed)
    Abstract [en]

    Iterative channel estimation and decoding based on probabilistic bias is investigated. In order to control the occurrence probability of transmitted symbols, biased convolutional codes (CCs) are proposed. A biased CC is obtained by puncturing the parity bit of a conventional (unbiased) CC and by inserting a fixed bit at the punctured position when the state is contained in a certain subset of all possible states. A priori information about the imposed bias is utilized for the initial linear minimum mean-squared error (LMMSE) channel estimation. This paper focuses on biased turbo codes that are constructed as the parallel concatenation of two biased CCs with interleaving, and proposes an iterative LMMSE channel estimation and decoding scheme based on approximate belief propagation. The convergence property of the iterative LMMSE channel estimation and decoding scheme is analyzed via density evolution (DE). The DE analysis allows one to design the magnitude of the bias according to the coherence time, in terms of the decoding threshold. The proposed scheme is numerically shown to outperform conventional pilot-based schemes in the moderate signal-to-noise ratio (SNR) regime, at the expense of a performance degradation in the high SNR regime.

  • 29.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    A New Signaling Scheme for Large DS-CDMA Channels without CSI2009In: 2009 7TH INTERNATIONAL SYMPOSIUM ON MODELING AND OPTIMIZATION IN MOBILE, AD HOC, AND WIRELESS, 2009, p. 478-484Conference paper (Refereed)
    Abstract [en]

    We propose a novel signaling scheme for wireless communication systems without channel state information (CSI). In that scheme, a bias of the occurrence probabilities of constellation points is utilized as pilot information known to the receiver, whereas pilot signals known to the receiver are sent in conventional pilot-based approaches. We evaluate the performance of the new scheme and conventional pilot-based schemes for a large direct-sequence code-division multiple-access (DS-CDMA) system, by using the replica method. It is shown that the new scheme outperforms the conventional pilot-based scheme when the amount of pilot information is large.

  • 30.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    University Erlangen-Nürnberg.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    On an Achievable Rate of Large Rayleigh Block-Fading MIMO Channels With No CSI2013In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 59, no 10, p. 6517-6541Article in journal (Refereed)
    Abstract [en]

    Training-based transmission over Rayleigh block-fading multiple-input multiple-output (MIMO) channels is investigated. As a training method a combination of a pilot-assisted scheme and a biased signaling scheme is considered. The achievable rates of successive decoding (SD) receivers based on the linear minimum mean-squared error (LMMSE) channel estimation are analyzed in the large-system limit, by using the replica method under the assumption of replica symmetry. It is shown that negligible pilot information is best in terms of the achievable rates of the SD receivers in the large-system limit. The obtained analytical formulas of the achievable rates can improve the existing lower bound on the capacity of the MIMO channel with no channel state information (CSI), derived by Hassibi and Hochwald, for all SNRs. The comparison between the obtained bound and a high-SNR approximation of the channel capacity, derived by Zheng and Tse, implies that the high-SNR approximation is unreliable unless quite high SNR is considered. Energy efficiency in the low-SNR regime is also investigated in terms of the power per information bit required for reliable communication. The required minimum power is shown to be achieved at a positive rate for the SD receiver with no CSI, whereas it is achieved in the zero-rate limit for the case of perfect CSI available at the receiver. Moreover, numerical simulations imply that the presented large-system analysis can provide a good approximation for not so large systems. The results in this paper imply that SD schemes can provide a significant performance gain in the low-to-moderate SNR regimes, compared to conventional receivers based on one-shot channel estimation.

  • 31.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Practical Signaling with Vanishing Pilot-Energy for Large Noncoherent Block-Fading MIMO Channels2009In: 2009 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, VOLS 1- 4, 2009, p. 759-763Conference paper (Refereed)
    Abstract [en]

    We propose a randomly-biased quadrature phase shift keying (QPSK) signaling scheme for a noncoherent Rayleigh block-fading multiple-input multiple-output (MIMO) channel. In order to optimize a prior of bias, we evaluate a lower bound of the spectral efficiency of the noncoherent MIMO channel with randomly-biased QPSK signaling in the large-system limit, by using the replica method. Our main result is that randomly-biased QPSK signaling with vanishing bias is optimal in the large-system limit for any signal-to-noise ratio.

  • 32.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Vehkaperä, Mikko
    Dept. Elec. and Telecommun., Norwegian University of Science and Technology.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Asymptotic Performance Bounds of Joint Channel Estimation and Multiuser Detection in Frequency-Selective Fading DS-CDMA Channels2008In: 2008 INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY AND ITS APPLICATIONS, VOLS 1-3, 2008, p. 358-363Conference paper (Refereed)
    Abstract [en]

    We derive asymptotic upper bounds of the performance of a one-shot MMSE multiuser detector (MUD) and an optimal MUD in frequency-selective fading DS-CDMA channels with imperfect CSI at the receiver, using the replica method. We find that the performance bound of the one-shot MMSE MUD is indistinguishable from the performance of the one-shot LMMSE MUD analyzed by Evans and Tse when signal-to-noise ratio is high and the system load is small, and that the performance gap between the optimal MUD and the one-shot LMMSE MUD is also small on the same conditions.

  • 33.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Large-System Analysis of Joint Channel and Data Estimation for MIMO DS-CDMA Systems2012In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 58, no 3, p. 1385-1412Article in journal (Refereed)
    Abstract [en]

    This paper presents a large-system analysis of the performance of joint channel estimation, multiuser detection, and per-user decoding (CE-MUDD) for randomly spread multiple-input multiple-output (MIMO) direct-sequence code-division multiple-access (DS-CDMA) systems. A suboptimal receiver based on successive decoding in conjunction with linear minimum mean-squared error (LMMSE) channel estimation is investigated. The replica method, developed in statistical mechanics, is used to evaluate the performance in the large-system limit, where the number of users and the spreading factor tend to infinity while their ratio and the number of transmit and receive antennas are kept constant. Joint CE-MUDD based on LMMSE channel estimation is compared to several methods of one-shot channel estimation, i.e., methods that do not utilize decoded data symbols to refine the initial channel estimates, in terms of spectral efficiency. Joint CE-MUDD is found to significantly reduce the rate loss caused by transmission of pilot signals when compared to the receivers based on one-shot channel estimation. This holds particularly for multiple-antenna systems. As a result, joint CE-MUDD can provide significant performance gains compared to the receivers based on one-shot channel estimation.

  • 34.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Performance analysis of optimal channel estimation and multiuser detection in a randomly-spread CDMA channel2010In: Journal of Systems Science and Complexity, ISSN 1009-6124, E-ISSN 1559-7067, Vol. 23, no 1, p. 22-34Article in journal (Refereed)
    Abstract [sv]

    This paper analyzes performance of optimal channel estimation and multiuser detection (MUD) in a block-fading code-division multiple-access (CDMA) channel on the assumptions of random spreading and large-system limit, by using the replica method developed in statistical mechanics. The authors find that the asymptotic spectral efficiency of the linear minimum mean-squared error (LMMSE) MUD which was proposed and analyzed by Evans and Tse in 2000 is indistinguishable from that of the optimal MUD for small system loads. Our results imply that performance of MUD scarcely improves even if one spends more computational cost than that of the LMMSE MUD, i.e., at most the cube of the number of users, on the above-described conditions

  • 35.
    Takeuchi, Keigo
    et al.
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Vehkaperä, Mikko
    Dept Elec. and Telecomrnun., Norwegian University of Science and Technology.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Replica Analysis of General Multiuser Detection in MIMO DS-CDMA Channels with Imperfect CSI2008In: 2008 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY PROCEEDINGS, VOLS 1-6, 2008, p. 514-518Conference paper (Refereed)
    Abstract [en]

    We consider impacts of channel estimation errors on performance of general multiuser detectors in MIMO DS-CDMA channels. We evaluate their performance in terms of asymptotic spectral efficiency, which is obtained via decoupling structure, by using the replica method. Numerical results imply that the performance of LMMSE detection is very close to that of MMSE detection for small system loads. Furthermore, we find that the spectral efficiency of MMSE detection grows discontinuously with the length of pilot sequences for large system loads, and that the critical length is close to the optimal length. While it is indistinguishable from that of LMMSE detection for short pilot sequences, the gap between the two is significantly large if the length of pilot sequences is longer than the critical length.

  • 36. Tsumura, Shigehiko
    et al.
    Vehkaperä, Mikko
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Li, Zexian
    Tujkovic, Djordje
    Juntti, Markku
    Department of Electrical and Information Engineering, University of Oulu.
    Performance evaluation of turbo and space-time turbo coded MC-CDMA downlink in single and multi-cell environments2004In: IEICE transactions on communications, ISSN 0916-8516, E-ISSN 1745-1345, Vol. E87B, no 10, p. 3011-3020Article in journal (Refereed)
  • 37. Tsumura, Shigehiko
    et al.
    Vehkaperä, Mikko
    Centre for Wireless Communications, University of Oulu.
    Li, Zexian
    Tujkovic, Djordje
    Juntti, Markku
    Department of Electrical and Information Engineering, University of Oulu.
    Hara, Shinsuke
    Graduate School of Engineering, Osaka City University.
    Performance evaluation of turbo and space-time turbo coded MC-CDMA downlink in multi-cell environment2004In: 2004 IEEE 15TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-4, PROCEEDINGS, 2004, p. 2308-2312Conference paper (Refereed)
    Abstract [en]

    In this paper, we evaluate the performance of single- and multi-antenna multi-carrier code division multiple access (MC-CDMA) downlink (base station to mobile terminal) systems in multi-cell environments. We first propose a minimum mean square error (MMSE) filter for a single input single output (SISO) MC-CDMA downlink system. Then, we apply it to a SIMO (single input multiple output) system with a conventional turbo coding. Furthermore, we compare the performance of SISO (1 x 1) and SIMO (1 x 2) MC-CDMA systems with that of a multiple input multiple output (MIMO) (2 x 2) system employing space-time turbo coded modulation (STTuCM) in a multi-cell environment with 7 cells by computer simulation. Based on the computer simulation results, it is found that the considered MIMO system can achieve twofold capacity with the same transmission power in the multi-cell environment.

  • 38.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. 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.
    Analysis of MMSE estimation for compressive sensing of block sparse signals2011In: 2011 IEEE Information Theory Workshop, ITW 2011, 2011, p. 553-557Conference paper (Refereed)
    Abstract [en]

    Minimum mean square error (MMSE) estimation of block sparse signals from noisy linear measurements is considered. Unlike in the standard compressive sensing setup where the non-zero entries of the signal are independently and uniformly distributed across the vector of interest, the information bearing components appear here in large mutually dependent clusters. Using the replica method from statistical physics, we derive a simple closed-form solution for the MMSE obtained by the optimum estimator. We show that the MMSE is a version of the Tse-Hanly formula with system load and MSE scaled by a parameter that depends on the sparsity pattern of the source. It turns out that this is equal to the MSE obtained by a genie-aided MMSE estimator which is informed in advance about the exact locations of the non-zero blocks. The asymptotic results obtained by the non-rigorous replica method are found to have an excellent agreement with finite sized numerical simulations.

  • 39.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Girnyk, Maksym
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Riihonen, Taneli
    Aalto University, Department of Signal Processing and Acoustics.
    Wichman, Risto
    Aalto University, Department of Signal Processing and Acoustics.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    On Achievable Rate Regions at Large-System Limit in Full-Duplex Wireless Local Access2013In: International Black Sea Conference on Communications and Networking, 2013Conference paper (Refereed)
    Abstract [en]

    High capacity requirements in wireless systems can be met, at the network level, by using dense small cell deployments and, at the link level, by improving spectral efficiency via spectrum reuse. In this context, we consider a small-area radio system, e.g. a pico- or femtocell, where a full-duplex access point serves simultaneously two half-duplex devices, one in downlink and one in uplink direction. All transceivers are equipped with multiple antennas exploited for spatial multiplexing. Instead of limiting the study to the total sum rate, we analyze the complete achievable rate regions of the two directions. We also take into account the effects of mismatched decoding at the receivers due to imperfect knowledge of the transceiver impairments. The analysis is conducted in the large-system limit using the replica method from statistical physics, which allows to encompass arbitrary channel input distributions. The analytical results characterize the effect of self-interference at the access point and inter-device interference on the achievable rate regions. Numerical examples for particular signaling schemes are also given.

  • 40.
    Vehkaperä, Mikko
    et al.
    Department of Electronics and Telecommunications, Trondheim, Norway.
    Juntti, Markku
    Department of Electrical and Information Engineering, University of Oulu.
    Analysis of space-time coded and spatially multiplexed MIMO systems with ZF receivers2007In: 2007 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-14, 2007, p. 738-743Conference paper (Refereed)
    Abstract [en]

    We present an asymptotically (in number of receive antennas) exact probability density function for the signal-to-noise-plus-interference ratio (SINR) of the output of a zero-forcing (ZF) estimator in a multi-antenna system utilizing group-wise layered space-time (GLST) transmission. We show that the approximation is extremely accurate also for finite and relatively. small numbers of receive antennas. Closed form expression for the uncoded bit error probability (BEP) is given in the case of binary or quadrature phase shift keying (BPSK / QPSK). Frame error probability (FEP) lower bound for turbo-like codes and iterative sum-product based decoder is presented.

  • 41.
    Vehkaperä, Mikko
    et al.
    Centre for Wireless Communications (CWC), University of Oulu.
    Juntti, Markku
    Department of Electrical and Information Engineering, University of Oulu.
    Frame error rate analysis of coded MIMO systems with spatial multiplexing2006In: 2006 Fortieth Asilomar Conference on Signals, Systems and Computers, Vols 1-5, 2006, p. 1606-1610Conference paper (Refereed)
    Abstract [en]

    Recently, El Gamal and Hammons (2001) proposed a simple method for deriving noise thresholds that fully determine the asymptotic error probability behavior of certain type of error correcting codes. In this paper, we use these thresholds and the asymptotic results presented by Li et al. (2006) to derive analytical lower bounds for the frame error rate of coded multiantenna systems utilizing spatial multiplexing at the transmitter and linear zero-forcing or minimum mean squared error based estimator at the receiver. In addition, Monte Carlo computer simulations are presented to validate the theoretical analysis.

  • 42.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Juntti, Markku
    Department of Electrical and Information Engineering, University of Oulu.
    On the Performance of Space-Time Coded and Spatially Multiplexed MIMO Systems with Linear Receivers2010In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 58, no 2, p. 642-651Article in journal (Refereed)
  • 43.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kabashima, Yoshiyuki
    Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Replica analysis of sparse l1-reconstruction with concatenated L-orthogonal basis2012In: Statistical Mechanics of Unsatisfiability and Glasses, 2012Conference paper (Refereed)
  • 44.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. Aalto Univ, Espoo 02150, Finland.
    Kabashima, Yoshiyuki
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Analysis of Regularized LS Reconstruction and Random Matrix Ensembles in Compressed Sensing2016In: IEEE Transactions on Information Theory, ISSN 0018-9448, E-ISSN 1557-9654, Vol. 62, no 4, p. 2100-2124Article in journal (Refereed)
    Abstract [en]

    The performance of regularized least-squares estimation in noisy compressed sensing is analyzed in the limit when the dimensions of the measurement matrix grow large. The sensing matrix is considered to be from a class of random ensembles that encloses as special cases standard Gaussian, row-orthogonal, geometric, and so-called T-orthogonal constructions. Source vectors that have non-uniform sparsity are included in the system model. Regularization based on l(1)-norm and leading to LASSO estimation, or basis pursuit denoising, is given the main emphasis in the analysis. Extensions to l(2)-norm and zero-norm regularization are also briefly discussed. The analysis is carried out using the replica method in conjunction with some novel matrix integration results. Numerical experiments for LASSO are provided to verify the accuracy of the analytical results. The numerical experiments show that for noisy compressed sensing, the standard Gaussian ensemble is a suboptimal choice for the measurement matrix. Orthogonal constructions provide a superior performance in all considered scenarios and are easier to implement in practical applications. It is also discovered that for non-uniform sparsity patterns, the T-orthogonal matrices can further improve the mean square error behavior of the reconstruction when the noise level is not too high. However, as the additive noise becomes more prominent in the system, the simple row-orthogonal measurement matrix appears to be the best choice out of the considered ensembles.

  • 45.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Aalto University, Finland .
    Kabashima, Yoshiyuki
    Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Statistical mechanics approach to sparse noise denoising2013In: 2013 Proceedings of the 21st European Signal Processing Conference (EUSIPCO), IEEE , 2013, p. 6811435-Conference paper (Refereed)
    Abstract [en]

    Reconstruction fidelity of sparse signals contaminated by sparse noise is considered. Statistical mechanics inspired tools are used to show that the l(1)-norm based convex optimization algorithm exhibits a phase transition between the possibility of perfect and imperfect reconstruction. Conditions characterizing this threshold are derived and the mean square error of the estimate is obtained for the case when perfect reconstruction is not possible. Detailed calculations are provided to expose the mathematical tools to a wide audience.

  • 46.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kabashima, Yoshiyuki
    Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology.
    Chatterjee, Saikat
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. 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.
    Rasmussen, Lars
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Analysis of Sparse Representations Using Bi-Orthogonal Dictionaries2012In: Information Theory Workshop (ITW), 2012 IEEE, IEEE , 2012, p. 647-651Conference paper (Refereed)
    Abstract [en]

    The sparse representation problem of recovering an N dimensional sparse vector x from M < N linear observations y = Dx given dictionary D is considered. The standard approach is to let the elements of the dictionary be independent and identically distributed (IID) zero-mean Gaussian and minimize the l1-norm of x under the constraint y = Dx. In this paper, the performance of l1-reconstruction is analyzed, when the dictionary is bi-orthogonal D = [O1 O2], where O1, O 2 are independent and drawn uniformly according to the Haar measure on the group of orthogonal M × M matrices. By an application of the replica method, we obtain the critical conditions under which perfect l 1-recovery is possible with bi-orthogonal dictionaries.

  • 47.
    Vehkaperä, Mikko
    et al.
    Centre for Wireless Communications, University of Oulu.
    Medard, Muriel
    Department of Electrical Engineering and and Research Laboratory of Electronics , MIT.
    A throughput-delay trade-off in packetized systems with erasures2005In: 2005 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY (ISIT), VOLS 1 AND 2, 2005, p. 1858-1862Conference paper (Refereed)
    Abstract [en]

    In this paper we propose an information theoretic framework for studying coding and throughput optimization for multi-layered packet transmission systems. Our approach assumes that the system is divided into two separate layers: One code word forms a packet at the physical layer and the code at the network layer spans over these packets. At the receiver, the network layer assumes that the decoded packets arriving from the physical layer either have no errors or are marked as deleted. Thus, albeit the packet loss may be caused, for example, by decoding error, congestion or channel conditions, the network layer treats all decoding errors as erasures regardless of the cause. This allows us to view the system at the network layer as transmission over memoryless erasure channel. We study the throughput optimization and code design across the layers under a total code length constraint while taking also into account the network layer imperfections in the transmission. We use random coding error exponents to achieve results that do not depend on specific coding scheme used. The proposed scheme provides also means for investigating important physical layer phenomena, such as, channel model and lower layer error correction coding in the packet erasure models. Our approach extends to fading channels and networks of multiple nodes and by viewing the two layers of coding as a concatenated coding scheme, a comparison between layer-by-layer and joint cross-layer rate optimization can be made, as outlined in this paper.

  • 48.
    Vehkaperä, Mikko
    et al.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Riihonen, Taneli
    Aalto University, Department of Signal Processing and Acoustics.
    Wichman, Risto
    Aalto University, Department of Signal Processing and Acoustics.
    Asymptotic Analysis of Full-Duplex Bidirectional MIMO Link with Transmitter Noise2013In: Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on, IEEE , 2013, p. 1265-1270Conference paper (Refereed)
    Abstract [en]

    Bidirectional wireless communication between two multi-antenna terminals that operate in a full-duplex mode is considered. The effects of loopback self-interference and transmit-side noise due to radio front-end imperfections are analyzed in the asymptotic regime where the number of antennas at both terminals grows large. The study compares two transparent mitigation schemes by which conventional spatial multiplexing can operate without being aware of the self-interference issue: spatial-domain null-space projection and time-domain subtractive cancellation. Both schemes eliminate the information-bearing part of the self-interference perfectly, but due to transmitter noise, the subtractive cancellation suffers from residual self-interference. The receive-side null-space projection, on the other hand, suppresses also the transmit-side noise, but at the cost of reduction in the degrees of freedom available for data reception. The results indicate that suppression becomes preferred when the level of transmit-side noise increases and the receiver does not have instantaneous knowledge about the spatial structure of the self-interference. Exhaustive Monte Carlo simulations also show that the asymptotic analytical results are useful for evaluating the performance of practical not-so-large systems.

  • 49.
    Vehkaperä, Mikko
    et al.
    Depart. of Electr. and Telecomm., Norwegian University of Science and Technology.
    Takeuchi, Keigo
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Analysis of Large MIMO DS-CDMA Systems With Imperfect CSI And Spatial Correlation2010In: 2010 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, 2010, p. 2098-2102Conference paper (Refereed)
    Abstract [en]

    The large system analysis of randomly spread MIMO DS-CDMA systems is provided. Correlated Rayleigh fading MIMO channels are assumed for all users. Linear multiuser detection with separate decoding and pilot-aided channel estimation are used. The results imply that with channel estimation, the performance can improve significantly as the correlation between the transmit antennas increases. No channel information at the transmitter is required, but the channel estimator needs knowlegde of the long term transmit correlation in advance. The numerical results demonstrate that in a 4 x 4 MIMO DS-CDMA system with two users per chip, high antenna correlation at the transmitter can double the ergodic spectral efficiency compared to the case of uncorrelated transmit antennas.

  • 50.
    Vehkaperä, Mikko
    et al.
    Depart. of Electr. and Telecomm., Norwegian University of Science and Technology.
    Takeuchi, Keigo
    University of Electro-Communications, Department of Communication Engineering and Informatics.
    Müller, Ralf R.
    Norwegian University of Science and Technology, Department of Electronics and Telecommunications.
    Tanaka, Toshiyuki
    Department of Systems Science, Kyoto University.
    Asymptotic analysis of iterative channel estimation and multiuser detection with soft feedback in multipath channels2008In: 16th European Signal Processing Conference (EUSIPCO 2008), 2008Conference paper (Refereed)
    Abstract [en]

    Large system analysis of a randomly spread direct-sequencecode-division multiple-access system in a frequency-selective channelis considered. The receiver uses iterative channel estimationand multiuser detection (MUD) with soft feedback from single-userdecoders to refine both the decisions of the linear minimum meansquare error (LMMSE) MUD, and the initial pilot-based estimatesof the LMMSE channel estimator. Replica method, a tool fromstatistical physics, and density evolution with Gaussian approximationare used to obtain the asymptotic performance of the LMMSEMUD with soft parallel interference cancellation. The results indicatethat as the channel coherence time grows, the performance ofcorresponding single-user system having perfect channel state informationcan be approached even in an overloaded multiuser systemusing channel estimation and vanishing pilot overhead.

12 1 - 50 of 57
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