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  • 1. Alty, S. R.
    et al.
    Jakobsson, A.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Efficient time-recursive implementation of matched filterbank spectral estimators2005Ingår i: IEEE Transactions on Circuits And Systems Part I: Fundamental Theory and Applications, ISSN 1057-7122, E-ISSN 1558-1268, Vol. 52, nr 3, s. 516-521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present a computationally efficient sliding window time updating of the Capon and amplitude and phase,estimation (APES) matched filterbank spectral estimators based on the time-variant displacement structure of the data covariance matrix. The presented algorithm forms a natural extension of the most computationally efficient algorithm to date, and offers a significant computational gain as compared to the computational complexity associated with the batch re-evaluation of the spectral estimates for each time-update. Furthermore, via simulations, the algorithm is found to be numerically superior to the time-updated spectral estimate formed from directly updating the data covariance matrix.

  • 2. Doroslovački, M. I.
    et al.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. George Washington University, United States .
    Nonuniform linear antenna arrays minimising Cramér-Rao bounds for joint estimation of single source range and direction of arrival2005Ingår i: IEE Proceedings-Radar Sonar and Navigation, Institution of Electrical Engineers (IEE), 2005, nr 4, s. 225-231Konferensbidrag (Refereegranskat)
    Abstract [en]

    Different antenna placements in nonuniform linear arrays for the joint estimation of the range and direction-of-arrival (DOA) of one source are considered. It is shown that the Cramér-Rao bound (CRB) for the range and DOA estimates can be expressed as a function of the angles at which the source sees the antennas. This new formulation of the CRB easily reveals the geometrical properties that the array should have in order to minimise the CRB. Based on the new representation of the CRB, a result found in the literature (which was concerned with the special case of a number of antennas that is divisible by four) is generalised to include the case of an arbitrary number of antennas. Furthermore, it is shown that symmetric arrays are close to uniformly optimal for different DOAs when the range is much larger than the aperture of the arrays.

  • 3.
    Du, Jinfeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Costa precoding in one dimension2006Ingår i: 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE conference proceedings, 2006, s. 717-720Konferensbidrag (Refereegranskat)
    Abstract [en]

    We design an optimum modulator for the Costa (dirty-paper) precoding problem under the constraint of a binary signaling alphabet, and assuming the interference symbols belong to a binary constellation. We evaluate the performance of our technique in terms of the mutual information between the channel input and output, and compare it to that of Tomlinson-Harashima precoding (THP) with optimized parameters. We show that our optimal modulator is always better than THP. In many relevant scenarios, the performance difference is significant.

  • 4.
    Du, Jinfeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Division for Communication Systems, Linköping University.
    Xiao, Ming
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Optimal Symbol-by-Symbol Costa Precoding for a Relay-Aided Downlink Channel2011Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 59, nr 8, s. 2274-2284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, we consider practical approaches to Costa precoding (also known as dirty paper coding). Specifically, we propose a symbol-by-symbol scheme for cancellation of interference known at the transmitter in a relay-aided downlink channel. For finite-alphabet signaling and interference, we derive the optimal (in terms of maximum mutual information) modulator under a given power constraint. A sub-optimal modulator is also proposed by formulating an optimization problem that maximizes the minimum distance of the signal constellation, and this non-convex optimization problem is approximately solved by semi-definite relaxation. For the case of binary signaling with binary interference, we obtain a closed-form solution for the sub-optimal modulator, which only suffers little performance degradation compared to the optimal modulator in the region of interest. For more general signal constellations and more general interference distributions, we propose an optimized Tomlinson-Harashima precoder (THP), which uniformly outperforms conventional THP with heuristic parameters. Bit-level simulation shows that the optimal and sub-optimal modulators can achieve significant gains over the THP benchmark as well as over non-Costa reference schemes, especially when the power of the interference is larger than the power of the noise.

  • 5.
    Jorswieck, Eduard A.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Multiuser gaussianity and constellation randomization for the MIMO multiple access channel: A unified view2007Ingår i: 2007 IEEE 8th Workshop On Signal Processing Advances In Wireless Communications, Vols 1 And 2, IEEE , 2007, s. 126-130Konferensbidrag (Refereegranskat)
    Abstract [en]

    In recent analyses of multiuser MIMO systems and their capacity achieving transmit strategies, Gaussian codebooks; are usually used. For the case in which the input signals are constrained to belong to a finite constellation, we study and explain two effects, namely Multiuser Gaussianity (MuG) and constellation randomization (CoRa). MuG means that the more users transmit simultaneously, the higher is the similarity of the received density to the optimal Gaussian one. Hence, the instantaneous mutual information is increased by MuG. This leads to a tradeoff between multiuser diversity and MuG. On the other hand, CoRa is done by linear precoding by random unitary matrices. Based on the observations from MuG, we explain why the outage capacity is increased by CoRa. The effects are illustrated by various numerical simulations.

  • 6.
    Jorswieck, Eduard A.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Linköping University Department of Electrical Engineering (ISY) Division of Communication Systems.
    The MISO interference channel from a game-theoretic perspective: A combination of selfishness and altruism achieves Pareto optimality2008Ingår i: 2008 IEEE International Conference On Acoustics, Speech And Signal Processing: Vols 1-12, 2008, s. 5364-5367Konferensbidrag (Refereegranskat)
    Abstract [en]

    We study the MISO interference channel from a game-theoretic perspective. Recently, it was shown that the rates at the non-cooperative Nash equilibrium (NE) strategy are poor especially in the medium and high SNR regimes. A reasonable outcome of the cooperative approach, close to the Pareto boundary of the achievable rate region, was shown to be the zero-forcing (ZF) strategy. In this work, we prove that any point on the Pareto boundary can be achieved by a certain linear combination of the NE and ZF strategies. A scalar weight per user chooses between "selfish" (NE) and altruistic (ZF) behavior. Thereby, the difficult beamforming optimization is reduced to a simple weight optimization. Different optimal operating points, e.g. maximum weighted sum-rate, the Nash-bargaining solution, or the Egalitarian solution, can be obtained by a computationally efficient iterative algorithm. The results are characterized by instantaneous achievable rate regions and the corresponding operating points.

  • 7.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Combining long-term and low-rate short-term channel state information over correlated MIMO channels2008Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, nr 7, s. 2409-2414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is combined with a unitary transformation based on the long-term channel statistics. The heavily quantized feedback link is directly optimized to maximize the expected achievable rate under different power constraints, using vector quantization and convex optimization techniques on a sample channel distribution. Robustness against errors in the feedback link is also pursued with tools in channel optimized vector quantization. Simulations indicate the benefits of the proposed scheme.

  • 8.
    Kim, Thanh Tung
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Combining short-term and long-term channel state information over correlated MIMO channels2006Ingår i: 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing, 2006, s. 13-16Konferensbidrag (Refereegranskat)
    Abstract [en]

    A simple structure to exploit both long-term and partial short-term channel state information at the transmitter (CSIT) over a family of correlated multiple-antenna channels is proposed. Partial short-term CSIT in the form of a weighting matrix is obtained via a resolution-constrained feedback link, combined with a unitary transformation based on the long-term channel statistics. The feedback link is optimized to maximize the expected achievable rate under different power constraints, using vector quantization techniques. Simulations indicate the benefits of the proposed scheme in all scenarios considered.

  • 9.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Model-averaged interference rejection combining2007Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 55, nr 2, s. 271-274Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a novel algorithm for interference suppression when the number of interferers is unknown. The key idea is to parameterize the second-order statistics of the interference via a mixture of several low-rank models. Numerical examples illustrate the performance of the method.

  • 10.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Cao, Y
    Collaborative transmit diversity with adaptive radio resource and power allocation2005Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 9, nr 6, s. 511-513Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider optimized collaborative transmit diversity schemes for the situation when the source and the relay know the magnitudes of all channel gains in the system. We demonstrate how one can optimally allocate not only transmit power but also the time and bandwidth used by the different nodes. Numerical examples illustrate the possible performance gain over non-adaptive collaboration.

  • 11.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Jaldén, Joakim
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Soft MIMO detection at fixed complexity2007Ingår i: GLOBECOM 2007: 2007 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2007, s. 1617-1621Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a new approach to soft demodulation for MIMO channels. The proposed method is an approximation to the exact a posteriori probability-per-bit computer. The main idea is to marginalize the posterior density for the received data exactly over the subset of the transmitted bits that are received with the lowest signal-to-noise-ratio, and then marginalize this density approximately over the remaining bits. Unlike the exact demodulator, whose complexity is huge due to the need for enumerating all possible combinations of transmitted constellation points, the proposed method has very low complexity. Additionally, its complexity is fixed, which makes it suitable for pipelined implementation. Numerical examples illustrate its performance on slow fading 4 x 4 and 6 x 6 complex MIMO channels.

  • 12. Larsson, Erik G.
    et al.
    Regnoli, Giorgio
    KTH, Skolan för elektro- och systemteknik (EES).
    Primary system detection for cognitive radio: Does small-scale fading help?2007Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 11, nr 10, s. 799-801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the effect of small-scale fading on the detection of weak signals in cognitive radio systems. We formulate a model for the detection problem taking fading into account, and give the associated likelihood ratio tests. Additionally we give an expression for the asymptotic detection performance and use this to consider the tradeoff between the detection performance and the coherence time and bandwidth of the channel.

  • 13.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Selen, Yngve
    Linear regression with a sparse parameter vector2006Ingår i: 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing, Vol III, Proceedings: signal processing theory and methods, design and implementation of signal processing systems, industry technology tracks, 2006, s. 309-Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider linear regression under a model where the parameter vector is known to be sparse. Using a Bayesian framework, we derive a computationally efficient approximation to the minimum mean-square error (MMSE) estimate of the parameter vector. The performance of the so-obtained estimate is illustrated via numerical examples.

  • 14.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Selén, Yngve
    Linear regression with a sparse parameter vector2007Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 55, nr 2, s. 451-460Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider linear regression under a model where the parameter vector is known to be sparse. Using a Bayesian framework, we derive the minimum mean-square error (MMSE) estimate of the parameter vector and a computationally efficient approximation of it. We also derive an empirical-Bayesian version of the estimator, which does not need any a priori information, nor does it need the selection of any user parameters. As a byproduct, we obtain a powerful model ("basis") selection tool for sparse models. The performance and robustness of our new estimators are illustrated via numerical examples.

  • 15.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Cognitive radio in a frequency planned environment: Can it work?2007Ingår i: GLOBECOM 2007: 2007 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2007, s. 3548-3552Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective of this work is to assess some fundamental limits of operation for cognitive radios in a frequency-planned environment. We present a first-order analysis of the carrier-to-noise-and-interference situation in a cellular wireless network, and analyze the impact of cognitive users starting to transmit. The main conclusion is that introducing cognitive transmitters in a frequency-planned cellular network without causing substantial interference is very challenging.

  • 16.
    Larsson, Erik G.
    et al.
    Linköping University, Dept. of Electrical Engineering (ISY), Division of Communication Systems.
    Skoglund, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Cognitive Radio in a Frequency-Planned Environment: Some Basic Limits2008Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 7, nr 12, s. 4800-4806Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this work is to assess some fundamental limits for opportunistic spectrum reuse via cognitive radio in a frequency-planned environment. We present a first-order analysis of the signal-to-noise-and-interference situation in a wireless cellular network, and analyze the impact of cognitive users starting to transmit. Two main conclusions emerge from our study. First, obtaining any substantial benefits from opportunistic spatial spectrum reuse in a frequency-planned network without causing substantial interference is going to be very challenging. Second, the cognitive users need to be more sensitive, by orders of magnitude, than the receivers in the primary system, especially if there is significant shadow fading. This latter problem can be alleviated by having cognitive users cooperate, but only if they are separated far apart so that they experience independent shadowing.

  • 17.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Vojcic, B. R.
    Cooperative transmit diversity via superposition coding2005Ingår i: Eurocon 2005: The International Conference on Computer as a Tool, Vol 1 and 2 , Proceedings, 2005, s. 13-16Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We propose a new strategy for cooperative transmit diversity based on superposition modulation and multiuser detection. The new scheme can outperform "classical" cooperative diversity based on decode-and-forward by about 1.5-2 dB in the SNR range of interest, and at the same computational complexity.

  • 18.
    Larsson, Erik G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Vojcic, Branimir R
    Cooperative transmit diversity based on superposition modulation2005Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 9, nr 9, s. 778-780Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a new strategy for cooperative transmit diversity based on superposition modulation and multiuser detection. The new scheme can outperform "classical" cooperative diversity based on decode-and-forward by about 1.5-2 dB in the SNR range of interest, and at the same computational complexity.

  • 19.
    Mowlér, Marc
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Lindmark, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Methods and bounds for antenna array coupling matrix estimation2007Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, s. 881-884Konferensbidrag (Refereegranskat)
    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.

  • 20.
    Mowlér, Marc
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Lindmark, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Joint estimation of mutual coupling, element factor, and phase center in antenna arrays2007Ingår i: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2007, nr 1, s. 030684-Artikel i tidskrift (Refereegranskat)
    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.

  • 21.
    Nasiri Khormuji, Majid
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    A spectrally efficient transmission scheme for half-duplex decode-and-forward relaying2007Ingår i: GLOBECOM 2007: 2007 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2007, s. 1663-1667Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose a spectrally efficient transmission scheme for the half-duplex relay channel. In the proposed scheme, the relay combines N detected r-dimensional symbols and generates M new r-dimensional symbols, where M < N, using a linear transformation. The proposed linear transformation preserves the signal energy, and it facilitates decoupled symbol detection at the receiver.

    We also present an optimized design for the case of complex scalar modulation (r = 2) with N = 2 and M = 1. This design increases the spectral efficiency by 33% compared to conventional decode- or amplify-and-forward relaying.

  • 22.
    Nasiri Khormuji, Majid
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Analytical results on block length optimization for decode-and-forward relaying with CSI feedback2007Ingår i: 2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications, IEEE , 2007, s. 96-100Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider block length optimization for collaborative transmit diversity using a decode-and-forward protocol assuming that the source and the relay have access to the magnitudes of all path gains. Moreover, we propose a simple scheme which requires only one bit of channel state information (CSI) feedback. We analyze the outage probabilities of all schemes for both selection combining and maximum ratio combining (MRC) at the destination. Analytical results show that even one bit of CSI feedback can provide a significant gain over conventional (non-adaptive) collaborative schemes.

  • 23.
    Nasiri Khormuji, Majid
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Department of Electrical Engineering (ISY), Linköping University.
    Cooperative Transmission Based on Decode-and-Forward Relaying with Partial Repetition Coding2009Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 8, nr 4, s. 1716-1725Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a novel half-duplex decode-and-forward relaying scheme based on partial repetition coding at the relay. In the proposed scheme, if the relay decodes the received message successfully, it re-encodes the message using the same channel code as the one used at the source, but retransmits only a fraction of the codeword. We analyze the proposed scheme and optimize the cooperation level (i.e., the fraction of the message that the relay should transmit). We compare our scheme with conventional repetition in which the relay retransmits the entire decoded message, with parallel coding, and additionally with dynamic decode-and-forward (DDF). We provide a finite-SNR analysis for all the collaborative schemes. The analysis reveals that the proposed partial repetition method can provide a gain of several dB over conventional repetition. It also shows that in general, power allocation is less important provided that one optimally allocates bandwidth. Surprisingly, the proposed scheme is able to achieve the same performance as that of parallel coding for some relay network configurations, but at a much lower complexity.

  • 24.
    Nasiri Khormuji, Majid
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Improving Collaborative Transmit Diversity by Using Constellation Rearrangement2007Ingår i: IEEE Wireless Communications and Networking Conference, WCNC, 2007, s. 804-808Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose an enhancement to cooperative transmit diversity based on uncoded detect-and-forward, by using so-called constellation rearrangement (CR) at the relay. With CR, the relay uses a bit-symbol mapping that is different from the one used by the source. We find the optimal bit-symbol mappings for both the source and the relay and the associated optimal detectors, and show that the improvement over conventional relaying with Gray mapping at the source and the relay can amount to a power gain of several dB. This performance improvement comes at no additional power or bandwidth expense, and at virtually no increase in complexity.

  • 25.
    Nasiri Khormuji, Majid
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Receiver Design for Wireless Relay Channels with Regenerative Relays2007Ingår i: IEEE International Conference on Communications, 2007, s. 4034-4039Konferensbidrag (Refereegranskat)
    Abstract [en]

    We develop a general framework for design of receivers for the wireless relay channel. We derive the optimum detectors for various degrees of channel state information (CSI) at the destination. We consider both the case when the destination has access to full knowledge of the CSI and the case when it only knows the statistics of the channel. High-SNR and low-SNR approximations of the detectors are presented as well.

  • 26. Selén, Y.
    et al.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Empirical bayes linear regression with unknown model order2007Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, Vol III, Pts 1-3, Proceedings, IEEE , 2007, s. 773-776Konferensbidrag (Refereegranskat)
    Abstract [en]

    We study the maximum a posteriori probability model order selection algorithm for linear regression models, assuming Gaussian distributed noise and coefficient vectors. For the same data model, we also derive the minimum mean-square error coefficient vector estimate. The approaches are denoted BOSS (Bayesian Order Selection Strategy) and BPM (Bayesian Parameter estimation Method), respectively. Both BOSS and BPM require a priori knowledge on the distribution of the coefficients. However, under the assumption that the coefficient variance profile is smooth, we derive "empirical Bayesian" versions of our algorithms, which require little or no information from the user. We show in numerical examples that the estimators can outperform several classical methods, including the well-known AIC and BIC for order selection.

  • 27. Selén, Y.
    et al.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Parameter estimation and order selection for linear regression problems2006Ingår i: European Signal Processing Conference, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Parameter estimation and model order selection for linear regression models are two classical problems. In this article we derive the minimum mean-square error (MMSE) parameter estimate for a linear regression model with unknown order. We call the so-obtained estimator the Bayesian Parameter estimation Method (BPM). We also derive the model order selection rule which maximizes the probability of selecting the correct model. The rule is denoted BOSS-Bayesian Order Selection Strategy. The estimators have several advantages: They satisfy certain optimality criteria, they are non-asymptotic and they have low computational complexity. We also derive "empirical Bayesian" versions of BPM and BOSS, which do not require any prior knowledge nor do they need the choice of any "user parameters". We show that our estimators outperform several classical methods, including the AIC and BIC for order selection.

  • 28. Selén, Yngve
    et al.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Empirical Bayes linear regression with unknown model order2008Ingår i: Digital signal processing (Print), ISSN 1051-2004, E-ISSN 1095-4333, Vol. 18, nr 2, s. 236-248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study maximum a posteriori probability model order selection for linear regression models, assuming Gaussian distributed noise and coefficient vectors. For the same data model, we also derive the minimum mean-square error coefficient vector estimate. The approaches are denoted BOSS (Bayesian order selection strategy) and BPM (Bayesian parameter estimation method), respectively. In their simplest form, both BOSS and BPM require a priori knowledge of the distribution of the coefficients. However, under the assumption that the coefficient variance profile is smooth, we derive "empirical Bayesian" versions of our algorithms which estimate the coefficient variance profile from the observations and thus require little or no information from the user. We show in numerical examples that the estimators can outperform several classical methods, including the well-known AICc and BIC for model order selection.

  • 29. Selén, Yngve
    et al.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    RAKE Receiver for Channels with a Sparse Impulse Response2007Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 6, nr 9, s. 3175-3180Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We derive the optimal receiver for RAKE diversity combining on channels with a sparse impulse response. The receiver is based on the Bayesian philosophy and thus it requires the knowledge of certain a priori parameters. However, we also derive an empirical Bayesian version of our receiver, which does not require any a priori knowledge, nor the choice of any user parameters. We show that both versions of our detector can outperform a classical training-based maximum-ratio-combining detector.

  • 30.
    Sjöbergh, Olof
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Jorswieck, Eduard A.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    Linköping University Department of Electrical Engineering (ISY) Division of Communication Systems.
    Greedy user selection for zero-forcing and MMSE multiuser beamforming with channel estimation errors2008Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2008, s. 3137-3140Konferensbidrag (Refereegranskat)
    Abstract [en]

    in a multi-user MIMO downlink where the base station has only estimates of the channels of the users, the sum-rate of multi-user beamforming saturates at high SNR. However, this is not the case for single-user beamforming. We propose a low-complexity user scheduling algorithm that selects the number of active users based on a closed-form approximation of the average sum-rate, and in particular does not add multiple users in the single-user optimality range. In order to develop this algorithm we derive the expected value of the rate of zero-forcing beamforming and MMSE beamforming with estimated channels and modify the greedy user selection accordingly. The gain of the proposed method is shown in numerical simulations.

  • 31.
    Skoglund, Mikael
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Optimal modulation for known interference2007Ingår i: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE , 2007, s. 233-236Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a symbol-by- symbol approach to the problem of canceling known interference at the transmitter in a communication system. In the envisioned system, the modulator maps an information symbol (taken from a finite alphabet) and an interference symbol (from the complex field) onto a transmitted constellation point. The demodulator picks the information symbol (as a function of the received symbol) which minimizes the average error probability. We find the optimal modulator-demodulator pair, in the minimum-probability-of-symbol-error sense, via an iterative optimization procedure, for fixed average transmit power. We illustrate that the new scheme can perform close to the no-interference bound, and in particular that it outperforms Tomlinson-Harashima precoding, which is a classical but suboptimal solution to the problem under study.

  • 32.
    Skoglund, Mikael
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Optimal Modulation for Known Interference2008Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 56, nr 11, s. 1892-1899Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a symbol-by-symbol approach to the problem of canceling known interference at the transmitter in a communication system. In the envisioned system, the modulator maps an information symbol (taken from a finite alphabet) and an interference symbol (from the complex field) onto a transmitted constellation point. Our scheme is based on joint optimization of a modulator and demodulator, subject to a constraint on the average transmit power. The demodulator picks the information symbol (as a function of the received symbol) that minimizes the average error probability. We emphasize that our focus is on transmission in a single (complex) dimension, and hence the proposed technique is a "modulation" rather than a "coding" scheme. We illustrate that the new scheme outperforms Tomlinson-Harashima precoding, which is a classical but suboptimal solution to the one-dimensional known-interference precoding problem. In our simulations, the new approach is able to perform close to the no-interference bound.

  • 33. Souryal, Michael R.
    et al.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Peric, Bojan
    Vojcic, Branimir R.
    Soft-decision metrics for coded orthogonal signaling in symmetric alpha-stable noise2008Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 56, nr 1, s. 266-273Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper derives new soft-decision metrics for coded orthogonal signaling in impulsive noise, more specifically symmetric alpha-stable noise. For the case of a known channel amplitude and known noise dispersion, exact metrics are derived both for Cauchy and Gaussian noise. For the case that the channel amplitude or the dispersion is unknown, approximate metrics are obtained in closed-form based on a generalized-likelihood ratio approach. The performance of the new metrics is compared numerically for a turbo-coded system, and the sensitivity to side information of the optimum receiver for Cauchy noise is considered. The gain that can be achieved by using a properly chosen decoding metric-is quantified, and it is shown that this gain is significant. The application of the results to frequency hopping ad hoc networks is also discussed.

  • 34.
    Thobaben, Ragnar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Sensor-network-aided cognitive radio: On the optimal receiver for estimate-and-forward protocols applied to the relay channel2007Ingår i: CONFERENCE RECORD OF THE FORTY-FIRST ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, VOLS 1-5, NEW YORK: IEEE , 2007, s. 777-781Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cognitive radio describes a promising concept for improving the utilization of radio spectrum. It allows secondary users to access licensed radio spectrum in an opportunistic fashion, given that the quality of service for primary users is maintained. In this scenario, the detection of unused radio spectrum is the main obstacle: it requires the recognition of low-power signals in a noisy environment. Therefore, we consider the case where cognitive users are supported by a wireless sensor network (WSN) providing beliefs on the event that the primary user is active. The beliefs provided by the WSN nodes are then combined by the cognitive radio in order to make a final decision. Due to limitations in complexity, power, and bandwidth, the WSN nodes apply the estimate-and-forward protocol to communicate their beliefs and to relay the beliefs of adjacent nodes. For the case where the WSN is subject to noisy communication links, we derive and analyze the optimal receiver which provides the cognitive radio with log-likelihood ratios for the estimated and forwarded hypotheses. The performance of the optimal receiver is compared to the performance of sub-optimal receivers.

  • 35. Zhang, Nan
    et al.
    Vojcic, Branimir
    Souryal, Michael R.
    Larsson, Erik G.
    KTH, Skolan för elektro- och systemteknik (EES), Kommunikationsteori.
    Exploiting multiuser diversity in reservation random access2006Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 5, nr 9, s. 2548-2554Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we study the uplink of a cellular network where reservation random access schemes such as reservation slotted ALOHA and reservation slotted nonpersistent ISMA are used for multiple access. When channel state information is not available to users when they contend for channel access, we find that capture effect inherent in wireless. communications can exploit the channel variations and reserve users with favorable channels for data transmission. We investigate two channel models where in the first model, channel variations come from time-varying Nakagami-m fading and in the second model, mobile users have both time-varying fading and path loss.

1 - 35 av 35
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