References of "Ottersten, Björn 50002797"
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See detailSatellite Cognitive Communications: Interference Modeling and Techniques Selection
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceeding of 6th Advanced Satellite Multimedia Systems Conference and the 12th Signal Processing for Space Communications Workshop (2012, September)

Due to increasing demand of high speed data rate for satellite multimedia and broadcasting services and spectrum scarcity problem in satellite bands, exploring new techniques for enhancing spectral ... [more ▼]

Due to increasing demand of high speed data rate for satellite multimedia and broadcasting services and spectrum scarcity problem in satellite bands, exploring new techniques for enhancing spectral efficiency in satellite communication has become an important research challenge. In this aspect, satellite cognitive communication can be considered as a promising solution to solve spectrum scarcity problem. In this paper, different cognitive techniques such as underlay, overlay, interweave and database related techniques are discussed by reviewing the current state of art. Exact beam patterns of a multi-beam satellite are plotted over the Europe map and interference modeling between terrestrial Base Station (BS) and satellite terminal is carried out on the basis of interference power level. Furthermore, suitable cognitive techniques are proposed in high and low interference regions in the context of satellite cognitive communication. [less ▲]

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See detailSpace-Frequency Coding for Dual Polarized Hybrid Mobile Satellite Systems
Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2012), 11(8), 2806-2814

An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions ... [more ▼]

An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions adopting multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) techniques. In this work, we build upon recent studies of dual polarization MIMO for each component and propose the use of full-rate full-diversity (FRFD) codes adopting a space-frequency paradigm. We also propose a scheme taking advantage of the separation between the subcarriers to enhance the coding gain. By critically assessing the different options for the 4 transmit, 2 receive hybrid scenario taking into account system and channel particularities, we demonstrate that the proposed scheme is a solution for enhancing the performance of next generation hybrid mobile satellite systems. [less ▲]

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See detailIterative Precoder Design and User Scheduling for Block-Diagonalized Systems
Tran, Le-Nam; Bengtsson, Mats; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2012), 60(7), 3726-3739

The block diagonalization (BD) scheme is a low-complexity suboptimal precoding technique for multiuser multiple input-multiple output (MIMO) downlink channels, which completely precancels the multiuser ... [more ▼]

The block diagonalization (BD) scheme is a low-complexity suboptimal precoding technique for multiuser multiple input-multiple output (MIMO) downlink channels, which completely precancels the multiuser interference. Accordingly, the precoder of each user lies in the null space of other users' channel matrices. In this paper, we propose an iterative algorithm using QR decompositions (QRDs) to compute the precoders. Specifically, to avoid dealing with a large concatenated matrix, we apply the QRD to a sequence of matrices of lower dimensions. One problem of BD schemes is that the number of users that can be simultaneously supported is limited due to zero interference constraints. When the number of users is large, a set of users must be selected, and selection algorithms should be designed to exploit the multiuser diversity gain. Finding the optimal set of users requires an exhaustive search, which has too high computational complexity to be practically useful. Based on the iterative precoder design, this paper proposes a low-complexity user selection algorithm using a greedy method, in which the precoders of selected users are recursively updated after each selection step. The selection metric of the proposed scheduling algorithm relies on the product of the squared row norms of the effective channel matrices, which is related to the eigenvalues by the Hadamard and Schur inequalities. An asymptotic analysis is provided to show that the proposed algorithm can achieve the optimal sum rate scaling of the MIMO broadcast channel. The numerical results show that the proposed algorithm achieves a good trade-off between sum rate performance and computational complexity. When users suffer different channel conditions, providing fairness among users is of critical importance. To address this problem, we also propose two fair scheduling (FS) algorithms, one imposing fairness in the approximation of the data rate, and another directly imposing fairness in the product of the sq- ared row norms of the effective channel matrices. [less ▲]

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See detailDistributed Multicell Beamforming Design Approaching Pareto Boundary with Max-Min Fairness
Huang, Yongming; Zheng, Gan UL; Bengtsson, Mats et al

in IEEE Transactions on Wireless Communications (2012), 11(8), 2921-2933

This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing ... [more ▼]

This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing. With the goal to reach the point on the Pareto boundary with max-min rate fairness, we first develop a two-step centralized optimization algorithm to design the joint beamforming vectors. This algorithm can achieve a further sum-rate improvement over the max-min optimal performance, and is shown to guarantee max-min Pareto optimality for scenarios with two base stations (BSs) each serving a single user. To realize a distributed solution with limited intercell communication, we then propose an iterative algorithm by exploiting an approximate uplink-downlink duality, in which only a small number of positive scalars are shared between cells in each iteration. Simulation results show that the proposed distributed solution achieves a fairness rate performance close to the centralized algorithm while it has a better sum-rate performance, and demonstrates a better tradeoff between sum-rate and fairness than the Nash Bargaining solution especially at high signal-to-noise ratio. [less ▲]

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See detailExploiting Polarization for Spectrum Sensing in Cognitive SatComs
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of 7th International Conference on Cognitive Radio Oriented Wireless Networks (2012, June)

Exploring new techniques for spectrum sensing (SS), which can detect the weak primary signals instantly, has been an important research challenge. In this paper, the problem of enhancing SS efficiency in ... [more ▼]

Exploring new techniques for spectrum sensing (SS), which can detect the weak primary signals instantly, has been an important research challenge. In this paper, the problem of enhancing SS efficiency in cognitive SatComs has been considered. The analysis of different combining techniques has been carried out for SS using dual polarized antenna. Furthermore, polarization states of received signals are exploited and based on obtained polarization states, Optimum Polarization Based Combining (OPBC) technique has been used for carrying out SS in the satellite terminal. The sensing performance of OPBC technique has been compared to selection combining (SC), equal gain combining (EGC) and maximum ratio combining (MRC) techniques. The simulation results show that OPBC technique achieves a great improvement in sensing efficiency over other considered techniques at the expense of complexity in a dual polarized AWGN channel. [less ▲]

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See detailPareto Characterization of the Multicell MIMO Performance Region With Simple Receivers
Björnson, Emil; Bengtsson, Mats; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2012), 60(8), 4464-4469

We study the performance region of a general multicell downlink scenario with multiantenna transmitters, hardware impairments, and low-complexity receivers that treat interference as noise. The Pareto ... [more ▼]

We study the performance region of a general multicell downlink scenario with multiantenna transmitters, hardware impairments, and low-complexity receivers that treat interference as noise. The Pareto boundary of this region describes all efficient resource allocations, but is generally hard to compute. We propose a novel explicit characterization that gives Pareto optimal transmit strategies using a set of positive parameters-fewer than in prior work. We also propose an implicit characterization that requires even fewer parameters and guarantees to find the Pareto boundary for every choice of parameters, but at the expense of solving quasi-convex optimization problems. The merits of the two characterizations are illustrated for interference channels and ideal network multiple-input multiple-output (MIMO). [less ▲]

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See detailPhysical Layer Security in Multibeam Satellite Systems
Zheng, Gan UL; Arapoglou, Pantelis-Daniel UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2012), 11(2), 852-863

Security threats introduced due to the vulnerability of the transmission medium may hinder the proliferation of Ka band multibeam satellite systems for civil and military data applications. This paper ... [more ▼]

Security threats introduced due to the vulnerability of the transmission medium may hinder the proliferation of Ka band multibeam satellite systems for civil and military data applications. This paper sets the analytical framework and then studies physical layer security techniques for fixed legitimate receivers dispersed throughout multiple beams, each possibly surrounded by multiple (passive) eavesdroppers. The design objective is to minimize via transmit beamforming the costly total transmit power on board the satellite, while satisfying individual intended users' secrecy rate constraints. Assuming state-of-the-art satellite channel models, when perfect channel state information (CSI) about the eavesdroppers is available at the satellite, a partial zero-forcing approach is proposed for obtaining a low-complexity sub-optimal solution. For the optimal solution, an iterative algorithm combining semi-definite programming relaxation and the gradient-based method is devised by studying the convexity of the problem. Furthermore, the use of artificial noise as an additional degree-of-freedom for protection against eavesdroppers is explored. When only partial CSI about the eavesdroppers is available, we study the problem of minimizing the eavesdroppers' received signal to interference-plus-noise ratios. Simulation results demonstrate substantial performance improvements over existing approaches. [less ▲]

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See detailDetection of sparse random signals using compressive measurements
Shankar, Bhavani UL; Chatterjee, Saikat; Ottersten, Björn UL

in Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on (2012)

We consider the problem of detecting a sparse random signal from the compressive measurements without reconstructing the signal. Using a subspace model for the sparse signal where the signal parameters ... [more ▼]

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

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See detailCapacity Analysis of Dual-Hop Amplify-and-Forward MIMO Multiple-Access Channels
Chatzinotas, Symeon UL; Ottersten, Björn UL

in International Conference on Wireless Communications and Signal Processing, WCSP 2012 (2012)

Relay channels have been heavily studied during the last decades as a means of improving spectral efficiency, availability and coverage in combination with multiple antenna transceivers. Relay channels ... [more ▼]

Relay channels have been heavily studied during the last decades as a means of improving spectral efficiency, availability and coverage in combination with multiple antenna transceivers. Relay channels can comprise many hops but the most practical approach at the time being would be a dual-hop system. In addition, the simplest method of relaying in terms of complexity is amplify and forward. In this direction, we investigate the ergodic capacity of a dual-hop amplify-and-forward MIMO MAC and we derive asymptotic closed-form expressions based on the principles of free probability theory. We extend the current literature by proposing a analytical model which can accommodate variance-profiled Gaussian matrices. Numerical results are utilized to verify the accuracy of the derived closed-form expressions and evaluate the effect of the channel parameters. [less ▲]

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See detailPower allocation in Multibeam satellites - A hybrid-Genetic Algorithm approach
Aravanis, Alexis; Shankar, Bhavani UL; Danoy, Grégoire UL et al

in ESA Workshop on Advanced Flexible Telecom Payloads (2012)

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See detailSuccessive zero-forcing DPC with sum power constraint: Low-complexity optimal designs
Tran, L.-N.; Juntti, M.; Bengtsson, M. et al

in 2012 IEEE International Conference on Communications, ICC 2012 (2012)

Successive zero-forcing dirty paper coding (SZF-DPC) is a simplified alternative to DPC for MIMO broadcast channels (MIMO BCs). In the SZF-DPC scheme, the noncausally-known interference is canceled by DPC ... [more ▼]

Successive zero-forcing dirty paper coding (SZF-DPC) is a simplified alternative to DPC for MIMO broadcast channels (MIMO BCs). In the SZF-DPC scheme, the noncausally-known interference is canceled by DPC, while the residual interference is suppressed by the ZF technique. Due to the ZF constraints, the precoders are constrained to lie in the null space of a matrix. For the sum rate maximization problem under a sum power constraint, the existing precoder designs naturally rely on the singular value decomposition (SVD). The SVD-based design is optimal but needs high computational complexity. Herein, we propose two low-complexity optimal precoder designs for SZF-DPC, all based on the QR decomposition (QRD), which requires lower complexity than SVD. The first design method is an iterative algorithm to find an orthonormal basis of the null space of a matrix that has a recursive structure. The second proposed method, which will be shown to require the lowest complexity, results from applying a single QRD to the matrix comprising all users' channel matrices. We analytically and numerically show that the two proposed precoder designs are optimal. © 2012 IEEE. [less ▲]

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See detailOn the optimality of beamformer design for zero-forcing DPC with QR decomposition
Tran, L.-N.; Juntti, M.; Bengtsson, M. et al

in IEEE International Conference on Communications (2012)

We consider the beamformer design for zero-forcing dirty paper coding (ZF-DPC), a suboptimal transmission technique for MISO broadcast channels (MISO BCs). Beamformers for ZF-DPC are designed to maximize ... [more ▼]

We consider the beamformer design for zero-forcing dirty paper coding (ZF-DPC), a suboptimal transmission technique for MISO broadcast channels (MISO BCs). Beamformers for ZF-DPC are designed to maximize a performance measure, subject to some power constraints and zero-interference constraints. For the sum rate maximization problem under a total power constraint, the existing beamformer designs in the literature are based on the QR decomposition (QRD), which is used to satisfy the ZF constraints. However, the optimality of the QRD-based design is still unknown. First, we prove that the QRD-based design is indeed optimal for ZF-DPC for any performance measure under a sum power constraint. For the per-antenna power constraints, the QRD-based designs become suboptimal, and we propose an optimal design, using a convex optimization framework. Low-complexity suboptimal designs are also presented. © 2012 IEEE. [less ▲]

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See detailSpatio-temporal ToF data enhancement by fusion
Garcia, F.; Aouada, D.; Mirbach, B. et al

in Proceedings - International Conference on Image Processing, ICIP (2012)

We propose an extension of our previous work on spatial domain Time-of-Flight (ToF) data enhancement to the temporal domain. Our goal is to generate enhanced depth maps at the same frame rate of the 2-D ... [more ▼]

We propose an extension of our previous work on spatial domain Time-of-Flight (ToF) data enhancement to the temporal domain. Our goal is to generate enhanced depth maps at the same frame rate of the 2-D camera that, coupled with a ToF camera, constitutes a hybrid ToF multi-camera rig. To that end, we first estimate the motion between consecutive 2-D frames, and then use it to predict their corresponding depth maps. The enhanced depth maps result from the fusion between the recorded 2-D frames and the predicted depth maps by using our previous contribution on ToF data enhancement. The experimental results show that the proposed approach overcomes the ToF camera drawbacks; namely, low resolution in space and time and high level of noise within depth measurements, providing enhanced depth maps at video frame rate. © 2012 IEEE. [less ▲]

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See detailSuccessive zero-forcing DPC with per-antenna power constraint: Optimal and suboptimal designs
Tran, L.-N.; Juntti, M.; Bengtsson, M. et al

in Proceedings of the 2012 IEEE International Conference on Communications (2012)

This paper considers the precoder designs for successive zero-forcing dirty paper coding (SZF-DPC), a suboptimal transmission technique for MIMO broadcast channels (MIMO BCs). Existing precoder designs ... [more ▼]

This paper considers the precoder designs for successive zero-forcing dirty paper coding (SZF-DPC), a suboptimal transmission technique for MIMO broadcast channels (MIMO BCs). Existing precoder designs for SZF-DPC often consider a sum power constraint. In this paper, we address the precoder design for SZF-DPC with per-antenna power constraints (PAPCs), which has not been well studied. First, we formulate the precoder design as a rank-constrained optimization problem, which is generally difficult to handle. To solve this problem, we follow a relaxation approach, and prove that the optimal solution of the relaxed problem is also optimal for the original problem. Considering the relaxed problem, we propose a numerically efficient algorithm to find the optimal solution, which exhibits a fast convergence rate. Suboptimal precoder designs, with lower computational complexity, are also presented, and compared with the optimal ones in terms of achievable sum rate and computational complexity. © 2012 IEEE. [less ▲]

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See detailInvestigation of Simple Algorithms for Estimation of Delay-Spread and Angle-Spread
Zetterberg, Per; Jaldén, Niklas; Ottersten, Björn UL et al

Scientific journal (2012)

In this paper we describe two simple methods for estimation of delay-spread and angle-spread, respectively. The algorithms are simple in the sense that the transmitted signal may consist of only three ... [more ▼]

In this paper we describe two simple methods for estimation of delay-spread and angle-spread, respectively. The algorithms are simple in the sense that the transmitted signal may consist of only three superimposed CW tones -and the receiver need only two antennas. The algorithms are also simple in the sense that the computational cost is very low. We verify the algorithms by applying them to wideband and multi-antenna measurement data, respectively. [less ▲]

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See detailCognitive interference alignment between small cells and a macrocell
Chatzinotas, Symeon UL; Ottersten, Björn UL

in 19th International Conference on Telecommunications (ICT) 2012 (2012)

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See detailMulti-gateway cooperation in multibeam satellite systems
Zheng, Gan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE 23rd International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC) (2012)

Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and ... [more ▼]

Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and precoding over multiple beams has shown great throughput potential in literature. However, feeding all this data from a single gateway is not feasible based on the current frequency allocations. In this context, we investigate a range of scenarios involving beam clusters where each cluster is managed by a single gateway. More specifically, the following cases are considered for handling intercluster interference: a) conventional frequency colouring, b) joint processing within cluster, c) partial CSI sharing among clusters, d) partial CSI and data sharing among clusters. CSI sharing does not provide considerable performance gains with respect to b) but combined with data sharing offers roughly a 40% improvement over a) and a 15% over b). [less ▲]

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See detailRobust Maximin MIMO Precoding for Arbitrary Convex Uncertainty Sets
Wang, Jiaheng; Bengtsson, Mats; Ottersten, Björn UL et al

in Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on (2012)

We consider a worst-case robust precoding design for multi-input multi-output (MIMO) communication systems with imperfect channel state information at the transmitter (CSIT). Instead of a particular ... [more ▼]

We consider a worst-case robust precoding design for multi-input multi-output (MIMO) communication systems with imperfect channel state information at the transmitter (CSIT). Instead of a particular choice, we consider a general imperfect CSIT model that only assumes the channel errors to be within a convex set, which includes most common imperfect CSIT models as special cases. The robust precoding design is formulated as a maximin problem, aiming at maximizing the worst-case received signal-to-noise ratio or minimizing the worst-case error probability. It is shown that the robust precoder can be easily obtained by solving a convex problem. We further provide an equivalent but more practical form of the convex problem that can be efficiently handled with common optimization methods and software packages. [less ▲]

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See detailMaximum likelihood based sparse and distributed conjoint analysis
Tsakonas, Efthymios; Jalden, Joakim; Sidiropoulos, Nicolas D. et al

in Statistical Signal Processing Workshop (SSP), 2012 IEEE (2012)

A new statistical model for choice-based conjoint analysis is proposed. The model uses auxiliary variables to account for outliers and to detect the salient features that influence decisions. Unlike ... [more ▼]

A new statistical model for choice-based conjoint analysis is proposed. The model uses auxiliary variables to account for outliers and to detect the salient features that influence decisions. Unlike recent classification-based approaches to choice-based conjoint analysis, a sparsity-aware maximum likelihood (ML) formulation is proposed to estimate the model parameters. The proposed approach is conceptually appealing, mathematically tractable, and is also well-suited for distributed implementation. Its performance is tested and compared to the prior state-of-art using synthetic as well as real data coming from a conjoint choice experiment for coffee makers, with very promising results. [less ▲]

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