References of "Ottersten, Björn 50002797"
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See detailBilateral Filter Evaluation Based on Exponential Kernels
Al Ismaeil, Kassem UL; Aouada, Djamila UL; Mirbach, Bruno et al

in Pattern Recognition (ICPR), 2012 21st International Conference on (2012)

The well-known bilateral filter is used to smooth noisy images while keeping their edges. This filter is commonly used with Gaussian kernel functions without real justification. The choice of the kernel ... [more ▼]

The well-known bilateral filter is used to smooth noisy images while keeping their edges. This filter is commonly used with Gaussian kernel functions without real justification. The choice of the kernel functions has a major effect on the filter behavior. We propose to use exponential kernels with L1 distances instead of Gaussian ones. We derive Stein's Unbiased Risk Estimate to find the optimal parameters of the new filter and compare its performance with the conventional one. We show that this new choice of the kernels has a comparable smoothing effect but with sharper edges due to the faster, smoothly decaying kernels. [less ▲]

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See detailSpecial issue on satellite communication systems and networking
Panagopoulos, A. D.; Scalise, S.; Ottersten, Björn UL et al

in Eurasip Journal on Wireless Communications and Networking (2012), 2012

[No abstract available]

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See detailLinear and nonlinear techniques for multibeam joint processing in satellite communications
Christopoulos, Dimitrios UL; Chatzinotas, Symeon UL; Zheng, Gan UL et al

in EURASIP Journal on Wireless Communications and Networking (2012), 2012(162),

Existing satellite communication standards such as DVB-S2 operate under highly-efficient adaptive coding and modulation schemes thus making significant progress in improving the spectral efficiencies of ... [more ▼]

Existing satellite communication standards such as DVB-S2 operate under highly-efficient adaptive coding and modulation schemes thus making significant progress in improving the spectral efficiencies of digital satellite broadcast systems. However, the constantly increasing demand for broadband and interactive satellite links emanates the need to apply novel interference mitigation techniques, striving towards Terabit throughput. In this direction, the objective of the present contribution is to investigate joint multiuser processing techniques for multibeam satellite systems. In the forward link, the performance of linear precoding is investigated with optimal non-linear precoding (i.e. Dirty Paper Coding) acting as the upper performance limit. To this end, the resulting power and precoder design problems are approached through optimization methods. Similarly, in the return link the concept of linear filtering (i.e. Linear Minimum Mean Square Error) is studied with the optimal successive interference cancellation acting as the performance limit. The derived capacity curves for both scenarios are compared to conventional satellite systems where beams are processed independently and interbeam interference is mitigated through a four color frequency reuse scheme, in order to quantify the potential gain of the proposed techniques. [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 detailDepth enhancement by fusion for passive and active sensing
Garcia, F.; Aouada, D.; Abdella, H. K. et al

in Lecture Notes in Computer Science (2012), 7585 LNCS(PART 3), 506-515

This paper presents a general refinement procedure that enhances any given depth map obtained by passive or active sensing. Given a depth map, either estimated by triangulation methods or directly ... [more ▼]

This paper presents a general refinement procedure that enhances any given depth map obtained by passive or active sensing. Given a depth map, either estimated by triangulation methods or directly provided by the sensing system, and its corresponding 2-D image, we correct the depth values by separately treating regions with undesired effects such as empty holes, texture copying or edge blurring due to homogeneous regions, occlusions, and shadowing. In this work, we use recent depth enhancement filters intended for Time-of-Flight cameras, and adapt them to alternative depth sensing modalities, both active using an RGB-D camera and passive using a dense stereo camera. To that end, we propose specific masks to tackle areas in the scene that require a special treatment. Our experimental results show that such areas are satisfactorily handled by replacing erroneous depth measurements with accurate ones. © 2012 Springer-Verlag. [less ▲]

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See detailReal-Time Distance-Dependent Mapping for a Hybrid ToF Multi-Camera Rig
Garcia Becerro, Frederic UL; Aouada, Djamila UL; Mirbach, Bruno et al

in IEEE Journal of Selected Topics in Signal Processing (2012), 6(5), 1-12

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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 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 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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See detailUsing simple relays to improve physical-layer security
Zheng, Gan UL; Jiangyuan, Li; Wong, Kai-Kit et al

in Communications in China (ICCC), 2012 1st IEEE International Conference on (2012)

This paper studies different uses of two cooperating relays to improve the secrecy rate of a wiretap channel. These two relays are assumed to perform only simple functions: either amplify-and-forward (AF ... [more ▼]

This paper studies different uses of two cooperating relays to improve the secrecy rate of a wiretap channel. These two relays are assumed to perform only simple functions: either amplify-and-forward (AF) or jamming. Complex functions such as decode-and-forward (DF) are not considered. We study three modes of cooperation: i) cooperative jamming (CJ), ii) AF-aided beamforming and iii) mixed AF-aided beamforming and CJ, all with individual relay power constraints. While i) is known in the literature, our efforts are spent on ii) and iii). In particular, for iii), we assume that the jamming signals in two communication stages are correlated, giving rise to improved performances. We also propose a heuristic approach for selecting the appropriate cooperating mode. Simulation results illustrate the performance gain of each scheme under different channel conditions and the effectiveness of the proposed mode selection method. [less ▲]

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See detailMulti-objective Optimization Approach to Power Allocation in Multibeam Systems
Aravanis, Alexis; Shankar, Bhavani UL; Danoy, Grégoire UL et al

in Proceedings of 30th AIAA International Communications Satellite Systems Conference (ICSSC), (2012)

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See detailNon-regenerative Two-Hop Wiretap Channels using Interference Neutralization
Gerbracht, Sabrina; Jorswieck, Eduard A.; Zheng, Gan UL et al

in Information Forensics and Security (WIFS), 2012 IEEE International Workshop on (2012)

In this paper, we analyze the achievable secrecy rates in the two-hop wiretap channel with four nodes, where the transmitter and the receiver have multiple antennas while the relay and the eavesdropper ... [more ▼]

In this paper, we analyze the achievable secrecy rates in the two-hop wiretap channel with four nodes, where the transmitter and the receiver have multiple antennas while the relay and the eavesdropper have only a single antenna each. The relay is operating in amplify-and-forward mode and all the channels between the nodes are known perfectly by the transmitter. We discuss different transmission and protection schemes like artificial noise (AN). Furthermore, we introduce interference neutralization (IN) as a new protection scheme. We compare the different schemes regarding the high-SNR slope and the high-SNR power offset and illustrate the performance by simulation results. It is shown analytically as well as by numerical simulations that the high SNR performance of the proposed IN scheme is better than the one of AN. [less ▲]

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See detailGeneric Optimization of Linear Precoding in Multibeam Satellite Systems
Zheng, Gan UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2012), 11(6), 2308-2320

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See detailOptimality Properties,Distributed Strategies, and Measurement-Based Evaluation of Coordinated Multicell OFDMA Transmission
Björnson, Emil; Jaldén, Niklas; Bengtsson, Mats et al

in IEEE Transactions on Signal Processing (2011), 59(12), 6086-6101

The throughput of multicell systems is inherently limited by interference and the available communication resources. Coordinated resource allocation is the key to efficient performance, but the demand on ... [more ▼]

The throughput of multicell systems is inherently limited by interference and the available communication resources. Coordinated resource allocation is the key to efficient performance, but the demand on backhaul signaling and computational resources grows rapidly with number of cells, terminals, and subcarriers. To handle this, we propose a novel multicell framework with dynamic cooperation clusters where each terminal is jointly served by a small set of base stations. Each base station coordinates interference to neighboring terminals only, thus limiting backhaul signalling and making the framework scalable. This framework can describe anything from interference channels to ideal joint multicell transmission. The resource allocation (i.e., precoding and scheduling) is formulated as an optimization problem (P1) with performance described by arbitrary monotonic functions of the signal-to-interference-and-noise ratios (SINRs) and arbitrary linear power constraints. Although (P1) is nonconvex and difficult to solve optimally, we are able to prove: 1) optimality of single-stream beamforming; 2) conditions for full power usage; and 3) a precoding parametrization based on a few parameters between zero and one. These optimality properties are used to propose low-complexity strategies: both a centralized scheme and a distributed version that only requires local channel knowledge and processing. We evaluate the performance on measured multicell channels and observe that the proposed strategies achieve close-to-optimal performance among centralized and distributed solutions, respectively. In addition, we show that multicell interference coordination can give substantial improvements in sum performance, but that joint transmission is very sensitive to synchronization errors and that some terminals can experience performance degradations. [less ▲]

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See detailSemidefinite Relaxations of Robust Binary Least Squares under Ellipsoidal Uncertainty Sets
Tsakonas, Efthymios; Jaldén, Joakim; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2011), 59(11), 5169-5180

The problem of finding the least squares solution s to a system of equations Hs = y is considered, when s is a vector of binary variables and the coefficient matrix H is unknown but of bounded uncertainty ... [more ▼]

The problem of finding the least squares solution s to a system of equations Hs = y is considered, when s is a vector of binary variables and the coefficient matrix H is unknown but of bounded uncertainty. Similar to previous approaches to robust binary least squares, we explore the potential of a min-max design with the aim to provide solutions that are less sensitive to the uncertainty in H. We concentrate on the important case of ellipsoidal uncertainty, i.e., the matrix H is assumed to be a deterministic unknown quantity which lies in a given uncertainty ellipsoid. The resulting problem is NP-hard, yet amenable to convex approximation techniques: Starting from a convenient reformulation of the original problem, we propose an approximation algorithm based on semidefinite relaxation that explicitly accounts for the ellipsoidal uncertainty in the coefficient matrix. Next, we show that it is possible to construct a tighter relaxation by suitably changing the description of the feasible region of the problem, and formulate an approximation algorithm that performs better in practice. Interestingly, both relaxations are derived as Lagrange bidual problems corresponding to the two equivalent problem reformulations. The strength of the proposed tightened relaxation is demonstrated by pertinent simulations. [less ▲]

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See detailChannel Quantization Design in Multiuser MIMO Systems: Asymptotic versus Practical Conclusions
Björnson, Emil; Ntontin, Konstantinos; Ottersten, Björn UL

in Channel Quantization Design in Multiuser MIMO Systems: Asymptotic versus Practical Conclusions (2011, May)

Feedback of channel state information (CSI) is necessary to achieve high throughput and low outage probability in multiuser multi antenna systems. There are two types of CSI: directional and quality ... [more ▼]

Feedback of channel state information (CSI) is necessary to achieve high throughput and low outage probability in multiuser multi antenna systems. There are two types of CSI: directional and quality information. Many papers have analyzed the importance of these in asymptotic regimes. However, we show that such results should be handled with care, as very different conclusions can be drawn depending on the spatial correlation and number of users. There fore, we propose a quantization framework and evaluate the tradeoff between directional and quality feedback under practical conditions. [less ▲]

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See detailExploiting Long-Term Channel Correlation in Limited Feddback SDMA through Channel Phase Codebook
Huang, Yongming; Yang, Luxi; Bengtsson, Mats et al

in IEEE Transactions on Signal Processing (2011), 59(3), 1217-1228

Improving channel information quality at the base station (BS) is crucial for the optimization of frequency division duplexed (FDD) multi-antenna multiuser downlink systems with limited feedback. To this ... [more ▼]

Improving channel information quality at the base station (BS) is crucial for the optimization of frequency division duplexed (FDD) multi-antenna multiuser downlink systems with limited feedback. To this end, this paper proposes to estimate a particular representation of channel state information (CSI) at the BS through channel norm feedback and a newly developed channel phase codebook, where the long-term channel correlation is efficiently exploited to improve performance. In particular, the channel representation is decomposed into a gain-related part and a phase-related part, with each of them estimated separately. More specifically, the gain-related part is estimated from the channel norm and channel correlation matrix, while the phase-related part is determined using a channel phase codebook, constructed with the generalized Lloyd algorithm. Using the estimated channel representation, joint optimization of multiuser precoding and opportunistic scheduling is performed to obtain an SDMA transmit scheme. Computer simulation results confirm the advantage of the proposed scheme over state of the art limited feedback SDMA schemes under correlated channel environment. [less ▲]

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See detailDistributed Multicell Beamforming with Limited Intercell Coordination
Huang, Yongming; Zheng, Gan UL; Bengtsson, Mats et al

in IEEE Transactions on Signal Processing (2011), 59(2), 728-738

This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell ... [more ▼]

This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell information exchange is permitted. With an aim to maximize the worst-user signal-to-interference-and-noise ratio (SINR), we devise a hierarchical iterative algorithm to optimize downlink beamforming and intercell power allocation jointly in a distributed manner. The proposed scheme is proved to converge to the global optimum. For fast convergence and to reduce the burden of intercell parameter exchange, we further propose to exploit previous iterations adaptively. Results illustrate that the proposed scheme can achieve near-optimal performance even with a few iterations, hence providing a good tradeoff between performance and backhaul consumption. The performance under quantized parameter exchange is also examined. [less ▲]

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See detailClustered Multicell Joint Decoding under Cochannel Interference
Chatzinotas, Symeon UL; Ottersten, Björn UL

in Clustered Multicell Joint Decoding under Cochannel Interference (2011)

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See detailJoint Precoding with Flexible Power Constraints in Multibeam Satellite Systems
Chatzinotas, Symeon UL; Zheng, Gan UL; Ottersten, Björn UL

in Joint Precoding with Flexible Power Constraints in Multibeam Satellite Systems (2011)

Detailed reference viewed: 185 (11 UL)