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Spatio-temporal ToF data enhancement by fusion ; ; 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 ▲] Detailed reference viewed: 204 (0 UL)Investigation of Simple Algorithms for Estimation of Delay-Spread and Angle-Spread ; ; Ottersten, Björn 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 ▲] Detailed reference viewed: 92 (0 UL)Spatio-Temporal ToF Data Enhancement by Fusion Garcia Becerro, Frederic ; Aouada, Djamila ; et al in 19th IEEE International Conference on Image Processing (2012) Detailed reference viewed: 198 (5 UL)Generic Optimization of Linear Precoding in Multibeam Satellite Systems Zheng, Gan ; Chatzinotas, Symeon ; Ottersten, Björn in IEEE Transactions on Wireless Communications (2012), 11(6), 2308-2320 Detailed reference viewed: 256 (19 UL)Non-regenerative Two-Hop Wiretap Channels using Interference Neutralization ; ; Zheng, Gan 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 ▲] Detailed reference viewed: 152 (0 UL)Power allocation in Multibeam satellites - A hybrid-Genetic Algorithm approach ; Shankar, Bhavani ; Danoy, Grégoire et al in ESA Workshop on Advanced Flexible Telecom Payloads (2012) Detailed reference viewed: 324 (30 UL)Depth enhancement by fusion for passive and active sensing ; ; 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 ▲] Detailed reference viewed: 175 (1 UL)Maximum likelihood based sparse and distributed conjoint analysis ; ; 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 ▲] Detailed reference viewed: 170 (0 UL)Cognitive interference alignment between small cells and a macrocell Chatzinotas, Symeon ; Ottersten, Björn in 19th International Conference on Telecommunications (ICT) 2012 (2012) Detailed reference viewed: 173 (1 UL)Successive zero-forcing DPC with per-antenna power constraint: Optimal and suboptimal designs ; ; 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 ▲] Detailed reference viewed: 208 (0 UL)Bilateral Filter Evaluation Based on Exponential Kernels Al Ismaeil, Kassem ; Aouada, Djamila ; 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 ▲] Detailed reference viewed: 155 (11 UL)Linear and nonlinear techniques for multibeam joint processing in satellite communications Christopoulos, Dimitrios ; Chatzinotas, Symeon ; Zheng, Gan 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 ▲] Detailed reference viewed: 321 (29 UL)Special issue on satellite communication systems and networking ; ; Ottersten, Björn et al in Eurasip Journal on Wireless Communications and Networking (2012), 2012 [No abstract available] Detailed reference viewed: 174 (0 UL)Depth Enhancement by Fusion for Passive and Active Sensing Garcia Becerro, Frederic ; Aouada, Djamila ; Abdella, Hashim Kemal et al in Computer Vision – ECCV 2012. Workshops and Demonstrations (2012) Detailed reference viewed: 266 (19 UL)Using simple relays to improve physical-layer security Zheng, Gan ; ; 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 ▲] Detailed reference viewed: 180 (0 UL)Fixed Full Duplex Relaying for Wireless Broadband Communication ; ; Zheng, Gan et al in Wireless Communications & Signal Processing (WCSP), 2012 International Conference on (2012) We compare full duplex (FD) and half duplex (HD) relaying in terms of coverage range. We consider a practical FD relay model where both the dynamic ranges of transmitter and receiver and the level of the ... [more ▼] We compare full duplex (FD) and half duplex (HD) relaying in terms of coverage range. We consider a practical FD relay model where both the dynamic ranges of transmitter and receiver and the level of the residual loop interference between transmitted and received signals are taken into account. We numerically evaluate the rate performance of the full duplex multi-hop (FD-MH) scheme and the half duplex decode-and-forward (HD-DF) scheme, where the former requires transmit power allocation under the dynamic range constraint. Results show that there is a tradeoff between these two relaying modes. [less ▲] Detailed reference viewed: 215 (0 UL)Detection of sparse random signals using compressive measurements Shankar, Bhavani ; ; Ottersten, Björn 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 ▲] Detailed reference viewed: 174 (5 UL)Robust Maximin MIMO Precoding for Arbitrary Convex Uncertainty Sets ; ; Ottersten, Björn 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 ▲] Detailed reference viewed: 157 (1 UL)Optimality Properties,Distributed Strategies, and Measurement-Based Evaluation of Coordinated Multicell OFDMA Transmission ; ; 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 ▲] Detailed reference viewed: 192 (0 UL)Semidefinite Relaxations of Robust Binary Least Squares under Ellipsoidal Uncertainty Sets ; ; Ottersten, Björn 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 ▲] Detailed reference viewed: 180 (2 UL) |
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