References of "Ottersten, Björn 50002797"
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See detailNon-parametric data predistortion for non-linear channels with memory
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on (2013, May 26)

With the growing application of high order modulation techniques, the mitigation of the non-linear distortions introduced by the power amplification, has become a major issue in telecommunication. More ... [more ▼]

With the growing application of high order modulation techniques, the mitigation of the non-linear distortions introduced by the power amplification, has become a major issue in telecommunication. More sophisticated techniques to counteract the strong generated interferences need to be investigated in order to achieve the desired power and spectral efficiency. This work proposes a novel approach for the definition of a transmitter technique (predistortion) that outperforms the standard methods with respect to both performance and efficiency. [less ▲]

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See detailAsymptotic Analysis of Eigenvalue-based Blind Spectrum Sensing Techniques
Chatzinotas, Symeon UL; Sharma, Shree Krishna UL; Ottersten, Björn UL

in proceedings of International Conference on Acoustics, Speech, and Signal Processing (ICASSP) 2013 (2013, May)

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See detailSimultaneous Estimation of Multi-Relay MIMO Channels
Mehrpouyan, H.; Blostein, S.D.; Ottersten, Björn UL

in IEEE Global Telecommunications Conference (GLOBECOM) (2013)

This paper addresses training-based channel estimation in distributed amplify-and-forward (AF) multi-input multi-output (MIMO) multi-relay networks. To reduce channel estimation overhead and delay, a ... [more ▼]

This paper addresses training-based channel estimation in distributed amplify-and-forward (AF) multi-input multi-output (MIMO) multi-relay networks. To reduce channel estimation overhead and delay, a training algorithm that allows for simultaneous estimation of the entire MIMO cooperative network’s channel parameters at the destination node is proposed. The exact Cram´er- Rao lower bound (CRLB) for the problem is presented in closedform. Channel estimators that are capable of estimating the overall source-relay-destination channel parameters at the destination are also derived. Numerical results show that while reducing delay, the proposed channel estimators are close to the derived CRLB over a wide range of signal-to-noise ratio values and outperform existing channel estimation methods. Finally, extensive simulations demonstrate that the proposed training method and channel estimators can be effectively deployed in combination with cooperative optimization algorithms to significantly enhance the performance of AF relaying MIMO systems in terms of average-bit-error-rate. [less ▲]

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See detailCooperative Communications against Jamming with Half-Duplex and Full-Duplex Relaying
Zheng, Gan UL; Jorswieck, E.A.; Ottersten, Björn UL

in Vehicular Technology Conference (VTC Spring), 2013 IEEE 77th (2013)

This paper studies the impact of jamming on the design of three-node two-hop cooperative amplify-and-forward (AF) communications with both half-duplex and full-duplex relaying. For the half-duplex ... [more ▼]

This paper studies the impact of jamming on the design of three-node two-hop cooperative amplify-and-forward (AF) communications with both half-duplex and full-duplex relaying. For the half-duplex relaying, the jammer is smart such that it can optimally allocate jamming power between listening and forwarding phases. Given separate source and relay power constraints, we derive the optimal jamming power allocation; with a total source and relay power constraint, we model the interaction between the legitimate system and the jammer as a noncooperative game and prove the existence and uniqueness of the Nash Equilibrium (NE). It is found that due to the fact that the end performance is limited by the weaker phase, the legitimate systems tries to balance the performance of two phases while the jammer attacks the system by making the two hops imbalanced. While for the full-duplex relaying, we show that if the self-interference can be properly controlled, it can bring substantial performance gain. Simulation results verify our analysis. [less ▲]

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See detailDSTBC based DF cooperative networks in the presence of timing and frequency offsets
Nasir, A.A.; Mehrpouyan, H.; Durrani, S. et al

in Signal Processing Advances in Wireless Communications (SPAWC), 2013 IEEE 14th Workshop on (2013)

In decode-and-forward (DF) relaying networks, the received signal at the destination may be affected by multiple impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple ... [more ▼]

In decode-and-forward (DF) relaying networks, the received signal at the destination may be affected by multiple impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple carrier frequency offsets (MCFOs). This paper proposes novel optimal and sub-optimal minimum mean-square error (MMSE) receiver designs at the destination node to detect the signal in the presence of these impairments. Distributed space-time block codes (DSTBCs) are used at the relays to achieve spatial diversity. The proposed sub-optimal receiver uses the estimated values of multiple channel gains, MTOs, and MCFOs, while the optimal receiver assumes perfect knowledge of these impairments at the destination and serves as a benchmark performance measure. To achieve robustness to estimation errors, the estimates statistical properties are exploited at the destination. Simulation results show that the proposed optimal and sub-optimal MMSE compensation receivers achieve full diversity gain in the presence of channel and synchronization impairments in DSTBC based DF cooperative networks. [less ▲]

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See detailConnections between sparse estimation and robust statistical learning
Tsakonas, Efthymios; Jalden, J.; Sidiropoulos, N.D. et al

in Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on (2013)

Recent literature on robust statistical inference suggests that promising outlier rejection schemes can be based on accounting explicitly for sparse gross errors in the modeling, and then relying on ... [more ▼]

Recent literature on robust statistical inference suggests that promising outlier rejection schemes can be based on accounting explicitly for sparse gross errors in the modeling, and then relying on compressed sensing ideas to perform the outlier detection. In this paper, we consider two models for recovering a sparse signal from noisy measurements, possibly also contaminated with outliers. The models considered here are a linear regression model, and its natural one-bit counterpart where measurements are additionally quantized to a single bit. Our contributions can be summarized as follows: We start by providing conditions for identification and the Cramér-Rao Lower Bounds (CRLBs) for these two models. Then, focusing on the one-bit model, we derive conditions for consistency of the associated Maximum Likelihood estimator, and show the performance of relevant ℓ1-based relaxation strategies by comparing against the theoretical CRLB. [less ▲]

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See detailSecrecy sum-rate for orthogonal random beamforming with opportunistic scheduling
Krikidis, Ioannis; Ottersten, Björn UL

in IEEE Signal Processing Letters (2013), 2(20), 141-144

In this letter, we employ orthogonal random beamforming (ORBF) for the worst-case multi-user downlink scenario where each user is wiretapped by one eavesdropper. Two opportunistic scheduling techniques ... [more ▼]

In this letter, we employ orthogonal random beamforming (ORBF) for the worst-case multi-user downlink scenario where each user is wiretapped by one eavesdropper. Two opportunistic scheduling techniques that ensure confidentiality by exploiting multi-user diversity are investigated; the first technique (optimal) requires limited feedback of the effective signal-to-interference ratio (SIR) from all the users and the eavesdroppers while the second technique (suboptimal) incorporates SIR knowledge from only the legitimate users. By using extreme value theory, we derive the achievable SIR-based secrecy sum-rate and the associated scaling laws for both scheduling techniques. [less ▲]

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See detailSatellite Cognitive Communications and Spectrum Regulation
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Hofmann, Mahulena (Ed.) International Regulations of Space Communications (2013)

Due to rapid increase of wireless users and the popularity of multimedia applications, the demand for wireless spectrum is increasing rapidly. However, due to current static spectrum policy, the available ... [more ▼]

Due to rapid increase of wireless users and the popularity of multimedia applications, the demand for wireless spectrum is increasing rapidly. However, due to current static spectrum policy, the available usable spectrum is becoming scarce while a significant amount of spectrum remains underutilized. In this aspect, cognitive communications can be considered as a promising technology to enhance spectrum usage efficiency by allowing the coexistence of heterogeneous networks within the same spectrum. In this paper, starting with the rationale of cognitive communication, we present two different coexistence scenarios in the context of satellite cognitive communication. We then present the current status of spectrum regulation in the context of Cognitive Radio (CR) and the relevant decisions of World Radio Conference 2012 (WRC-12). Finally, we present the technical aspects and regulatory challenges of this technology and provide some suggestions from research, industrial and regulatory perspectives. [less ▲]

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See detailWeighted sum rate maximization for MIMO broadcast channels using dirty paper coding and zero-forcing methods
Le-Nam, Tran; Juntti, M.; Bengtsson, M. et al

in IEEE Transactions on Communications (2013), 6(61), 2362-2373

We consider precoder design for maximizing the weighted sum rate (WSR) of successive zero-forcing dirty paper coding (SZF-DPC). For this problem, the existing precoder designs often assume a sum power ... [more ▼]

We consider precoder design for maximizing the weighted sum rate (WSR) of successive zero-forcing dirty paper coding (SZF-DPC). For this problem, the existing precoder designs often assume a sum power constraint (SPC) and rely on the singular value decomposition (SVD). The SVD-based designs are known to be optimal but require high complexity. We first propose a low-complexity optimal precoder design for SZF-DPC under SPC, using the QR decomposition. Then, we propose an efficient numerical algorithm to find the optimal precoders subject to per-antenna power constraints (PAPCs). To this end, the precoder design for PAPCs is formulated as an optimization problem with a rank constraint on the covariance matrices. A well-known approach to solve this problem is to relax the rank constraints and solve the relaxed problem. Interestingly, for SZF-DPC, we are able to prove that the rank relaxation is tight. Consequently, the optimal precoder design for PAPCs is computed by solving the relaxed problem, for which we propose a customized interior-point method that exhibits a superlinear convergence rate. Two suboptimal precoder designs are also presented and compared to the optimal ones. We also show that the proposed numerical method is applicable for finding the optimal precoders for block diagonalization scheme. [less ▲]

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See detailReal-time depth enhancement by fusion for RGB-D cameras
Garcia Becerro, Frederic UL; Aouada, Djamila UL; Solignac, Thomas et al

in IET Computer Vision (2013), 7(5), 335345

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See detailMISO interference channel with QoS and RF energy harvesting constraints
Krikidis, I.; Timotheou, S.; Ottersten, Björn UL

in Communications (ICC), 2013 IEEE International Conference on (2013)

This paper deals with a multiple-input single-output (MISO) network where the receivers are characterized by both quality-of-service (QoS) and radio-frequency (RF) energy harvesting (EH) constraints. We ... [more ▼]

This paper deals with a multiple-input single-output (MISO) network where the receivers are characterized by both quality-of-service (QoS) and radio-frequency (RF) energy harvesting (EH) constraints. We consider the power splitting RF-EH technique where each receiver divides the received signal into two parts a) the first part for information decoding and b) the second part for battery charging. The minimum required energy that supports both the QoS and the RF-EH constraints at each receiver is formulated by an optimization problem and is discussed for two standard beamforming designs, the zero-forcing (ZF) and the maximum ratio transmission (MRT). The optimal solution for ZF beamforming is derived in closed-form, while optimization algorithms based on second-order cone programming (SOCP) and Linear Programming (LP) are developed for MRT beamforming to solve the problem. Numerical results indicate that MRT significantly outperforms ZF in terms of transmitted power, as the associated cross-interference becomes beneficial from an EH standpoint, while ZF always ensures the existence of a solution for the optimization problem considered. [less ▲]

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See detailOptimal training sequences for joint timing synchronization and channel estimation in distributed communication networks
Nasir, Ali A.; Mehrpouyan, Hani; Durrani, Salman et al

in IEEE Transactions on Communications (2013), 7(61), 3002-3015

For distributed multi-user and multi-relay cooperative networks, the received signal may be affected by multiple timing offsets (MTOs) and multiple channels that need to be jointly estimated for ... [more ▼]

For distributed multi-user and multi-relay cooperative networks, the received signal may be affected by multiple timing offsets (MTOs) and multiple channels that need to be jointly estimated for successful decoding at the receiver. This paper addresses the design of optimal training sequences for efficient estimation of MTOs and multiple channel parameters. A new hybrid Cramer-Rao lower bound (HCRB) for joint estimation of MTOs and channels is derived. Subsequently, by minimizing the derived HCRB as a function of training sequences, three training sequence design guidelines are derived and according to these guidelines, two training sequences are proposed. In order to show that the proposed design guidelines also improve estimation accuracy, the conditional Cramer-Rao lower bound (ECRB), which is a tighter lower bound on the estimation accuracy compared to the HCRB, is also derived. Numerical results show that the proposed training sequence design guidelines not only lower the HCRB, but they also lower the ECRB and the mean-square error of the proposed maximum a posteriori estimator. Moreover, extensive simulations demonstrate that application of the proposed training sequences significantly lowers the bit-error rate performance of multi-relay cooperative networks when compared to training sequences that violate these design guidelines. [less ▲]

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See detailData Aware User Selection in Cognitive Downlink MISO Precoding Systems
Alodeh, Maha UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings on Signal Processing and Information Technology (2013)

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See detailTransceiver design for distributed STBC based AF cooperative networks in the presence of timing and frequency offsets
Nasir, A.A.; Mehrpouyan, H.; Durrani, S. et al

in IEEE Transactions on Signal Processing (2013), 12(61), 3143-3158

In multi-relay cooperative systems, the signal at the destination is affected by impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple carrier frequency offsets (MCFOs ... [more ▼]

In multi-relay cooperative systems, the signal at the destination is affected by impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple carrier frequency offsets (MCFOs). In this paper we account for all these impairments and propose a new transceiver structure at the relays and a novel receiver design at the destination in distributed space-time block code (DSTBC) based amplify-and-forward (AF) cooperative networks. The Cramér-Rao lower bounds and a least squares (LS) estimator for the multi-parameter estimation problem are derived. In order to significantly reduce the receiver complexity at the destination, a differential evolution (DE) based estimation algorithm is applied and the initialization and constraints for the convergence of the proposed DE algorithm are investigated. In order to detect the signal from multiple relays in the presence of unknown channels, MTOs, and MCFOs, novel optimal and sub-optimal minimum mean-square error receiver designs at the destination node are proposed. Simulation results show that the proposed estimation and compensation methods achieve full diversity gain in the presence of channel and synchronization impairments in multi-relay AF cooperative networks. [less ▲]

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See detailBeamformer designs for MISO broadcast channels with zero-forcing dirty paper coding
Le-Nam, Tran; Juntti, M.; Bengtsson, M. et al

in IEEE Transactions on Wireless Communications (2013), 3(12), 1173-1185

We consider the beamformer design for multiple-input multiple-output (MISO) broadcast channels (MISO BCs) using zero-forcing dirty paper coding (ZF-DPC). Assuming a sum power constraint (SPC), most ... [more ▼]

We consider the beamformer design for multiple-input multiple-output (MISO) broadcast channels (MISO BCs) using zero-forcing dirty paper coding (ZF-DPC). Assuming a sum power constraint (SPC), most previously proposed beamformer designs are based on the QR decomposition (QRD), which is a natural choice to satisfy the ZF constraints. However, the optimality of the QRD-based design for ZF-DPC has remained unknown. In this paper, first, we analytically establish that the QRD-based design is indeed optimal for any performance measure under a SPC. Then, we propose an optimal beamformer design method for ZF-DPC with per-antenna power constraints (PAPCs), using a convex optimization framework. The beamformer design is first formulated as a rank-1-constrained optimization problem. Exploiting the special structure of the ZF-DPC scheme, we prove that the rank constraint can be relaxed and still provide the same solution. In addition, we propose a fast converging algorithm to the beamformer design problem, under the duality framework between the BCs and multiple access channels (MACs). More specifically, we show that a BC with ZF-DPC has the dual MAC with ZF-based successive interference cancellation (ZF-SIC). In this way, the beamformer design for ZF-DPC is transformed into a power allocation problem for ZF-SIC, which can be solved more efficiently. [less ▲]

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See detailDetection of pilot contamination attack using random training and massive MIMO
Kapetanovic, D.; Zheng, Gan UL; Wong et al

in Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on (2013)

Channel estimation attacks can degrade the performance of the legitimate system and facilitate eavesdropping. It is known that pilot contamination can alter the legitimate transmit precoder design and ... [more ▼]

Channel estimation attacks can degrade the performance of the legitimate system and facilitate eavesdropping. It is known that pilot contamination can alter the legitimate transmit precoder design and strengthen the quality of the received signal at the eavesdropper, without being detected. In this paper, we devise a technique which employs random pilots chosen from a known set of phase-shift keying (PSK) symbols to detect pilot contamination. The scheme only requires two training periods without any prior channel knowledge. Our analysis demonstrates that using the proposed technique in a massive MIMO system, the detection probability of pilot contamination attacks can be made arbitrarily close to 1. Simulation results reveal that the proposed technique can significantly increase the detection probability and is robust to noise power as well as the eavesdropper's power. [less ▲]

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See detailImproving Physical Layer Secrecy Using Full-Duplex Jamming Receivers
Zheng, Gan UL; Krikidis, Ioannis; Jiangyuan, Li et al

in IEEE Transactions on Signal Processing (2013), 20(61), 4962-4974

This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy ... [more ▼]

This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy performance as the system is interference-limited. In the literature, assuming that the receiver operates in half duplex (HD) mode, the aforementioned problem has been addressed via use of cooperating nodes who act as jammers to confound the eavesdropper. This paper investigates an alternative solution, which assumes the availability of a full duplex (FD) receiver. In particular, while receiving data, the receiver transmits jamming noise to degrade the eavesdropper channel. The proposed self-protection scheme eliminates the need for external helpers and provides system robustness. For the case in which global channel state information is available, we aim to design the optimal jamming covariance matrix that maximizes the secrecy rate and mitigates loop interference associated with the FD operation. We consider both fixed and optimal linear receiver design at the destination, and show that the optimal jamming covariance matrix is rank-1, and can be found via an efficient 1-D search. For the case in which only statistical information on the eavesdropper channel is available, the optimal power allocation is studied in terms of ergodic and outage secrecy rates. Simulation results verify the analysis and demonstrate substantial performance gain over conventional HD operation at the destination. [less ▲]

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See detailCooperative cognitive networks: Optimal, distributed and low-complexity algorithms
Zheng, Gan UL; Song, Shenghui; Wong, Kai-Kit et al

in IEEE Transactions on Signal Processing (2013), 11(61), 2778-2790

This paper considers the cooperation between a cognitive system and a primary system where multiple cognitive base stations (CBSs) relay the primary user's (PU) signals in exchange for more opportunity to ... [more ▼]

This paper considers the cooperation between a cognitive system and a primary system where multiple cognitive base stations (CBSs) relay the primary user's (PU) signals in exchange for more opportunity to transmit their own signals. The CBSs use amplify-and-forward (AF) relaying and coordinated beamforming to relay the primary signals and transmit their own signals. The objective is to minimize the overall transmit power of the CBSs given the rate requirements of the PU and the cognitive users (CUs). We show that the relaying matrices have unity rank and perform two functions: Matched filter receive beamforming and transmit beamforming. We then develop two efficient algorithms to find the optimal solution. The first one has a linear convergence rate and is suitable for distributed implementation, while the second one enjoys superlinear convergence but requires centralized processing. Further, we derive the beamforming vectors for the linear conventional zero-forcing (CZF) and prior zero-forcing (PZF) schemes, which provide much simpler solutions. Simulation results demonstrate the improvement in terms of outage performance due to the cooperation between the primary and cognitive systems. [less ▲]

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See detailDepth Super-Resolution by Enhanced Shift and Add
Al Ismaeil, Kassem UL; Aouada, Djamila UL; Mirbach, Bruno et al

in Computer Analysis of Images and Patterns, 15th International Conference, CAIP 2013, York, UK, August 27-29, 2013, Proceedings, Part II (2013)

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See detailMutli-Frame Super-Resolution by Enhanced Shift & Add
Al Ismaeil, Kassem UL; Aouada, Djamila UL; Mirbach, Bruno et al

in 8th International Symposium on Image and Signal Processing and Analysis (2013)

A critical step in multi-frame super-resolution is the registration of frames based on their motion. We improve the performance of current state-of-the-art super-resolution techniques by proposing a more ... [more ▼]

A critical step in multi-frame super-resolution is the registration of frames based on their motion. We improve the performance of current state-of-the-art super-resolution techniques by proposing a more robust and accurate registration as early as in the initialization stage of the high resolution estimate. Indeed, we solve the limitations on scale and motion inherent to the classical Shift & Add approach by upsampling the low resolution frames up to the super-resolution factor prior to estimating motion or to median filtering. This is followed by an appropriate selective optimization, leading to an enhanced Shift & Add. Quantitative and qualitative evaluations have been conducted at two levels; the initial estimation and the final optimized super-resolution. Results show that the proposed algorithm outperforms existing state-of-art methods. [less ▲]

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