References of "Ottersten, Björn 50002797"
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See detailMultiobjective Signal Processing Optimization : The way to balance conflicting metrics in 5G systems
Bjornson, Emil; Jorswieck; Debbah et al

in IEEE Signal Processing Magazine (2014), 31(6), 14-23

The evolution of cellular networks is driven by the dream of ubiquitous wireless connectivity: any data service is instantly accessible everywhere. With each generation of cellular networks, we have moved ... [more ▼]

The evolution of cellular networks is driven by the dream of ubiquitous wireless connectivity: any data service is instantly accessible everywhere. With each generation of cellular networks, we have moved closer to this wireless dream; first by delivering wireless access to voice communications, then by providing wireless data services, and recently by delivering a Wi-Fi-like experience with wide-area coverage and user mobility management. The support for high data rates has been the main objective in recent years [1], as seen from the academic focus on sum-rate optimization and the efforts from standardization bodies to meet the peak rate requirements specified in IMT-Advanced. In contrast, a variety of metrics/objectives are put forward in the technological preparations for fifth-generation (5G) networks: higher peak rates, improved coverage with uniform user experience, higher reliability and lower latency, better energy efficiency (EE), lower-cost user devices and services, better scalability with number of devices, etc. These multiple objectives are coupled, often in a conflicting manner such that improvements in one objective lead to degradation in the other objectives. Hence, the design of future networks calls for new optimization tools that properly handle the existence of multiple objectives and tradeoffs between them. [less ▲]

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See detailCPU-based real-time surface and solid voxelization for incomplete point cloud
Garcia, Frederic D.; Ottersten, Björn UL

in Proceedings of the 22nd International Conference on Pattern Recognition (2014)

This paper presents a surface and solid voxelization approach for incomplete point cloud datasets. Voxelization stands for a discrete approximation of 3-D objects into a volumetric representation, a ... [more ▼]

This paper presents a surface and solid voxelization approach for incomplete point cloud datasets. Voxelization stands for a discrete approximation of 3-D objects into a volumetric representation, a process which is commonly employed in computer graphics and increasingly being used in computer vision. In contrast to surface voxelization, solid voxelization not only set those voxels related to the object surface but also those voxels considered to be inside the object. To that end, we first approximate the given point set, usually describing the external object surface, to an axis-aligned voxel grid. Then, we slice-wise construct a shell containing all surface voxels along each grid-axis pair. Finally, voxels inside the constructed shell are set. Solid voxelization results from the combination of all slices, resulting in a watertight and gap-free representation of the object. The experimental results show a high performance when voxelizing point cloud datasets, independently of the object's complexity, robust to noise, and handling large portions of data missing. © 2014 IEEE. [less ▲]

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See detailFull frequency reuse multibeam satcoms: frame based precoding and user scheduling
Christopoulos, Dimitrios; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2014)

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See detailCompressive Sparsity Order Estimation for Wideband Cognitive Radio Receiver
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2014)

Compressive Sensing (CS) has been widely investigated in the Cognitive Radio (CR) literature in order to reduce the hardware cost of sensing wideband signals assuming prior knowledge of the sparsity ... [more ▼]

Compressive Sensing (CS) has been widely investigated in the Cognitive Radio (CR) literature in order to reduce the hardware cost of sensing wideband signals assuming prior knowledge of the sparsity pattern. However, the sparsity order of the channel occupancy is time-varying and the sampling rate of the CS receiver needs to be adjusted based on its value in order to fully exploit the potential of CS-based techniques. In this context, investigating blind Sparsity Order Estimation (SOE) techniques is an open research issue. To address this, we study an eigenvalue-based compressive SOE technique using asymptotic Random Matrix Theory. We carry out detailed theoretical analysis for the signal plus noise case to derive the asymptotic eigenvalue probability distribution function (aepdf) of the measured signal’s covariance matrix for sparse signals. Subsequently, based on the derived aepdf expressions, we propose a technique to estimate the sparsity order of the wideband spectrum with compressive measurements using the maximum eigenvalue of the measured signal’s covariance matrix. The performance of the proposed technique is evaluated in terms of normalized SOE Error (SOEE). It is shown that the sparsity order of the wideband spectrum can be reliably estimated using the proposed technique for a variety of scenarios. [less ▲]

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See detailSNR Estimation for Multi-dimensional Cognitive Receiver under Correlated Channel/Noise
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2013), 12(12), 6392-6405

In addition to Spectrum Sensing (SS) capability required by a Cognitive Radio (CR), Signal to Noise Ratio (SNR) estimation of the primary signals at the CR receiver is crucial in order to adapt its ... [more ▼]

In addition to Spectrum Sensing (SS) capability required by a Cognitive Radio (CR), Signal to Noise Ratio (SNR) estimation of the primary signals at the CR receiver is crucial in order to adapt its coverage area dynamically using underlay techniques. In practical scenarios, channel and noise may be correlated due to various reasons and SNR estimation techniques with the assumption of white noise and uncorrelated channel may not be suitable for estimating the primary SNR. In this paper, firstly, we study the performance of different eigenvaluebased SS techniques in the presence of channel or/and noise correlation. Secondly, we carry out detailed theoretical analysis of the signal plus noise hypothesis to derive the asymptotic eigenvalue probability distribution function (a.e.p.d.f.) of the received signal’s covariance matrix under the following two cases: (i) correlated channel and white noise, and (ii) correlated channel and correlated noise, which is the main contribution of this paper. Finally, an SNR estimation technique based on the derived a.e.p.d.f is proposed in the presence of channel/noise correlation and its performance is evaluated in terms of normalized Mean Square Error (MSE). It is shown that the PU SNR can be reliably estimated when the CR sensing module is aware of the channel/noise correlation. [less ▲]

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See detailProtocols and Stability Analysis for Energy Harvesting TDMA Systems with/without Relaying
Ottersten, Björn UL; Krikidis, Ioannis; Zheng, Gan UL

in IEEE Global Telecommunications Conference (GLOBECOM) (2013, December)

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See detailEigenvalue Based Sensing and SNR Estimation for Cognitive Radio in Presence of Noise Correlation
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in IEEE Transactions on Vehicular Technology (2013), 62(8), 3671-3684

Herein, we present a detailed analysis of an eigenvalue based sensing technique in the presence of correlated noise in the context of a Cognitive Radio (CR). We use a Standard Condition Number (SCN) based ... [more ▼]

Herein, we present a detailed analysis of an eigenvalue based sensing technique in the presence of correlated noise in the context of a Cognitive Radio (CR). We use a Standard Condition Number (SCN) based decision statistic based on asymptotic Random Matrix Theory (RMT) for decision process. Firstly, the effect of noise correlation on eigenvalue based Spectrum Sensing (SS) is studied analytically under both the noise only and the signal plus noise hypotheses. Secondly, new bounds for the SCN are proposed for achieving improved sensing in correlated noise scenarios. Thirdly, the performance of Fractional Sampling (FS) based SS is studied and a method for determining the operating point for the FS rate in terms of sensing performance and complexity is suggested. Finally, a Signal to Noise Ratio (SNR) estimation technique based on the maximum eigenvalue of the received signal’s covariance matrix is proposed. It is shown that proposed SCN-based threshold improves sensing performance in correlated noise scenarios and SNRs up to 0 dB can be reliably estimated with less than 1 % normalized Mean Square Error (MSE) in the presence of correlated noise without the knowledge of noise variance. [less ▲]

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See detailInline Interference Mitigation Techniques for Spectral Coexistence of GEO and NGEO Satellites
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of 19th ka band and 31st AIAA ICSSC conference (2013, October)

The requirement of low latency for real time systems and high demand of broad- band data are leading to the rapid deployment of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellite systems in several ... [more ▼]

The requirement of low latency for real time systems and high demand of broad- band data are leading to the rapid deployment of Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) satellite systems in several frequency bands. When the number of usable non-geostationary (NGEO) satellites i.e., LEO/MEO in space increases, the need for frequency coexistence between the NGEO satellite systems with the already existing geostationary (GEO) satellite networks increases rapidly. In this context, it is crucial to explore interference mitigation techniques between GEO and NGEO systems in order to allow their spectral coexistence. More specifically, in the coexistence scenario of GEO and NGEO satellite networks, in-line interfer- ence may be a serious problem and it arises whenever an NGEO satellite passes through a line of sight path between a GEO earth station and a GEO satellite. In this paper, we carry out interference analysis between GEO and NGEO systems considering the case of O3b satellite systems and propose an adaptive power control technique for both the uplink and the downlink coexistence scenarios in order to mitigate the in-line interference. Furthermore, we provide several cognitive solu- tions for mitigating the in-line interference. [less ▲]

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See detailDetection of Pilot Contamination Attack Using Random Training and Massive MIMO
Kapetanovic, Dzevdan UL; Zheng, Gan UL; Wong, Kai-Kit et al

in IEEE Personal Indoor, Mobile and Radio Conference (PIMRC) 2013 (2013, September 09)

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 detailSecondary User Scheduling Under Throughput Guarantees for the Primary Network
Kapetanovic, Dzevdan UL; Butt, Majid; Chatzinotas, Symeon UL et al

in IEEE Vehicular Technology Conference (VTC), Fall 2013 (2013, September 02)

This work addresses scheduling in a cognitive radio scenario where a minimum throughput for the downlink primary network (PN) is guaranteed to each user with an associated violation probability ... [more ▼]

This work addresses scheduling in a cognitive radio scenario where a minimum throughput for the downlink primary network (PN) is guaranteed to each user with an associated violation probability (probability of not obtaining the guaranteed throughput). The primary network is surrounded by multiple downlink secondary networks, each aiming to maximize its network throughput. Scheduling in PN is performed independent of the secondary networks. Some information about the PN is available at the central scheduler that is responsible for scheduling the secondary networks. The contribution of this work is to apply a novel scheduler to the PN which is more robust to QoS degradations resulting from the secondary networks than other state of the art schedulers. This is validated by numerical simulations of the cognitive radio network. [less ▲]

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See detailMaximizing Energy Efficiency for Loss Tolerant Applications: The Packet Buffering Case
Butt, Majid; Jorswieck, Eduard A.; Ottersten, Björn UL

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

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See detailFrequency Packing for Interference Alignment-based Cognitive Dual Satellite Systems
Chatzinotas, Symeon UL; Sharma, Shree Krishna UL; Ottersten, Björn UL

in Proceedings of IEEE 78th Vehicular Technology Conference: VTC2013-Fall (2013, September)

Interference Alignment (IA) has been considered a promising technique for spectral coexistence of different wireless systems in an underlay cognitive mode. Furthermore, Frequency Packing (FP) can be ... [more ▼]

Interference Alignment (IA) has been considered a promising technique for spectral coexistence of different wireless systems in an underlay cognitive mode. Furthermore, Frequency Packing (FP) can be considered as an important technique for enhancing the spectrum efficiency in spectrum-limited satellite applications. In this paper, we consider a spectral coexistence scenario of a multibeam satellite and a monobeam satellite with the monobeam satellite as primary and the multibeam satellite as secondary. In this context, this paper focuses on examining the effect of FP on the performance of multi-carrier based IA technique. For this purpose, different IA techniques such as coordinated IA, uncoordinated IA and static IA have been considered. The effect of FP on the performance of different IA techniques in the considered scenario is evaluated in terms of system sum rate and primary rate protection ratio. It is shown that the system sum rate increases with the FP factor for all the techniques and the primary rate is perfectly protected with the coordinated IA technique even with dense FP. [less ▲]

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See detailCognitive Radio Techniques for Satellite Communication Systems
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of IEEE 78th Vehicular Technology Conference: VTC2013-Fall (2013, September)

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast, multimedia and interactive services. In this context, cognitive satellite communications has received ... [more ▼]

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast, multimedia and interactive services. In this context, cognitive satellite communications has received important attention lately in the research community. Exploring efficient spectrum sharing techniques for enhancing spectral efficiency in satellite communication has become an important research challenge. In this paper, we study the main aspects of satellite cognitive communications and present possible practical scenarios for hybrid/dual cognitive satellite systems. Furthermore, suitable cognitive techniques for the considered scenarios are identified. More specifically, Spectrum Sensing (SS), interference modeling, and beamforming techniques are discussed for hybrid cognitive scenario and SS, interference alignment, and cognitive beamhopping techniques are discussed for dual satellite systems. This paper concludes by providing interesting open research issues in this domain. [less ▲]

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See detailDynamic Super Resolution of Depth Sequences with Non-Rigid Motions
Al Ismaeil, Kassem UL; Aouada, Djamila UL; Mirbach, Bruno et al

in 20th International Conference on Image Processing (2013, September)

We enhance the resolution of depth videos acquired with low resolution time-of-flight cameras. To that end, we propose a new dedicated dynamic super-resolution that is capable to accurately super-resolve a ... [more ▼]

We enhance the resolution of depth videos acquired with low resolution time-of-flight cameras. To that end, we propose a new dedicated dynamic super-resolution that is capable to accurately super-resolve a depth sequence containing one or multiple moving objects without strong constraints on their shape or motion, thus clearly outperforming any existing super-resolution techniques that perform poorly on depth data and are either restricted to global motions or not precise because of an implicit estimation of motion. Our proposed approach is based on a new data model that leads to a robust registration of all depth frames after a dense upsampling. The texture-less nature of depth images allows to robustly handle sequences with multiple moving objects as confirmed by our experiments. [less ▲]

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See detailMMSE Filtering for Amplify & Forward SIMO Multiple Access Channel with Ill-conditioned Second Hop
Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proc of Asia-Pacific Conference on Communications, APCC 2013 (2013, August)

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See detailGateway Switching in Q/V Band Satellite Feeder Links
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Panagopoulos, Athanasios et al

in IEEE Communications Letters (2013), 17(7), 1384-1387

A main challenge towards realizing the next generation Terabit/s broadband satellite communications (SatCom) is the limited spectrum available in the Ka band. An attractive solution is to move the feeder ... [more ▼]

A main challenge towards realizing the next generation Terabit/s broadband satellite communications (SatCom) is the limited spectrum available in the Ka band. An attractive solution is to move the feeder link to the higher Q/V band, where more spectrum is available. When utilizing the Q/V band, due to heavy rain attenuation, gateway diversity is considered a necessity to ensure the required feeder link availability. Although receive site diversity has been studied in the past for SatCom, there is much less maturity in terms of transmit diversity techniques. In this paper, a modified switch and stay combining scheme is proposed for a Q/V band feeder link, but its performance is also evaluated over an end-to-end satellite link. The proposed scheme is pragmatic and has close to optimal performance with notably lower complexity. [less ▲]

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See detailCognitive Beamhopping for Spectral Coexistence of Multibeam Satellites
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Future Network and MobileSummit 2013 (2013, July)

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast and multimedia services. In this context, we consider the problem of enhancing spectral efficiency in ... [more ▼]

The usable satellite spectrum is becoming scarce due to continuously increasing demand for broadcast and multimedia services. In this context, we consider the problem of enhancing spectral efficiency in multibeam satellite networks. The spectral coexistence scenario of two multibeam satellites over a common coverage area is studied with a primary satellite having larger beams and a secondary satellite having smaller beams. Furthermore, a novel cognitive beamhopping satellite system is proposed. The system performance of the proposed system is evaluated and compared with that of conventional multibeam and beamhopping systems in terms of system throughput. It is shown that the proposed system significantly enhances the spectral efficiency in comparison to other systems. Moreover, the scenario of the presence of multiple secondary users within an inactive primary beam is considered with power control on the secondary transmission. The system performance is evaluated by considering partial and full frequency sharing approaches. It is noted that the total spectral efficiency increases with the number of secondary users in the full frequency reuse approach. [less ▲]

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See detailTransmit Beamforming for Spectral Coexistence of Satellite and Terrestrial Networks
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in Proceedings of 8th International Conference on Cognitive Radio Oriented Wireless Networks 2013 (2013, July)

Herein, we study transmit beamforming techniques in an underlay cognitive mode for the coexistence of satellite and terrestrial networks with the satellite forward link as primary and the terrestrial ... [more ▼]

Herein, we study transmit beamforming techniques in an underlay cognitive mode for the coexistence of satellite and terrestrial networks with the satellite forward link as primary and the terrestrial downlink as secondary. Since geostationary satellite terminals have predetermined propagation characteristics so that they always point towards the geostationary satellite, the interference received by the satellite terminals from the terrestrial Base Station (BS) is confined in an angular sector. Based on this a priori knowledge, we propose transmit beamforming techniques at the BS to maximize the Signal to Interference plus Noise Ratio (SINR) towards the desired secondary user and to mitigate the interference towards the primary satellite terminals. Different types of Linearly Constrained Minimum Variance (LCMV) techniques have been proposed for our considered scenario where the exact locations and the number of satellite terminals within a specific angular sector are not known while designing the beamformer. Furthermore, an optimization problem is formulated for maximizing the Secondary User (SU) rate and it is shown that the worst case SU rate depends on the Primary User (PU) distance, PU interference threshold and the angular separation of the desired SU from the region of interest. [less ▲]

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See detailData Predistortion for Multicarrier Satellite Channels using Orthogonal Memory polynomials
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in International Workshop on Signal Processing Advances for Wireless Communications (2013) (2013, June 16)

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See detailSpatial Filtering for Underlay Cognitive SatComs
Sharma, Shree Krishna UL; Chatzinotas, Symeon UL; Ottersten, Björn UL

in proceedings of 5th International Conference on Personal Satellite Services (2013, June)

Herein, we study an underlay beamforming technique for the coexistence scenario of satellite and terrestrial networks with the satel- lite return link as primary and the terrestrial uplink as secondary ... [more ▼]

Herein, we study an underlay beamforming technique for the coexistence scenario of satellite and terrestrial networks with the satel- lite return link as primary and the terrestrial uplink as secondary. Since satellite terminals are unique in that they always point towards the geo- stationary satellite, interference received by the terrestrial Base Station (BS) is concentrated in a specific angular sector. The priori knowledge that all the geostationary satellite terminals are facing south for the European coverage can be used in designing a beamformer at the ter- restrial BS. Based on this concept, we propose a receive beamformer at the BS to maximize the Signal to Interference plus Noise Ratio (SINR) towards the desired user and to mitigate the interference coming from the interfering satellite terminals. The performances of Minimum Vari- ance Distortionless (MVDR) and Linear Constrained Minimum Variance (LCMV) beamformers are compared for our considered scenario. It is shown that LCMV beamformer is better suited in rejecting interference even in case of Direction of Arrival (DoA) uncertainty of interfering satel- lite terminals as long as DoA range of the interfering sector is known to the beamformer. Furthermore, it is noted that MVDR beamformer is suitable for a large number of interferers. [less ▲]

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