![]() ; Christopoulos, Dimitrios ![]() ![]() in Wireless Communications, IEEE Transactions on (2014), 13(11), 6286-6299 Rain attenuation is among the major impairments for satellite systems operating in the K-band and above. In this paper, we investigate the impact of spatially correlated rain attenuation on the ... [more ▼] Rain attenuation is among the major impairments for satellite systems operating in the K-band and above. In this paper, we investigate the impact of spatially correlated rain attenuation on the performance of a multibeam satellite return link. For a comprehensive assessment, an analytical model for the antenna pattern that generates the beams is also proposed. We focus on the outage capacity of the link and obtain analytical approximations at high and low signal-to-noise ratio. The derived approximations provide insights into the effect of key system parameters such as the interuser distance, the satellite beam radius, or the rain intensity, and simulation results show that it fits tightly with the Monte Carlo results. Additionally, the derived expressions can be easily particularized for the single-user case, providing some novel insights. [less ▲] Detailed reference viewed: 189 (21 UL)![]() Aouada, Djamila ![]() ![]() in 11th IEEE International Conference on Advanced Video and Signal-Based Surveillance (AVSS'14) (2014) We address the limitation of low resolution depth cameras in the context of face recognition. Considering a face as a surface in 3-D, we reformulate the recently proposed Upsampling for Precise ... [more ▼] We address the limitation of low resolution depth cameras in the context of face recognition. Considering a face as a surface in 3-D, we reformulate the recently proposed Upsampling for Precise Super–Resolution algorithm as a new approach on three dimensional points. This reformulation allows an efficient implementation, and leads to a largely enhanced 3-D face reconstruction. Moreover, combined with a dedicated face detection and representation pipeline, the proposed method provides an improved face recognition system using low resolution depth cameras. We show experimentally that this system increases the face recognition rate as compared to directly using the low resolution raw data. [less ▲] Detailed reference viewed: 250 (31 UL)![]() Correa Bahnsen, Alejandro ![]() ![]() ![]() in Proceedings of the fourteenth SIAM International Conference on Data Mining, Philadelphia, Pennsylvania, USA, April 24-26, 2014. (2014) Previous analysis has shown that applying Bayes minimum risk to detect credit card fraud leads to better results measured by monetary savings, as compared with traditional methodologies. Nevertheless ... [more ▼] Previous analysis has shown that applying Bayes minimum risk to detect credit card fraud leads to better results measured by monetary savings, as compared with traditional methodologies. Nevertheless, this approach requires good probability estimates that not only separate well between positive and negative examples, but also assess the real probability of the event. Unfortunately, not all classification algorithms satisfy this restriction. In this paper, two different methods for calibrating probabilities are evaluated and analyzed in the context of credit card fraud detection, with the objective of finding the model that minimizes the real losses due to fraud. Even though under-sampling is often used in the context of classification with unbalanced datasets, it is shown that when probabilistic models are used to make decisions based on minimizing risk, using the full dataset provides significantly better results. In order to test the algorithms, a real dataset provided by a large European card processing company is used. It is shown that by calibrating the probabilities and then using Bayes minimum Risk the losses due to fraud are reduced. Furthermore, because of the good overall results, the aforementioned card processing company is currently incorporating the methodology proposed in this paper into their fraud detection system. Finally, the methodology has been tested on a different application, namely, direct marketing. [less ▲] Detailed reference viewed: 566 (34 UL)![]() Afzal, Hassan ![]() ![]() ![]() in Second International Conference on 3D Vision (2014) In this work we propose KinectDeform, an algorithm which targets enhanced 3D reconstruction of scenes containing non-rigidly deforming objects. It provides an innovation to the existing class of ... [more ▼] In this work we propose KinectDeform, an algorithm which targets enhanced 3D reconstruction of scenes containing non-rigidly deforming objects. It provides an innovation to the existing class of algorithms which either target scenes with rigid objects only or allow for very limited non-rigid deformations or use pre-computed templates to track them. KinectDeform combines a fast non-rigid scene tracking algorithm based on octree data representation and hierarchical voxel associations with a recursive data filtering mechanism. We analyze its performance on both real and simulated data and show improved results in terms of smoothness and feature preserving 3D reconstructions with reduced noise. [less ▲] Detailed reference viewed: 483 (64 UL)![]() ; Chatzinotas, Symeon ![]() ![]() in IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS (2014), 14(9), 4695--4707 The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to ... [more ▼] The present work focuses on the forward link of a broadband multibeam satellite system that aggressively reuses the user link frequency resources. Two fundamental practical challenges, namely the need to frame multiple users per transmission and the per-antenna transmit power limitations, are addressed. To this end, the so-called frame-based precoding problem is optimally solved using the principles of physical layer multicasting to multiple co-channel groups under per-antenna constraints. In this context, a novel optimization problem that aims at maximizing the system sum rate under individual power constraints is proposed. Added to that, the formulation is further extended to include availability constraints. As a result, the high gains of the sum rate optimal design are traded off to satisfy the stringent availability requirements of satellite systems. Moreover, the throughput maximization with a granular spectral efficiency versus SINR function, is formulated and solved. Finally, a multicast-aware user scheduling policy, based on the channel state information, is developed. Thus, substantial multiuser diversity gains are gleaned. Numerical results over a realistic simulation environment exhibit as much as 30% gains over conventional systems, even for 7 users per frame, without modifying the framing structure of legacy communication standards. [less ▲] Detailed reference viewed: 185 (5 UL)![]() Kapetanovic, Dzevdan ![]() ![]() ![]() in ICC 2014 (2014) Distributed storage systems have been receiving increasing attention lately due to the developments in cloud and grid computing. Furthermore, a major part of the stored information comprises of multimedia ... [more ▼] Distributed storage systems have been receiving increasing attention lately due to the developments in cloud and grid computing. Furthermore, a major part of the stored information comprises of multimedia, whose content can be communicated even with a lossy (non-perfect) reconstruction. In this context, Multiple Description Lattice Quantizers (MDLQ) can be employed to encode such sources for distributed storage and store them across distributed nodes. Their inherent properties yield that having access to all nodes gives perfect reconstruction of the source, while the reconstruction quality decreases gracefully with fewer available nodes. If a set of nodes fails, lossy repair techniques could be applied to reconstruct the failed nodes from the available ones. This problem has mostly been studied with the lossless (perfect) reconstruction assumption. In this work, a general model, Multiple Description Lattice Quantizer with Repairs (MDLQR), is introduced that encompasses the lossy repair problem for distributed storage applications. New performance measures and repair techniques are introduced for MDLQR, and a non-trivial identity is derived, which is related to other results in the literature. This enables us to find the optimal encoder for a certain repair technique used in the MDLQR. Furthermore, simulation results are used to evaluate the performance of the different repair techniques. © 2014 IEEE. [less ▲] Detailed reference viewed: 169 (0 UL)![]() Tsakmalis, Anestis ![]() ![]() ![]() in Proceedings of 7th Advanced Satellite Multimedia Systems Conference (ASMS) and 13th Signal Processing for Space Communications Workshop (SPSC) 2014 (2014) Detailed reference viewed: 299 (22 UL)![]() ; ; Ottersten, Björn ![]() in arXiv preprint arXiv:1404.6544 (2014) The recent commercial trends towards using smaller dish antennas for satellite receivers, and the growing density of broadcasting satellites, necessitate the application of robust adjacent satellite ... [more ▼] The recent commercial trends towards using smaller dish antennas for satellite receivers, and the growing density of broadcasting satellites, necessitate the application of robust adjacent satellite interference (ASI) cancellation schemes. This orbital density growth along with the wider beamwidth of a smaller dish have imposed an overloaded scenario at the satellite receiver, where the number of transmitting satellites exceeds the number of receiving elements at the dish antenna. To ensure successful operation in this practical scenario, we propose a satellite receiver that enhances signal detection from the desired satellite by mitigating the interference from neighboring satellites. Towards this objective, we propose a reduced complexity list-based group-wise search detection (RC-LGSD) receiver under the assumption of spatially correlated additive noise. To further enhance detection performance, the proposed satellite receiver utilizes a newly designed whitening filter to remove the spatial correlation amongst the noise parameters, while also applying a preprocessor that maximizes the signal-to-interference-plus-noise ratio (SINR). Extensive simulations under practical scenarios show that the proposed receiver enhances the performance of satellite broadcast systems in the presence of ASI compared to existing methods [less ▲] Detailed reference viewed: 132 (13 UL)![]() ; ; Ottersten, Björn ![]() in IEEE Signal Processing Magazine (2014), 31(4), 142-148 Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the ... [more ▼] Transmit beamforming is a versatile technique for signal transmission from an array of antennas to one or multiple users [1]. In wireless communications, the goal is to increase the signal power at the intended user and reduce interference to nonintended users. A high signal power is achieved by transmitting the same data signal from all antennas but with different amplitudes and phases, such that the signal components add coherently at the user. Low interference is accomplished by making the signal components add destructively at nonintended users. This corresponds mathematically to designing beamforming vectors (that describe the amplitudes and phases) to have large inner products with the vectors describing the intended channels and small inner products with nonintended user channels. [less ▲] Detailed reference viewed: 312 (18 UL)![]() Ottersten, Björn ![]() ![]() in IEEE Global Telecommunications Conference (GLOBECOM) (2013, December) Detailed reference viewed: 175 (2 UL)![]() Sharma, Shree Krishna ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 328 (25 UL)![]() Sharma, Shree Krishna ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 267 (28 UL)![]() Sharma, Shree Krishna ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 325 (45 UL)![]() Kapetanovic, Dzevdan ![]() ![]() 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 ▲] Detailed reference viewed: 194 (1 UL)![]() Kapetanovic, Dzevdan ![]() ![]() 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 ▲] Detailed reference viewed: 183 (1 UL)![]() Al Ismaeil, Kassem ![]() ![]() 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 ▲] Detailed reference viewed: 263 (23 UL)![]() Sharma, Shree Krishna ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 407 (17 UL)![]() Chatzinotas, Symeon ![]() ![]() ![]() 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 ▲] Detailed reference viewed: 222 (15 UL)![]() ; ; Ottersten, Björn ![]() in IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) (2013, September) Detailed reference viewed: 169 (3 UL)![]() Chatzinotas, Symeon ![]() ![]() in Proc of Asia-Pacific Conference on Communications, APCC 2013 (2013, August) Detailed reference viewed: 121 (1 UL) |
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