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  • 1. Abdu, Tedros Salih
    et al.
    Kisseleff, Steven
    Lagunas, Eva
    Chatzinotas, Symeon
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg, Luxembourg.
    Demand and Interference Aware Adaptive Resource Management for High Throughput GEO Satellite Systems2022In: IEEE Open Journal of the Communications Society, E-ISSN 2644-125X, Vol. 3, p. 759-775Article in journal (Refereed)
    Abstract [en]

    The scarce spectrum and power resources, the inter-beam interference, together with the high traffic demand, pose new major challenges for the next generation of Very High Throughput Satellite (VHTS) systems. Accordingly, future satellites are expected to employ advanced resource/interference management techniques to achieve high system spectrum efficiency and low power consumption while ensuring user demand satisfaction. This paper proposes a novel demand and interference aware adaptive resource management for geostationary (GEO) VHTS systems. For this, we formulate a multi-objective optimization problem to minimize the total transmit power consumption and system bandwidth usage while matching the offered capacity with the demand per beam. In this context, we consider resource management for a system with full-precoding, i.e., all beams are precoded; without precoding, i.e., no precoding is applied to any beam; and with partial precoding, i.e., only some beams are precoded. The nature of the problem is non-convex and we solve it by jointly using the Dinkelbach and Successive Convex Approximation (SCA) methods. The simulation results show that the proposed method outperforms the benchmark schemes. Specifically, we show that the proposed method requires low resource consumption, low computational time, and simultaneously achieves a high demand satisfaction.

  • 2. Abdu, Tedros Salih
    et al.
    Kisseleff, Steven
    Lagunas, Eva
    Grotz, Joel
    Chatzinotas, Symeon
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg, Luxembourg.
    Demand-Aware Onboard Payload Processor Management for High Throughput NGSO Satellite Systems2023In: IEEE Transactions on Aerospace and Electronic Systems, ISSN 00189251, p. 1-18Article in journal (Refereed)
    Abstract [en]

    High-Throughput Satellite (HTS) systems with digital payload technology have been identified as a key enabler to support 5G/6G high-data connectivity with wider coverage area. The satellite community has extensively explored resource allocation methods to achieve this target. Typically, these methods do not consider the intrinsic architecture of the flexible satellite digital payload, which consists of multiple processors responsible for receiving, processing, and transmitting the signals. This paper presents a demand-aware onboard processor management scheme for broadband Non-Geostationary (NGSO) satellites. In this context, we formulate an optimization problem to minimize the number of active on-board processors while meeting the system constraints and user requirements. As the problem is non-convex, we solve it in two steps. First, we transform the problem into demand-driven bandwidth allocation while fixing the number of processors. Second, using the bandwidth allocation solution, we determine the required number of processors with two methods: 1) sequential optimization with the Branch & Bound method and 2) Bin Packing with Next Fit, First Fit, and Best Fit methods. Finally, we demonstrate the proposed methods with extensive numerical results. It is shown that the Branch & Bound, Best Fit, and First Fit methods manage the processors better than the Next Fit method. Furthermore, Branch & Bound requires fewer processors than the above methods.

  • 3. Abdullah, Zaid
    et al.
    Kisseleff, Steven
    Alves Martins, Wallace
    Chen, Gaojie
    Sanguinetti, Luca
    Ntontin, Konstantinos
    Papazafeiropoulos, Anastasios
    Chatzinotas, Symeon
    Ottersten, Björn
    University of Luxembourg, Luxembourg.
    Cooperative Hybrid Networks with Active Relays and RISs for B5G: Applications, Challenges, and Research Directions2022In: IEEE Wireless Communications, ISSN 15361284, p. 1-7Article in journal (Refereed)
    Abstract [en]

    Among the recent advances and innovations in wireless technologies, reconfigurable intelligent surfaces (RISs) have received much attention and are envisioned to be one of the enabling technologies for beyond 5G (B5G) networks. On the other hand, active (or classical) cooperative relays have played a key role in providing reliable and power-efficient communications in previous wireless generations. In this article, we focus on hybrid network architectures that amalgamate both active relays and RISs. The operation concept and protocols of each technology are first discussed. Subsequently, we present multiple use cases of cooperative hybrid networks where both active relays and RISs can coexist harmoniously for enhanced rate performance. Furthermore, a case study is provided which demonstrates the achievable rate performance of a communication network assisted by either an active relay, an RIS, or both, and with different relaying protocols. Finally, we provide the reader with the challenges and key research directions in this area.

  • 4.
    Abdullah, Zaid
    et al.
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Papazafeiropoulos, Anastasios
    Communications and Intelligent Systems Research Group, University of Hertfordshire, Hatfield AL10 9AB, U.K., and also with the SnT, University of Luxembourg, Luxembourg..
    Kisseleff, Steven
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Chatzinotas, Symeon
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (Sn T), University of Luxembourg, L-1855, Luxembourg..
    Impact of Phase-Noise and Spatial Correlation on Double-RIS-Assisted Multiuser MISO Networks2022In: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, p. 1-1Article in journal (Refereed)
  • 5. Abu-Shaban, Z.
    et al.
    Bhavani Shankar Mysore, R.
    Mehrpouyan, H.
    Ottersten, Björn
    SnT - Univ. of Luxembourg, Luxembourg, Luxembourg.
    Enhanced List-based Group-wise overloaded receiver with application to satellite reception2014In: 2014 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2014, p. 5616-5621Conference paper (Refereed)
    Abstract [en]

    The market trends towards the use of smaller dish antennas for TV satellite receivers, as well as the growing density of broadcasting satellites in orbit require the application of robust adjacent satellite interference (ASI) cancellation algorithms at the receivers. The wider beamwidth of a small size dish and the growing number of satellites in orbit impose an overloaded scenario, i.e., a scenario where the number of transmitting satellites exceeds the number of receiving antennas. For such a scenario, we present a two stage receiver to enhance signal detection from the satellite of interest, i.e., the satellite that the dish is pointing to, while reducing interference from neighboring satellites. Towards this objective, we propose an enhanced List-based Group-wise Search Detection (LGSD) receiver architecture that takes into account the spatially correlated additive noise and uses the signal-to-interference-plus-noise ratio (SINR) maximization criterion to improve detection performance. Simulations show that the proposed receiver structure enhances the performance of satellite systems in the presence of ASI when compared to existing methods.

  • 6. Abu-Shaban, Z.
    et al.
    Mehrpouyan, H.
    Grotz, J.
    Ottersten, Björn
    SnT - University of Luxembourg, Luxembourg .
    Overloaded satellite receiver using SIC with hybrid beamforming and ML detection2013In: 2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications (SPAWC), New York: IEEE , 2013, p. 450-454Conference paper (Refereed)
    Abstract [en]

    In this paper, a new receiver structure that is intended to detect the signals from multiple adjacent satellites in the presence of other interfering satellites is proposed. We tackle the worst case interference conditions, i.e., it is assumed that uncoded signals that fully overlap in frequency arrive at a multiple-element small-size parabolic antenna in a spatially correlated noise environment. The proposed successive interference cancellation (SIC) receiver, denoted by SIC Hy/ML, employs hybrid beamforming and disjoint maximum likelihood (ML) detection. Depending on the individual signals spatial position, the proposed SIC Hy/ML scheme takes advantage of two types of beamformers: a maximum ratio combining (MRC) beamformer and a compromised array response (CAR) beamformer. The performance of the proposed receiver is compared to an SIC receiver that uses only MRC beamforming scheme with ML detection for all signals, a joint ML detector, and a minimum mean square error detector. It is found that SIC Hy/ML outperforms the other schemes by a large margin.

  • 7. Abu-Shaban, Zohair
    et al.
    Mehrpouyan, Hani
    M. R., Bhavani Shankar
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust at the University of Luxembourg, Luxembourg.
    Reduced complexity satellite broadcast receiver with interference mitigation in correlated noise2018In: International Journal of Satellite Communications And Networking, ISSN 1542-0973, E-ISSN 1542-0981, Vol. 36, no 5, p. 402-415Article in journal (Refereed)
    Abstract [en]

    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 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 an enhanced list-based group-wise search detection (E-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 among the noise parameters, while also applying a preprocessor that maximizes the signal-to-interference-plus-noise ratio. We exploit the structure of this filter and propose a reduced complexity LGSD (RC-LGSD) receiver. Extensive simulations under practical scenarios show that the proposed receiver enhances the performance of satellite broadcast systems in the presence of adjacent satellite interference compared with existing methods. Also, under pointing error, RC-LGSD exhibits similar behavior to that of the optimum receiver

  • 8. Afzal, H.
    et al.
    Aouada, D.
    Font, D.
    Mirbach, B.
    Ottersten, Björn
    RGB-D multi-view system calibration for full 3D scene reconstruction2014In: 2014 22nd International Conference on Pattern Recognition, IEEE conference proceedings, 2014, p. 2459-2464Conference paper (Refereed)
    Abstract [en]

    One of the most crucial requirements for building a multi-view system is the estimation of relative poses of all cameras. An approach tailored for a RGB-D cameras based multi-view system is missing. We propose BAICP+ which combines Bundle Adjustment (BA) and Iterative Closest Point (ICP) algorithms to take into account both 2D visual and 3D shape information in one minimization formulation to estimate relative pose parameters of each camera. BAICP+ is generic enough to take different types of visual features into account and can be easily adapted to varying quality of 2D and 3D data. We perform experiments on real and simulated data. Results show that with the right weighting factor BAICP+ has an optimal performance when compared to BA and ICP used independently or sequentially.

  • 9. Afzal, Hassan
    et al.
    Aouada, Djamila
    Mirbach, Bruno
    Ottersten, Björn
    University of Luxembourg, Interdisciplinary Centre for Security, Reliability and Trust (SnT), Luxembourg, L-1855, Luxembourg.
    Full 3D Reconstruction of Non-Rigidly Deforming Objects2018In: ACM Transactions on Multimedia Computing, Communications, and Applications (TOMCCAP), ISSN 1551-6857, E-ISSN 1551-6865, Vol. 14, no 1s, article id A24Article in journal (Refereed)
    Abstract [en]

    In this article, we discuss enhanced full 360 degrees 3D reconstruction of dynamic scenes containing non-rigidly deforming objects using data acquired from commodity depth or 3D cameras. Several approaches for enhanced and full 3D reconstruction of non-rigid objects have been proposed in the literature. These approaches suffer from several limitations due to requirement of a template, inability to tackle large local deformations and topology changes, inability to tackle highly noisy and low-resolution data, and inability to produce online results. We target online and template-free enhancement of the quality of noisy and low-resolution full 3D reconstructions of dynamic non-rigid objects. For this purpose, we propose a view-independent recursive and dynamic multi-frame 3D super-resolution scheme for noise removal and resolution enhancement of 3D measurements. The proposed scheme tracks the position and motion of each 3D point at every timestep by making use of the current acquisition and the result of the previous iteration. The effects of system blur due to per-point tracking are subsequently tackled by introducing a novel and efficient multi-level 3D bilateral total variation regularization. These characteristics enable the proposed scheme to handle large deformations and topology changes accurately. A thorough evaluation of the proposed scheme on both real and simulated data is carried out. The results show that the proposed scheme improves upon the performance of the state-of-the-art methods and is able to accurately enhance the quality of low-resolution and highly noisy 3D reconstructions while being robust to large local deformations.

  • 10. Ai, Yun
    et al.
    Pereira de Figueiredo, Felipe Augusto
    Kong, Long
    Cheffena, Michael
    Chatzinotas, Symeon
    Ottersten, Björn
    University of Luxembourg, Esch-sur-Alzette, Luxembourg.
    Secure Vehicular Communications through Reconfigurable Intelligent Surfaces2021In: IEEE Transactions on Vehicular Technology, ISSN 00189545, Vol. 70, no 7, p. 7272-7276Article in journal (Refereed)
  • 11. Al Ismaeil, K.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust, Universtity of Luxembourg, Luxembourg.
    Depth super-resolution by enhanced shift and add2013In: Computer Analysis of Images and Patterns: 15th International Conference, CAIP 2013, York, UK, August 27-29, 2013, Proceedings, Part II, Springer, 2013, Vol. 8048 LNCS, no PART 2, p. 100-107Conference paper (Refereed)
    Abstract [en]

    We use multi-frame super-resolution, specifically, Shift & Add, to increase the resolution of depth data. In order to be able to deploy such a framework in practice, without requiring a very high number of observed low resolution frames, we improve the initial estimation of the high resolution frame. To that end, we propose a new data model that leads to a median estimation from densely upsampled low resolution frames. We show that this new formulation solves the problem of undefined pixels and further allows to improve the performance of pyramidal motion estimation in the context of super-resolution without additional computational cost. As a consequence, it increases the motion diversity within a small number of observed frames, making the enhancement of depth data more practical. Quantitative experiments run on the Middlebury dataset show that our method outperforms state-of-the-art techniques in terms of accuracy and robustness to the number of frames and to the noise level.

  • 12. Al Ismaeil, K.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    Advanced Engineering - IEE S.A., Luxembourg .
    Dynamic super resolution of depth sequences with non-rigid motions2013In: 2013 IEEE International Conference on Image Processing, ICIP 2013 - Proceedings, IEEE Signal Processing Society, 2013, p. 660-664Conference paper (Refereed)
    Abstract [en]

    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. The proposed approach is based on a new data model that leads to a robust registration of all depth frames after a dense upsampling. The textureless nature of depth images allows to robustly handle sequences with multiple moving objects as confirmed by our experiments.

  • 13. Al Ismaeil, K.
    et al.
    Aouada, D.
    Mirbach, B.
    Ottersten, Björn
    SnT - Universtity of Luxembourg, Luxembourg .
    Multi-frame super-resolution by enhanced shift & add2013In: 2013 8th International Symposium on Image and Signal Processing and Analysis (ISPA), IEEE , 2013, p. 171-176Conference paper (Refereed)
    Abstract [en]

    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 superresolution. Results show that the proposed algorithm outperforms existing state-of-art methods.

  • 14. Al Ismaeil, Kassem
    et al.
    Aouada, Djamila
    Mirbach, Bruno
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bilateral Filter Evaluation Based on Exponential Kernels2012Conference paper (Refereed)
    Abstract [en]

    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.

  • 15. Alaee-Kerahroodi, M.
    et al.
    Bhavani Shankar, M. R.
    Mishra, K. V.
    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, LUXEMBOURG.
    Meeting the lower bound on designing set of unimodular sequences with small aperiodic/periodic ISL2019Conference paper (Refereed)
  • 16. Alaee-Kerahroodi, M.
    et al.
    Imani, S.
    Bhavani Shankar, M. R.
    Nayebi, M. M.
    Ottersten, Björn
    Interdisciplinary Centre for Security, University of Luxembourg.
    A coordinate descent framework to joint design of MPSK sequences and receive filter weights in MIMO radar systems2019Conference paper (Refereed)
  • 17. Alaee-Kerahroodi, M.
    et al.
    Mishra, K. V.
    Bhavani Shankar, M. R.
    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg.
    Discrete-Phase Sequence Design for Coexistence of MIMO Radar and MIMO Communications2019Conference paper (Refereed)
  • 18. Alaee-Kerahroodi, M.
    et al.
    Modarres-Hashemi, M.
    Naghsh, M. M.
    Bhavani Shankar, M. R.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg.
    Binary sequences set with small ISL for MIMO radar systems2018Conference paper (Refereed)
  • 19. Alaee-Kerahroodi, M.
    et al.
    Sedighi, S.
    Bhavani Shankar, M. R.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg.
    Designing (In)finite-alphabet Sequences via Shaping the Radar Ambiguity Function2019Conference paper (Refereed)
  • 20. Alaee-Kerharoodi, M.
    et al.
    Bhavani, S. M. R.
    Mishra, K. V.
    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, University of Luxembourg.
    Information Theoretic Approach for Waveform Design in Coexisting MIMO Radar and MIMO Communications2020Conference paper (Refereed)
  • 21. Al-Hraishawi, Hayder
    et al.
    Abdullah, Osamah A.
    Chatzinotas, Symeon
    Ottersten, Björn
    Reliability and Trust, University of Luxembourg, Interdisciplinary Centre for Security, Luxembourg City, 1855, Luxembourg.
    Energy Harvesting from Jamming Attacks in Multi-User Massive MIMO Networks2023In: IEEE Transactions on Green Communications and Networking, ISSN 24732400, Vol. 7, no 3, p. 1181-1191Article in journal (Refereed)
    Abstract [en]

    Fifth-generation (5G) and beyond communication systems offer new functionalities and significant performance improvements but that comes at the cost of tougher energy requirements on user devices. Addressing this issue while reducing the environmental impact of the substantial increase in energy consumption can be achieved through energy-neutral systems that operate using energy harvested from radio frequency (RF) transmissions. In this direction, this work examines the concept of utilizing an unconventional source for RF energy harvesting. Specifically, the performance of an RF energy harvesting scheme for multi-user massive multiple-input multiple-output (MIMO) is investigated in the presence of multiple active jammers. The key idea is to exploit the jamming transmissions as an energy source to be harvested by the legitimate users. To this end, the feasibility of this concept is studied via system performance analysis for a training-based massive MIMO encompasses imperfectly estimated channel state information (CSI) at the base-station and employing the time-switching protocol. In particular, the achievable uplink sum rate expressions are derived in closed-form for two different antenna configurations at the base-station. Two optimal time-switching schemes are also proposed based on maximum sum rate and user-fairness criteria. The essential trade-off between the harvested energy and achievable sum rate in time-switching protocol are quantified in closed-form as well. Our analysis reveals that the proposed energy harvesting scheme from jamming signals is viable and can boost massive MIMO uplink performance by exploiting the surrounding RF signals of the jamming attacks for increasing the amount of harvested energy at the served users. Finally, numerical results validate the theoretical analyses and the effectiveness of the derived closed-form expressions through simulations.

  • 22. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    A multicast approach for constructive interference precoding in MISO downlink channel2014In: 2014 IEEE International Symposium on Information Theory, IEEE conference proceedings, 2014, p. 2534-2538Conference paper (Refereed)
    Abstract [en]

    This paper studies the concept of jointly utilizing the data information (DI) and channel state information (CSI) in order to design symbol-level precoders for a multiple input and single output (MISO) downlink channel. In this direction, the interference among the simultaneous data streams is transformed to useful signal that can improve the signal to interference noise ratio (SINR) of the downlink transmissions. We propose a maximum ratio transmissions (MRT) based algorithm that jointly exploits DI and CSI to gain the benefits from these useful signals. In this context, a novel framework to minimize the power consumption is proposed by formalizing the duality between the constructive interference downlink channel and the multicast channels. The numerical results have shown that the proposed schemes outperform other state of the art techniques.

  • 23. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Energy-Efficient Symbol-Level Precoding in Multiuser MISO Based on Relaxed Detection Region2016In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, no 5, p. 3755-3767Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of exploiting interference among simultaneous multiuser transmissions in the downlink of multiple-antenna systems. Using symbol-level precoding, a new approach toward addressing the multiuser interference is discussed through jointly utilizing the channel state information (CSI) and data information (DI). The interference among the data streams is transformed under certain conditions to a useful signal that can improve the signal-to-interference noise ratio (SINR) of the downlink transmissions and as a result the system's energy efficiency. In this context, new constructive interference precoding techniques that tackle the transmit power minimization (min power) with individual SINR constraints at each user's receiver have been proposed. In this paper, we generalize the constructive interference (CI) precoding design under the assumption that the received MPSK symbol can reside in a relaxed region in order to be correctly detected. Moreover, a weighted maximization of the minimum SNR among all users is studied taking into account the relaxed detection region. Symbol error rate analysis (SER) for the proposed precoding is discussed to characterize the tradeoff between transmit power reduction and SER increase due to the relaxation. Based on this tradeoff, the energy efficiency performance of the proposed technique is analyzed. Finally, extensive numerical results show that the proposed schemes outperform other state-of-the-art techniques.

  • 24. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Joint channel estimation and pilot allocation in underlay cognitive MISO networks2014In: 2014 International Wireless Communications and Mobile Computing Conference (IWCMC), IEEE conference proceedings, 2014, p. 797-802Conference paper (Refereed)
    Abstract [en]

    Cognitive radios have been proposed as agile technologies to boost the spectrum utilization. This paper tackles the problem of channel estimation and its impact on downlink transmissions in an underlay cognitive radio scenario. We consider primary and cognitive base stations, each equipped with multiple antennas and serving multiple users. Primary networks often suffer from the cognitive interference, which can be mitigated by deploying beamforming at the cognitive systems to spatially direct the transmissions away from the primary receivers. The accuracy of the estimated channel state information (CSI) plays an important role in designing accurate beamformers that can regulate the amount of interference. However, channel estimate is affected by interference. Therefore, we propose different channel estimation and pilot allocation techniques to deal with the channel estimation at the cognitive systems, and to reduce the impact of contamination at the primary and cognitive systems. In an effort to tackle the contamination problem in primary and cognitive systems, we exploit the information embedded in the covariance matrices to successfully separate the channel estimate from other users' channels in correlated cognitive single input multiple input (SIMO) channels. A minimum mean square error (MMSE) framework is proposed by utilizing the second order statistics to separate the overlapping spatial paths that create the interference. We validate our algorithms by simulation and compare them to the state of the art techniques.

  • 25. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Spatial DCT-based least square estimation in multi-antenna multi-cell interference channels2014In: 2014 IEEE International Conference on Communications (ICC), IEEE conference proceedings, 2014, p. 4729-4734Conference paper (Refereed)
    Abstract [en]

    Interference management techniques in multicell multiple input multiple output (MIMO) networks require accurate channel state information (CSI). A popular technique for acquiring this CSI in time division duplex (TDD) systems is uplink training by exploiting the reciprocity of the wireless medium. Recently, the pilot contamination problem has been identified as one of the limiting factors for such kind of CSI acquisition. In an effort to tackle the problem of contamination, we utilize the compression capability of discrete cosine transform (DCT) and covariance matrices to spatially separate the estimate for the scenario of correlated single input multiple input (SIMO) channels. A least square estimation framework is proposed by utilizing the DCT to separate the overlapping spatial paths that create the interference. The spatial domain is thus exploited to mitigate the contamination which is able to discriminate across the interfering users. We validate our algorithms by simulation and compare them to the state of the art techniques.

  • 26. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Symbol-Level Multiuser MISO Precoding for Multi-Level Adaptive Modulation2017In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 16, no 8, p. 5511-5524Article in journal (Refereed)
    Abstract [en]

    Symbol-level precoding is a new paradigm for multiuser multiple-antenna downlink systems aimed at creating constructive interference among transmitted data streams. This can be enabled by designing the precoded signal of the multiantenna transmitter on a symbol level, taking into account both channel state information and data symbols. Previous literature has studied this paradigm for Mary phase shift keying modulations by addressing various performance metrics, such as power minimization and maximization of the minimum rate. In this paper, we extend this to generic multi-level modulations, i.e., Mary quadrature amplitude modulation by establishing connection to PHY layer multicasting with phase constraints. Furthermore, we address the adaptive modulation schemes which are crucial in enabling the throughput scaling of symbol-level precoded systems. In this direction, we design the signal processing algorithms for minimizing the required power under per-user signal to interference noise ratio or goodput constraints. Extensive numerical results show that the proposed algorithm provides considerable power and energy efficiency gains, while adapting the employed modulation scheme to match the requested data rate.

  • 27. Alodeh, M.
    et al.
    Chatzinotas, S.
    Ottersten, Björn
    Interdisciplinary Centre for Security Reliability and Trust (SnT), University of Luxembourg.
    User selection for symbol-level multigroup multicasting precoding in the downlink of MISO channels2018Conference paper (Refereed)
  • 28. Alodeh, M.
    et al.
    Spano, D.
    Kalantari, A.
    Tsinos, C. G.
    Christopoulos, D.
    Chatzinotas, S.
    Ottersten, Björn
    Interdisciplinary Centre for Security Reliability and Trust, University of Luxembourg, Luxembourg City, Luxembourg.
    Symbol-level and multicast precoding for multiuser multiantenna downlink: A state-of-the-art, classification, and challenges2018In: IEEE Communications Surveys and Tutorials, ISSN 1553877X, Vol. 20, no 3, p. 1733-1757, article id 8359237Article in journal (Refereed)
    Abstract [en]

    Precoding has been conventionally considered as an effective means of mitigating or exploiting the interference in the multiantenna downlink channel, where multiple users are simultaneously served with independent information over the same channel resources. The early works in this area were focused on transmitting an individual information stream to each user by constructing weighted linear combinations of symbol blocks (codewords). However, more recent works have moved beyond this traditional view by: 1) transmitting distinct data streams to groups of users and 2) applying precoding on a symbol-per-symbol basis. In this context, the current survey presents a unified view and classification of precoding techniques with respect to two main axes: 1) the switching rate of the precoding weights, leading to the classes of block-level and symbol-level precoding and 2) the number of users that each stream is addressed to, hence unicast, multicast, and broadcast precoding. Furthermore, the classified techniques are compared through representative numerical results to demonstrate their relative performance and uncover fundamental insights. Finally, a list of open theoretical problems and practical challenges are presented to inspire further research in this area1.1The concepts of precoding and beamforming are used interchangeably throughout this paper.

  • 29. Alodeh, Maha
    et al.
    Chatzinotas, Symeon
    Ottersten, Björn E.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Spatial DCT-Based Channel Estimation in Multi-Antenna Multi-Cell Interference Channels2015In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, no 6, p. 1404-1418Article in journal (Refereed)
    Abstract [en]

    This work addresses channel estimation in multiple antenna multicell interference-limited networks. Channel state information (CSI) acquisition is vital for interference mitigation. Wireless networks often suffer from multicell interference, which can be mitigated by deploying beamforming to spatially direct the transmissions. The accuracy of the estimated CSI plays an important role in designing accurate beamformers that can control the amount of interference created from simultaneous spatial transmissions to mobile users. Therefore, a new technique based on the structure of the spatial covariance matrix and the discrete cosine transform (DCT) is proposed to enhance channel estimation in the presence of interference. Bayesian estimation and least squares estimation frameworks are introduced by utilizing the DCT to separate the overlapping spatial paths that create the interference. The spatial domain is thus exploited to mitigate the contamination which is able to discriminate across interfering users. Gains over conventional channel estimation techniques are presented in our simulations which are also valid for a small number of antennas.

  • 30. Aouada, D.
    et al.
    Al Ismaeil, K.
    Idris, K. K.
    Ottersten, Björn
    Surface UP-SR for an improved face recognition using low resolution depth cameras2014In: 2014 11th IEEE International Conference on Advanced Video and Signal Based Surveillance (AVSS), IEEE conference proceedings, 2014, p. 107-112Conference paper (Refereed)
    Abstract [en]

    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.1.

  • 31.
    Arapoglou, Pantelis-Daniel
    et al.
    University of Luxembourg, Luxembourg.
    Shankar, M. R. Bhavani
    University of Luxembourg, Luxembourg.
    Panagopoulos, Athanasios
    University of Luxembourg, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gateway Diversity Strategies in Q/V Band Feeder Links2011In: Proceedings 17th Ka and Broadband Communications Conference, 2011Conference paper (Refereed)
  • 32. Aravanis, Alexis
    et al.
    Shankar Bhavani, M.R.
    Danoy, Gregoire
    Arapoglou, Pantelis-Daniel
    Cottis, Panayotis
    Ottersten, Björn
    Multi-objective Optimization Approach to Power Allocation in Multibeam Systems2012Conference paper (Refereed)
  • 33. Aravanis, Alexis
    et al.
    Shankar Bhavani, M.R.
    Danoy, Gregoire
    Arapoglou, Pantelis-Daniel
    Cottis, Panayotis
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Power allocation in multibeam satellites: A hybrid-genetic algorithm approach2012Conference paper (Refereed)
  • 34. Arnau, J.
    et al.
    Christopoulos, D.
    Chatzinotas, S.
    Mosquera, C.
    Ottersten, Björn
    Performance of the multibeam satellite return link with correlated rain attenuation2014In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 13, no 11, p. 6286-6299Article in journal (Refereed)
    Abstract [en]

    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.

  • 35. Arora, A.
    et al.
    Bhavani Shankar Mysore, R.
    Ottersten, Björn
    Interdisciplinary Centre for Security, University of Luxembourg.
    Cramer-Rao Bound on DOA Estimation of Finite Bandwidth Signals Using a Moving Sensor2020Conference paper (Refereed)
  • 36. Arora, A.
    et al.
    Maleki, S.
    Rama Rao, B. S. M.
    Grotz, J.
    Ottersten, Björn
    SnT - Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg.
    Interference localization on-board the satellite using drift induced virtual array2018Conference paper (Refereed)
  • 37. Arora, A.
    et al.
    Tsinos, C. G.
    Bhavani Shankar Mysore, R.
    Chatzinotas, S.
    Ottersten, Björn
    University of Luxembourg.
    MM-based solution for partially connected hybrid transceivers with large scale antenna arrays2019Conference paper (Refereed)
  • 38. Arora, A.
    et al.
    Tsinos, C. G.
    Rao, B. S. M. R.
    Chatzinotas, S.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg, U.K..
    Hybrid Transceivers Design for Large-Scale Antenna Arrays Using Majorization-Minimization Algorithms2020In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 68, p. 701-714, article id 8926431Article in journal (Refereed)
  • 39. Arora, A.
    et al.
    Tsinos, C. G.
    Shankar, B.
    Chatzinotas, S.
    Ottersten, Björn
    Interdiscipl. Centre for Security, Reliability & Trust, Univ. of Luxembourg, Luxembourg City, Luxembourg.
    Hybrid analog-digital precoding design for satellite systems2019Conference paper (Refereed)
  • 40. Arora, A.
    et al.
    Tsinos, C. G.
    Shankar Mysore R, B.
    Chatzinotas, S.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg.
    Majorization-minimization algorithms for analog beamforming with large-scale antenna arrays2019Conference paper (Refereed)
  • 41. Arora, Aakash
    et al.
    Tsinos, Christos G.
    Mysore R, Bhavani Shankar
    Chatzinotas, Symeon
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg, Luxembourg.
    Efficient Algorithms for Constant-Modulus Analog Beamforming2022In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 70, p. 756-771Article in journal (Refereed)
  • 42.
    Astély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Constrained Complexity Spatio-Temporal Interference Rejection Combining1999In: Proceedings of SPAWC’99, Signal Processing Advances in Wireless Communications, IEEE , 1999, p. 110-113Conference paper (Refereed)
    Abstract [en]

    Space-time processing for co-channel interference (CCI) rejection and equalization with antenna arrays may provide large gains over space-only processing, especially in interference limited scenarios. However, taking thetemporal correlation of the noise and CCI process into account leads to sequence detection with highercomplexity as compared to space-only processing that neglects this correlation. We propose the use of the generalized Viterbi algorithm for sequence detection with lower complexity. Special cases include the M-algorithm and the delayed decision feedback sequence estimator. A relevant comparison between spatial andspatio-temporal processing with sequence detectors of the same complexity may thus be performed. Numerical examples show substantial gains for spatio-temporal processing as compared to space-only processing also in this case when the optimality of the sequence detector is traded for interference rejection.

  • 43.
    Astély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    MLSE and Spatio-Temporal Interference Rejection Combining with Antenna Arrays1998In: Proceedings of Eusipco-98, Ninth European Signal Processing Conference, Island of Rhodes, Greece, 1998, p. 1341-1344Conference paper (Refereed)
  • 44.
    Astély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    On Spatio-Temporal Interference Rejection Combining with Antenna Arrays1998Other (Refereed)
  • 45.
    Astély, David
    et al.
    Ericsson Research.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Spatio-Temporal Interference Rejection Combining2005In: Smart Antennas - State-of-the-Art / [ed] Kaiser, Thomas, Hindawi Publishing Corporation , 2005, p. 5-26Chapter in book (Other academic)
  • 46.
    Astély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    The effects of local scattering on direction of arrival estimation with MUSIC1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 47, no 12, p. 3220-3234Article in journal (Refereed)
    Abstract [en]

    In wireless communication scenarios, multipath propagation may cause angular spreading as seen from a base station antenna array. Environments where most energy incident on the array is from scatterers local to the mobile transmitters are considered, and the effects on direction of arrival (DOA) estimation with the MUSIC algorithm are studied. Previous work has studied rapidly time-varying channels and concluded that local scattering has a minor effect on DOA estimation in such scenarios. In this work, a channel that is time-invariant during the observation period is considered, and under the assumption of small angular spread, an approximate distribution for the DOA estimates is derived. The results show that local scattering has a significant impact on DOA estimation in the time invariant case. Numerical examples are included to illustrate the analysis and to demonstrate that the results may be used to formulate a simple estimator of angular spread. An extension to more general Rayleigh and Ricean fading channels is also included, In addition, results from processing experimental data collected in suburban environments are presented. Good agreement with the derived distributions is obtained.

  • 47.
    Astély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Swindlehurst, Andrew Lee
    Department of Electrical and Computer Engineering, Brigham Young University, Provo, UT 84602 USA.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Spatial signature estimation for uniform linear arrays with unknown receiver gains and phases1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 47, no 8, p. 2128-2138Article in journal (Refereed)
    Abstract [en]

    The problem of spatial signature estimation using a uniform linear array (ULA) with unknown receiver gain and phase responses is studied. Sufficient conditions for identifying the spatial signatures are derived, and a closed-Form ESPRIT-like estimator is proposed, The performance of the method is investigated by means of simulations and on experimental data collected with an antenna array in a suburban environment. The results show that the absence of receiver calibration is not critical for uplink signal waveform estimation using a plane wave model.

  • 48.
    Asztély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Kristensson, Martin
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Spatio-Temporal Processing for Wireless Communications1998In: First Annual UCSD Conference on Wireless Communications, 1998Conference paper (Refereed)
  • 49.
    Asztély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Modified Array Manifold for Signal Waveform Estimation in Wireless Communications1996In: 30:th Asilomar Conference on Signals, Systems & Computers, IEEE , 1996, p. 738-741Conference paper (Refereed)
    Abstract [en]

    In wireless communication scenarios, local scatterers in the vicinity of the sources cause angular spreading. A parameterization of the spatial signature in the presence of local scattering is presented which applies to uniform linear arrays (ULAs). The spatial signature is shown to be approximately a Vandermonde vector for a ULA inenvironments with small angular spread. An estimator of the spatial signature is formulated based on ESPRIT. Fora simple signal waveform estimator the gain may be considerable in scenarios with multiple sources, as compared with using the ideal manifold parameterized by direction of arrival (DOA).

  • 50.
    Asztély, David
    et al.
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments (pre-2005), Signals, Sensors and Systems.
    The Effects of Local Scattering on Direction of Arrival Estimation with MUSIC and ESPRIT1998In: Acoustics, Speech and Signal Processing, ICASSP 98., IEEE , 1998, p. 3333-3336Conference paper (Refereed)
    Abstract [en]

    In wireless communication scenarios, multipath propagation from local scatterers in the vicinity of mobile sources may cause angular spreading as seen from a base station antenna array. This paper studies the effects of suchlocal scattering on direction of arrival (DOA) estimation with the MUSIC and ESPRIT algorithms. Previous work has considered rapidly time-varying scenarios, and concluded that local scattering has a minor effect on DOAestimation in such scenarios. This work considers the case in which the channel is time-invariant during theobservation period. The distribution of the DOA estimates is derived, and the results show that local scatteringhas a significant impact on DOA estimation in the time-invariant case. In addition, numerical examples are included to illustrate the analysis, and to demonstrate that the results may be used to formulate simple estimators of angular spread.

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