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Multi-User Detection in Multibeam Mobile Satellite Systems: A Fair Performance Evaluation Christopoulos, Dimitrios ; Chatzinotas, Symeon ; et al in Proceedings of Vehicular Technology Conference, Spring 2013 (2013) Multi-User Detection (MUD) techniques are currently being examined as promising technologies for the next generation of broadband, interactive, multibeam satellite communication (SatCom) systems. Results ... [more ▼] Multi-User Detection (MUD) techniques are currently being examined as promising technologies for the next generation of broadband, interactive, multibeam satellite communication (SatCom) systems. Results in the existing literature have shown that when full frequency and polarization reuse is employed and user signals are jointly processed at the gateway, more than threefold gains in terms of spectral efficiency over conventional systems can be obtained. However, the information theoretic results for the capacity of the multibeam satellite channel are given under ideal assumptions, disregarding the implementation constraints of such an approach. Considering a real system implementation, the adoption of full resource reuse is bound to increase the payload complexity and power consumption. Since these novel techniques require extra payload resources, fairness issues in the comparison among the two approaches arise. The present contribution evaluates in a fair manner, the performance of the return link (RL) of a SatCom system serving mobile users that are jointly decoded at the receiver. In this context, the throughput performance of the assumed system is compared to that of a conventional one, under the constraint of equal physical layer resource utilization; thus the comparison can be regarded as fair. Results show, that even when systems operate under the same payload requirements as the conventional systems, a significant gain can be realized, especially in the high SNR region. Finally, existing analytical formulas are also employed to provide closed form descriptions of the performance of clustered systems, thus introducing insights on how the performance scales with respect to the system parameters. [less ▲] Detailed reference viewed: 379 (49 UL)Robust MIMO precoding for several classes of channel uncertainty ; ; Ottersten, Björn et al in IEEE Transactions on Signal Processing (2013), 12(61), 3056-3070 The full potential of multi-input multi-output (MIMO) communication systems relies on exploiting channel state information at the transmitter (CSIT), which is, however, often subject to some uncertainty ... [more ▼] The full potential of multi-input multi-output (MIMO) communication systems relies on exploiting channel state information at the transmitter (CSIT), which is, however, often subject to some uncertainty. In this paper, following the worst-case robust philosophy, we consider a robust MIMO precoding design with deterministic imperfect CSIT, formulated as a maximin problem, to maximize the worst-case received signal-to-noise ratio or minimize the worst-case error probability. Given different types of imperfect CSIT in practice, a unified framework is lacking in the literature to tackle various channel uncertainty. In this paper, we address this open problem by considering several classes of uncertainty sets that include most deterministic imperfect CSIT as special cases. We show that, for general convex uncertainty sets, the robust precoder, as the solution to the maximin problem, can be efficiently computed by solving a single convex optimization problem. Furthermore, when it comes to unitarily-invariant convex uncertainty sets, we prove the optimality of a channel-diagonalizing structure and simplify the complex-matrix problem to a real-vector power allocation problem, which is then analytically solved in a waterfilling manner. Finally, for uncertainty sets defined by a generic matrix norm, called the Schatten norm, we provide a fully closed-form solution to the robust precoding design, based on which the robustness of beamforming and uniform-power transmission is investigated. [less ▲] Detailed reference viewed: 362 (3 UL)Receive combining vs. multi-stream multiplexing in downlink systems with multi-antenna users ; ; Ottersten, Björn in IEEE Transactions on Signal Processing (2013), 13(61), 3431-3446 In downlink multi-antenna systems with many users, the multiplexing gain is strictly limited by the number of transmit antennas N and the use of these antennas. Assuming that the total number of receive ... [more ▼] In downlink multi-antenna systems with many users, the multiplexing gain is strictly limited by the number of transmit antennas N and the use of these antennas. Assuming that the total number of receive antennas at the multi-antenna users is much larger than N, the maximal multiplexing gain can be achieved with many different transmission/reception strategies. For example, the excess number of receive antennas can be utilized to schedule users with effective channels that are near-orthogonal, for multi-stream multiplexing to users with well-conditioned channels, and/or to enable interference-aware receive combining. In this paper, we try to answer the question if the N data streams should be divided among few users (many streams per user) or many users (few streams per user, enabling receive combining). Analytic results are derived to show how user selection, spatial correlation, heterogeneous user conditions, and imperfect channel acquisition (quantization or estimation errors) affect the performance when sending the maximal number of streams or one stream per scheduled user-the two extremes in data stream allocation. While contradicting observations on this topic have been reported in prior works, we show that selecting many users and allocating one stream per user (i.e., exploiting receive combining) is the best candidate under realistic conditions. This is explained by the provably stronger resilience towards spatial correlation and the larger benefit from multi-user diversity. This fundamental result has positive implications for the design of downlink systems as it reduces the hardware requirements at the user devices and simplifies the throughput optimization. [less ▲] Detailed reference viewed: 175 (2 UL)Capacity limits and multiplexing gains of MIMO channels with transceiver impairments ; ; et al in IEEE Communications Letters (2013), 1(17), 91-94 The capacity of ideal MIMO channels has a high-SNR slope that equals the minimum of the number of transmit and receive antennas. This letter analyzes if this result holds when there are distortions from ... [more ▼] The capacity of ideal MIMO channels has a high-SNR slope that equals the minimum of the number of transmit and receive antennas. This letter analyzes if this result holds when there are distortions from physical transceiver impairments. We prove analytically that such physical MIMO channels have a finite upper capacity limit, for any channel distribution and SNR. The high-SNR slope thus collapses to zero. This appears discouraging, but we prove the encouraging result that the relative capacity gain of employing MIMO is at least as large as with ideal transceivers. [less ▲] Detailed reference viewed: 198 (1 UL)Spectrum Sensing in Dual Polarized Fading Channels for Cognitive SatComs Sharma, Shree Krishna ; Chatzinotas, Symeon ; Ottersten, Björn in Proceedings of IEEE Globecom Conference 2012 (2012, December) Next generation networks are moving towards the convergence of mobile, fixed and broadcasting services in one standard platform, which requires the co-existence of satellite and terrestrial networks in ... [more ▼] Next generation networks are moving towards the convergence of mobile, fixed and broadcasting services in one standard platform, which requires the co-existence of satellite and terrestrial networks in the same spectrum. This framework has motivated the concept of cognitive Satellite Communication (SatComs). In this aspect, the problem of exploiting Spectrum Sensing (SS) techniques for a dual polarized fading channel is considered. In this paper, the performance of Energy Detection (ED) technique is evaluated in the context of a co-existence scenario of a satellite and a terrestrial link. Diversity combining techniques such as Equal Gain Combining (EGC) and Selection Combining (SC) are considered to enhance the SS efficiency. Furthermore, analytical expressions for probability of detection (Pd) and probability of false alarm (Pf ) are presented for these techniques in the considered fading channel and the sensing performance is studied through analytical and simulation results. Moreover, the effect of Cross Polar Discrimination (XPD) on the sensing performance is presented and it is shown that SS efficiency improves for low XPD. [less ▲] Detailed reference viewed: 211 (13 UL)Satellite Cognitive Communications: Interference Modeling and Techniques Selection Sharma, Shree Krishna ; Chatzinotas, Symeon ; Ottersten, Björn in Proceeding of 6th Advanced Satellite Multimedia Systems Conference and the 12th Signal Processing for Space Communications Workshop (2012, September) Due to increasing demand of high speed data rate for satellite multimedia and broadcasting services and spectrum scarcity problem in satellite bands, exploring new techniques for enhancing spectral ... [more ▼] Due to increasing demand of high speed data rate for satellite multimedia and broadcasting services and spectrum scarcity problem in satellite bands, exploring new techniques for enhancing spectral efficiency in satellite communication has become an important research challenge. In this aspect, satellite cognitive communication can be considered as a promising solution to solve spectrum scarcity problem. In this paper, different cognitive techniques such as underlay, overlay, interweave and database related techniques are discussed by reviewing the current state of art. Exact beam patterns of a multi-beam satellite are plotted over the Europe map and interference modeling between terrestrial Base Station (BS) and satellite terminal is carried out on the basis of interference power level. Furthermore, suitable cognitive techniques are proposed in high and low interference regions in the context of satellite cognitive communication. [less ▲] Detailed reference viewed: 210 (15 UL)Space-Frequency Coding for Dual Polarized Hybrid Mobile Satellite Systems Shankar, Bhavani ; Arapoglou, Pantelis-Daniel ; Ottersten, Björn in IEEE Transactions on Wireless Communications (2012), 11(8), 2806-2814 An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions ... [more ▼] An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions adopting multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) techniques. In this work, we build upon recent studies of dual polarization MIMO for each component and propose the use of full-rate full-diversity (FRFD) codes adopting a space-frequency paradigm. We also propose a scheme taking advantage of the separation between the subcarriers to enhance the coding gain. By critically assessing the different options for the 4 transmit, 2 receive hybrid scenario taking into account system and channel particularities, we demonstrate that the proposed scheme is a solution for enhancing the performance of next generation hybrid mobile satellite systems. [less ▲] Detailed reference viewed: 215 (4 UL)Iterative Precoder Design and User Scheduling for Block-Diagonalized Systems ; ; Ottersten, Björn in IEEE Transactions on Signal Processing (2012), 60(7), 3726-3739 The block diagonalization (BD) scheme is a low-complexity suboptimal precoding technique for multiuser multiple input-multiple output (MIMO) downlink channels, which completely precancels the multiuser ... [more ▼] The block diagonalization (BD) scheme is a low-complexity suboptimal precoding technique for multiuser multiple input-multiple output (MIMO) downlink channels, which completely precancels the multiuser interference. Accordingly, the precoder of each user lies in the null space of other users' channel matrices. In this paper, we propose an iterative algorithm using QR decompositions (QRDs) to compute the precoders. Specifically, to avoid dealing with a large concatenated matrix, we apply the QRD to a sequence of matrices of lower dimensions. One problem of BD schemes is that the number of users that can be simultaneously supported is limited due to zero interference constraints. When the number of users is large, a set of users must be selected, and selection algorithms should be designed to exploit the multiuser diversity gain. Finding the optimal set of users requires an exhaustive search, which has too high computational complexity to be practically useful. Based on the iterative precoder design, this paper proposes a low-complexity user selection algorithm using a greedy method, in which the precoders of selected users are recursively updated after each selection step. The selection metric of the proposed scheduling algorithm relies on the product of the squared row norms of the effective channel matrices, which is related to the eigenvalues by the Hadamard and Schur inequalities. An asymptotic analysis is provided to show that the proposed algorithm can achieve the optimal sum rate scaling of the MIMO broadcast channel. The numerical results show that the proposed algorithm achieves a good trade-off between sum rate performance and computational complexity. When users suffer different channel conditions, providing fairness among users is of critical importance. To address this problem, we also propose two fair scheduling (FS) algorithms, one imposing fairness in the approximation of the data rate, and another directly imposing fairness in the product of the sq- ared row norms of the effective channel matrices. [less ▲] Detailed reference viewed: 168 (3 UL)Distributed Multicell Beamforming Design Approaching Pareto Boundary with Max-Min Fairness ; Zheng, Gan ; et al in IEEE Transactions on Wireless Communications (2012), 11(8), 2921-2933 This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing ... [more ▼] This paper addresses coordinated downlink beamforming optimization in multicell time division duplex (TDD) systems where a small number of parameters are exchanged between cells but with no data sharing. With the goal to reach the point on the Pareto boundary with max-min rate fairness, we first develop a two-step centralized optimization algorithm to design the joint beamforming vectors. This algorithm can achieve a further sum-rate improvement over the max-min optimal performance, and is shown to guarantee max-min Pareto optimality for scenarios with two base stations (BSs) each serving a single user. To realize a distributed solution with limited intercell communication, we then propose an iterative algorithm by exploiting an approximate uplink-downlink duality, in which only a small number of positive scalars are shared between cells in each iteration. Simulation results show that the proposed distributed solution achieves a fairness rate performance close to the centralized algorithm while it has a better sum-rate performance, and demonstrates a better tradeoff between sum-rate and fairness than the Nash Bargaining solution especially at high signal-to-noise ratio. [less ▲] Detailed reference viewed: 181 (1 UL)Exploiting Polarization for Spectrum Sensing in Cognitive SatComs Sharma, Shree Krishna ; Chatzinotas, Symeon ; Ottersten, Björn in Proceedings of 7th International Conference on Cognitive Radio Oriented Wireless Networks (2012, June) Exploring new techniques for spectrum sensing (SS), which can detect the weak primary signals instantly, has been an important research challenge. In this paper, the problem of enhancing SS efficiency in ... [more ▼] Exploring new techniques for spectrum sensing (SS), which can detect the weak primary signals instantly, has been an important research challenge. In this paper, the problem of enhancing SS efficiency in cognitive SatComs has been considered. The analysis of different combining techniques has been carried out for SS using dual polarized antenna. Furthermore, polarization states of received signals are exploited and based on obtained polarization states, Optimum Polarization Based Combining (OPBC) technique has been used for carrying out SS in the satellite terminal. The sensing performance of OPBC technique has been compared to selection combining (SC), equal gain combining (EGC) and maximum ratio combining (MRC) techniques. The simulation results show that OPBC technique achieves a great improvement in sensing efficiency over other considered techniques at the expense of complexity in a dual polarized AWGN channel. [less ▲] Detailed reference viewed: 194 (7 UL)Pareto Characterization of the Multicell MIMO Performance Region With Simple Receivers ; ; Ottersten, Björn in IEEE Transactions on Signal Processing (2012), 60(8), 4464-4469 We study the performance region of a general multicell downlink scenario with multiantenna transmitters, hardware impairments, and low-complexity receivers that treat interference as noise. The Pareto ... [more ▼] We study the performance region of a general multicell downlink scenario with multiantenna transmitters, hardware impairments, and low-complexity receivers that treat interference as noise. The Pareto boundary of this region describes all efficient resource allocations, but is generally hard to compute. We propose a novel explicit characterization that gives Pareto optimal transmit strategies using a set of positive parameters-fewer than in prior work. We also propose an implicit characterization that requires even fewer parameters and guarantees to find the Pareto boundary for every choice of parameters, but at the expense of solving quasi-convex optimization problems. The merits of the two characterizations are illustrated for interference channels and ideal network multiple-input multiple-output (MIMO). [less ▲] Detailed reference viewed: 167 (0 UL)Physical Layer Security in Multibeam Satellite Systems Zheng, Gan ; Arapoglou, Pantelis-Daniel ; Ottersten, Björn in IEEE Transactions on Wireless Communications (2012), 11(2), 852-863 Security threats introduced due to the vulnerability of the transmission medium may hinder the proliferation of Ka band multibeam satellite systems for civil and military data applications. This paper ... [more ▼] Security threats introduced due to the vulnerability of the transmission medium may hinder the proliferation of Ka band multibeam satellite systems for civil and military data applications. This paper sets the analytical framework and then studies physical layer security techniques for fixed legitimate receivers dispersed throughout multiple beams, each possibly surrounded by multiple (passive) eavesdroppers. The design objective is to minimize via transmit beamforming the costly total transmit power on board the satellite, while satisfying individual intended users' secrecy rate constraints. Assuming state-of-the-art satellite channel models, when perfect channel state information (CSI) about the eavesdroppers is available at the satellite, a partial zero-forcing approach is proposed for obtaining a low-complexity sub-optimal solution. For the optimal solution, an iterative algorithm combining semi-definite programming relaxation and the gradient-based method is devised by studying the convexity of the problem. Furthermore, the use of artificial noise as an additional degree-of-freedom for protection against eavesdroppers is explored. When only partial CSI about the eavesdroppers is available, we study the problem of minimizing the eavesdroppers' received signal to interference-plus-noise ratios. Simulation results demonstrate substantial performance improvements over existing approaches. [less ▲] Detailed reference viewed: 312 (0 UL)Multi-gateway cooperation in multibeam satellite systems Zheng, Gan ; Chatzinotas, Symeon ; Ottersten, Björn in IEEE 23rd International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC) (2012) Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and ... [more ▼] Multibeam systems with hundreds of beams have been recently deployed in order to provide higher capacities by employing fractional frequency reuse. Furthermore, employing full frequency reuse and precoding over multiple beams has shown great throughput potential in literature. However, feeding all this data from a single gateway is not feasible based on the current frequency allocations. In this context, we investigate a range of scenarios involving beam clusters where each cluster is managed by a single gateway. More specifically, the following cases are considered for handling intercluster interference: a) conventional frequency colouring, b) joint processing within cluster, c) partial CSI sharing among clusters, d) partial CSI and data sharing among clusters. CSI sharing does not provide considerable performance gains with respect to b) but combined with data sharing offers roughly a 40% improvement over a) and a 15% over b). [less ▲] Detailed reference viewed: 193 (10 UL)Robust Monotonic Optimization Framework for Multicell MISO Systems ; Zheng, Gan ; et al in IEEE Transactions on Signal Processing (2012), 60(5), 2508-2523 The performance of multiuser systems is both difficult to measure fairly and to optimize. Most resource allocation problems are nonconvex and NP-hard, even under simplifying assumptions such as perfect ... [more ▼] The performance of multiuser systems is both difficult to measure fairly and to optimize. Most resource allocation problems are nonconvex and NP-hard, even under simplifying assumptions such as perfect channel knowledge, homogeneous channel properties among users, and simple power constraints. We establish a general optimization framework that systematically solves these problems to global optimality. The proposed branch-reduce-and-bound (BRB) algorithm handles general multicell downlink systems with single-antenna users, multiantenna transmitters, arbitrary quadratic power constraints, and robust- ness to channel uncertainty. A robust fairness-profile optimization (RFO) problem is solved at each iteration, which is a quasiconvex problem and a novel generalization of max-min fairness. The BRB algorithm is computationally costly, but it shows better convergence than the previously proposed outer polyblock approximation algorithm. Our framework is suitable for computing benchmarks in general multicell systems with or without channel uncertainty. We illustrate this by deriving and evaluating a zero-forcing solution to the general problem. [less ▲] Detailed reference viewed: 183 (2 UL)Multi-objective Optimization Approach to Power Allocation in Multibeam Systems ; Shankar, Bhavani ; Danoy, Grégoire et al in Proceedings of 30th AIAA International Communications Satellite Systems Conference (ICSSC), (2012) Detailed reference viewed: 257 (30 UL)Capacity Analysis of Dual-Hop Amplify-and-Forward MIMO Multiple-Access Channels Chatzinotas, Symeon ; Ottersten, Björn in International Conference on Wireless Communications and Signal Processing, WCSP 2012 (2012) Relay channels have been heavily studied during the last decades as a means of improving spectral efficiency, availability and coverage in combination with multiple antenna transceivers. Relay channels ... [more ▼] Relay channels have been heavily studied during the last decades as a means of improving spectral efficiency, availability and coverage in combination with multiple antenna transceivers. Relay channels can comprise many hops but the most practical approach at the time being would be a dual-hop system. In addition, the simplest method of relaying in terms of complexity is amplify and forward. In this direction, we investigate the ergodic capacity of a dual-hop amplify-and-forward MIMO MAC and we derive asymptotic closed-form expressions based on the principles of free probability theory. We extend the current literature by proposing a analytical model which can accommodate variance-profiled Gaussian matrices. Numerical results are utilized to verify the accuracy of the derived closed-form expressions and evaluate the effect of the channel parameters. [less ▲] Detailed reference viewed: 168 (1 UL)Coordinated MultiPoint Uplink Capacity over a MIMO Composite Fading Channel Chatzinotas, Symeon ; Ottersten, Björn in ICNC 2012 (2012) Detailed reference viewed: 158 (2 UL)Real-Time Distance-Dependent Mapping for a Hybrid ToF Multi-Camera Rig Garcia Becerro, Frederic ; Aouada, Djamila ; et al in IEEE Journal of Selected Topics in Signal Processing (2012), 6(5), 1-12 Detailed reference viewed: 236 (6 UL)Successive zero-forcing DPC with sum power constraint: Low-complexity optimal designs ; ; et al in 2012 IEEE International Conference on Communications, ICC 2012 (2012) Successive zero-forcing dirty paper coding (SZF-DPC) is a simplified alternative to DPC for MIMO broadcast channels (MIMO BCs). In the SZF-DPC scheme, the noncausally-known interference is canceled by DPC ... [more ▼] Successive zero-forcing dirty paper coding (SZF-DPC) is a simplified alternative to DPC for MIMO broadcast channels (MIMO BCs). In the SZF-DPC scheme, the noncausally-known interference is canceled by DPC, while the residual interference is suppressed by the ZF technique. Due to the ZF constraints, the precoders are constrained to lie in the null space of a matrix. For the sum rate maximization problem under a sum power constraint, the existing precoder designs naturally rely on the singular value decomposition (SVD). The SVD-based design is optimal but needs high computational complexity. Herein, we propose two low-complexity optimal precoder designs for SZF-DPC, all based on the QR decomposition (QRD), which requires lower complexity than SVD. The first design method is an iterative algorithm to find an orthonormal basis of the null space of a matrix that has a recursive structure. The second proposed method, which will be shown to require the lowest complexity, results from applying a single QRD to the matrix comprising all users' channel matrices. We analytically and numerically show that the two proposed precoder designs are optimal. © 2012 IEEE. [less ▲] Detailed reference viewed: 168 (0 UL)On the optimality of beamformer design for zero-forcing DPC with QR decomposition ; ; et al in IEEE International Conference on Communications (2012) We consider the beamformer design for zero-forcing dirty paper coding (ZF-DPC), a suboptimal transmission technique for MISO broadcast channels (MISO BCs). Beamformers for ZF-DPC are designed to maximize ... [more ▼] We consider the beamformer design for zero-forcing dirty paper coding (ZF-DPC), a suboptimal transmission technique for MISO broadcast channels (MISO BCs). Beamformers for ZF-DPC are designed to maximize a performance measure, subject to some power constraints and zero-interference constraints. For the sum rate maximization problem under a total power constraint, the existing beamformer designs in the literature are based on the QR decomposition (QRD), which is used to satisfy the ZF constraints. However, the optimality of the QRD-based design is still unknown. First, we prove that the QRD-based design is indeed optimal for ZF-DPC for any performance measure under a sum power constraint. For the per-antenna power constraints, the QRD-based designs become suboptimal, and we propose an optimal design, using a convex optimization framework. Low-complexity suboptimal designs are also presented. © 2012 IEEE. [less ▲] Detailed reference viewed: 145 (0 UL) |
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