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Träfflista för sökning "WFRF:(Debbah Merouane) srt2:(2010-2014)"

Sökning: WFRF:(Debbah Merouane) > (2010-2014)

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1.
  • Björnson, Emil, et al. (författare)
  • Circuit-aware design of energy-efficient massive MIMO systems
  • 2014
  • Ingår i: ISCCSP 2014 - 2014 6th International Symposium on Communications, Control and Signal Processing, Proceedings. - 9781479928903 ; , s. 101-104
  • Konferensbidrag (refereegranskat)abstract
    • Densification is a key to greater throughput in cellular networks. The full potential of coordinated multipoint (CoMP) can be realized by massive multiple-input multiple-output (MIMO) systems, where each base station (BS) has very many antennas. However, the improved throughput comes at the price of more infrastructure; hardware cost and circuit power consumption scale linearly/affinely with the number of antennas. In this paper, we show that one can make the circuit power increase with only the square root of the number of antennas by circuit-aware system design. To this end, we derive achievable user rates for a system model with hardware imperfections and show how the level of imperfections can be gradually increased while maintaining high throughput. The connection between this scaling law and the circuit power consumption is established for different circuits at the BS.
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2.
  • Björnson, Emil, et al. (författare)
  • Massive MIMO Systems With Non-Ideal Hardware : Energy Efficiency, Estimation, and Capacity Limits
  • 2014
  • Ingår i: IEEE Transactions on Information Theory. - : IEEE Press. - 0018-9448 .- 1557-9654. ; 60:11, s. 7112-7139
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of large-scale antenna arrays can bring substantial improvements in energy and/or spectral efficiency to wireless systems due to the greatly improved spatial resolution and array gain. Recent works in the field of massive multiple-input multiple-output (MIMO) show that the user channels decorrelate when the number of antennas at the base stations (BSs) increases, thus strong signal gains are achievable with little interuser interference. Since these results rely on asymptotics, it is important to investigate whether the conventional system models are reasonable in this asymptotic regime. This paper considers a new system model that incorporates general transceiver hardware impairments at both the BSs (equipped with large antenna arrays) and the single-antenna user equipments (UEs). As opposed to the conventional case of ideal hardware, we show that hardware impairments create finite ceilings on the channel estimation accuracy and on the downlink/uplink capacity of each UE. Surprisingly, the capacity is mainly limited by the hardware at the UE, while the impact of impairments in the large-scale arrays vanishes asymptotically and interuser interference (in particular, pilot contamination) becomes negligible. Furthermore, we prove that the huge degrees of freedom offered by massive MIMO can be used to reduce the transmit power and/or to tolerate larger hardware impairments, which allows for the use of inexpensive and energy-efficient antenna elements.
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3.
  • Björnson, Emil, et al. (författare)
  • Multiobjective Signal Processing Optimization : The way to balance conflicting metrics in 5G systems
  • 2014
  • Ingår i: IEEE signal processing magazine (Print). - : IEEE. - 1053-5888 .- 1558-0792. ; 31:6, s. 14-23
  • Tidskriftsartikel (refereegranskat)abstract
    • The evolution of cellular networks is driven by the dream of ubiquitous wireless connectivity: any data service is instantly accessible everywhere. With each generation of cellular networks, we have moved closer to this wireless dream; first by delivering wireless access to voice communications, then by providing wireless data services, and recently by delivering a Wi-Fi-like experience with wide-area coverage and user mobility management. The support for high data rates has been the main objective in recent years [1], as seen from the academic focus on sum-rate optimization and the efforts from standardization bodies to meet the peak rate requirements specified in IMT-Advanced. In contrast, a variety of metrics/objectives are put forward in the technological preparations for fifth-generation (5G) networks: higher peak rates, improved coverage with uniform user experience, higher reliability and lower latency, better energy efficiency (EE), lower-cost user devices and services, better scalability with number of devices, etc. These multiple objectives are coupled, often in a conflicting manner such that improvements in one objective lead to degradation in the other objectives. Hence, the design of future networks calls for new optimization tools that properly handle the existence of multiple objectives and tradeoffs between them.
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4.
  • Björnson, Emil, Professor, 1983-, et al. (författare)
  • On the impact of transceiver impairments on af relaying
  • 2013
  • Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 4948-4952, s. 4948-4952
  • Konferensbidrag (refereegranskat)abstract
    • Recently, it was shown that transceiver hardware impairments have a detrimental impact on the performance of communication systems, especially for high-rate systems. The vast majority of technical contributions in the area of relaying assume ideal transceiver hardware. This paper quantifies the impact of transceiver hardware impairments in dual-hop Amplify-and-Forward (AF) relaying, both for fixed and variable gain relays. The outage probability (OP) in this practical scenario is a function of the instantaneous end-to-end signal-to-noise-and-distortion ratio (SNDR). This paper derives closed-form expressions for the exact and asymptotic OPs under Rayleigh fading, accounting for hardware impairments at both the transmitter and the relay. The performance loss is small at low spectral efficiency, but can otherwise be very substantial. In particular, it turns out that for high signal-to-noise ratio (SNR), the instantaneous end-to-end SNDR converges to a deterministic constant, called the SNDR ceiling, which is inversely proportional to the level of impairments. This stands in stark contrast to the ideal hardware case for which the end-to-end SNDR grows without bound in the high SNR regime.
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5.
  • Björnson, Emil, et al. (författare)
  • Optimizing multi-cell massive MIMO for spectral efficiency : How Many users should be scheduled?
  • 2014
  • Ingår i: 2014 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2014. - : IEEE conference proceedings. - 9781479970889 ; , s. 612-616
  • Konferensbidrag (refereegranskat)abstract
    • Massive MIMO is a promising technique to increase the spectral efficiency of cellular networks, by deploying antenna arrays with hundreds or thousands of active elements at the base stations and performing coherent beamforming. A common rule-of-thumb is that these systems should have an order of magnitude more antennas, N, than scheduled users, K, because the users' channels are then likely to be quasi-orthogonal. However, it has not been proved that this rule-of-thumb actually maximizes the spectral efficiency. In this paper, we analyze how the optimal number of scheduled users, K, depends on N and other system parameters. The value of K in the large-N regime is derived in closed form, while simulations are used to show what happens at finite N, in different interference scenarios, and for different beamforming.
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6.
  • Gabry, Frederic (författare)
  • Secrecy in Cognitive Radio Networks
  • 2014
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • With the considerable growth of wireless networks in recent years, the issue of network security has taken an important role in the design of communication devices and protocols. Indeed, due to the broadcast nature of these networks, communications can potentially be attacked by malicious parties, and therefore, the protection of transmitted data has become a main concern in today's communications. On the other hand the cooperation of nodes overhearing the transmission may potentially lead to a better performance. In this thesis we combine both fundamental concepts of cooperation and secrecy in wireless networks. In particular we investigate the cooperation between transmitters in a cognitive radio network where the secondary receiver is treated as a potential eavesdropper to the primary transmission. We study this novel model focusing on several fundamental aspects.First we derive achievable rate regions for different transmission schemes, such as cooperative jamming and relaying, with and without primary message knowledge at the secondary transmitter. For these schemes, we formulate and solve three relevant power allocation problems: the maximization of the achievable primary and secondary rates, and the minimization of the secondary transmitting power. We model the interaction between the transmitting users as a Stackelberg game corresponding to a more realistic power allocation problem. We solve the game and illustrate its impact on the achievable rates.Secondly we generalize our system model by introducing the multi-phase clean relaying (CR) scheme, which takes into account the message-learning constraint at the secondary transmitter, and we derive the achievable rate region for this scheme. We compare our CR scheme to other transmission strategies such as dirty paper coding, interference neutralization, and pure cooperative jamming. Thirdly we extend our model to the generalized scenario where multiple secondary transmitter-receiver pairs wish to access the spectrum. For this scenario, we define and study several types of games between the primary network and the secondary pairs, such as Stackelberg games, power control games, and auction games. We derive the equilibrium of each game considered, which allows us to predict the behavior of the users in the cognitive radio network with multiple secondary pairs.Moreover we consider the important concept of energy efficiency (EE) for the performance of the cognitive radio network and we derive the power allocation and power splitting maximizing the secondary transmitter's energy efficiency. An important EE Stackelberg game between the two transmitters is formulated, and the impact of the game theoretic interaction is analyzed. Finally we motivate and investigate information theoretic secrecy using key agreement techniques in wireless networks. In particular we derive achievable secret key rate regions for two different key agreement schemes in Gaussian channels using several transmission strategies such as power control and cooperative jamming. The interaction between transmitting users is analyzed from a game theoretic perspective using non-cooperative game theory.For every fundamental perspective considered for the analysis of the model studied in the thesis, our results are illustrated through numerical examples based on a geometrical setup, highlighting the impact of the node geometry on the achievable rates, the optimal strategies, the games' equilibria and the impact of the game theoretic interaction between transmitters on the system performance.
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7.
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8.
  • Kammoun, Abla, et al. (författare)
  • Linear Precoding Based on Polynomial Expansion : Large-Scale Multi-Cell MIMO Systems
  • 2014
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 8:5, s. 861-875
  • Tidskriftsartikel (refereegranskat)abstract
    • Large-scale MIMO systems can yield a substantial improvements in spectral efficiency for future communication systems. Due to the finer spatial resolution and array gain achieved by a massive number of antennas at the base station, these systems have shown to be robust to inter-user interference and the use of linear precoding appears to be asymptotically optimal. However, from a practical point of view, most precoding schemes exhibit prohibitively high computational complexity as the system dimensions increase. For example, the near-optimal regularized zero forcing (RZF) precoding requires the inversion of a large matrix. To solve this issue, we propose in this paper to approximate the matrix inverse by a truncated polynomial expansion (TPE), where the polynomial coefficients are optimized to maximize the system performance. This technique has been recently applied in single cell scenarios and it was shown that a small number of coefficients is sufficient to reach performance similar to that of RZF, while it was not possible to surpass RZF. In a realistic multi-cell scenario involving large-scale multi-user MIMO systems, the optimization of RZF precoding has, thus far, not been feasible. This is mainly attributed to the high complexity of the scenario and the non-linear impact of the necessary regularizing parameters. On the other hand, the scalar coefficients in TPE precoding give hope for possible throughput optimization. To this end, we exploit random matrix theory to derive a deterministic expression of the asymptotic signal-to-interference-and-noise ratio for each user based on channel statistics. We also provide an optimization algorithm to approximate the coefficients that maximize the network-wide weighted max-min fairness. The optimization weights can be used to mimic the user throughput distribution of RZF precoding. Using simulations, we compare the network throughput of the proposed TPE precoding with that of the suboptimal RZF scheme and show that our scheme can achieve higher throughput using a TPE order of only 5.
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9.
  • Lindskog, Stefan, et al. (författare)
  • NEWCOM++ DRA.2: Advanced algorithms and metrics for wireless secrecy and security
  • 2010
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The report deals with Advanced Algorithms and Metrics for Wireless Secrecy and Security developed within the framework of Newcom++ (contrarily to the first report which was an overview of existing results). As far as wireless secrecy is concerned, the notion of information theoretic secrecy capacity is extended to different types of channels such as the interference channel, the relay channel as well as the wiretap frequency selective channel. Practical algorithms are derived in the case of multi-carrier channels such as the OFDM case through the notion of Vandermonde precoding. In the second part of the report, Wireless security focuses on Wireless Sensor Networks. After an overview of different wireless technologies, a risk analysis approach is proposed together with a taxonomy of wireless security attacks and descriptions of threats and known vulnerabilities in wireless networks in general. Finally, a framework that enables a formal reasoning and description of a WSN system is provided
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10.
  • Lindskog, Stefan, et al. (författare)
  • NEWCOM++ DRA.3: Final report about security in wireless networks
  • 2010
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The report deals with advanced schemes for Wireless Secrecy and Security evaluation tools developed within the framework of Newcom++. As far as wireless secrecy is concerned, different cases are treated, namely the multi-antenna fading case, the frequency selective channel case (with OFDM modulation) and the the relay channel case. Besides the major information theoretic consideration related to capacity issues, physical layer coding, Secure Lossy Source Coding as well as classical precoding (through beamforming) schemes are analyzed. The second part of the report is dedicated to security evaluation tools and provides a framework for a formal reasoning and description of wireless sensor networks (WSN). Some input models for the design and evaluation of WSN security are provided, especially for 6LoWPAN Networks. The report finishes with an important contribution related to a Penetration Testing tool developed for 6LoWPAN
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11.
  • Marzetta, Thomas L., et al. (författare)
  • Special issue on Massive MIMO
  • 2013
  • Ingår i: Journal of Communications and Networks. - : IEEE. - 1229-2370 .- 1976-5541. ; 15:4, s. 333-337
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Demand for wireless communications is projected to grow by more than a factor of forty or more over the next five years. A potential technology for meeting this demand is Massive MIMO (also called Large-Scale Antenna Systems, Large-Scale MIMO, ARGOS, Full-Dimension MIMO, or Hyper-MIMO), a form of multiuser multipleantenna wireless which promises orders-of-magnitude improvements in spectral-efficiency over 4G technology, and accompanying improvements in radiated energy-efficiency. The distinguishing feature of Massive MIMO is that a large number of service-antennas ?? possibly hundreds or even thousands ?? work for a significantly smaller number of active autonomous terminals. Upsetting the traditional parity between service antennas and terminals in this manner is a game-changer: The simplest multiplexing precoding and decoding algorithms can be nearly optimal, expensive ultra-linear forty-Watt power amplifiers are replaced by many low-power units, and the favorable action of the law of large numbers can greatly facilitate power-control and resource-allocation.
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12.
  • Matthaiou, Michail, et al. (författare)
  • Two-Way Relaying Under the Presence of Relay Transceiver Hardware Impairments
  • 2013
  • Ingår i: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 17:6, s. 1136-1139
  • Tidskriftsartikel (refereegranskat)abstract
    • Hardware impairments in physical transceivers are known to have a deleterious effect on communication systems; however, very few contributions have investigated their impact on relaying. This paper quantifies the impact of transceiver impairments in a two-way amplify-and-forward configuration. More specifically, the effective signal-to-noise-and-distortion ratios at both transmitter nodes are obtained. These are used to deduce exact and asymptotic closed-form expressions for the outage probabilities (OPs), as well as tractable formulations for the symbol error rates (SERs). It is explicitly shown that non-zero lower bounds on the OP and SER exist in the high-power regime-this stands in contrast to the special case of ideal hardware, where the OP and SER go asymptotically to zero.
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13.
  • Sanguinetti, Luca, et al. (författare)
  • Energy Consumption in Multi-User MIMO Systems : Impact of User Mobility
  • 2014
  • Ingår i: 2014 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 4743-4747
  • Konferensbidrag (refereegranskat)abstract
    • In this work, we consider the downlink of a single-cell multi-user multiple-input multiple-output system in which zero-forcing precoding is used at the base station (BS) to serve a certain number of user equipments (UEs). A fixed data rate is guaranteed at each UE. The UEs move around in the cell according to a Brownian motion, thus the path losses change over time and the energy consumption fluctuates accordingly. We aim at determining the distribution of the energy consumption. To this end, we analyze the asymptotic regime where the number of antennas at the BS and the number of UEs grow large with a given ratio. It turns out that the energy consumption is asymptotically a Gaussian random variable whose mean and variance are derived analytically. These results can, for example, be used to approximate the probability that a battery-powered BS runs out of energy within a certain time period.
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14.
  • Shalmashi, Serveh, et al. (författare)
  • Closed-Form Optimality Characterization of Network-Assisted Device-to-Device Communications
  • 2014
  • Ingår i: Proceedings of the IEEE Wireless Communications and Networking Conference (WCNC).
  • Konferensbidrag (refereegranskat)abstract
    • This paper considers the mode selection problem for network-assisted device-to-device (D2D) communications with multiple antennas at base station. We study transmission in both dedicated and shared frequency bands. Given the type of resources (i.e., dedicated or shared), the user equipment (UE) decides to transmit in the conventional cellular mode or directly to its corresponding receiver in D2D mode. We formulate this problem under two different objectives. The first problem is to maximize the quality-of-service (QoS) given a transmit power, and the second problem is to minimize the transmit power given a QoS requirement. We derive closed-form results for the optimal decision and show that the two problem formulations behave differently. Taking a geometrical approach, we study the area around the transmitter UE where the receiving UE should be to have D2D mode optimality, and how it is affected by the transmit power, QoS, and the number of base station antennas.
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15.
  • Shariati, Nafiseh, et al. (författare)
  • Low-Complexity Channel Estimation in Large-Scale MIMO using Polynomial Expansion
  • 2013
  • Ingår i: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC). - : IEEE conference proceedings. - 9781467362351 ; , s. 1157-1162
  • Konferensbidrag (refereegranskat)abstract
    • This paper considers pilot-based channel estimation in large-scale multiple-input multiple-output (MIMO) communication systems, also known as "massive MIMO". Unlike previous works on this topic, which mainly considered the impact of inter-cell disturbance due to pilot reuse (so-called pilot contamination), we are concerned with the computational complexity. The conventional minimum mean square error (MMSE) and minimum variance unbiased (MVU) channel estimators rely on inverting covariance matrices, which has cubic complexity in the multiplication of number of antennas at each side. Since this is extremely expensive when there are hundreds of antennas, we propose to approximate the inversion by an L-order matrix polynomial. A set of low-complexity Bayesian channel estimators, coined Polynomial ExpAnsion CHannel (PEACH) estimators, are introduced. The coefficients of the polynomials are optimized to yield small mean square error (MSE). We show numerically that near-optimal performance is achieved with low polynomial orders. In practice, the order L can be selected to balance between complexity and MSE. Interestingly, pilot contamination is beneficial to the PEACH estimators in the sense that smaller L can be used to achieve near-optimal MSEs.
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16.
  • Shariati, Nafiseh, et al. (författare)
  • Low-Complexity Polynomial Channel Estimation in Large-Scale MIMO with Arbitrary Statistics
  • 2014
  • Ingår i: IEEE Journal on Selected Topics in Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1932-4553 .- 1941-0484. ; 8:5, s. 815-830
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper considers pilot-based channel estimation in large-scale multiple-input multiple-output (MIMO) communication systems, also known as “massive MIMO”, where there are hundreds of antennas at one side of the link. Motivated by the fact that computational complexity is one of the main challenges in such systems, a set of low-complexity Bayesian channel estimators, coined Polynomial ExpAnsion CHannel (PEACH) estimators, are introduced for arbitrary channel and interference statistics. While the conventional minimum mean square error (MMSE) estimator has cubic complexity in the dimension of the covariance matrices, due to an inversion operation, our proposed estimators significantly reduce this to square complexity by approximating the inverse by a L-degree matrix polynomial. The coefficients of the polynomial are optimized to minimize the mean square error (MSE) of the estimate. We show numerically that near-optimal MSEs are achieved with low polynomial degrees. We also derive the exact computational complexity of the proposed estimators, in terms of the floating-point operations (FLOPs), by which we prove that the proposed estimators outperform the conventional estimators in large-scale MIMO systems of practical dimensions while providing a reasonable MSEs. Moreover, we show that L needs not scale with the system dimensions to maintain a certain normalized MSE. By analyzing different interference scenarios, we observe that the relative MSE loss of using the low-complexity PEACH estimators is smaller in realistic scenarios with pilot contamination. On the other hand, PEACH estimators are not well suited for noise-limited scenarios with high pilot power; therefore, we also introduce the low-complexity diagonalized estimator that performs well in this regime. Finally, we also investigate numerically how the estimation performance is affected by having imperfect statistical knowledge. High robustness is achieved for large-dimensional matrices by us- ng a new covariance estimate which is an affine function of the sample covariance matrix and a regularization term.
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