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30
Network mimo with linear zeroforcing beamforming: Large system analysis, impact of channel estimation, and reducedcomplexity scheduling,” Information Theory
 IEEE Transactions on
, 2012
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Massive MIMO Systems with NonIdeal Hardware: Energy Efficiency, Estimation, and Capacity Limits
, 2014
"... The use of largescale 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 multipleinput multipleoutput (MIMO) show that the user channels dec ..."
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Cited by 29 (6 self)
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The use of largescale 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 multipleinput multipleoutput (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 singleantenna 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 largescale 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 energyefficient antenna elements.
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
"... This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without rely ..."
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Cited by 18 (1 self)
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This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without relying on higherlayer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on informationtheoretic security. We then describe the evolution of secure transmission strategies from pointtopoint channels to multipleantenna systems, followed by generalizations to multiuser broadcast, multipleaccess, interference, and relay networks. Secretkey generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of interdisciplinary approaches based on game theory and stochastic geometry. The associated problem of physical layer message authentication is also briefly introduced. The survey concludes with observations on potential research directions in this area.
An overview of massive MIMO: Benefits and challenges
 IEEE J. SEL. TOPICS SIGNAL PROCESS
, 2014
"... Massive multipleinput multipleoutput (MIMO) wireless communications refers to the idea equipping cellular base stations (BSs) with a very large number of antennas, and has been shown to potentially allow for orders of magnitude improvement in spectral and energy efficiency using relatively simple ..."
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Cited by 12 (4 self)
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Massive multipleinput multipleoutput (MIMO) wireless communications refers to the idea equipping cellular base stations (BSs) with a very large number of antennas, and has been shown to potentially allow for orders of magnitude improvement in spectral and energy efficiency using relatively simple (linear) processing. In this paper, we present a comprehensive overview of stateoftheart research on the topic, which has recently attracted considerable attention. We begin with an information theoretic analysis to illustrate the conjectured advantages of massive MIMO, and then we address implementation issues related to channel estimation, detection and precoding schemes. We particularly focus on the potential impact of pilot contamination caused by the use of nonorthogonal pilot sequences by users in adjacent cells. We also analyze the energy efficiency achieved by massive MIMO systems, and demonstrate how the degrees of freedom provided by massive MIMO systems enable efficient singlecarrier transmission. Finally, the challenges and opportunities associated with implementing massive MIMO in future wireless communications systems are discussed.
1 Robust MEstimation for Array Processing: A Random Matrix Approach
"... Abstract—This article studies the limiting behavior of a robust Mestimator of population covariance matrices as both the number of available samples and the population size are large. Using tools from random matrix theory, we prove that the difference between the sample covariance matrix and (a sca ..."
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Cited by 10 (5 self)
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Abstract—This article studies the limiting behavior of a robust Mestimator of population covariance matrices as both the number of available samples and the population size are large. Using tools from random matrix theory, we prove that the difference between the sample covariance matrix and (a scaled version of) the robust Mestimator tends to zero in spectral norm, almost surely. This result is applied to prove that recent subspace methods arising from random matrix theory can be made robust without altering their first order behavior. I.
Linear precoding based on polynomial expansion: Reducing complexity . . .
 IEEE J. SEL. TOPICS SIGNAL PROCESS
, 2014
"... Massive multipleinput multipleoutput (MIMO) techniques have the potential to bring tremendous improvements in spectral efficiency to future communication systems. Counterintuitively, the practical issues of having uncertain channel knowledge, high propagation losses, and implementing optimal non ..."
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Cited by 10 (5 self)
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Massive multipleinput multipleoutput (MIMO) techniques have the potential to bring tremendous improvements in spectral efficiency to future communication systems. Counterintuitively, the practical issues of having uncertain channel knowledge, high propagation losses, and implementing optimal nonlinear precoding are solved moreorless automatically by enlarging system dimensions. However, the computational precoding complexity grows with the system dimensions. For example, the closetooptimal and relatively “antennaefficient ” regularized zeroforcing (RZF) precoding is very complicated to implement in practice, since it requires fast inversions of large matrices in every coherence period. Motivated by the high performance of RZF, we propose to replace the matrix inversion and multiplication by a truncated polynomial expansion (TPE), thereby obtaining the new TPE precoding scheme which is more suitable for realtime hardware implementation and significantly reduces the delay to the first transmitted symbol. The degree of the matrix polynomial can be adapted to the available hardware resources and enables smooth transition between simple maximum ratio transmission and more advanced RZF. By deriving new random matrix results, we obtain a deterministic expression for the asymptotic signaltointerferenceandnoise ratio (SINR) achieved by TPE precoding in massive MIMO systems. Furthermore, we provide a closedform expression for the polynomial coefficients that maximizes this SINR. To maintain a fixed peruser rate loss as compared to RZF, the polynomial degree does not need to scale with the system, but it should be increased with the quality of the channel knowledge and the signaltonoise ratio.
Secrecy rates in the broadcast channel with confidential messages and external eavesdroppers,” submitted to
 IEEE Trans. Wireless Commun
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Random Beamforming over QuasiStatic and Fading Channels: A Deterministic Equivalent Approach
"... In this work, we study the performance of random isometric precoding over quasistatic and correlated fading channels. We derive deterministic approximations of the mutual information and the signaltointerferenceplusnoise ratio (SINR) at the output of the minimummeansquareerror (MMSE) receive ..."
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Cited by 4 (2 self)
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In this work, we study the performance of random isometric precoding over quasistatic and correlated fading channels. We derive deterministic approximations of the mutual information and the signaltointerferenceplusnoise ratio (SINR) at the output of the minimummeansquareerror (MMSE) receiver and provide simple provably converging fixedpoint algorithms for their computation. Although the deterministic approximations are only asymptotically exact, almost surely, we show by simulations that they are very accurate for small system dimensions. The analysis is based on the Stieltjes transform method which enables the derivation of deterministic equivalents of functionals of largedimensional random matrices. In contrast to previous works, our analysis does not rely on arguments from free probability theory which allows us to consider random matrix models for which asymptotic freeness does not hold. Thus, the results of this work are also a novel contribution to the field of random matrix theory and are shown to be applicable to a wide spectrum of practical systems. In this article, we specifically characterize the performance of multicellular communication systems, multipleinput multipleoutput multipleaccess channels (MIMOMAC), and MIMO interference channels.
Analysis and Management of Heterogeneous User Mobility in Largescale Downlink Systems
 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS, UNITED STATES
, 2013
"... Modern cellular networks need to serve user terminals with large disparities in mobility, which incurs different accuracy of the channel state information for each user. The impact of such heterogeneous mobility on the multicell downlink is analyzed in this paper. The base stations serve a multitu ..."
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Cited by 4 (0 self)
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Modern cellular networks need to serve user terminals with large disparities in mobility, which incurs different accuracy of the channel state information for each user. The impact of such heterogeneous mobility on the multicell downlink is analyzed in this paper. The base stations serve a multitude of users by coordinated beamforming. We derive deterministic equivalents for the user performance in a large scale system where the number of transmit antennas and user terminals grow large at a fixed ratio. We show that low and high mobility users can coexist and be served simultaneously, since the CSI imperfections of a user only harms the performance of this particular user. Simulations are used to verify the applicability of our large scale approximations for systems of practical dimensions. Furthermore, we show that the performance of high mobility users can be improved by explicitly managing the user priorities in the network.