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15
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.
Backhaulconstrained multicell cooperation using compressive sensing and spectral clustering
 in Proc. Signal Processing Advances in Wireless Communications (SPAWC
, 2012
"... Multicell cooperative processing with limited backhaul traffic is considered for cellular uplinks. To parsimoniously select a set of cooperating base stations, a sparse multicell receivefilter is obtained through convex optimization using compressive sensing techniques. Clustered cooperation is ..."
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Cited by 9 (0 self)
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Multicell cooperative processing with limited backhaul traffic is considered for cellular uplinks. To parsimoniously select a set of cooperating base stations, a sparse multicell receivefilter is obtained through convex optimization using compressive sensing techniques. Clustered cooperation is also considered, where sparsity is promoted on intercluster feedback. A joint equalizer design and dynamic partitioning problem is formulated and solved using an iterative spectral clustering approach. Numerical tests verify the efficacy of proposed methods. 1.
Analysis of Multicell Cooperation with Random User Locations Via Deterministic Equivalents
"... Abstract—We consider the uplink of a onedimensional 2cell network with fixed base stations (BSs) and randomly distributed user terminals (UTs). Assuming that the number of antennas per BS and the number of UTs grow infinitely large, we derive tight approximations of the ergodic sum rate with and w ..."
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Abstract—We consider the uplink of a onedimensional 2cell network with fixed base stations (BSs) and randomly distributed user terminals (UTs). Assuming that the number of antennas per BS and the number of UTs grow infinitely large, we derive tight approximations of the ergodic sum rate with and without multicell processing for optimal and suboptimal detectors. We use these results to find the optimal BS placement to maximize the system capacity. This work can be seen as a first attempt to apply large random matrix theory to the study of networks with random topologies. We demonstrate that such an approach is feasible and leads to analytically tractable expressions of the average system performance. Moreover, these results can be used to optimize certain system parameters for a given distribution of user terminals and to assess the gains of multicell cooperation. I.
A Deterministic Equivalent for the Analysis of NonGaussian Correlated MIMO Multiple Access Channels
, 2011
"... Large dimensional random matrix theory (RMT) has provided an efficient analytical tool to understand multipleinput multipleoutput (MIMO) channels and to aid the design of MIMO wireless communication systems. However, previous studies based on large dimensional RMT rely on the assumption that the ..."
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Cited by 1 (0 self)
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Large dimensional random matrix theory (RMT) has provided an efficient analytical tool to understand multipleinput multipleoutput (MIMO) channels and to aid the design of MIMO wireless communication systems. However, previous studies based on large dimensional RMT rely on the assumption that the transmit correlation matrix is diagonal or the propagation channel matrix is Gaussian. There is an increasing interest in the channels where the transmit correlation matrices are generally nonnegative definite and the channel entries are nonGaussian. This class of channel models appears in several applications in MIMO multiple access systems, such as small cell networks (SCNs). To address these problems, we use the generalized Lindeberg principle to show that the Stieltjes transforms of this class of random matrices with Gaussian or nonGaussian independent entries coincide in the large dimensional regime. This result permits to derive the deterministic equivalents (e.g., the Stieltjes transform and the ergodic mutual information) for nonGaussian MIMO channels from the known results developed for Gaussian MIMO channels, and is of great importance in characterizing the spectral efficiency of SCNs.
Front Cover: Illustration of Base Station Coordination in a TwoCell Network
"... This thesis has been prepared using LATEX. ..."
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Iterative Deterministic Equivalents for the Performance Analysis of Communication Systems
, 2011
"... In this article, we introduce iterative deterministic equivalents as a novel technique for the performance analysis of communication systems whose channels are modeled by complex combinations of independent random matrices. This technique extends the deterministic equivalent approach for the study ..."
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In this article, we introduce iterative deterministic equivalents as a novel technique for the performance analysis of communication systems whose channels are modeled by complex combinations of independent random matrices. This technique extends the deterministic equivalent approach for the study of functionals of large random matrices to a broader class of random matrix models which naturally arise as channel models in wireless communications. We present two specific applications: First, we consider a multihop amplifyandforward (AF) MIMO relay channel with noise at each stage and derive deterministic approximations of the mutual information after the Kth hop. Second, we study a MIMO multiple access channel (MAC) where the channel between each transmitter and the receiver is represented by the doublescattering channel model. We provide deterministic approximations of the mutual information, the signaltointerferenceplusnoise ratio (SINR) and sumrate with minimummeansquareerror (MMSE) detection and derive the asymptotically optimal precoding matrices. In both scenarios, the approximations can be computed by simple and provably converging fixedpoint algorithms and are shown to be almost surely tight in the limit when the number of antennas at each node grows infinitely large. Simulations suggest that the approximations are accurate for realistic system dimensions. The technique of iterative deterministic equivalents can be easily extended to other channel models of interest and is, therefore, also a new contribution to the field of random matrix theory.
Télécommunications et des Systèmes »
"... Ecole Doctorale « Sciences et Technologies de l’Information des ..."
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Cognitive Orthogonal Precoder for Twotiered Networks Deployment 1
, 2014
"... In this work, we consider a twotiered network, where a tier of cognitive small base stations is deployed inside the coverage area of a preexisting macrocell. The crosstier interference caused by a complete bandwidth sharing is managed by introducing a new orthogonal precoder based mechanism, impl ..."
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In this work, we consider a twotiered network, where a tier of cognitive small base stations is deployed inside the coverage area of a preexisting macrocell. The crosstier interference caused by a complete bandwidth sharing is managed by introducing a new orthogonal precoder based mechanism, implemented by the small base stations. This technique, called multiuser Vandermondesubspace division multiplexing (MUVFDM), allows to cancel the interference generated by several cognitive small base stations towards legacy macro cell receivers, without any cooperation between the two tiers. The achievable sum rate of the smallcell network, satisfying the interference cancelation requirement, is evaluated for perfect/imperfect channel state information at the transmitter (CSIT). Simulation results for MUVFDM show a comparable performance to that of stateoftheart dirty paper coding technique, for the case of a dense cellular layout. Finally, we propose a comparison between MUVFDM and a standard spectrum partitioning strategy, and show promising gains in terms of achievable rate for the twotiered network w.r.t. the traditional bandwidth management approach.
1Optimal Antenna Cluster Size in CellFree LargeScale DistributedAntenna Systems with Imperfect CSI and InterCluster Interference
"... tems (LDAS), the antennas are distributed over the intended coverage area. Introducing cooperation among the antennas can significantly improve the system throughput. Whereas only finiteclustersize (limited) cooperation with LDAS antennaclusters is realistic due to practical limitations. In thi ..."
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tems (LDAS), the antennas are distributed over the intended coverage area. Introducing cooperation among the antennas can significantly improve the system throughput. Whereas only finiteclustersize (limited) cooperation with LDAS antennaclusters is realistic due to practical limitations. In this paper, the impact of antenna cluster size on the downlink sum rate of frequencydivision duplex (FDD) cellfree LDAS is analyzed considering imperfect channel state information (CSI) and intercluster interference (ICLI). We investigate the optimal cluster size, in terms of maximizing the downlink sum rate with respect to the overhead of imperfect channel training and feedback. When the number of users is sufficiently large, closedform lower bounds of the ergodic sum capacity, which are leveraged to analyze the system performance, are derived by constructing different rateachieving user scheduling schemes. Both analog and digital feedback schemes are considered to evaluate the imperfect channel feedback. Based upon these, closedform expressions of the optimal cluster size for onedimensional antennatopology systems and the corresponding achievable rates are derived. The scaling law of the optimal cluster size for twodimensional antennatopology systems is also given. Numerical results demonstrate the impact of signaltonoise ratio (SNR) and the block length on the achievable rates and the optimal cluster size, which agree with our analytical results. Index Terms—Distributed largescale antenna systems, Frequencydivisionduplex, Broadcast channel, Imperfect CSI. I.