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Joint beamforming and power control in coordinated multicell: Maxmin duality, effective network and large system transition
 IEEE TRANS. WIRELESS COMMUN
, 2013
"... This paper studies joint beamforming and power control in a coordinated multicell downlink system that serves multiple users per cell to maximize the minimum weighted signaltointerferenceplusnoise ratio. The optimal solution and distributed algorithm with geometrically fast convergence rate are ..."
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This paper studies joint beamforming and power control in a coordinated multicell downlink system that serves multiple users per cell to maximize the minimum weighted signaltointerferenceplusnoise ratio. The optimal solution and distributed algorithm with geometrically fast convergence rate are derived by employing the nonlinear PerronFrobenius theory and the multicell network duality. The iterative algorithm, though operating in a distributed manner, still requires instantaneous power update within the coordinated cluster through the backhaul. The backhaul information exchange and message passing may become prohibitive with increasing number of transmit antennas and increasing number of users. In order to derive asymptotically optimal solution, random matrix theory is leveraged to design a distributed algorithm that only requires statistical information. The advantage of our approach is that there is no instantaneous power update through backhaul. Moreover, by using nonlinear PerronFrobenius theory and random matrix theory, an effective primal network and an effective dual network are proposed to characterize and interpret the asymptotic solution.
Large system analysis of cooperative multicell downlink transmission via regularized channel inversion with imperfect CSIT
 IEEE Trans. Wireless Commun
, 2013
"... Abstract—In this paper, we analyze the ergodic sumrate of a multicell downlink system with base station (BS) cooperation using regularized zeroforcing (RZF) precoding. Our model assumes that the channels between BSs and users have independent spatial correlations and imperfect channel state info ..."
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Abstract—In this paper, we analyze the ergodic sumrate of a multicell downlink system with base station (BS) cooperation using regularized zeroforcing (RZF) precoding. Our model assumes that the channels between BSs and users have independent spatial correlations and imperfect channel state information at the transmitter (CSIT) is available. Our derivations are based on large dimensional random matrix theory (RMT) under the assumption that the numbers of antennas at the BS and users approach to infinity with some fixed ratios. In particular, a deterministic equivalent expression of the ergodic sumrate is obtained and is instrumental in getting insight about the joint operations of BSs, which leads to an efficient method to find the asymptoticoptimal regularization parameter for the RZF. In another application, we use the deterministic channel rate to study the optimal feedback bit allocation among the BSs for maximizing the ergodic sumrate, subject to a total number of feedback bits constraint. By inspecting the properties of the allocation, we further propose a scheme to greatly reduce the search space for optimization. Simulation results demonstrate that the ergodic sumrates achievable by a subspace search provides comparable results to those by an exhaustive search under various typical settings. Index Terms—Large dimensional RMT, multicell cooperation, regularized zeroforcing, feedback bit allocation. I.
An ESPRITbased approach for 2D localization of incoherently distributed sources in massive MIMO systems
 IEEE J. Sel. Topics Signal Process
, 2014
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Uplink Linear Receivers for MultiCell Multiuser MIMO With Pilot Contamination: Large System Analysis
, 2013
"... Abstract—Base stations with a large number of transmit antennas can potentially serve a large number of users at high rates. However, the receiver processing in the uplink relies on channel estimates, which are known to suffer from pilot interference. In this paper, making use of the similarity of ..."
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Abstract—Base stations with a large number of transmit antennas can potentially serve a large number of users at high rates. However, the receiver processing in the uplink relies on channel estimates, which are known to suffer from pilot interference. In this paper, making use of the similarity of the uplink received signal in CDMA with that of a multicell multiantenna system, we perform a large system analysis when the receiver employs an MMSE filter with a pilot contaminated estimate. We assume a Rayleigh fading channel with different received powers from users. We find the asymptotic signal to interference plus noise ratio (SINR) as the number of antennas and number of users per base station grow larger while maintaining a fixed ratio. Through the SINR expression we explore the scenario where the number of users being served are comparable to the number of antennas at the base station. The SINR explicitly captures the effect of pilot contamination and is found to be the same as that employing a matched filter with a pilot contaminated estimate. We also find the exact expression for the interference suppression obtained using an MMSE filter, which is an important factor when there are a significant number of users in the system as compared to the number of antennas. In a typical set up, in terms of the five percentile SINR, the MMSE filter is shown to provide significant gains over matched filtering and is within 5 dB of MMSE filter with perfect channel estimate. Simulation results for achievable rates are close to large system limits for even a 10antenna base station with 3 or more users per cell. Index Terms—Massive MIMO, MUMIMO, large scale antenna systems (LSAS), pilot contamination, channel estimation, land mobile radio cellular systems, OFDM, multiuser detection, large system analysis. I.
Asymptotic analysis of downlink MISO systems over Rician fading channels,” in
 Proc. IEEE ICASSP,
, 2016
"... ABSTRACT In this work, we focus on the ergodic sum rate in the downlink of a singlecell largescale multiuser MIMO system in which the base station employs N antennas to communicate with K singleantenna user equipments. A regularized zeroforcing (RZF) scheme is used for precoding under the assu ..."
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ABSTRACT In this work, we focus on the ergodic sum rate in the downlink of a singlecell largescale multiuser MIMO system in which the base station employs N antennas to communicate with K singleantenna user equipments. A regularized zeroforcing (RZF) scheme is used for precoding under the assumption that each link forms a spatially correlated MIMO Rician fading channel. The analysis is conducted assuming N and K grow large with a non trivial ratio and perfect channel state information is available at the base station. Recent results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signaltointerferenceplusnoise ratio as a function of the system parameters, the spatial correlation matrix and the Rician factor. Numerical results are used to evaluate the performance gap in the finite system regime under different operating conditions.
ABSTRACT OF THE DISSERTATION Coverage and Capacity of Next Generation Cellular Radio Systems: Bandwidth Sharing and Massive MIMO
, 2013
"... In the first part of the thesis we investigate bandwidth allocation in next generation cellular systems employing relays similar to LTE advanced systems with typeI relays. We jointly optimize the bandwidth and power usage under constraints on required rate, bandwidth and transmit power. We study sc ..."
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In the first part of the thesis we investigate bandwidth allocation in next generation cellular systems employing relays similar to LTE advanced systems with typeI relays. We jointly optimize the bandwidth and power usage under constraints on required rate, bandwidth and transmit power. We study scenarios wherein, the relay acts as a forwarder for multiple User Equipments (UEs/users) in both uplink and/or downlink. This includes scenarios when the relay has its own data to send along with forwarding the data of other users. We examine the weighted power minimization problem for relaying with multiple users. We also show specific results with N user scenario and also single user case in order to understand how the bandwidth and power are allocated. Numerical evaluations with N users on a three sector LTEA cell employing Fractional Frequency Reuse (FFR) indicate that power savings of at least 3 dB can be achieved by optimizing over both bandwidth and power. Base stations with a large number of transmit antennas have the potential to serve a large number of users simultaneously at higher rates. They also promise a lower power consumption due to coherent combining at the receiver. However, the receiver
ASYMPTOTIC ANALYSIS OF DOWNLINKMISO SYSTEMS OVER RICIAN FADING CHANNELS
"... In this work, we focus on the ergodic sum rate in the downlink of a singlecell largescale multiuser MIMO system in which the base station employs N antennas to communicate withK singleantenna user equipments. A regularized zeroforcing (RZF) scheme is used for precoding under the assumption that ..."
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In this work, we focus on the ergodic sum rate in the downlink of a singlecell largescale multiuser MIMO system in which the base station employs N antennas to communicate withK singleantenna user equipments. A regularized zeroforcing (RZF) scheme is used for precoding under the assumption that each link forms a homogeneous spatially correlated MIMO Rician fading channel. The analysis is conducted assuming N and K grow large with a non trivial ratio and perfect channel state information is available at the base station. Recent results from random matrix theory and large system analysis are used to compute an asymptotic expression of the signaltointerferenceplusnoise ratio as a function of the system parameters, the spatial correlation matrix and the Rician factor. Numerical results are used to evaluate the performance gap in the finite system regime under different operating conditions. 1.
Transmitter Design for Uplink MIMO Systems With Antenna Correlation
"... Abstract—We study the uplink transmission in multipleinput multipleoutput (MIMO) systems with antenna correlation. We focus on schemes that require only channel covariance information at the transmitter (CCIT), which involves lower cost than full channel state information at the transmitter (CSIT) ..."
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Abstract—We study the uplink transmission in multipleinput multipleoutput (MIMO) systems with antenna correlation. We focus on schemes that require only channel covariance information at the transmitter (CCIT), which involves lower cost than full channel state information at the transmitter (CSIT). We start from mutual information analysis and show that a simple CCITbased scheme, referred to as statistical waterfilling (SWF), can perform close to the optimal full CSITbased one in MIMO systems with more receive antennas than transmit ones. We then focus on the implementation of SWF in practically coded systems. An iterative linear minimum mean squared error (LMMSE) receiver is assumed and an extrinsic information transfer (EXIT) chart type curve matching technique is developed based on Hadamard precoding techniques. Simulation results show that the proposed scheme can obtain significant performance improvement compared to the conventional equal power transmission. Finally, we show that the proposed scheme is also very efficient in multiuser uplink MIMO systems with distributed channel information. Index Terms—Uplink MIMO, antenna correlation, channel covariance information. I.
Performance Analysis and Location Optimization for Massive MIMO Systems with Circularly Distributed Antennas
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1Asymptotic Rate Analysis of Downlink Multiuser Systems with Colocated and Distributed Antennas
"... A great deal of efforts have been made on the performance evaluation of distributed antenna systems (DASs). Most of them assume a regular basestation (BS) antenna layout where the number of BS antennas is usually small. With the growing interest in cellular systems with large antenna arrays at BSs, ..."
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A great deal of efforts have been made on the performance evaluation of distributed antenna systems (DASs). Most of them assume a regular basestation (BS) antenna layout where the number of BS antennas is usually small. With the growing interest in cellular systems with large antenna arrays at BSs, it becomes increasingly important for us to study how the BS antenna layout affects the rate performance when a massive number of BS antennas are employed. This paper presents a comparative study of the asymptotic rate performance of downlink multiuser systems with multiple BS antennas either colocated or uniformly distributed within a circular cell. Two representative linear precoding schemes, maximum ratio transmission (MRT) and zeroforcing beamforming (ZFBF), are considered, with which the effect of BS antenna layout on the rate performance is characterized. The analysis shows that as the number of BS antennas L and the number of users K grow infinitely while L/K→υ, the asymptotic average user rates with the colocated antenna (CA) layout for both MRT and ZFBF are logarithmic functions of the ratio υ. With the distributed antenna (DA) layout, in contrast, the scaling behavior of the average user rate closely depends on the precoding schemes. With ZFBF, for instance, the average user rate grows unboundedly as L,K→ ∞ and L/K→υ>1, which indicates that substantial rate gains over the CA layout can be achieved when the number of BS antennas L is large. The gain, nevertheless, becomes marginal when MRT is adopted. Index Terms Asymptotic rate analysis, downlink multiuser system, distributed antenna system (DAS), linear precoding, maximum ratio transmission (MRT), zeroforcing beamforming (ZFBF).