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52
Large system analysis of linear precoding in correlated MISO broadcast channels under limited feedback
- IEEE TRANS. INF. THEORY
, 2012
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Design and Experimental Evaluation of Multi-User Beamforming in Wireless LANs
"... Multi-User MIMO promises to increase the spectral efficiency of next generation wireless systems and is currently being incorporated in future industry standards. Although a significant amount of research has focused on theoretical capacity analysis, little is known about the performance of such sys ..."
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Cited by 49 (6 self)
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Multi-User MIMO promises to increase the spectral efficiency of next generation wireless systems and is currently being incorporated in future industry standards. Although a significant amount of research has focused on theoretical capacity analysis, little is known about the performance of such systems in practice. In this paper, we present the design and implementation of the first multiuser beamforming system and experimental framework for wireless LANs. Using extensive measurements in an indoor environment, we evaluate the impact of receiver separation distance, outdated channel information due to mobility and environmental variation, and the potential for increasing spatial reuse. For the measured indoor environment, our results reveal that two receivers achieve close to maximum performance with a minimum separation distance of a quarter of a wavelength. We also show that the required channel information update rate is dependent on environmental variation and user mobility as well as a per-link SNR requirement. Assuming that a link can tolerate an SNR decrease of 3 dB, the required channel update rate is equal to 100 and 10 ms for non-mobile receivers and mobile receivers with a pedestrian speed of 3 mph respectively. Our results also show that spatial reuse can be increased by efficiently eliminating interference at any desired location; however, this may come at the expense of a significant drop in the quality of the served users.
Cooperative Multi-cell Block Diagonalization with Per-Base-Station Power Constraints
, 2010
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Large System Analysis of Linear Precoding in MISO Broadcast Channels with Limited Feedback
, 2010
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Robust monotonic optimization framework for multicell MISO systems
- IEEE Trans. Signal Process
, 2012
"... Abstract—The performance of multiuser systems is both diffi-cult to measure fairly and to optimize. Most resource allocation problems are non-convex and NP-hard, even under simplifying assumptions such as perfect channel knowledge, homogeneous channel properties among users, and simple power constra ..."
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Cited by 22 (3 self)
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Abstract—The performance of multiuser systems is both diffi-cult to measure fairly and to optimize. Most resource allocation problems are non-convex 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 system-atically solves these problems to global optimality. The pro-posed branch-reduce-and-bound (BRB) algorithm handles general multicell downlink systems with single-antenna users, multi-antenna transmitters, arbitrary quadratic power constraints, and robustness to channel uncertainty. A robust fairness-profile optimization (RFO) problem is solved at each iteration, which is a quasi-convex 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. Index Terms—Branch-reduce-and-bound, dynamic coopera-tion clusters, fairness-profile, Network MIMO, optimal resource allocation, performance region, worst-case robustness.
Rethinking network MIMO: cost of CSIT, performance analysis, and architecture comparisons
- in Proc Info Theory and App Workshop
, 2010
"... Abstract—We compare the downlink throughput of various cellular architectures with multi-antenna base stations and multiple single-antenna users per cell, by considering a number of inherent physical layer issues such as path-loss and time and frequency selective fading. In particular, we focus on M ..."
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Cited by 20 (0 self)
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Abstract—We compare the downlink throughput of various cellular architectures with multi-antenna base stations and multiple single-antenna users per cell, by considering a number of inherent physical layer issues such as path-loss and time and frequency selective fading. In particular, we focus on Multiuser MIMO (MU-MIMO) downlink techniques that require channel state information at the transmitter (CSIT). Our analysis takes explicit account of the cost of CSIT estimation and illuminates the tradeoffs between CSIT, estimation error, and system resource dedicated to training. This tradeoff shows that the number of antennas that can be jointly coordinated (either on the same base station or across multiple base stations) is intrinsically limited not just by “external factors, ” such as complexity and rate of the backbone wired network, but by the inherent time and frequency variability of the fading channels. Our analysis, in agreement with a number of recent simulation results, shows that conventional MU-MIMO cellular architectures may outperform schemes based on coordinated transmission from base stations (referred to as Network MIMO schemes, NW-MIMO), at the negligible cost of a few extra antennas per station. In light of these results, it appears that the inherent bottleneck of NW-MIMO systems is not the backbone network (which here is assumed ideal with infinite capacity) but the intrinsic dimensional limitation of estimating the channels. I.
Optimality Properties, Distributed Strategies, and Measurement-Based Evaluation of Coordinated Multicell OFDMA Transmission
, 2011
"... The throughput of multicell systems is inherently limited by interference and the available communication re-sources. Coordinated resource allocation is the key to efficient performance, but the demand on backhaul signaling and compu-tational resources grows rapidly with number of cells, terminals, ..."
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Cited by 14 (4 self)
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The throughput of multicell systems is inherently limited by interference and the available communication re-sources. Coordinated resource allocation is the key to efficient performance, but the demand on backhaul signaling and compu-tational resources grows rapidly with number of cells, terminals, and subcarriers. To handle this, we propose a novel multicell framework with dynamic cooperation clusters where each termi-nal is jointly served by a small set of base stations. Each base station coordinates interference to neighboring terminals only, thus limiting backhaul signalling and making the framework scalable. This framework can describe anything from interference channels to ideal joint multicell transmission. The resource allocation (i.e., precoding and scheduling) is formulated as an optimization problem (P1) with performance described by arbitrary monotonic functions of the signal-to-
Pareto Characterization of the Multicell MIMO Performance Region With Simple Receivers
- IEEE TRANSACTIONS ON SIGNAL PROCESSING
, 2012
"... 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 com ..."
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Cited by 9 (1 self)
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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).
Generic optimization of linear precoding in multibeam satellite systems
- IEEE Trans. Wireless Commun
, 2012
"... Abstract—Multibeam satellite systems have been employed to provide interactive broadband services to geographical areas under-served by terrestrial infrastructure. In this context, this paper studies joint multiuser linear precoding design in the forward link of fixed multibeam satellite systems. We ..."
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Cited by 6 (4 self)
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Abstract—Multibeam satellite systems have been employed to provide interactive broadband services to geographical areas under-served by terrestrial infrastructure. In this context, this paper studies joint multiuser linear precoding design in the forward link of fixed multibeam satellite systems. We provide a generic optimization framework for linear precoding design to handle any objective functions of data rate with general linear and nonlinear power constraints. To achieve this, an iterative algorithm which optimizes the precoding vectors and power allocation alternatingly is proposed and most importantly, the proposed algorithm is proved to always converge. The proposed optimization algorithm is also applicable to nonlinear dirty paper coding. As a special case, a more efficient algorithm is devised to find the optimal solution to the problem of maximizing the proportional fairness among served users. In addition, the aforementioned problems and algorithms are extended to the case that each terminal has multiple co-polarization or dual-polarization antennas. Simulation results demonstrate substantial performance improvement of the proposed schemes over conven-tional multibeam satellite systems, zero-forcing and regularized zero-forcing precoding schemes in terms of meeting the traffic demand, e.g., using real beam patterns, over twice higher throughput can be achieved compared with the conventional scheme. The performance of the proposed linear precoding scheme is also shown to be very close to the dirty paper coding. Index Terms—Multibeam satellite, precoding, optimization, dual-polarization.
NEMOx: Scalable Network MIMO for Wireless Networks
- In Proc. ACM Int. Conf. Mobile Computing and Networking (MobiCom
, 2013
"... Network MIMO (netMIMO) has potential for significantly enhanc-ing the capacity of wireless networks with tight coordination of ac-cess points (APs) to serve multiple users concurrently. Existing schemes realize netMIMO by integrating distributed APs into one “giant ” MIMO but do not scale well owing ..."
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Cited by 6 (2 self)
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Network MIMO (netMIMO) has potential for significantly enhanc-ing the capacity of wireless networks with tight coordination of ac-cess points (APs) to serve multiple users concurrently. Existing schemes realize netMIMO by integrating distributed APs into one “giant ” MIMO but do not scale well owing to their global synchro-nization requirement and overhead in sharing data between APs. To remedy this limitation, we propose a novel system, NEMOx, that realizes netMIMO downlink transmission for large-scale wireless networks. NEMOx organizes a network into practical-size clusters, each containing multiple distributed APs (dAPs) that opportunis-tically synchronize with each other for netMIMO downlink trans-mission. Inter-cluster interference is managed with a decentralized channel-access algorithm, which is designed to balance between the dAPs ’ cooperation gain and spatial reuse—a unique tradeoff in netMIMO. Within each cluster, NEMOx optimizes the power bud-geting among dAPs and the set of users to serve, ensuring fairness and effective cancellation of cross-talk interference. We have im-plemented and evaluated a prototype of NEMOx in a software radio testbed, demonstrating its throughput scalability and multiple folds of performance gain over current wireless LAN architecture and alternative netMIMO schemes.
