The Experts below are selected from a list of 14937 Experts worldwide ranked by ideXlab platform
Robert W. Heath - One of the best experts on this subject based on the ideXlab platform.
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Overcoming interference in Spatial Multiplexing mimo cellular networks
IEEE Wireless Communications, 2007Co-Authors: Jeffrey G. Andrews, Wan Choi, Robert W. HeathAbstract:Multi-antenna transmission and reception (known as MIMO) is widely touted as the key technology for enabling wireless broadband services, whose widespread success will require 10 times higher spectral efficiency than current cellular systems, at 10 times lower cost per bit. Spectrally efficient, inexpensive cellular systems are by definition densely populated and interference-limited. But Spatial Multiplexing MIMO systems- whose principal merit is a supposed dramatic increase in spectral efficiency- lose much of their effectiveness in high levels of interference. This article overviews several approaches to handling interference in multicell MIMO systems. The discussion is applicable to any multi-antenna cellular network, including 802.16e/WiMAX, 3GPP (HSDPA and 3GPP LTE), and 3GPP2 (lxEVDO). We argue that many of the traditional interference management techniques have limited usefulness (or are even counterproductive) when viewed in concert with MIMO. The problem of interference in MIMO systems is too large in scope to be handled with a single technique: in practice a combination of complementary countermeasures will be needed. We overview emerging system-level interference-reducing strategies based on cooperation, which will be important for overcoming interference in future Spatial Multiplexing cellular systems.
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Multimode antenna selection for Spatial Multiplexing systems with linear receivers
IEEE Transactions on Signal Processing, 2005Co-Authors: Robert W. Heath, David James LoveAbstract:Spatial Multiplexing is a simple transmission technique for multiple-input multiple-output (MIMO) wireless communication links in which data is multiplexed across the transmit antennas. In Rayleigh fading matrix channels, however, Spatial Multiplexing with low-complexity linear receivers suffers due to a lack of diversity advantage. This paper proposes multimode antenna selection, which uses a low-rate feedback channel to improve the error rate performance of Spatial Multiplexing systems with linear receivers. In the proposed technique, both the number of substreams and the mapping of substreams to antennas are dynamically adjusted, for a fixed total data rate, to the channel based on limited feedback from the receiver. Dual-mode selection, where Spatial Multiplexing or selection diversity is adaptively chosen, dramatically improves the diversity gain achieved. Multimode selection (i.e., allowing any number of substreams to be dynamically selected) provides additional array gain. Various criteria for selecting the number of substreams and the optimal mapping of substreams to transmit antennas are derived. Relationships are made between the selection criteria and the eigenmodes of the channel. A probabilistic analysis of the selection criteria are provided for Rayleigh fading channels. Applications to nonlinear receivers are mentioned. Monte Carlo simulations demonstrate significant performance improvements in independent and identically distributed (i.i.d.) flat-fading Rayleigh matrix channels with minimal feedback.
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Limited feedback unitary precoding for Spatial Multiplexing systems
IEEE Transactions on Information Theory, 2005Co-Authors: David James Love, Robert W. HeathAbstract:Multiple-input multiple-output (MIMO) wireless systems use antenna\narrays at both the transmitter and receiver to provide communication\nlinks with substantial diversity and capacity. Spatial Multiplexing\nis a common space-time modulation technique for MIMO communication\nsystems where independent information streams are sent over different\ntransmit antennas. Unfortunately, Spatial Multiplexing is sensitive\nto ill-conditioning of the channel matrix. Precoding can improve\nthe resilience of Spatial Multiplexing at the expense of full channel\nknowledge at the transmitter-which is often not realistic. This correspondence\nproposes a quantized precoding system where the optimal precoder\nis chosen from a finite codebook known to both receiver and transmitter.\nThe index of the optimal precoder is conveyed from the receiver to\nthe transmitter over a low-delay feedback link. Criteria are presented\nfor selecting the optimal precoding matrix based on the error rate\nand mutual information for different receiver designs. Codebook design\ncriteria are proposed for each selection criterion by minimizing\na bound on the average distortion assuming a Rayleigh-fading matrix\nchannel. The design criteria are shown to be equivalent to packing\nsubspaces in the Grassmann manifold using the projection two-norm\nand Fubini-Study distances. Simulation results show that the proposed\nsystem outperforms antenna subset selection and performs close to\noptimal unitary precoding with a minimal amount of feedback.
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limited feedback precoding for Spatial Multiplexing systems
Global Communications Conference, 2003Co-Authors: David James Love, Robert W. HeathAbstract:Spatial Multiplexing multiple-input multiple-output (MIMO) wireless systems are of both theoretical and practical importance because they can achieve high spectral efficiencies by deMultiplexing the incoming bit stream into multiple substreams. It has been shown that sending fewer substreams than the number of transmit antennas by linear precoding can provide improved error rate performance. Methods for designing linear precoders using perfect channel knowledge have previously been proposed. In many wireless systems, the assumption of complete channel knowledge is unrealistic because of the lack of forward and reverse channel reciprocity. To overcome this difficulty, we propose a precoding scheme that does not require transmit channel knowledge. The precoder is designed at the receiver and conveyed to the transmitter using a limited number of bits. The limited feedback represents an index within a finite set, or codebook, of precoding matrices. The receiver selects one of these codebook matrices using a modified version of a previously proposed full channel knowledge precoder selection criterion. A precoder codebook design method for maximizing the average effective channel power is shown to relate to chordal distance Grassmannian subspace packing. Simulation results show this technique outperforms antenna subset selection Spatial Multiplexing.
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Limited feedback precoding for Spatial Multiplexing systems using linear receivers
IEEE Military Communications Conference 2003. MILCOM 2003., 2003Co-Authors: David James Love, Robert W. HeathAbstract:Multiple-input multiple-output (MIMO) Spatial Multiplexing wireless systems achieve high spectral efficiencies by deMultiplexing the incoming bit stream into multiple substreams. Spatial Multiplexing is of practical importance because the multiple substreams can be decoded using linear receivers. Unfortunately, this reduction in complexity degrades the probability of error performance. To overcome this difficulty, error rate performance of Spatial Multiplexing systems can be improved by sending fewer substreams than the number of transmit antennas by linear preceding. Criteria have been proposed for designing these precoders when complete channel knowledge is available to the transmitter. The assumption of complete channel knowledge is often unrealistic in many communication systems such as those with low rate feedback channels. Thus a quantized preceding scheme is proposed where the receiver sends back a fixed number of bits to the transmitter. This bit pattern corresponds to an index within a finite set of preceding matrices. A previously proposed criterion is used to determine the matrix in this precoder codebook to choose. A design method for these codebooks using techniques from Grassmannian subspace packing is presented. Simulation results show this technique outperforms typical antenna selection.
Zhang Ping - One of the best experts on this subject based on the ideXlab platform.
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Spatial Multiplexing MIMO Scheme with Beamforming
Computer Simulation, 2008Co-Authors: Zhang PingAbstract:A Spatial Multiplexing MIMO scheme with beamforming was proposed. The proposed scheme combines Spatial Multiplexing and beamforming, which has the advantages of both techniques. It is able to transmit parallel data streams as well as combating interference and noise efficiently and improve the system performance significantly. The proposed scheme provides better BER performance and greater spectrum efficiency than VBLAST and beamforming techniques under the same simulation environment.
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VTC Fall - A Spatial Multiplexing MIMO Scheme with Beamforming for Downlink Transmission
2007 IEEE 66th Vehicular Technology Conference, 2007Co-Authors: Li Lihua, Tao Xiaofeng, Zhang PingAbstract:This paper investigates a Spatial Multiplexing MIMO scheme with beamforming for downlink transmission. The proposed scheme combines Spatial Multiplexing MIMO technique with beamforming, which has the advantages of both techniques. The proposed scheme utilizes the uplink direction of arrival (DOA) to perform downlink beamforming. It is able to transmit parallel data streams as well as providing beamforming gain and improve the system performance significantly. The proposed scheme provides better BER performance than the traditional Spatial Multiplexing and beamforming techniques under the same simulation environment.
Dacheng Yang - One of the best experts on this subject based on the ideXlab platform.
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GLOBECOM - Transmission capacities for overlaid wireless networks with Spatial Multiplexing
2012 IEEE Global Communications Conference (GLOBECOM), 2012Co-Authors: Xianling Wang, Xin Zhang, Jian Geng, Xiaoyi Liu, Dacheng YangAbstract:In this paper, we investigate the performance of open-loop Spatial Multiplexing in overlaid ad hoc networks. Based on a stochastic geometry model, we derive exact closed-form expressions for the transmission capacity of two coexisting networks (a primary network vs. a secondary network) employing Spatial Multiplexing with zero-forcing (ZF) receivers. Simulation results confirm the accuracy of our expressions. In addition, we discuss the impact of multi-antenna scheme on the transmission capacity of the overlaid networks. Our findings show that the sum transmission capacity of the overlaid networks will improve significantly over that of a single network if a slight outage probability increase is allowable for the primary network. This improvement can be further boosted if Spatial Multiplexing is employed with more antennas. But when the antenna number exceeds a certain limit, Spatial Multiplexing may produce negative effect for the overlaid network.
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VTC Fall - Spatial Multiplexing with Opportunistic Multiuser Scheduling in Ad Hoc Networks
2012 IEEE Vehicular Technology Conference (VTC Fall), 2012Co-Authors: Xianling Wang, Xin Zhang, Jian Geng, Dacheng YangAbstract:In this paper, we investigate the performance of multiuser scheduling with open-loop Spatial Multiplexing in ad hoc networks. Closed-form expressions for outage probability and Spatial throughput are derived for Spatial Multiplexing transmission with zero forcing (ZF) receiver and multiuser scheduling. Monte Carlo simulation results reveal that these expressions accurately demonstrate the performance of multiuser scheduling with open-loop Spatial Multiplexing. Based on these expressions, transmission capacity performance is analyzed and the effects of system parameters over network performance metrics are studied. Our finding indicates that Spatial Multiplexing with opportunistic multiuser scheduling can provide boosted network performance for ad hoc network by exploiting multiuser diversity gain, whilst requiring very low feedback requirements.
Peter J Winzer - One of the best experts on this subject based on the ideXlab platform.
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Making Spatial Multiplexing a reality
Nature Photonics, 2014Co-Authors: Peter J WinzerAbstract:To avoid a 'capacity crunch', future optical networks will need to simultaneously transmit multiple Spatial channels. For Spatial Multiplexing to be practical, the upgrade path from legacy wavelength-division multiplexed systems needs to be smooth and to consider integration-induced crosstalk from the outset.
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Spatial Multiplexing: The next frontier in network capacity scaling
39th European Conference and Exhibition on Optical Communication (ECOC 2013), 2013Co-Authors: Peter J WinzerAbstract:We outline a smooth evolution path of optical networks to Spatial Multiplexing by complementing deployed fiber infrastructure and existing WDM components with new integrated technologies.
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Spatial Multiplexing for long-haul transmission
IEEE Photonics Conference 2012, 2012Co-Authors: Sebastian Randel, Peter J WinzerAbstract:Spatial Multiplexing has the potential to overcome the capacity-bottleneck of single-fiber long-haul links. We review recent experimental progress and discuss relevant performance vs. complexity trade-offs from a systems perspective.
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energy efficient optical transport capacity scaling through Spatial Multiplexing
IEEE Photonics Technology Letters, 2011Co-Authors: Peter J WinzerAbstract:We discuss the role of parallel transport options such as Spatial Multiplexing or multiband transmission in the capacity scaling of optical transport systems. Taking current experimental spectral efficiency records as a baseline, a system supporting 20 b/s/Hz over 1500 km can be about 100 times more energy efficient when it is built using Spatial Multiplexing than when it is built using a single waveguide at high capacity.
Inkyu Lee - One of the best experts on this subject based on the ideXlab platform.
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VTC Fall - Orthogonalized Spatial Multiplexing for MIMO Systems
IEEE Vehicular Technology Conference, 2006Co-Authors: Heunchul Lee, Seok-hwan Park, Inkyu LeeAbstract:In this paper, we propose a new Spatial Multiplexing scheme for transmission over flat-fading multiple-input multiple-output (MIMO) channels, which allows a simple maximum-likelihood decoding at the receiver with small feedback information. We begin with a real-valued representation of the complex-valued system model and show that we can achieve orthogonality between transmitted signals by applying a proper rotation to transmitted symbols. Based on the minimum Euclidean distance between received vectors, we also present a simple antenna selection metric for the proposed Spatial Multiplexing systems. Simulation results demonstrate that our Spatial Multiplexing system performs close to the optimum closed loop system with much reduced complexity and feedback overhead.
