The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
William J Dally - One of the best experts on this subject based on the ideXlab platform.
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SC - Allocator implementations for network-on-chip routers
Proceedings of the Conference on High Performance Computing Networking Storage and Analysis - SC '09, 2009Co-Authors: Daniel U. Becker, William J DallyAbstract:The present contribution explores the design space for Virtual Channel (VC) and switch allocators in network-on-chip (NoC) routers. Based on detailed RTL-level implementations, we evaluate representative allocator architectures in terms of matching quality, delay, area and power and investigate the sensitivity of these properties to key network parameters. We introduce a scheme for sparse VC allocation that limits transitions between groups of VCs based on the function they perform, and reduces the VC allocator's delay, area and power by up to 41%, 90% and 83%, respectively. Furthermore, we propose a pessimistic mechanism for speculative switch allocation that reduces switch allocator delay by up to 23% compared to a conventional implementation without increasing the router's zero-load latency. Finally, we quantify the effects of the various design choices discussed in the paper on overall network performance by presenting simulation results for two exemplary 64-node NoC topologies.
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In Proceedings of the 7th International Symposium on High-Performance Computer Architecture, Jan. 22-24, 2001, Monterrey, Mexico, pp. 255-266.
2007Co-Authors: Best Student Paper, Li-shiuan Peh, William J DallyAbstract:models key aspects of modern routers. The model accounts for the pipelined nature of contemporary routers, the specific flow control method employed, the delay of the flowcontrol credit path, and the sharing of crossbar ports across Virtual Channels. Motivated by this model, we introduce a microarchitecture for a speculative Virtual-Channel router that significantly reduces its router latency to that of a wormhole router. Simulations using our pipelined model give results that differ considerably from the commonlyassumed `unit-latency' model which is unreasonably optimistic. Using realistic pipeline models, we compare wormhole [6] and Virtual-Channel flow control [4]. Our results show that a speculative Virtual-Channel router has the same per-hop router latency as a wormhole router, while improving throughput by up to 40%
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A delay model and speculative architecture for pipelined routers
2001Co-Authors: Li-shiuan Peh, William J DallyAbstract:This paper introduces a router delay model that accurately models key aspects of modern routers. The model accounts for the pipelined nature of contemporary routers, the specific flow control method employed, the delay of the flowcontrol credit path, and the sharing of crossbar ports across Virtual Channels. Motivated by this model, we introduce a microarchitecture for a speculative Virtual-Channel router that significantly reduces its router latency to that of a wormhole router. Simulations using our pipelined model give results that differ considerably from the commonlyassumed ‘unit-latency ’ model which is unreasonably optimistic. Using realistic pipeline models, we compare wormhole [6] and Virtual-Channel flow control [4]. Our results show that a speculative Virtual-Channel router has the same per-hop router latency as a wormhole router, while improving throughput by up to 40%. 1
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a delay model for router microarchitectures
IEEE Micro, 2001Co-Authors: Li-shiuan Peh, William J DallyAbstract:This article introduces a router delay model that takes into account the pipelined nature of contemporary routers and proposes pipelines matched to the specific flow control method employed. Given the type of flow control and router parameters, the model returns router latency in technology-independent units and the number of pipeline stages as a function of cycle time. We apply this model to derive realistic pipelines for wormhole and Virtual-Channel routers and compare their performance. Contrary to the conclusions of previous models, our results show that the latency of a Virtual Channel router doesn't increase as we scale the number of Virtual Channels up to 8 per physical Channel. Our simulation results also show that a Virtual-Channel router gains throughput of up to 40 % over a wormhole router.
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A Delay Model and Speculative Architecture for Pipelined Routers
2001Co-Authors: Li-shiuan Peh, William J DallyAbstract:This paper introduces a router delay model that accurately models key aspects of modern routers. The model accounts for the pipelined nature of contemporary routers, the specific flow control method employed, the delay of the flowcontrol credit path, and the sharing of crossbar ports across Virtual Channels. Motivated by this model, we introduce a microarchitecture for a speculative Virtual-Channel router that significantly reduces its router latency to that of a wormhole router. Simulations using our pipelined model give results that differ considerably from the commonly- assumed `unit-latency' model which is unreasonably optimistic. Using realistic pipeline models, we compare wormhole [6] and Virtual-Channel flow control [4]. Our results show that a speculative Virtual-Channel router has the same per-hop router latency as a wormhole router, while improving throughput by up to 40%. 1. Introduction Interconnection networks are used to connect processors to memories in multicomputers ..
A M Sayeed - One of the best experts on this subject based on the ideXlab platform.
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Channel estimation and precoder design for millimeter wave communications the sparse way
Asilomar Conference on Signals Systems and Computers, 2014Co-Authors: Philip Schniter, A M SayeedAbstract:We propose strategies for mmWave communications that exploit the inherent sparsity of mmWave Channels in the angle and delay domains. In particular, we propose the use of aperture shaping to ensure a sparse Virtual-domain MIMO Channel representation; fast FFT-based modulation and demodulation schemes to expose the Virtual-Channel coefficients; a pilot design that facilitates fast LASSO-based sparse-Channel estimation; and spectrally efficient precoding and decoding, via the Lanczos algorithm and waterfilling over both frequency and angle. Numerical experiments suggest that our approach comes close to achieving the perfect-CSI capacity of the mmWave Channel.
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experimental study of mimo Channel statistics and capacity via Virtual Channel representation
2006Co-Authors: Yan Zhou, A M Sayeed, Markus Herdin, E BonekAbstract:This work presents an experimental study of MIMO Channel statistics and capacity via the recently proposed Virtual Channel representation, which describes the Channel by a finite number of fixed Virtual transmit/receive angles and delays. Our results confirm two important implications of Virtual path partitioning: the Virtual coefficients are approximately uncorrelated, and there exist fundamental angle-delay dependencies which limit the degrees of freedom in MIMO Channels. The Virtual Channel power matrix reflects the distribution of Channel power in angle-delay domain, quantifies the spatial-frequency correlation of actual Channel coefficients, and also provides an intuitive explanation of the impact of scattering environments on capacity. The modeling accuracy of the popular Kronecker model, as well as the recently proposed eigenbeam model, is compared to the Virtual Channel model. The results indicate that both the Virtual and eigenbeam models achieve good prediction accuracy, because they can model nonseparable 2D angular spectrum, while the Kronecker model results in larger prediction error due to the restrictive structure.
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fundamental dependencies in angle delay doppler in wireless Channels
International Conference on Acoustics Speech and Signal Processing, 2004Co-Authors: A M SayeedAbstract:The degrees of freedom (DoF) in a wireless Channel determine its statistics and capacity. The DoF in turn depend on the number and spatial distribution of physical propagation paths in the environment as well as the signal space dimensions (number of antennas, bandwidth). In this paper, we use a Virtual representation of time- and frequency-selective MIMO Channels to relate the DoF to the physical propagation paths. The Virtual representation is characterized by Virtual Channel coefficients in angle-delay-Doppler space. It induces a partitioning of paths that reveals the contribution of each path to the DoF as well as fundamental dependencies in angle, delay and Doppler that constrain the DoF. As the signal space dimensions increase, the DoF increase whereas the statistics of the Virtual Channel coefficients deviate from Gaussian (Rayleigh) to "specular" in which the amplitude of the coefficients is deterministic and the Channel variations are manifested solely in the phase. Implications of the angle-delay-Doppler dependencies on Channel structure and capacity are discussed, which are particularly relevant to ultra-wideband systems.
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spatial multiplexing in correlated fading via the Virtual Channel representation
IEEE Journal on Selected Areas in Communications, 2003Co-Authors: Zhihong Hong, Ke Liu, Robert W Heath, A M SayeedAbstract:Spatial multiplexing techniques send independent data streams on different transmit antennas to maximally exploit the capacity of multiple-input multiple-output (MIMO) fading Channels. Most existing multiplexing techniques are based on an idealized MIMO Channel model representing a rich scattering environment. Realistic Channels corresponding to scattering clusters exhibit correlated fading and can significantly compromise the performance of such techniques. In this paper, we study the design and performance of spatial multiplexing techniques based on a Virtual representation of realistic MIMO fading Channels. Since the nonvanishing elements of the Virtual Channel matrix are uncorrelated, they capture the essential degrees of freedom in the Channel and provide a simple characterization of Channel statistics. In particular, the pairwise-error probability (PEP) analysis for correlated Channels is greatly simplified in the Virtual representation. Using the PEP analysis, various precoding schemes are introduced to improve performance in Virtual Channels. Unitary precoding is proposed to provide robustness to unknown Channel statistics. Nonunitary precoding techniques are proposed to exploit Channel structure when Channel statistics are known at the transmitter. Numerical results are presented to illustrate the attractive performance of the precoding techniques.
Xiaoyang Huang - One of the best experts on this subject based on the ideXlab platform.
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Manipulation of ferrofluid droplets using planar coils
Applied Physics Letters, 2006Co-Authors: Xiaoyang HuangAbstract:In this letter, the authors report a system for magnetic manipulation of ferrofluid droplets and their dynamic behavior. The magnetic field was generated by an array of planar coils, which were fabricated on a double-sided printed circuit board (PCB). The permanent magnetic moment of the ferrofluid droplet was created by the field of a pair of permanent magnets. The motion of the ferrofluid droplet is further aligned in a Virtual Channel formed by a pair of planar coils. Two other planar coils on the other side of the PCB drive the droplet along this Virtual Channel. The direction of the droplet motion can be controlled by reversing the electric current in the coils. Based on the experimental results, a larger droplet size, a lower viscosity of the surrounding medium, and a higher electric current will increase the droplet velocity.
Y Pan - One of the best experts on this subject based on the ideXlab platform.
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deadlock free adaptive routing in meshes based on cost effective deadlock avoidance schemes
International Conference on Parallel Processing, 2007Co-Authors: Dong Xiang, Yueli Zhang, Y PanAbstract:A new deadlock-free adaptive routing algorithm is proposed for n-dimensional meshes with only two Virtual Channels, where a Virtual Channel can be shared by two consecutive planes without any cyclic Channel dependency. A message is routed along a series of planes. The proposed planar adaptive routing algorithm is enhanced to a fully adaptive routing version for 3-dimensional meshes using the idle Virtual Channels along the last dimension. Another deadlock avoidance technique is proposed for 3- dimensional meshes using a new Virtual network partitioning scheme with only two Virtual Channels. Two Virtual networks can share some common Virtual Channel based on the Virtual network partitioning scheme. The deadlock-free adaptive routing scheme is then modified to a deadlock-free adaptive fault-tolerant routing scheme based on a planarly constructed MCC fault model. Sufficient simulation results are presented to demonstrate the effectiveness of the proposed algorithm.
Ender Ayanoglu - One of the best experts on this subject based on the ideXlab platform.
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downlink precoding for massive mimo systems exploiting Virtual Channel model sparsity
International Conference on Communications, 2018Co-Authors: Thomas Ketseoglou, Ender AyanogluAbstract:In this paper, the problem of designing a forward link linear precoder for Massive Multiple-Input Multiple-Output (MIMO) systems in conjunction with Quadrature Amplitude Modulation (QAM) is addressed. A challenge in such system design is to consider finite alphabet inputs, especially with larger constellation sizes such as $M\geq 16$. First, we employ a novel and efficient methodology that allows for a sparse representation of multiple users and groups in a fashion similar to Joint Spatial Division and Multiplexing (JSDM), thus offering an extension of JSDM to finite alphabet data symbols. We term the new approach JSDM for finite alphabets (JSDM-FA). We show that similarly to ordinary JSDM, the optimal pre-beamforming matrix for Massive MIMO in JSDM-FA becomes the DFT matrix. The proposed methodology is next applied jointly with the complexity-reducing Per-Group Processing within groups (PGP-WG) technique, on a per user group basis, in conjunction with QAM modulation and in simulations, for constellation size up to $M=64$. We show by numerical results that the precoders developed offer significantly better performance than the configuration with no precoder or the plain beamformer and with $M\geq 16$.
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downlink precoding for massive mimo systems exploiting Virtual Channel model sparsity
IEEE Transactions on Communications, 2018Co-Authors: Thomas Ketseoglou, Ender AyanogluAbstract:In this paper, the problem of designing a forward link linear precoder for massive multiple-input multiple-output (MIMO) systems in conjunction with quadrature amplitude modulation (QAM) is addressed. A challenge in such system design is to consider finite alphabet inputs, especially with larger constellation sizes, such as $M\geq 16$ . First, we employ a novel and efficient methodology that allows for an orthogonal, sparse representation of multiple users and groups in a fashion similar to joint spatial division and multiplexing (JSDM), thus offering an extension of JSDM to finite alphabet data symbols. We term the new approach JSDM for finite alphabets (JSDM-FA). JSDM-FA employs Virtual Channel model beams in order to explore the orthogonality between different groups. Then, we present a natural generalization of JSDM-FA to the frequency-selective case with orthogonal frequency-division multiplexing (OFDM) and also enhance OFDM with combined frequency and spatial division and multiplexing. This configuration offers high flexibility in Massive MIMO systems, as it is capable of offering separate decoding of each user data within a group or increase the spectral efficiency of spatially overlapping groups without sacrificing the overall cell spectral efficiency. The proposed methodology is next applied jointly with the complexity-reducing Per-Group Processing within groups technique, on a per user group basis, in conjunction with QAM modulation and in simulations, for constellation size up to $M=64$ . We show by numerical results that the precoders developed offer significantly better performance than the configuration with no precoder or the plain beamformer and with $M\geq 16$ .
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downlink precoding for massive mimo systems exploiting Virtual Channel model sparsity
arXiv: Information Theory, 2017Co-Authors: Thomas Ketseoglou, Ender AyanogluAbstract:In this paper, the problem of designing a forward link linear precoder for Massive Multiple-Input Multiple-Output (MIMO) systems in conjunction with Quadrature Amplitude Modulation (QAM) is addressed. First, we employ a novel and efficient methodology that allows for a sparse representation of multiple users and groups in a fashion similar to Joint Spatial Division and Multiplexing. Then, the method is generalized to include Orthogonal Frequency Division Multiplexing (OFDM) for frequency selective Channels, resulting in Combined Frequency and Spatial Division and Multiplexing, a configuration that offers high flexibility in Massive MIMO systems. A challenge in such system design is to consider finite alphabet inputs, especially with larger constellation sizes such as $M\geq 16$. The proposed methodology is next applied jointly with the complexity-reducing Per-Group Processing (PGP) technique, on a per user group basis, in conjunction with QAM modulation and in simulations, for constellation size up to $M=64$. We show by numerical results that the precoders developed offer significantly better performance than the configuration with no precoder or the plain beamformer and with $M\geq 16$.
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mimo linear precoders with reduced complexity
Wireless Telecommunications Symposium, 2015Co-Authors: Thomas Ketseoglou, Ender AyanogluAbstract:In this paper, the problem of designing a linear precoder for Multiple-Input Multiple-Output (MIMO) systems employing Low-Density Parity-Check (LDPC) codes is addressed under the constraint of independent receiving Virtual antenna output groups, thus reducing the relevant transmitter and receiver complexities. Our approach constitutes an interesting generalization of Bit-Interleaved Coded Multiple Beamforming (BICMB) which has shown many benefits in MIMO systems. After examining the properties associated with independent output grouping, we proceed to propose an alternative, practical technique, called Per-Group Precoding (PGP), which groups together multiple input symbol streams and corresponding receiving branches in the “Virtual” Channel domain (after singular value decomposition of the original MIMO Channel), and thus results in independent transmitting/receiving streams between groups. We show with numerical results that PGP offers almost optimal performance, albeit with significant reduction both in the precoder optimization and LDPC EXIT chart based decoding complexities.
