The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform

Jing Wang - One of the best experts on this subject based on the ideXlab platform.

  • A multi-Cell MMSE detector for massive MIMO systems and new large system analysis
    2015 IEEE Global Communications Conference GLOBECOM 2015, 2015
    Co-Authors: Xueru Li, Emil Björnson, Erik G. Larsson, Shidong Zhou, Jing Wang
    Abstract:

    In this paper, a new multi-Cell MMSE detector is proposed for massive MIMO systems. Let K and B denote the number of users in each Cell and the number of available pilot sequences in the network, respectively, with B = βK, where β ≥ 1 is called the pilot reuse factor. The novelty of the multi-Cell MMSE detector is that it utilizes all B channel directions that can be estimated locally at a base station, so that intra-Cell interference, parts of the inter-Cell interference and the noise can all be actively suppressed, while conventional detectors only use the K intra-Cell Channels. Furthermore, in the large- system limit, a deterministic equivalent expression of the uplink SINR for the proposed multi-Cell MMSE is derived. The expression is easy to compute and accounts for power control for the pilot and payload, imperfect channel estimation and arbitrary pilot allocation. Numerical results show that significant sum spectral efficiency gains can be obtained by the multi-Cell MMSE over the conventional single-Cell MMSE and the recent multi-Cell ZF, and the gains become more significant as β and/or K increases. Furthermore, the deterministic equivalent is shown to be very accurate even for relatively small system dimensions.

Chaoyang Wang - One of the best experts on this subject based on the ideXlab platform.

  • Analytical model of flow maldistribution in polymer electrolyte fuel Cell Channels
    Chemical Engineering Science, 2010
    Co-Authors: Suman Basu, Chaoyang Wang, Ken S. Chen
    Abstract:

    Gas–liquid, two-phase flow through Channels of a polymer electrolyte fuel Cell (PEFC) is of great interest as reactant oxygen is supplied and liquid product water is removed via these PEFC Channels. Gas diffusion layer (GDL) intrusion in the Channels, which is inherent to the process of PEFC Cell and stack assembling, increases the local flow resistance in the intruded Channels and consequently lowers their flowrates. This flow maldistribution renders the intruded Channels more susceptible to liquid water accumulation or flooding. A one-dimensional analytical model is developed in this work to elucidate the two-phase flow maldistribution in PEFC Channels resulting from GDL intrusion. Relative humidity (RH) and the stoichiometric flow ratio of inlet gases are found to be the two key parameters controlling the flow maldistribution in PEFC Channels. Interestingly, our analysis shows that decreasing the inlet RH worsens flow maldistribution. As GDL intrusion in Channels is inevitable, a good flow-field design must be inherently tolerable to flow maldistribution. Using the analytical model presented herein, the number of flow Channels and their U-turns are optimized to minimize the detrimental effect of GDL intrusion.

  • modeling two phase flow in pem fuel Cell Channels
    Journal of Power Sources, 2008
    Co-Authors: Yun Wang, Suman Basu, Chaoyang Wang
    Abstract:

    This paper is concerned with the simultaneous flow of liquid water and gaseous reactants in mini-Channels of a proton exchange membrane (PEM) fuel Cell. Envisaging the mini-Channels as structured and ordered porous media, we develop a continuum model of two-phase channel flow based on two-phase Darcy’s law and the M 2 formalism, which allow estimate of the parameters key to fuel Cell operation such as overall pressure drop and liquid saturation profiles along the axial flow direction. Analytical solutions of liquid water saturation and species concentrations along the channel are derived to explore the dependences of these physical variables vital to Cell performance on operating parameters such as flow stoichiometric ratio and relative humility. The two-phase channel model is further implemented for three-dimensional numerical simulations of two-phase, multi-component transport in a single fuel-Cell channel. Three issues critical to optimizing channel design and mitigating channel flooding in PEM fuel Cells are fully discussed: liquid water buildup towards the fuel Cell outlet, saturation spike in the vicinity of flow cross-sectional heterogeneity, and two-phase pressure drop. Both the two-phase model and analytical solutions presented in this paper may be applicable to more general two-phase flow phenomena through mini- and micro-Channels. © 2008 Elsevier B.V. All rights reserved.

Xueru Li - One of the best experts on this subject based on the ideXlab platform.

  • A multi-Cell MMSE detector for massive MIMO systems and new large system analysis
    2015 IEEE Global Communications Conference GLOBECOM 2015, 2015
    Co-Authors: Xueru Li, Emil Björnson, Erik G. Larsson, Shidong Zhou, Jing Wang
    Abstract:

    In this paper, a new multi-Cell MMSE detector is proposed for massive MIMO systems. Let K and B denote the number of users in each Cell and the number of available pilot sequences in the network, respectively, with B = βK, where β ≥ 1 is called the pilot reuse factor. The novelty of the multi-Cell MMSE detector is that it utilizes all B channel directions that can be estimated locally at a base station, so that intra-Cell interference, parts of the inter-Cell interference and the noise can all be actively suppressed, while conventional detectors only use the K intra-Cell Channels. Furthermore, in the large- system limit, a deterministic equivalent expression of the uplink SINR for the proposed multi-Cell MMSE is derived. The expression is easy to compute and accounts for power control for the pilot and payload, imperfect channel estimation and arbitrary pilot allocation. Numerical results show that significant sum spectral efficiency gains can be obtained by the multi-Cell MMSE over the conventional single-Cell MMSE and the recent multi-Cell ZF, and the gains become more significant as β and/or K increases. Furthermore, the deterministic equivalent is shown to be very accurate even for relatively small system dimensions.

Yun Wang - One of the best experts on this subject based on the ideXlab platform.

  • Modeling two-phase transport in PEM fuel Cell Channels
    2011
    Co-Authors: Yun Wang, Ken S. Chen
    Abstract:

    The study on polymer electrolyte fuel Cells (PEFCs) has been a rapidly growing field of research [1]. Water management is crucial for achieving high performance of fuel Cells: inadequate hydration in the membrane will increase the electrolyte ionic resistance, whereas excess water floods electrodes, reducing the limiting current density. Given low operating temperatures during normal startup (25 C) and hence low-saturation pressures, two-phase phenomena are unavoidable in automotive fuel Cells. At current, most of the two-phase studies are focused on the catalyst layers and GDLs, and few models for channel two-phase transport have been reported in the literature [2]. In practice, however, two-phase flow and transport in gas flow Channels is of paramount importance for fuel Cell operation, particularly in the most energyefficient regime involving high Cell voltage and therefore low-current density. In this regime, flow rates of hydrogen and air through Channels are exceedingly low, resulting in substantial liquid water accumulation.

  • modeling two phase flow in pem fuel Cell Channels
    Journal of Power Sources, 2008
    Co-Authors: Yun Wang, Suman Basu, Chaoyang Wang
    Abstract:

    This paper is concerned with the simultaneous flow of liquid water and gaseous reactants in mini-Channels of a proton exchange membrane (PEM) fuel Cell. Envisaging the mini-Channels as structured and ordered porous media, we develop a continuum model of two-phase channel flow based on two-phase Darcy’s law and the M 2 formalism, which allow estimate of the parameters key to fuel Cell operation such as overall pressure drop and liquid saturation profiles along the axial flow direction. Analytical solutions of liquid water saturation and species concentrations along the channel are derived to explore the dependences of these physical variables vital to Cell performance on operating parameters such as flow stoichiometric ratio and relative humility. The two-phase channel model is further implemented for three-dimensional numerical simulations of two-phase, multi-component transport in a single fuel-Cell channel. Three issues critical to optimizing channel design and mitigating channel flooding in PEM fuel Cells are fully discussed: liquid water buildup towards the fuel Cell outlet, saturation spike in the vicinity of flow cross-sectional heterogeneity, and two-phase pressure drop. Both the two-phase model and analytical solutions presented in this paper may be applicable to more general two-phase flow phenomena through mini- and micro-Channels. © 2008 Elsevier B.V. All rights reserved.

Suman Basu - One of the best experts on this subject based on the ideXlab platform.

  • Analytical model of flow maldistribution in polymer electrolyte fuel Cell Channels
    Chemical Engineering Science, 2010
    Co-Authors: Suman Basu, Chaoyang Wang, Ken S. Chen
    Abstract:

    Gas–liquid, two-phase flow through Channels of a polymer electrolyte fuel Cell (PEFC) is of great interest as reactant oxygen is supplied and liquid product water is removed via these PEFC Channels. Gas diffusion layer (GDL) intrusion in the Channels, which is inherent to the process of PEFC Cell and stack assembling, increases the local flow resistance in the intruded Channels and consequently lowers their flowrates. This flow maldistribution renders the intruded Channels more susceptible to liquid water accumulation or flooding. A one-dimensional analytical model is developed in this work to elucidate the two-phase flow maldistribution in PEFC Channels resulting from GDL intrusion. Relative humidity (RH) and the stoichiometric flow ratio of inlet gases are found to be the two key parameters controlling the flow maldistribution in PEFC Channels. Interestingly, our analysis shows that decreasing the inlet RH worsens flow maldistribution. As GDL intrusion in Channels is inevitable, a good flow-field design must be inherently tolerable to flow maldistribution. Using the analytical model presented herein, the number of flow Channels and their U-turns are optimized to minimize the detrimental effect of GDL intrusion.

  • modeling two phase flow in pem fuel Cell Channels
    Journal of Power Sources, 2008
    Co-Authors: Yun Wang, Suman Basu, Chaoyang Wang
    Abstract:

    This paper is concerned with the simultaneous flow of liquid water and gaseous reactants in mini-Channels of a proton exchange membrane (PEM) fuel Cell. Envisaging the mini-Channels as structured and ordered porous media, we develop a continuum model of two-phase channel flow based on two-phase Darcy’s law and the M 2 formalism, which allow estimate of the parameters key to fuel Cell operation such as overall pressure drop and liquid saturation profiles along the axial flow direction. Analytical solutions of liquid water saturation and species concentrations along the channel are derived to explore the dependences of these physical variables vital to Cell performance on operating parameters such as flow stoichiometric ratio and relative humility. The two-phase channel model is further implemented for three-dimensional numerical simulations of two-phase, multi-component transport in a single fuel-Cell channel. Three issues critical to optimizing channel design and mitigating channel flooding in PEM fuel Cells are fully discussed: liquid water buildup towards the fuel Cell outlet, saturation spike in the vicinity of flow cross-sectional heterogeneity, and two-phase pressure drop. Both the two-phase model and analytical solutions presented in this paper may be applicable to more general two-phase flow phenomena through mini- and micro-Channels. © 2008 Elsevier B.V. All rights reserved.