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Yunxia Feng - One of the best experts on this subject based on the ideXlab platform.

  • a weighted interference Estimation Scheme for interface switching wireless mesh networks
    Communications and Mobile Computing, 2009
    Co-Authors: Yunxia Feng
    Abstract:

    The co-channel interference problem in wireless mesh networks (WMN) is extremely serious due to the heavy aggregated traffic loads and limited available channels. It is preferable for mesh routers to dynamically switch channels according to the accurate Estimation of co-channel interference level in the neighborhood. Most developed interference Estimation Schemes, however, do not consider the impact of interface switching. Furthermore, the interference in wireless networks has been extensively considered as an all-or-nothing event. In this paper, we develop a weighted interference Estimation Scheme (WIES) for interface-switching WMN. WIES takes a new version of multi-interface conflict graph that considers the impacts of frequent interface switching as the interference relationship Estimation Scheme. Besides, WIES uses a weight to estimate the interference level between links. The weight utilizes two empirical functions to denote the impacts of the relative distance and characteristics of traffic loads in WMN. Extensive NS2 simulations show that WIES achieves significant performance improvements, especially when the interference level of the network is high. We also validate that the interference level of networks is affected by several system parameters such as the number of available channels and the ratio between interference range and transmission range. Copyright © 2008 John Wiley & Sons, Ltd.

  • a weighted interference Estimation Scheme for interface switching wireless mesh networks
    International Conference on Parallel and Distributed Systems, 2007
    Co-Authors: Yunxia Feng
    Abstract:

    The number of available channels in a specific wireless network is bounded. Therefore, co-channel interference is inevitable in most wireless networks. The co-channel interference problem in wireless mesh networks is more serious than that in single-hop wireless networks. It is preferable for mesh nodes to dynamically adjust channels to elevate the interference level of networks. In this paper, we introduce the conception of communication constraint to denote the strategies that decide the mode of interface switching. We develop an interference Estimation Scheme. The proposed Scheme uses a weight to represent the effects of loads distribution and relative distance between nodes on the interference level of network. We compare the performance of our solution with the model presented by Gupta and Kumar [14] through both graph-based and NS2 simulations. Extensive results show that our solution achieves better performance than the compared Scheme when the number of available channels is small.

Jongtae Lim - One of the best experts on this subject based on the ideXlab platform.

  • two step channel Estimation Scheme for ofdm systems over fast rayleigh fading channels
    IEEE Communications Letters, 2010
    Co-Authors: Jongtae Lim
    Abstract:

    This paper proposes a two step pilot-based channel Estimation Scheme for orthogonal frequency-division multiplexing (OFDM) systems over fast Rayleigh fading channels. In the proposed Scheme, the detected symbol from the first step is propagated into the second step to improve the performance of estimator. Specifically, we introduce the adaptive threshold using a noise variance Estimation with the different posterior probability to exclude the false detected symbols. The simulation results show that the proposed Scheme is better compared to the conventional methods over fast Rayleigh fading channels.

  • map based channel Estimation for mimo ofdm over fast rayleigh fading channels
    IEEE Transactions on Vehicular Technology, 2008
    Co-Authors: Jingoog Kim, Jongtae Lim
    Abstract:

    This paper presents a channel Estimation Scheme for multiple-input multiple-output with orthogonal frequency-division multiplexing (MIMO-OFDM) in fast varying Rayleigh channels. To handle rapid variation of channels within a transmission block, we propose a novel maximum a posteriori probability-based channel Estimation Scheme using pilot symbols. With the estimate of the channel matrix for the current symbol interval, a zero-forcing (ZF) receiver is applied to detect the spatially multiplexed data. In simulation results, the effectiveness of the proposed method is shown, as compared with the polynomial and the perfect channel estimates.

  • pilot symbol aided channel Estimation for ofdm with fast fading channels
    IEEE Transactions on Broadcasting, 2003
    Co-Authors: Wongyu Song, Jongtae Lim
    Abstract:

    In this paper, we address the problem of estimating a rapidly-varying channel in orthogonal frequency division multiplexing (OFDM) systems. To handle rapid variation within a transmission block, we propose a novel pilot-based Estimation Scheme which uses channel interpolation. In addition, we develop a simple Doppler frequency Estimation Scheme. We show that the proposed Scheme has better performance in the high-Doppler frequency by simulations.

Seokho Yoon - One of the best experts on this subject based on the ideXlab platform.

  • a low complexity integer frequency offset Estimation Scheme based on coherence phase bandwidth for ofdm systems
    Applied Mechanics and Materials, 2013
    Co-Authors: Youngseok Lee, Seong Ro Lee, Seungsoo Yoo, Jeongyoon Shim, Jaewoo Lee, Seokho Yoon
    Abstract:

    In this paper, we propose a low complexity integer frequency offset Estimation Scheme based on coherence phase bandwidth for orthogonal frequency division multiplexing (OFDM) systems. The proposed Scheme overcomes the effect of the timing offset via correlating the local and received OFDM training symbols in a coherence phase bandwidth block unit. Moreover, by utilizing a threshold to determine an interger frequency offset etimate, the proposed Scheme need not calculate correlation values for all possible interger frequency offset candidates. From numerical results, it is demonstrated that the proposed Scheme can estimate the integer freqeuncy offset with a reduced complexity while minataining the same level of the Estimation performance.

  • low complexity sequential Estimation Scheme for pseudo noise code acquisition
    Vehicular Technology Conference, 2011
    Co-Authors: Jeehyeon Baek, Dahae Chong, Seung Goo Kang, Seokho Yoon
    Abstract:

    In this paper, a low complexity sequential Estimation Scheme for pseudo noise (PN) code acquisition is proposed, which can not only achieve code acquisition for both inverted and non-inverted PN codes, but also demodulate the spreading data. Numerical results show that the proposed Scheme has approximately half the complexity of the conventional Scheme while exhibiting a similar mean acquisition time performance to that of the conventional Scheme.

  • a novel frequency offset Estimation Scheme using coherence phase bandwidth and threshold for ofdm systems
    International Conference on Advanced Communication Technology, 2006
    Co-Authors: Sanghun Kim, Seokho Yoon, Sun Yong Kim
    Abstract:

    We first investigate the effect of the timing offset on the frequency offset Estimation in orthogonal frequency division multiplexing (OFDM) systems. Then, we propose an efficient frequency offset Estimation Scheme using the coherence phase bandwidth (CPB) and a threshold in the presence of the timing offset. The numerical results demonstrate that the proposed Scheme has lower computational complexity compared with the conventional Schemes and performs robust operation in the presence of the timing offset.

Changick Song - One of the best experts on this subject based on the ideXlab platform.

  • a new data pilot aided channel Estimation Scheme for fast time varying channels in ieee 802 11p systems
    IEEE Transactions on Vehicular Technology, 2019
    Co-Authors: Seunghwan Baek, Inkyu Lee, Changick Song
    Abstract:

    The channel Estimation in the IEEE 802.11p vehicle-to-everything (V2X) communication systems is generally a challenging task due to high mobility and insufficient number of pilots. Conventional data pilot-aided channel Estimation Schemes are difficult to apply in practice due to high complexity and the error propagation problem. In this correspondence paper, we propose a new data pilot-aided channel Estimation Scheme to overcome both issues. To this end, we develop a state feedback decision algorithm that enables us to extract reliable data pilots within a few received symbols. As a result, we can minimize both the error propagation effect and the computational complexity. We verify the complexity gain of the proposed Scheme through the complexity analysis. Finally, we demonstrate the accuracy of the proposed channel Estimation Scheme in terms of the packet error rate performance.

Shaopin Song - One of the best experts on this subject based on the ideXlab platform.

  • an iiw residual stress profile Estimation Scheme for girth welds in pressure vessel and piping components
    Welding in The World, 2016
    Co-Authors: Pingsha Dong, Shaopin Song
    Abstract:

    Over the years, one major objective of IIW Joint Working Group (JWG) on residual stresses and distortion prediction (RSDP) has been the development of consistent residual stress profiles for supporting fitness-for-service assessment of welded components. As a result of the JWG activities and further in-depth investigations, this paper presents a major development on a novel full-field residual stress Estimation Scheme that can be used for describing through-thickness residual stress profiles not only within a weld region, but also at any location away from a weld in pressure vessel and piping components. Within weld region, a systematic parametric finite element analysis is used to establish key parameters that govern through-thickness residual stress distribution characteristics by introducing membrane, bending, and self-equilibrating based decomposition technique. Away from weld region, a shell theory based method is developed for describing through-thickness residual stress distribution at any distance away from weld toe. This paper presents detailed results for single “V” joint preparation with pipe wall thickness varying from 6.25 to 250 mm and wall thickness to pipe radius ratio (r/t) varying from 2 to 100. The residual stress Estimation method can be applied for double V and narrow groove joint preparations for girth welded components since all three joint preparations have been shown to follow a similar functional form to that seen in single V joint preparation.

  • a full field residual stress Estimation Scheme for fitness for service assessment of pipe girth welds part ii a shell theory based implementation
    International Journal of Pressure Vessels and Piping, 2015
    Co-Authors: Shaopin Song, Pingsha Dong
    Abstract:

    Abstract With the two key controlling parameters identified and their effectiveness demonstrated in Part I of this study series for constructing a continuous residual stress profile at weld region, a classical shell theory based model is proposed in this paper (Part II) for describing through-thickness residual stress distributions of both axial and hoop components at any axial location beyond weld region. The shell theory based model is analytically constructed through an assembly of two parts: One represents weld region and the other represents the remaining component section away from weld. The final assembly of the two parts leads to a closed form solution to both axial and hoop residual stress components as a function of axial distance from weld toe position. The effectiveness of the full-field residual stress Estimation Scheme is demonstrated by comparing with a series of finite element modeling results over a broad range of pipe weld geometries and welding conditions. The present development should provide a consistent and effective means for estimating through-thickness residual stress profile as a continuous function of pipe geometry, welding heat input, as well as material characteristics.

  • a full field residual stress profile Estimation Scheme for pipe girth welds
    Volume 9: Rudy Scavuzzo Student Paper Symposium and Competition, 2012
    Co-Authors: Shaopin Song, Pingsha Dong, Jinmiao Zhang
    Abstract:

    For supporting fitness-for-service (FFS) assessment, this paper presents a method for providing a full field description of through-thickness residual stress profiles for pipe girth welds, beyond weld locations (e.g., at weld centerline and weld toe). The paper starts with a brief introduction of the finite element modeling procedure used in this study. Experimental validations are performed for a pipe weld geometry on which detailed experimental data have recently become available in the literature. Then, a large number of parametric residual stress analyses are performed to identify key parameters that govern through-thickness residual stress distribution characteristics. These parameters are not only shown to uniquely contribute to some of the important residual stress distribution characteristics of interest to FFS, but also can be formulated, to the first approximation, using basic mechanics and physics principle. Finally, a detailed application of the proposed full field residual stress Estimation Scheme is illustrated for various girth weld conditions.Copyright © 2012 by ASME