Pub Date : 2008-02-02DOI: 10.1109/TCSI.2008.916418
Yi-Sheng Chen, Ching-An Lin
We propose a blind identification method for MIMO single carrier zero padding block transmission systems. The method uses periodic preceding on the source signal before transmission. The estimation of channel impulse response matrix consists of two steps: (i) obtain the channel product matrix by solving a lower-triangular linear system and (ii) obtain the channel impulse response matrix by computing the positive eigenvalues and eigenvectors of a Hermitian matrix formed from the channel product matrix. A sufficient condition for identifiability is simply that the channel impulse response matrix is full column rank. The design of the precoding sequence to minimize the noise effect in covariance matrix estimation is proposed. Simulation examples are used to demonstrate the performance of the method
{"title":"Blind Channel Identification for MIMO Single Carrier Zero Padding Block Transmission Systems","authors":"Yi-Sheng Chen, Ching-An Lin","doi":"10.1109/TCSI.2008.916418","DOIUrl":"https://doi.org/10.1109/TCSI.2008.916418","url":null,"abstract":"We propose a blind identification method for MIMO single carrier zero padding block transmission systems. The method uses periodic preceding on the source signal before transmission. The estimation of channel impulse response matrix consists of two steps: (i) obtain the channel product matrix by solving a lower-triangular linear system and (ii) obtain the channel impulse response matrix by computing the positive eigenvalues and eigenvectors of a Hermitian matrix formed from the channel product matrix. A sufficient condition for identifiability is simply that the channel impulse response matrix is full column rank. The design of the precoding sequence to minimize the noise effect in covariance matrix estimation is proposed. Simulation examples are used to demonstrate the performance of the method","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129908879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346381
T. Fusco, M. Tanda
In this paper we consider the problem of blind feedforward carrier-frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems in multipath channels. Specifically, by exploiting the least-squares approach a closed-form blind CFO estimator is derived. The proposed algorithm does not require the knowledge of the channel impulse response and/or the insertion of virtual subcarriers. Computer simulation results show that the derived CFO estimator can outperform previously proposed blind CFO synchronization algorithms
{"title":"A Blind Feedforward Frequency Offset Estimator for OFDM Systems in Multipath Channels","authors":"T. Fusco, M. Tanda","doi":"10.1109/SPAWC.2006.346381","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346381","url":null,"abstract":"In this paper we consider the problem of blind feedforward carrier-frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems in multipath channels. Specifically, by exploiting the least-squares approach a closed-form blind CFO estimator is derived. The proposed algorithm does not require the knowledge of the channel impulse response and/or the insertion of virtual subcarriers. Computer simulation results show that the derived CFO estimator can outperform previously proposed blind CFO synchronization algorithms","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114988054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346364
Zijian Tang, G. Leus, P. Banelli
In this paper, we deal with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems. The channels are assumed to be time-varying (TV) and approximated by a basis expansion model (BEM). Due to the time-variation, the resulting channel matrix in the frequency domain is no longer diagonal, but can be approximated as banded. Based on this band approximation, we propose a channel estimator that can combat both the additive noise and the out-of-band interference. Compared to our previous work, the proposed channel estimator can span multiple OFDM symbol intervals such that more time-correlation information can be explored to improve the estimation accuracy
{"title":"Pilot-Assisted Time-Varying OFDM Channel Estimation Based on Multiple OFDM Symbols","authors":"Zijian Tang, G. Leus, P. Banelli","doi":"10.1109/SPAWC.2006.346364","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346364","url":null,"abstract":"In this paper, we deal with channel estimation for orthogonal frequency-division multiplexing (OFDM) systems. The channels are assumed to be time-varying (TV) and approximated by a basis expansion model (BEM). Due to the time-variation, the resulting channel matrix in the frequency domain is no longer diagonal, but can be approximated as banded. Based on this band approximation, we propose a channel estimator that can combat both the additive noise and the out-of-band interference. Compared to our previous work, the proposed channel estimator can span multiple OFDM symbol intervals such that more time-correlation information can be explored to improve the estimation accuracy","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115287005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346460
G. Dietl, W. Utschick
Reduced-rank approximations of finite impulse response equalizers in Krylov subspaces, e.g., the conjugate gradient algorithm, can be used to decrease computational complexity involved in calculating the filter coefficients. However, an alternative approach would be to reduce the order of the corresponding full-rank filter or to even combine rank and order reduction. In this paper, we compare both reduction methods based on (G, D)-charts where we analyze the mean square error of the reduced-rank equalizers on complexity isosets, i.e., for tuples of the filter length G and its rank D resulting in a certain number of floating point operations. The application of (G, D)-charts to a coded system with an iterative receiver (turbo equalization) reveals the superiority of rank reduction, especially, if one is interested in low-complexity implementations
{"title":"Low-Complexity Equalizers---Rank Versus Order Reduction","authors":"G. Dietl, W. Utschick","doi":"10.1109/SPAWC.2006.346460","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346460","url":null,"abstract":"Reduced-rank approximations of finite impulse response equalizers in Krylov subspaces, e.g., the conjugate gradient algorithm, can be used to decrease computational complexity involved in calculating the filter coefficients. However, an alternative approach would be to reduce the order of the corresponding full-rank filter or to even combine rank and order reduction. In this paper, we compare both reduction methods based on (G, D)-charts where we analyze the mean square error of the reduced-rank equalizers on complexity isosets, i.e., for tuples of the filter length G and its rank D resulting in a certain number of floating point operations. The application of (G, D)-charts to a coded system with an iterative receiver (turbo equalization) reveals the superiority of rank reduction, especially, if one is interested in low-complexity implementations","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115631702","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346343
S. Sadough, M. Ichir, E. Jaffrot, P. Duhamel
This paper introduces an expectation-maximization (EM) algorithm within a wavelet domain Bayesian framework for semi-blind channel estimation of multiband OFDM based UWB communications. A prior distribution is chosen for the wavelet coefficients of the unknown channel impulse response, in order to capture the well known sparseness property of the wavelet representation. This prior yields, in maximum a posteriori estimation, a thresholding rule within the EM algorithm. We particularly focus on reducing the number of estimated parameters by iteratively discarding "unsignificant" wavelet coefficients from the estimation process. In addition, the proposed algorithm enhances the estimation accuracy in terms of mean square error with less computational complexity than traditional semi-blind methods. Simulation results using IEEE UWB channel models show that the proposed algorithm outperforms pilot based channel estimation in terms of mean square error and bit error rate
{"title":"Multiband OFDM UWB Channel Estimation Via a Wavelet Based EM-MAP Algorithm","authors":"S. Sadough, M. Ichir, E. Jaffrot, P. Duhamel","doi":"10.1109/SPAWC.2006.346343","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346343","url":null,"abstract":"This paper introduces an expectation-maximization (EM) algorithm within a wavelet domain Bayesian framework for semi-blind channel estimation of multiband OFDM based UWB communications. A prior distribution is chosen for the wavelet coefficients of the unknown channel impulse response, in order to capture the well known sparseness property of the wavelet representation. This prior yields, in maximum a posteriori estimation, a thresholding rule within the EM algorithm. We particularly focus on reducing the number of estimated parameters by iteratively discarding \"unsignificant\" wavelet coefficients from the estimation process. In addition, the proposed algorithm enhances the estimation accuracy in terms of mean square error with less computational complexity than traditional semi-blind methods. Simulation results using IEEE UWB channel models show that the proposed algorithm outperforms pilot based channel estimation in terms of mean square error and bit error rate","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124963114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346349
D. Yacoub, W. Teich, J. Lindner
MIMO systems, although they offer high transmission rates and robustness against channel fading, often suffer from antenna correlations. In this paper, we investigate the effect of spreading and symbol rotation on a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system with correlations. A novel family of orthogonal spreading matrices multi-carrier-cyclic antenna frequency spread (MC-CAFS) - is used for spreading. These matrices make use of both the spatial and the frequency dimensions offered by MIMO-OFDM. We describe how transmit vector rotations can be applied to MC-CAFS spreading matrices. Three new rotation methods are introduced in this paper. We compare the performance of MC-CAFS (with and without rotations) with that of the unspread system and with multi-carrier-code division multiplexing (MIMO-MC-CDM), also with and without rotations
{"title":"Rotated MC-Cyclic Antenna Frequency Spread: Effect of Rotations in Correlated MIMO-OFDM Systems","authors":"D. Yacoub, W. Teich, J. Lindner","doi":"10.1109/SPAWC.2006.346349","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346349","url":null,"abstract":"MIMO systems, although they offer high transmission rates and robustness against channel fading, often suffer from antenna correlations. In this paper, we investigate the effect of spreading and symbol rotation on a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system with correlations. A novel family of orthogonal spreading matrices multi-carrier-cyclic antenna frequency spread (MC-CAFS) - is used for spreading. These matrices make use of both the spatial and the frequency dimensions offered by MIMO-OFDM. We describe how transmit vector rotations can be applied to MC-CAFS spreading matrices. Three new rotation methods are introduced in this paper. We compare the performance of MC-CAFS (with and without rotations) with that of the unspread system and with multi-carrier-code division multiplexing (MIMO-MC-CDM), also with and without rotations","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125007164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346345
P. Wrycza, M. Bengtsson, B. Ottersten
We consider SDMA in a multi-user downlink MIMO system with several access points, each serving one or more users. The problem of minimizing the total transmitted power satisfying the SINR requirements at all users is considered. This is a non-linear and non-convex optimization problem with three sets of variables: the transmitter powers, the transmitter weights and the receiver weights. Global system knowledge will be assumed at the access points and the provided results can be seen as benchmarks in system performance. We present a new initialization strategy and investigate its convergence behavior for a proposed algorithm. A numerical study is performed to analyze the dependence of the target SINRs on the optimal solution. The performance of this initialization process is evaluated and compared to an existing beamforming algorithm
{"title":"On Convergence Properties of Joint Optimal Power Control and Transmit-Receive Beamforming in Multi-User MIMO Systems","authors":"P. Wrycza, M. Bengtsson, B. Ottersten","doi":"10.1109/SPAWC.2006.346345","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346345","url":null,"abstract":"We consider SDMA in a multi-user downlink MIMO system with several access points, each serving one or more users. The problem of minimizing the total transmitted power satisfying the SINR requirements at all users is considered. This is a non-linear and non-convex optimization problem with three sets of variables: the transmitter powers, the transmitter weights and the receiver weights. Global system knowledge will be assumed at the access points and the provided results can be seen as benchmarks in system performance. We present a new initialization strategy and investigate its convergence behavior for a proposed algorithm. A numerical study is performed to analyze the dependence of the target SINRs on the optimal solution. The performance of this initialization process is evaluated and compared to an existing beamforming algorithm","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"744 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122891724","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346465
C. Steiner, F. Althaus, A. Wittneben
Geo-regioning is an approach to localize ultra-wideband (UWB) transmitters by means of their channel impulse responses (CIRs) exploiting the capability of high temporal resolution of multipath components due to the large system bandwidth. Recently, the principle feasibility of this method was shown and a first geo-regioning algorithm was presented in (F. Althaus et al., 2005). In this paper, this algorithm is analyzed and the achievable performance in terms of pairwise error probability (PEP) is computed. In order to calculate the PEP analytically, a simple and accurate approximation of the probability density function (PDF) of a weighted sum of squared real valued Gaussian random variables (RVs) is presented. In the course of this analysis a distance measure is found, which reveals the important characteristics of individual geo-regions determining the PEP
地理定位是一种利用信道脉冲响应(cir)对超宽带发射机进行定位的方法，该方法利用了系统带宽大所带来的多径分量的高时间分辨率。最近，该方法的原理可行性得到了证明，并在(F. Althaus et al.， 2005)中提出了第一种地理区划算法。本文对该算法进行了分析，并从成对误差概率(PEP)的角度计算了该算法的可实现性能。为了解析地计算PEP，给出了实值高斯随机变量加权平方和的概率密度函数(PDF)的一个简单而精确的近似。在分析过程中，发现了一个距离度量，它揭示了个别地理区域决定PEP的重要特征
{"title":"On the Performance of UWB Geo-Regioning","authors":"C. Steiner, F. Althaus, A. Wittneben","doi":"10.1109/SPAWC.2006.346465","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346465","url":null,"abstract":"Geo-regioning is an approach to localize ultra-wideband (UWB) transmitters by means of their channel impulse responses (CIRs) exploiting the capability of high temporal resolution of multipath components due to the large system bandwidth. Recently, the principle feasibility of this method was shown and a first geo-regioning algorithm was presented in (F. Althaus et al., 2005). In this paper, this algorithm is analyzed and the achievable performance in terms of pairwise error probability (PEP) is computed. In order to calculate the PEP analytically, a simple and accurate approximation of the probability density function (PDF) of a weighted sum of squared real valued Gaussian random variables (RVs) is presented. In the course of this analysis a distance measure is found, which reveals the important characteristics of individual geo-regions determining the PEP","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122101099","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346484
A. Vakili, B. Hassibi
In a broadcast channel in which one transmitter provides independent streams of data for n receivers, the amount of channel state information (CSI) at the transmitter can affect the capacity region dramatically. Having the accurate SNR of all users at the transmitter, the opportunistic strategy can be used to maximize the throughput (sum-rate) of the system. However, evaluating the SNR is basically an estimation problem at the receiver which in practice is not error free. In this paper, we analyze the effect of the noisy estimation of SNR on the throughput of a broadcast channel. We propose a modified opportunistic scheme in which the transmitter serves the user with the highest estimated SNR, but backs off on the transmit rate based on the variance of the estimation error. This scheme can achieve the maximum achievable rate while the CSI is limited to a noisy estimation of channel coefficients. We obtain the optimum rate back off and find the asymptotic behavior of the throughput under the scheduling scheme we have proposed. We show that the effect of a nonzero estimation error variance can be modeled as an SNR hit proportional to this variance
{"title":"On the Throughput of Broadcast Channels with Imperfect CSI","authors":"A. Vakili, B. Hassibi","doi":"10.1109/SPAWC.2006.346484","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346484","url":null,"abstract":"In a broadcast channel in which one transmitter provides independent streams of data for n receivers, the amount of channel state information (CSI) at the transmitter can affect the capacity region dramatically. Having the accurate SNR of all users at the transmitter, the opportunistic strategy can be used to maximize the throughput (sum-rate) of the system. However, evaluating the SNR is basically an estimation problem at the receiver which in practice is not error free. In this paper, we analyze the effect of the noisy estimation of SNR on the throughput of a broadcast channel. We propose a modified opportunistic scheme in which the transmitter serves the user with the highest estimated SNR, but backs off on the transmit rate based on the variance of the estimation error. This scheme can achieve the maximum achievable rate while the CSI is limited to a noisy estimation of channel coefficients. We obtain the optimum rate back off and find the asymptotic behavior of the throughput under the scheduling scheme we have proposed. We show that the effect of a nonzero estimation error variance can be modeled as an SNR hit proportional to this variance","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122199961","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346418
A. Cipriano, I. Kammoun
We propose an approximated generalized likelihood ratio test (GLRT) for noncoherent systems which use constellations over the Grassmannian generated by the exponential map. By means of this approximation we succeeded in coping with the strong non-linearity introduced by the exponential map. The new simplified decoder, which implements the approximated GLRT, is in fact quasi-optimal with respect to the GLRT. We analyze the performance of the new decoder in terms of structure, complexity and error probability for uncoded and coded noncoherent constellations
{"title":"Linear Approximation of the Exponential Map with Application to Simplified Detection of Noncoherent Systems","authors":"A. Cipriano, I. Kammoun","doi":"10.1109/SPAWC.2006.346418","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346418","url":null,"abstract":"We propose an approximated generalized likelihood ratio test (GLRT) for noncoherent systems which use constellations over the Grassmannian generated by the exponential map. By means of this approximation we succeeded in coping with the strong non-linearity introduced by the exponential map. The new simplified decoder, which implements the approximated GLRT, is in fact quasi-optimal with respect to the GLRT. We analyze the performance of the new decoder in terms of structure, complexity and error probability for uncoded and coded noncoherent constellations","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"133 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117268636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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