Pub Date : 2006-07-02DOI: 10.1109/SPAWC.2006.346427
C. Rizogiannis, E. Kofidis, C. Papadias, S. Theodoridis
The aim of this paper is to investigate receiver techniques for ML joint channel/data estimation in flat fading MIMO channels that are both i) data efficient and ii) computationally attractive. The performance of iterative least squares (LS) for channel estimation combined with sphere decoding (SD) for data detection is examined in the first part, for block fading channels, demonstrating the data efficiency provided by the semi-blind approach. In the second part, the case of continuous fading channels is addressed with the aid of recursive least squares (RLS). The observed relative robustness of the ML solution to channel variations is exploited in deriving a block QR-based RLS-SD scheme, which allows significant complexity savings with little or no performance loss
{"title":"Semi-Blind Maximum Likelihood Joint Channel Estimation / Data Detection for MIMO Fading Channels","authors":"C. Rizogiannis, E. Kofidis, C. Papadias, S. Theodoridis","doi":"10.1109/SPAWC.2006.346427","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346427","url":null,"abstract":"The aim of this paper is to investigate receiver techniques for ML joint channel/data estimation in flat fading MIMO channels that are both i) data efficient and ii) computationally attractive. The performance of iterative least squares (LS) for channel estimation combined with sphere decoding (SD) for data detection is examined in the first part, for block fading channels, demonstrating the data efficiency provided by the semi-blind approach. In the second part, the case of continuous fading channels is addressed with the aid of recursive least squares (RLS). The observed relative robustness of the ML solution to channel variations is exploited in deriving a block QR-based RLS-SD scheme, which allows significant complexity savings with little or no performance loss","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"41 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":"134284542","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.2006.346399
Mats Rydström, E. Ström, A. Svensson
We consider the problem of locating a signal-source node, using characteristic signals emitted by the node that are captured by a set of sensor nodes. This estimation problem has often been formulated as a weighted least-squares problem in the literature. Received signal strength and asynchronous time-of-arrival measurements, however, give rise to objective functions with multiple local minima and saddle-points, complicating the optimization process. Recently, the method of projection onto convex sets (POCS) was suggested as a means to estimate source position, when received signal strength measurements are available. POCS has been shown to be robust to local minima in the objective function, is of low complexity, and is possible to distribute over the sensor nodes in the network. The drawback of POCS, when convex sets bounded by circles are used, is its poor performance in locating source nodes outside the outer perimeter of sensor nodes. We propose an extension to the presented POCS algorithm, called hyperbolic POCS, that increases the performance of circular POCS, allows for positioning of source nodes outside the outer perimeter of sensor nodes, and is applicable also for the case of asynchronous time-of-arrival measurements
{"title":"Robust Sensor Network Positioning Based on Projections onto Circular and Hyperbolic Convex Sets (POCS)","authors":"Mats Rydström, E. Ström, A. Svensson","doi":"10.1109/SPAWC.2006.346399","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346399","url":null,"abstract":"We consider the problem of locating a signal-source node, using characteristic signals emitted by the node that are captured by a set of sensor nodes. This estimation problem has often been formulated as a weighted least-squares problem in the literature. Received signal strength and asynchronous time-of-arrival measurements, however, give rise to objective functions with multiple local minima and saddle-points, complicating the optimization process. Recently, the method of projection onto convex sets (POCS) was suggested as a means to estimate source position, when received signal strength measurements are available. POCS has been shown to be robust to local minima in the objective function, is of low complexity, and is possible to distribute over the sensor nodes in the network. The drawback of POCS, when convex sets bounded by circles are used, is its poor performance in locating source nodes outside the outer perimeter of sensor nodes. We propose an extension to the presented POCS algorithm, called hyperbolic POCS, that increases the performance of circular POCS, allows for positioning of source nodes outside the outer perimeter of sensor nodes, and is applicable also for the case of asynchronous time-of-arrival measurements","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"125 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":"132529359","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.2006.346493
R. El Assir, F. Dietrich, M. Joham, W. Utschick
Linear precoding for the wireless MIMO broadcast channel with multiple antennas at the transmitter and non-cooperative single antenna receivers is considered. For statistical channel state information (CSI) at the transmitter a novel optimization problem for adaptive precoding based on the mean square error (MSE) is solved, which can also deal with incomplete CSI at the receivers, i.e., the receivers' channel estimates rely on a common pilot channel. We explicitly model the receivers' (limited) processing capabilities, which leads to a performance advantage over existing signal-to-interference-and-noise-ratio (SINR) approaches
{"title":"Min-Max MSE Precoding for Broadcast Channels Based on Statistical Channel State Information","authors":"R. El Assir, F. Dietrich, M. Joham, W. Utschick","doi":"10.1109/SPAWC.2006.346493","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346493","url":null,"abstract":"Linear precoding for the wireless MIMO broadcast channel with multiple antennas at the transmitter and non-cooperative single antenna receivers is considered. For statistical channel state information (CSI) at the transmitter a novel optimization problem for adaptive precoding based on the mean square error (MSE) is solved, which can also deal with incomplete CSI at the receivers, i.e., the receivers' channel estimates rely on a common pilot channel. We explicitly model the receivers' (limited) processing capabilities, which leads to a performance advantage over existing signal-to-interference-and-noise-ratio (SINR) approaches","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"60 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":"133435570","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.2006.346445
X. Yin, Troels Pedersen, N. Czink, B. Fleury
In this contribution, we derive a probability distribution suitable for characterizing bi-azimuth (azimuth of arrival and azimuth of departure) direction dispersion of individual path components in the response of the propagation channel. This distribution belongs to the family of generalized von-Mises-Fisher distributions. The elements in this family maximize the entropy under the constraint that the expectations and correlation matrix of the directions are known. The probability density function (pdf) of the proposed distribution is used to describe the bi-azimuth power spectrum of individual path components. An estimator of the parameters of the pdf is derived and applied to characterize the spreads in both azimuth of departure and azimuth of arrival, as well as the correlation between both azimuths of individual path components. Preliminary results from an experimental investigation demonstrate the applicability of the proposed characterization in real environments
{"title":"Parametric Characterization and Estimation of Bi-Azimuth Dispersion Path Components","authors":"X. Yin, Troels Pedersen, N. Czink, B. Fleury","doi":"10.1109/SPAWC.2006.346445","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346445","url":null,"abstract":"In this contribution, we derive a probability distribution suitable for characterizing bi-azimuth (azimuth of arrival and azimuth of departure) direction dispersion of individual path components in the response of the propagation channel. This distribution belongs to the family of generalized von-Mises-Fisher distributions. The elements in this family maximize the entropy under the constraint that the expectations and correlation matrix of the directions are known. The probability density function (pdf) of the proposed distribution is used to describe the bi-azimuth power spectrum of individual path components. An estimator of the parameters of the pdf is derived and applied to characterize the spreads in both azimuth of departure and azimuth of arrival, as well as the correlation between both azimuths of individual path components. Preliminary results from an experimental investigation demonstrate the applicability of the proposed characterization in real environments","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"7 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":"130905145","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.2006.346348
A. Pascual-Iserte, M. Payaró, A. Pérez-Neira, M. Lagunas
This paper deals with the problem of the design of a multi-antenna system assuming that only a statistical channel knowledge is available at the transmitter. More precisely, in the proposed design it is considered that an optimum maximum likelihood detector is employed at the receiver side and that the channel has a line of sight component. The design is obtained to minimize the worst pairwise error probability, which is averaged over the channel statistics. The benefits of exploiting this statistical channel knowledge are compared with a system requiring no channel state information at the transmitter. Finally, the asymptotic gain at high transmit power thanks to the line of sight component is found in closed-form
{"title":"Impact of a Line of Sight Component on the Performance of a MIMO System Designed under Statistical Channel Knowledge","authors":"A. Pascual-Iserte, M. Payaró, A. Pérez-Neira, M. Lagunas","doi":"10.1109/SPAWC.2006.346348","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346348","url":null,"abstract":"This paper deals with the problem of the design of a multi-antenna system assuming that only a statistical channel knowledge is available at the transmitter. More precisely, in the proposed design it is considered that an optimum maximum likelihood detector is employed at the receiver side and that the channel has a line of sight component. The design is obtained to minimize the worst pairwise error probability, which is averaged over the channel statistics. The benefits of exploiting this statistical channel knowledge are compared with a system requiring no channel state information at the transmitter. Finally, the asymptotic gain at high transmit power thanks to the line of sight component is found in closed-form","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"80 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":"117138090","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.2006.346468
M. Beko, J. Xavier, V. Barroso
We address the problem of codebook design for the low signal-to-noise ratio (SNR) fast non-coherent MIMO block fading channel. The channel matrix is assumed deterministic (no stochastic model attached) and unknown at both the receiver and the transmitter. To handle the unknown deterministic space-time channel, a generalized likelihood ratio test (GLRT) receiver is implemented. The case of single transmit antenna is considered and it is shown that the problem of finding good codes corresponds geometrically to a packing problem in the complex projective space. We provide new constellations and demonstrate that they perform substantially better than state-of-art known solutions which assume equal prior probabilities for the transmitted codewords. Our results are also of interest for Bayesian receivers which decode constellations with non-uniform priors
{"title":"Codebook Design for the Non-Coherent GLRT Receiver and Low SNR MIMO Block Fading Channel","authors":"M. Beko, J. Xavier, V. Barroso","doi":"10.1109/SPAWC.2006.346468","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346468","url":null,"abstract":"We address the problem of codebook design for the low signal-to-noise ratio (SNR) fast non-coherent MIMO block fading channel. The channel matrix is assumed deterministic (no stochastic model attached) and unknown at both the receiver and the transmitter. To handle the unknown deterministic space-time channel, a generalized likelihood ratio test (GLRT) receiver is implemented. The case of single transmit antenna is considered and it is shown that the problem of finding good codes corresponds geometrically to a packing problem in the complex projective space. We provide new constellations and demonstrate that they perform substantially better than state-of-art known solutions which assume equal prior probabilities for the transmitted codewords. Our results are also of interest for Bayesian receivers which decode constellations with non-uniform priors","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"16 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":"124442916","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.2006.346397
G. Chabriel, J. Barrère
In this paper, we study the blind separation of mixtures of propagating waves (delayed sources) encountered for example in underwater telephone (UWT) systems. We suggest a new second-order statistics method using as many observations as sources. First, we show that each of the N delayed sources can be developed as a particular linear combination of the different temporal-derivatives of the N observations. Under some assumptions, an instantaneous rectangular separating matrix is then identified by the joint diagonalization of a set of covariance matrices estimated from the observations and its derivatives. The algorithm used takes into account the particular structure of the spectral mixing matrix encountered. A numerical simulation is provided in a 3-sources/3- observations case for propagating audio signals
{"title":"Second-Order Blind Source Separation: A New Expression of Instantaneous Separating Matrix for Mixtures of Delayed Sources","authors":"G. Chabriel, J. Barrère","doi":"10.1109/SPAWC.2006.346397","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346397","url":null,"abstract":"In this paper, we study the blind separation of mixtures of propagating waves (delayed sources) encountered for example in underwater telephone (UWT) systems. We suggest a new second-order statistics method using as many observations as sources. First, we show that each of the N delayed sources can be developed as a particular linear combination of the different temporal-derivatives of the N observations. Under some assumptions, an instantaneous rectangular separating matrix is then identified by the joint diagonalization of a set of covariance matrices estimated from the observations and its derivatives. The algorithm used takes into account the particular structure of the spectral mixing matrix encountered. A numerical simulation is provided in a 3-sources/3- observations case for propagating audio signals","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"160 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":"115240766","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.2006.346438
C. Botella, G. Piñero, Alberto Gonzalez, M. D. Diego
A new spreading sequence assignment scheme for WCDMA is proposed in this paper. It is based on a simple but exhaustive model of the interferences involved: multiple access (MAI) and inter-finger interferences (IFI) at a mobile RAKE receiver output. These interferences are mainly determined in this work by the correlation properties of the spreading sequences. The new approach assigns spreading sequences in a way that minimum interference power between active users can be achieved. Simulation results show that the new scheme outperforms natural (consecutive ordering) scheme for the typical central situation of antenna arrays in a cell, but these benefits are even higher for a configuration of distributed antenna arrays around the cell
{"title":"Spreading Sequence Assignment in WCDMA for Distributed Antenna Arrays Based on Interference Model","authors":"C. Botella, G. Piñero, Alberto Gonzalez, M. D. Diego","doi":"10.1109/SPAWC.2006.346438","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346438","url":null,"abstract":"A new spreading sequence assignment scheme for WCDMA is proposed in this paper. It is based on a simple but exhaustive model of the interferences involved: multiple access (MAI) and inter-finger interferences (IFI) at a mobile RAKE receiver output. These interferences are mainly determined in this work by the correlation properties of the spreading sequences. The new approach assigns spreading sequences in a way that minimum interference power between active users can be achieved. Simulation results show that the new scheme outperforms natural (consecutive ordering) scheme for the typical central situation of antenna arrays in a cell, but these benefits are even higher for a configuration of distributed antenna arrays around the cell","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"59 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":"125207754","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.2006.346469
G. Wunder, T. Michel
Recently, in a companion paper we introduced the delay-limited capacity (DLC) region of an orthogonal frequency division multiplexing (OFDM) broadcast channel (BC). The DLC region is of utmost interest, since it e.g. provides an ultimate performance limit for all minimum sum power algorithms with given rate requirements. In this work we use the principle of rate water-filling to derive bounds on the OFDM DLC based on order statistics. We enhance these results to develop analytical lower bounds on the OFDM BC DLC region. The bounds are based on frequency division multiple access (FDMA) and ordinal channel state information (CSI), suggesting suboptimal but simple resource allocation schemes. Finally, these schemes are compared to a new algorithm using full CSI. Every practical sum power minimization algorithm using FDMA has to compete with these lower and upper bounds
最近，在另一篇论文中，我们介绍了正交频分复用(OFDM)广播信道(BC)的延迟限制容量(DLC)区域。DLC区域是最令人感兴趣的，因为它为给定速率要求的所有最小和功率算法提供了最终性能限制。在这项工作中，我们利用速率充水原理来推导基于阶统计量的OFDM DLC的边界。我们加强这些结果，以发展OFDM BC DLC区域的解析下界。边界是基于频分多址(FDMA)和有序信道状态信息(CSI)，建议次优但简单的资源分配方案。最后，将这些方案与使用全CSI的新算法进行了比较。每一种实用的FDMA和功率最小化算法都要与这些下界和上界竞争
{"title":"Approaching the Delay-Limited OFDM Broadcast Capacity with OFDMA","authors":"G. Wunder, T. Michel","doi":"10.1109/SPAWC.2006.346469","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346469","url":null,"abstract":"Recently, in a companion paper we introduced the delay-limited capacity (DLC) region of an orthogonal frequency division multiplexing (OFDM) broadcast channel (BC). The DLC region is of utmost interest, since it e.g. provides an ultimate performance limit for all minimum sum power algorithms with given rate requirements. In this work we use the principle of rate water-filling to derive bounds on the OFDM DLC based on order statistics. We enhance these results to develop analytical lower bounds on the OFDM BC DLC region. The bounds are based on frequency division multiple access (FDMA) and ordinal channel state information (CSI), suggesting suboptimal but simple resource allocation schemes. Finally, these schemes are compared to a new algorithm using full CSI. Every practical sum power minimization algorithm using FDMA has to compete with these lower and upper bounds","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"26 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":"116668916","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.2006.346431
J. Brehmer, C. Guthy, W. Utschick
A block-fading multi-user OFDMA downlink can be characterized by its outage probability region. For application in wireless resource allocation, a computationally efficient approximation of the outage region is required. The outage region is fully characterized by its Pareto efficient boundary. As a result, a finite set of well-distributed Pareto efficient samples provides the desired efficient approximation. The method of proper equality constraints (PEC) is employed to compute efficient points. In addition, an algorithm for choosing the equality constraints is presented, which provides a good distribution of samples and ensures fast convergence of the nonconvex PEC optimization
{"title":"An Efficient Approximation of the OFDMA Outage Probability Region","authors":"J. Brehmer, C. Guthy, W. Utschick","doi":"10.1109/SPAWC.2006.346431","DOIUrl":"https://doi.org/10.1109/SPAWC.2006.346431","url":null,"abstract":"A block-fading multi-user OFDMA downlink can be characterized by its outage probability region. For application in wireless resource allocation, a computationally efficient approximation of the outage region is required. The outage region is fully characterized by its Pareto efficient boundary. As a result, a finite set of well-distributed Pareto efficient samples provides the desired efficient approximation. The method of proper equality constraints (PEC) is employed to compute efficient points. In addition, an algorithm for choosing the equality constraints is presented, which provides a good distribution of samples and ensures fast convergence of the nonconvex PEC optimization","PeriodicalId":414942,"journal":{"name":"2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications","volume":"12 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":"128097247","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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