Pub Date : 2002-08-07DOI: 10.1109/IZSBC.2002.991794
J. Maucher, G. Kunz, A. Rinkel
For the UMTS radio access network, the problems of dimensioning/planning and algorithm evaluation/optimization is a challenging task, which requires methods and tools that are essentially different from the ones applied for 2nd generation systems. In order to generate reliable results for the highly flexible and dynamic UMTS, sophisticated simulation tools have to be applied. A UMTS model and its implementation is described. It allows an efficient evaluation of UMTS in terms of system performance figures such as capacity, coverage and QoS.
{"title":"UMTS EASYCOPE: a tool for UMTS network and algorithm evaluation","authors":"J. Maucher, G. Kunz, A. Rinkel","doi":"10.1109/IZSBC.2002.991794","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991794","url":null,"abstract":"For the UMTS radio access network, the problems of dimensioning/planning and algorithm evaluation/optimization is a challenging task, which requires methods and tools that are essentially different from the ones applied for 2nd generation systems. In order to generate reliable results for the highly flexible and dynamic UMTS, sophisticated simulation tools have to be applied. A UMTS model and its implementation is described. It allows an efficient evaluation of UMTS in terms of system performance figures such as capacity, coverage and QoS.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117170127","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991760
Liang Zhang, A. Yongaçoğlu
If impulse noise is not taken into account, turbo codes are highly attractive for transmissions over asymmetric digital subscriber lines. We show that impulse noise could devastate turbo coding performance if appropriate precautions are not taken. A possible solution of using an outer Reed-Solomon code to combat impulse noise results in very large delays. We propose erasure turbo decoding to improve the turbo trellis coded modulation performance against impulse noise. We also show that when a concatenated coding structure is employed, in addition to improving the bit error rate performance, erasure turbo decoding can also significantly reduce the delay of the outer Reed-Solomon code.
{"title":"Turbo decoding with erasures for high-speed transmission in the presence of impulse noise","authors":"Liang Zhang, A. Yongaçoğlu","doi":"10.1109/IZSBC.2002.991760","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991760","url":null,"abstract":"If impulse noise is not taken into account, turbo codes are highly attractive for transmissions over asymmetric digital subscriber lines. We show that impulse noise could devastate turbo coding performance if appropriate precautions are not taken. A possible solution of using an outer Reed-Solomon code to combat impulse noise results in very large delays. We propose erasure turbo decoding to improve the turbo trellis coded modulation performance against impulse noise. We also show that when a concatenated coding structure is employed, in addition to improving the bit error rate performance, erasure turbo decoding can also significantly reduce the delay of the outer Reed-Solomon code.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116611832","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991785
R. Schober, L. Lampe, W. Gerstacker, S. Pasupathy
In this paper, modulation diversity (MD) for Rayleigh fading intersymbol interference (ISI) channels is proposed. In particular, the achievable performance with MD is analyzed and a design criterion for MD codes is deduced from an upper bound on the pairwise error probability. This design rule is similar to the well-known design rule for MD codes for flat fading and does not depend on the power delay profile of the fading channel. Several examples for MD codes with prescribed properties are given and compared. Simulation results confirm that considerable performance gains can be achieved with MD even if suboptimum equalization schemes are adopted at the receiver.
{"title":"Modulation diversity for fading ISI channels: performance analysis and code design","authors":"R. Schober, L. Lampe, W. Gerstacker, S. Pasupathy","doi":"10.1109/IZSBC.2002.991785","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991785","url":null,"abstract":"In this paper, modulation diversity (MD) for Rayleigh fading intersymbol interference (ISI) channels is proposed. In particular, the achievable performance with MD is analyzed and a design criterion for MD codes is deduced from an upper bound on the pairwise error probability. This design rule is similar to the well-known design rule for MD codes for flat fading and does not depend on the power delay profile of the fading channel. Several examples for MD codes with prescribed properties are given and compared. Simulation results confirm that considerable performance gains can be achieved with MD even if suboptimum equalization schemes are adopted at the receiver.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130364206","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991746
Y. Hara
The weight convergence analysis of adaptive array antennas based on a sample matrix inversion (SMI) algorithm is presented. Firstly, we derive the required number of samples for weight computation to achieve an output signal-to-interference-plus-noise ratio (SINR) -10 log/sub 10/ r [dB] (r/spl les/1) below an optimum value. Next, we present the weight convergence of CDMA adaptive array antennas based on the SMI algorithm, where two types of weight computational methods are compared between "chip-level computation" and "symbol-level computation". Analytical and simulation results reveal that "chip-level computation" before the despreading process enables faster convergence than "symbol-level computation" after the despreading process.
提出了一种基于样本矩阵反演(SMI)算法的自适应阵列天线权值收敛分析方法。首先，我们推导出权重计算所需的样本数，以实现低于最佳值的输出信噪比(SINR) -10 log/sub 10/ r [dB] (r/spl les/1)。其次，提出了基于SMI算法的CDMA自适应阵列天线的权值收敛问题，比较了“芯片级计算”和“符号级计算”两种权值计算方法。分析和仿真结果表明，解扩前的“芯片级计算”比解扩后的“符号级计算”收敛速度更快。
{"title":"Weight convergence analysis of adaptive array antennas based on SMI algorithm","authors":"Y. Hara","doi":"10.1109/IZSBC.2002.991746","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991746","url":null,"abstract":"The weight convergence analysis of adaptive array antennas based on a sample matrix inversion (SMI) algorithm is presented. Firstly, we derive the required number of samples for weight computation to achieve an output signal-to-interference-plus-noise ratio (SINR) -10 log/sub 10/ r [dB] (r/spl les/1) below an optimum value. Next, we present the weight convergence of CDMA adaptive array antennas based on the SMI algorithm, where two types of weight computational methods are compared between \"chip-level computation\" and \"symbol-level computation\". Analytical and simulation results reveal that \"chip-level computation\" before the despreading process enables faster convergence than \"symbol-level computation\" after the despreading process.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114231011","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991770
M. Schubert, H. Boche
The problem of multiuser beamforming and power control for spatially dispersive, frequency flat channels is addressed, assuming that the base station is equipped with an antenna array and knows the second-order statistics of the channel. There is an interesting duality between the uplink and the downlink problem. In particular, it is shown that both cases can be solved efficiently by an iterative optimization scheme, wherein the conventional uplink beamformer plays a central role. The antenna weights that solve the uplink problem also solve the more complicated downlink problem. The reason for this can be found in the special structure of the crosstalk matrix coupling all users. This leads to an elegant theory, which may also prove useful for solving related problems.
{"title":"A unifying theory for uplink and downlink multiuser beamforming","authors":"M. Schubert, H. Boche","doi":"10.1109/IZSBC.2002.991770","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991770","url":null,"abstract":"The problem of multiuser beamforming and power control for spatially dispersive, frequency flat channels is addressed, assuming that the base station is equipped with an antenna array and knows the second-order statistics of the channel. There is an interesting duality between the uplink and the downlink problem. In particular, it is shown that both cases can be solved efficiently by an iterative optimization scheme, wherein the conventional uplink beamformer plays a central role. The antenna weights that solve the uplink problem also solve the more complicated downlink problem. The reason for this can be found in the special structure of the crosstalk matrix coupling all users. This leads to an elegant theory, which may also prove useful for solving related problems.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132492859","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991787
I. Barhumi, G. Leus, M. Moonen
This paper describes a channel estimation and tracking scheme for MIMO OFDM systems based on pilot tones. The mean square error of the proposed scheme is derived, and through this we derive optimal training sequences and placement of the pilot tones. It is shown in this paper that the minimum mean square error (MMSE) is obtained with equispaced pilot tones in frequency, equipowered, orthogonal and phase shift orthogonal training sequences. For channels with large excess delay the number of pilot tones required for training is quite large, though a scheme for channel estimation over multiple blocks is proposed. Through simulations it is shown that the optimal training sequences derived in this paper outperform both the random and orthogonal training sequences which appear to be suboptimal. Moreover, an RLS like method is also proposed to enhance channel estimation.
{"title":"Optimal training sequences for channel estimation in MIMO OFDM systems in mobile wireless channels","authors":"I. Barhumi, G. Leus, M. Moonen","doi":"10.1109/IZSBC.2002.991787","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991787","url":null,"abstract":"This paper describes a channel estimation and tracking scheme for MIMO OFDM systems based on pilot tones. The mean square error of the proposed scheme is derived, and through this we derive optimal training sequences and placement of the pilot tones. It is shown in this paper that the minimum mean square error (MMSE) is obtained with equispaced pilot tones in frequency, equipowered, orthogonal and phase shift orthogonal training sequences. For channels with large excess delay the number of pilot tones required for training is quite large, though a scheme for channel estimation over multiple blocks is proposed. Through simulations it is shown that the optimal training sequences derived in this paper outperform both the random and orthogonal training sequences which appear to be suboptimal. Moreover, an RLS like method is also proposed to enhance channel estimation.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"84 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124830796","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991748
A. Burg, E. Beck, M. Rupp, D. Perels, N. Felber, W. Fichtner
Multiple input/multiple output (MIMO) systems have received great attention to boost the capacity of wireless communication systems. Multiple antennas at the transmitter and receiver are used to exploit the spatial diversity in a rich scattering environment to concurrently transmit multiple data streams in the same frequency band thereby increasing spectral efficiency. Besides the actual MIMO decoder a significant part of the implementation complexity of such a system turns out to be in the receiver front-end. In this paper an efficient implementation of a MIMO receiver frontend based on a modified FDD UMTS downlink is presented. A new method for the efficient realization of a MIMO channel estimation is being introduced. The implementation of the RAKE receiver as well as the frequency-offset estimation is also discussed.
{"title":"FPGA implementation of a MIMO receiver front-end for the UMTS downlink","authors":"A. Burg, E. Beck, M. Rupp, D. Perels, N. Felber, W. Fichtner","doi":"10.1109/IZSBC.2002.991748","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991748","url":null,"abstract":"Multiple input/multiple output (MIMO) systems have received great attention to boost the capacity of wireless communication systems. Multiple antennas at the transmitter and receiver are used to exploit the spatial diversity in a rich scattering environment to concurrently transmit multiple data streams in the same frequency band thereby increasing spectral efficiency. Besides the actual MIMO decoder a significant part of the implementation complexity of such a system turns out to be in the receiver front-end. In this paper an efficient implementation of a MIMO receiver frontend based on a modified FDD UMTS downlink is presented. A new method for the efficient realization of a MIMO channel estimation is being introduced. The implementation of the RAKE receiver as well as the frequency-offset estimation is also discussed.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130690401","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991793
Max Kamenetskyt, Matthias Unbehaud
Wireless LANs (WLANs) are becoming increasingly popular for providing high data rate network access to mobile computers. Most of the currently deployed systems operate in the 2.4 GHz unlicensed frequency band. However, increasing demand for higher data rates and network capacities has led to new system standards for the 5 GHz band. We examine methods for obtaining a close-to-optimal positioning of WLAN access points (APs) and evaluate their performance in a typical downtown or campus environment. The system performance is evaluated using an objective function which aims to maximize both the coverage area and the overall signal quality. The optimization algorithms evaluate this objective function over a discrete search space, thereby considerably reducing the inherent complexity of the problem, while at the same time providing a reasonable approximation to the continuous optimization problem. Numerical results show that random search algorithms, such as simulated annealing, can yield very good solutions. However, the convergence speed of simulated annealing strongly depends on the fine-tuning of simulation parameters and a good choice of the initial set of transmitter positions. Successive removal algorithms, such as pruning, though usually producing sub-optimal solutions, converge in polynomial time. We therefore propose a combination of the two approaches - using pruning for obtaining an initial set of transmitter positions and refining these by using either neighborhood search or simulated annealing.
{"title":"Coverage planning for outdoor wireless LAN systems","authors":"Max Kamenetskyt, Matthias Unbehaud","doi":"10.1109/IZSBC.2002.991793","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991793","url":null,"abstract":"Wireless LANs (WLANs) are becoming increasingly popular for providing high data rate network access to mobile computers. Most of the currently deployed systems operate in the 2.4 GHz unlicensed frequency band. However, increasing demand for higher data rates and network capacities has led to new system standards for the 5 GHz band. We examine methods for obtaining a close-to-optimal positioning of WLAN access points (APs) and evaluate their performance in a typical downtown or campus environment. The system performance is evaluated using an objective function which aims to maximize both the coverage area and the overall signal quality. The optimization algorithms evaluate this objective function over a discrete search space, thereby considerably reducing the inherent complexity of the problem, while at the same time providing a reasonable approximation to the continuous optimization problem. Numerical results show that random search algorithms, such as simulated annealing, can yield very good solutions. However, the convergence speed of simulated annealing strongly depends on the fine-tuning of simulation parameters and a good choice of the initial set of transmitter positions. Successive removal algorithms, such as pruning, though usually producing sub-optimal solutions, converge in polynomial time. We therefore propose a combination of the two approaches - using pruning for obtaining an initial set of transmitter positions and refining these by using either neighborhood search or simulated annealing.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133767156","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991776
Hyun-Cheol Jeon, Yoon-seok Jung, B. Kwon, J. Ihm
CDMA2000 is the 3rd generation (3G) communication system based on the 2/sup nd/ generation standard, IS-95. Because the 3G system has more complex features than IS-95, more accuracy analysis on coverage and capacity in adoption of repeater systems are needed. Especially, the issue of whether to use a base station or repeater system to cover the shadow region effectively, taking quality of service (QoS) and economy into consideration, is of critical importance for mobile communication engineers. In this paper, QoS related system capacity and coverage analysis results are provided by simulation. We describe the advantages and disadvantages of repeater systems as a new remote cell with real CDMA2000 environment.
{"title":"Analysis on coverage and capacity in adoption of repeater systems in CDMA2000","authors":"Hyun-Cheol Jeon, Yoon-seok Jung, B. Kwon, J. Ihm","doi":"10.1109/IZSBC.2002.991776","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991776","url":null,"abstract":"CDMA2000 is the 3rd generation (3G) communication system based on the 2/sup nd/ generation standard, IS-95. Because the 3G system has more complex features than IS-95, more accuracy analysis on coverage and capacity in adoption of repeater systems are needed. Especially, the issue of whether to use a base station or repeater system to cover the shadow region effectively, taking quality of service (QoS) and economy into consideration, is of critical importance for mobile communication engineers. In this paper, QoS related system capacity and coverage analysis results are provided by simulation. We describe the advantages and disadvantages of repeater systems as a new remote cell with real CDMA2000 environment.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114247481","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 : 2002-08-07DOI: 10.1109/IZSBC.2002.991759
Jürgen F. Rößler, W. Gerstacker, Alexander Lampe, Johannes B. Huber
In this paper, two novel equalization algorithms applying soft-decision feedback, designed for quaternary phase-shift keying (QPSK) transmission are introduced. The first one uses a matched filter (MF) as a front end and is derived from Gerstacker et al. (2000) where it was originally developed for binary transmission. The second one is an improved version of the first, employing a minimum mean-squared error (MMSE) filter in each iteration in order to refine the data estimates. The rule for generating soft decisions is adapted continuously to the current state of the algorithm. In most cases, standard DFE methods are clearly outperformed. In contrast to the algorithm of Gerstacker, a performance close to that of maximum-likelihood sequence estimation can be obtained for the MMSE-based scheme for a broad class of channels.
{"title":"Matched-filter- and MMSE-based iterative equalization with soft feedback for QPSK transmission","authors":"Jürgen F. Rößler, W. Gerstacker, Alexander Lampe, Johannes B. Huber","doi":"10.1109/IZSBC.2002.991759","DOIUrl":"https://doi.org/10.1109/IZSBC.2002.991759","url":null,"abstract":"In this paper, two novel equalization algorithms applying soft-decision feedback, designed for quaternary phase-shift keying (QPSK) transmission are introduced. The first one uses a matched filter (MF) as a front end and is derived from Gerstacker et al. (2000) where it was originally developed for binary transmission. The second one is an improved version of the first, employing a minimum mean-squared error (MMSE) filter in each iteration in order to refine the data estimates. The rule for generating soft decisions is adapted continuously to the current state of the algorithm. In most cases, standard DFE methods are clearly outperformed. In contrast to the algorithm of Gerstacker, a performance close to that of maximum-likelihood sequence estimation can be obtained for the MMSE-based scheme for a broad class of channels.","PeriodicalId":336991,"journal":{"name":"2002 International Zurich Seminar on Broadband Communications Access - Transmission - Networking (Cat. No.02TH8599)","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2002-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126930155","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：