Pub Date : 1982-10-01DOI: 10.1109/MILCOM.1982.4805944
D. Grieco
The effectiveness of a pulse jammer against a digital voice link using direct-sequence spread spectrum is considered. Voice digitization is CVSD at 16 kbps, so that a 10% bit error rate is selected as the criterion for acceptable speech intelligibility. The data modulation is DPSK. A fast AGC, wherein the attack and release times are very small in relation to the bit duration (62.5 microseconds), is shown to play an important role. A variety of pulse formats are considered, including multiple-bit and partial-bit pulse widths. In all cases it is found that pulse jamming is not an effective strategy against digital voice, but can be effective against data where a lower BER is required. Also, it is shown that the optimum jammer always entirely overlaps one data symbol in a DPSK format.
{"title":"Pulse Jamming Effectiveness against a Spread-Spectrum Digital Voice Link","authors":"D. Grieco","doi":"10.1109/MILCOM.1982.4805944","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805944","url":null,"abstract":"The effectiveness of a pulse jammer against a digital voice link using direct-sequence spread spectrum is considered. Voice digitization is CVSD at 16 kbps, so that a 10% bit error rate is selected as the criterion for acceptable speech intelligibility. The data modulation is DPSK. A fast AGC, wherein the attack and release times are very small in relation to the bit duration (62.5 microseconds), is shown to play an important role. A variety of pulse formats are considered, including multiple-bit and partial-bit pulse widths. In all cases it is found that pulse jamming is not an effective strategy against digital voice, but can be effective against data where a lower BER is required. Also, it is shown that the optimum jammer always entirely overlaps one data symbol in a DPSK format.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115385756","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4805920
S. Pupolin, C. Tomasi
The pseudonoise sequences generated by linear feedback shift registers are of great interest in spread spectrum communication systems. In particular a deep knowledge of the properties of subsequences of them is needed when studying the acquisition phase of synchronization between the locally generated and the received sequence. Some mathematical results about the computation of the moments of the above mentioned subsequences are presented.
{"title":"Moments of the Weights of Pseudo-Noise Subsequences","authors":"S. Pupolin, C. Tomasi","doi":"10.1109/MILCOM.1982.4805920","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805920","url":null,"abstract":"The pseudonoise sequences generated by linear feedback shift registers are of great interest in spread spectrum communication systems. In particular a deep knowledge of the properties of subsequences of them is needed when studying the acquisition phase of synchronization between the locally generated and the received sequence. Some mathematical results about the computation of the moments of the above mentioned subsequences are presented.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115692774","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4805899
G. Cooper, L. Cooper
This paper describes a method of communicating with a low probability of intercept by using a purely random spreading function. Binary message modulation is achieved by introducing appropriate delays and the message is recovered with a correlation operation. The performance of both binary and M-ary systems is analyzed and the bit error probability obtained as function of the system bandwidth and the receiver input signal-to-noise ratio. The analysis reveals that with adequate bandwidth it is possible to achieve acceptable bit error probabilities with receiver input signal-to-noise ratios on the order of ¿30 to ¿40 dB.
{"title":"Covert Communication with a Purely Random Spreading Function","authors":"G. Cooper, L. Cooper","doi":"10.1109/MILCOM.1982.4805899","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805899","url":null,"abstract":"This paper describes a method of communicating with a low probability of intercept by using a purely random spreading function. Binary message modulation is achieved by introducing appropriate delays and the message is recovered with a correlation operation. The performance of both binary and M-ary systems is analyzed and the bit error probability obtained as function of the system bandwidth and the receiver input signal-to-noise ratio. The analysis reveals that with adequate bandwidth it is possible to achieve acceptable bit error probabilities with receiver input signal-to-noise ratios on the order of ¿30 to ¿40 dB.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125143431","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4805962
N. Broome
A digital joint maximum a posteriori (MAP) symbol synchronizer and phase estimator is realized for minimum shift keying (MSK) modulation. This development permits direct digital implementation of closed loop synchronization and coherent demodulation. Advantages derived from this approach are parameter stability and accuracy with system flexibility and reliability.
{"title":"An All Digital Maximum a Posteriori based Synchronizer for MSK","authors":"N. Broome","doi":"10.1109/MILCOM.1982.4805962","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805962","url":null,"abstract":"A digital joint maximum a posteriori (MAP) symbol synchronizer and phase estimator is realized for minimum shift keying (MSK) modulation. This development permits direct digital implementation of closed loop synchronization and coherent demodulation. Advantages derived from this approach are parameter stability and accuracy with system flexibility and reliability.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131670027","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4806010
I. Mayk, H. Henderson
Results from a digital computer simulation of a network of approximately 50 nodes, typifying a spread spectrum time division multiple access (TDMA) system such as the Joint Tactical Information Distribution System (JTIDS), in a ground environment, are presented, and discussed. The results apply to initialization performance of network synchronization. The results provide an insight into network management tradeoffs which may be made with respect to: a) method of network synchronization, b) system capacity needed for network synchronization, and c) degree of network connectivity. The results provide qualitative as well as quantitative assessment of the impact of changing any of the above network management variables when the others remain fixed at various operating points. Since a wide range of time delays, typically from, few to many minutes may be incurred, it is concluded that network management techniques may be optimized to meet the initialization performance requirements of a given network. Such optimizations, however, depend upon specific implementations of the network synchronization process, the dynamics of the network nodes and the environment (electromagnetic, terrain, and weather) affecting their connectivity.
{"title":"Network Synchronization Initialization Performance of a TDMA System in the Ground Environment","authors":"I. Mayk, H. Henderson","doi":"10.1109/MILCOM.1982.4806010","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4806010","url":null,"abstract":"Results from a digital computer simulation of a network of approximately 50 nodes, typifying a spread spectrum time division multiple access (TDMA) system such as the Joint Tactical Information Distribution System (JTIDS), in a ground environment, are presented, and discussed. The results apply to initialization performance of network synchronization. The results provide an insight into network management tradeoffs which may be made with respect to: a) method of network synchronization, b) system capacity needed for network synchronization, and c) degree of network connectivity. The results provide qualitative as well as quantitative assessment of the impact of changing any of the above network management variables when the others remain fixed at various operating points. Since a wide range of time delays, typically from, few to many minutes may be incurred, it is concluded that network management techniques may be optimized to meet the initialization performance requirements of a given network. Such optimizations, however, depend upon specific implementations of the network synchronization process, the dynamics of the network nodes and the environment (electromagnetic, terrain, and weather) affecting their connectivity.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"72 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129687254","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4805923
S. El-Khamy
The design of matched direct-sequence spread spectrum (DS-SS) signals for transmission through slowly fading dispersive channels is considered in this paper. For large processing gains, these signal overcome the channel dispersion and minimize the effect of intersymbol interference (ISI). The matched signals are on the form of quaternary phase modulated (QPM) signals with constant envelopes. Their base-band equivalent are on the form of combined codes with outer components which are the usual spreaded data codes of DS-SS signals and inner components which are binary codes that are matched to the channel impulse response.
{"title":"Matched Spread Spectrum Techniques","authors":"S. El-Khamy","doi":"10.1109/MILCOM.1982.4805923","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805923","url":null,"abstract":"The design of matched direct-sequence spread spectrum (DS-SS) signals for transmission through slowly fading dispersive channels is considered in this paper. For large processing gains, these signal overcome the channel dispersion and minimize the effect of intersymbol interference (ISI). The matched signals are on the form of quaternary phase modulated (QPM) signals with constant envelopes. Their base-band equivalent are on the form of combined codes with outer components which are the usual spreaded data codes of DS-SS signals and inner components which are binary codes that are matched to the channel impulse response.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131020682","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4806023
Jack Rubin
The Joint Tactical Information Distribution System (JTIDS) is a tri-service, multi-channel, multi-function system. Distributed TDMA, the defined baseline for JTIDS Phase II (JTIDS II) expands the basic TDMA (Phase I) capability by providing increased data rate capacity and additional C-N-I functions. ITTAV has been the prime U. S. Navy contractor for the development of a series of JTIDS/DTDMA Advanced Development Model terminals. Under a contract from the Naval Air Development Center, Warminster, Pennsylvania, ITTAV has designed, built and extensively tested four terminals and a JTIDS signal simulator. Testing in both laboratory and flight test environments has validated the high levels of security and jam-resistance plus the multi-function, multi-netting flexibility inherent in the. DTDMA architecture. This paper will provide some more detailed information on the functional capabilities and design features of these JTIDS/DTDMA terminals, and the test highlight results. As a result of the successful completion of the ADM program the U. S. Navy is undertaking the Full Scale Development of JTIDS/DTDMA under contract with ITT and Hughes in a joint venture known as TADCOM.
{"title":"The Development of JTIDS Distributed TDMA (DTDMA) Advanced Development Model (ADM) Terminals","authors":"Jack Rubin","doi":"10.1109/MILCOM.1982.4806023","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4806023","url":null,"abstract":"The Joint Tactical Information Distribution System (JTIDS) is a tri-service, multi-channel, multi-function system. Distributed TDMA, the defined baseline for JTIDS Phase II (JTIDS II) expands the basic TDMA (Phase I) capability by providing increased data rate capacity and additional C-N-I functions. ITTAV has been the prime U. S. Navy contractor for the development of a series of JTIDS/DTDMA Advanced Development Model terminals. Under a contract from the Naval Air Development Center, Warminster, Pennsylvania, ITTAV has designed, built and extensively tested four terminals and a JTIDS signal simulator. Testing in both laboratory and flight test environments has validated the high levels of security and jam-resistance plus the multi-function, multi-netting flexibility inherent in the. DTDMA architecture. This paper will provide some more detailed information on the functional capabilities and design features of these JTIDS/DTDMA terminals, and the test highlight results. As a result of the successful completion of the ADM program the U. S. Navy is undertaking the Full Scale Development of JTIDS/DTDMA under contract with ITT and Hughes in a joint venture known as TADCOM.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133369139","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4805993
D. Leimer
A scheme to adaptively null narrowband interference of a PN direct-sequence signal is described. The nulling strategy is to minimize the mean-square output of a transversal filter with one tap weight constrained to be non-zero. The achievable improvement in processing gain is first established by analyzing the nulling performance of a Wiener filter for the hypothetical case of interference with known parameters. Next, the LMS algorithm is applied and simulation results of the adaptive interference nuller are described. When the interference is narrowband, the potential improvement in antijam processing gain is shown to be very large, typically 40 dB. When the interference is wideband, however, the nulling scheme becomes ineffective. Nevertheless, the theoretical processing gain is never less than the conventional processing gain of a PN system. Digital processing techniques for both the adaptation and PN correlation are proposed. Implementation considerations and the resulting quantization effects are discussed. The practical considerations of acquisition and tracking in the presence of interference nulling are also discussed. For example, correlation sidelobes are induced by the nulling scheme. This does not affect acquisition since the sidelobes are delayed in time, however, multiple delay-lock tracking points are created. A modification to eliminate this limitation is described.
{"title":"Adaptive Processing for Improved Jamming Resistance against Narrowband Interference","authors":"D. Leimer","doi":"10.1109/MILCOM.1982.4805993","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805993","url":null,"abstract":"A scheme to adaptively null narrowband interference of a PN direct-sequence signal is described. The nulling strategy is to minimize the mean-square output of a transversal filter with one tap weight constrained to be non-zero. The achievable improvement in processing gain is first established by analyzing the nulling performance of a Wiener filter for the hypothetical case of interference with known parameters. Next, the LMS algorithm is applied and simulation results of the adaptive interference nuller are described. When the interference is narrowband, the potential improvement in antijam processing gain is shown to be very large, typically 40 dB. When the interference is wideband, however, the nulling scheme becomes ineffective. Nevertheless, the theoretical processing gain is never less than the conventional processing gain of a PN system. Digital processing techniques for both the adaptation and PN correlation are proposed. Implementation considerations and the resulting quantization effects are discussed. The practical considerations of acquisition and tracking in the presence of interference nulling are also discussed. For example, correlation sidelobes are induced by the nulling scheme. This does not affect acquisition since the sidelobes are delayed in time, however, multiple delay-lock tracking points are created. A modification to eliminate this limitation is described.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"31 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133390953","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4806012
William I. MacGregor, J. Westcott, M. Beeler
This paper presents a design recently implemented by the Packet Radio project for control of large networks. The network is built on a carrier sense, multiple access broadcast channel and is populated with mobile store and forward nodes known as packet radio units, or PRs. Until recently, the packet radio network operated with centralized routing controlled by one node, the station. To increase the size of the network and to provide redundant control a multiple station design, "multistation", was necessary. The PRs gather local connectivity information which is then forwarded to the controlling nodes (stations). Each station is responsible for up to 40 PRs located near it in connectivity and uses these PRs to communicate with other stations. Questions important to the development of multistation include: How are packet radios matched with controlling stations? How do stations find and communicate with each other? How are long routes crossing the borders of many stations determined, and how is their successful setup insured? How is control traffic minimized?
{"title":"Multiple Control Stations in Packet Radio Networks","authors":"William I. MacGregor, J. Westcott, M. Beeler","doi":"10.1109/MILCOM.1982.4806012","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4806012","url":null,"abstract":"This paper presents a design recently implemented by the Packet Radio project for control of large networks. The network is built on a carrier sense, multiple access broadcast channel and is populated with mobile store and forward nodes known as packet radio units, or PRs. Until recently, the packet radio network operated with centralized routing controlled by one node, the station. To increase the size of the network and to provide redundant control a multiple station design, \"multistation\", was necessary. The PRs gather local connectivity information which is then forwarded to the controlling nodes (stations). Each station is responsible for up to 40 PRs located near it in connectivity and uses these PRs to communicate with other stations. Questions important to the development of multistation include: How are packet radios matched with controlling stations? How do stations find and communicate with each other? How are long routes crossing the borders of many stations determined, and how is their successful setup insured? How is control traffic minimized?","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133322851","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 : 1982-10-01DOI: 10.1109/MILCOM.1982.4805900
George Huang, Jay Jones, Lee Murphy, B. Olevsky
Spread-Spectrum waveforms are used commonly for Anti-Jam (A/J) and Low-Probability-of-Intercept (LPI) applications, but their effectiveness is difficult to assess owing to the diversity of system parameters and to various user requirements. This paper describes a spread-spectrum analysis and design laboratory system consisting of a software analysis subsystem and a hardware breadboarding facility. The laboratory system provides both A/J and intercept threat analysis capabilities. Through figure-of-merit expressions, design trade-offs can be conducted and design verifications made by breadboard experiments. As the number of military spread-spectrum systems increases in the future, the conventional analysis and design approach will not be flexible enough to accommodate the growing number of candidate waveforms. This laboratory system provides a cost-effective and flexible alternative. Examples presented in the paper describe the analysis and design procedures and the results for a spread-spectrum communication system to combat various intercept threats including radiometers (wideband and channelized), chip-rate detectors, and hop-rate detectors. A unique laboratory breadboard hierarchical approach is also presented, where multiple waveform generation is possible through a basic communications modem. Most MFSK, FH, and PN waveforms and their combinations can be generated by the hierarchical structure.
{"title":"A Spread-Spectrum Analysis and Design Laboratory System","authors":"George Huang, Jay Jones, Lee Murphy, B. Olevsky","doi":"10.1109/MILCOM.1982.4805900","DOIUrl":"https://doi.org/10.1109/MILCOM.1982.4805900","url":null,"abstract":"Spread-Spectrum waveforms are used commonly for Anti-Jam (A/J) and Low-Probability-of-Intercept (LPI) applications, but their effectiveness is difficult to assess owing to the diversity of system parameters and to various user requirements. This paper describes a spread-spectrum analysis and design laboratory system consisting of a software analysis subsystem and a hardware breadboarding facility. The laboratory system provides both A/J and intercept threat analysis capabilities. Through figure-of-merit expressions, design trade-offs can be conducted and design verifications made by breadboard experiments. As the number of military spread-spectrum systems increases in the future, the conventional analysis and design approach will not be flexible enough to accommodate the growing number of candidate waveforms. This laboratory system provides a cost-effective and flexible alternative. Examples presented in the paper describe the analysis and design procedures and the results for a spread-spectrum communication system to combat various intercept threats including radiometers (wideband and channelized), chip-rate detectors, and hop-rate detectors. A unique laboratory breadboard hierarchical approach is also presented, where multiple waveform generation is possible through a basic communications modem. Most MFSK, FH, and PN waveforms and their combinations can be generated by the hierarchical structure.","PeriodicalId":179832,"journal":{"name":"MILCOM 1982 - IEEE Military Communications Conference - Progress in Spread Spectrum Communications","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125527744","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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