Pub Date : 2011-10-24DOI: 10.1109/ICUWB.2011.6058844
Michael Mirbach, W. Menzel
A simple 3D surface estimation algorithm for ultra-wideband (UWB) pulse radars is presented. This algorithm based on trilateration is easy to implement and needs no preprocessing of measurement data. Mathematical derivations of the formulas for both monostatic and bistatic radar imaging setups are derived. The performance of the proposed algorithm is verified in 3D surface measurements, and a good agreement with well-established methods is shown.
{"title":"A simple surface estimation algorithm for UWB pulse radars based on trilateration","authors":"Michael Mirbach, W. Menzel","doi":"10.1109/ICUWB.2011.6058844","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058844","url":null,"abstract":"A simple 3D surface estimation algorithm for ultra-wideband (UWB) pulse radars is presented. This algorithm based on trilateration is easy to implement and needs no preprocessing of measurement data. Mathematical derivations of the formulas for both monostatic and bistatic radar imaging setups are derived. The performance of the proposed algorithm is verified in 3D surface measurements, and a good agreement with well-established methods is shown.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121428580","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058877
Y. Takei, H. Katsuta, K. Takizawa, K. Hamaguchi, T. Ikegami
This paper presents a prototype of ultra-wideband-based wireless body area networks and tests the prototype in experiments held in an anechoic chamber. Physical and Media Access Control specifications are based on the draft standard in IEEE802.15.6. The Media Access Control is based on a superframe structure comprising time slots assigned to a beacon, contention access period, or contention-free period. The physical layer achieves a bit rate of 258 kbps in differential binary phase-shift keying with direct sequence spreading. The center frequency is 4.096 GHz. In the experiments, the throughput performance of the prototype is measured for the scenario of the wireless monitoring of vital signs with a sensor device and hub device. In this scenario, a bit rate of 18 kbps is required to convey a measured physiological waveform. The experiment results show that the requirement is continuously met, although the throughput is affected by body movement.
{"title":"A prototype of ultra wideband-based wireless body area networks","authors":"Y. Takei, H. Katsuta, K. Takizawa, K. Hamaguchi, T. Ikegami","doi":"10.1109/ICUWB.2011.6058877","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058877","url":null,"abstract":"This paper presents a prototype of ultra-wideband-based wireless body area networks and tests the prototype in experiments held in an anechoic chamber. Physical and Media Access Control specifications are based on the draft standard in IEEE802.15.6. The Media Access Control is based on a superframe structure comprising time slots assigned to a beacon, contention access period, or contention-free period. The physical layer achieves a bit rate of 258 kbps in differential binary phase-shift keying with direct sequence spreading. The center frequency is 4.096 GHz. In the experiments, the throughput performance of the prototype is measured for the scenario of the wireless monitoring of vital signs with a sensor device and hub device. In this scenario, a bit rate of 18 kbps is required to convey a measured physiological waveform. The experiment results show that the requirement is continuously met, although the throughput is affected by body movement.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"70 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122677107","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058894
Eun Chor Shin, Chul-Min Shin, Cheonhee Lee, Joo-Sung Park, S. Kahng
The design of a new UWB lower-half bandpass filter is proposed, which is based upon the microstrip Composite Right-and Left-Handed Transmission-line(CRLH-TL) metamaterial. Particularly, the interdigital coupled(IDC) lines of the CRLH geometry are proposed to be separated by inserting open stubs to meet the specs on the passband. Also, there is another pair of stubs to complete the design in a limited space. The measurement is shown to be acceptable and agreeable with the circuit and Electromagnetic field simulations
{"title":"Low band UWB BPF using CRLH-TL metamaterial structure","authors":"Eun Chor Shin, Chul-Min Shin, Cheonhee Lee, Joo-Sung Park, S. Kahng","doi":"10.1109/ICUWB.2011.6058894","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058894","url":null,"abstract":"The design of a new UWB lower-half bandpass filter is proposed, which is based upon the microstrip Composite Right-and Left-Handed Transmission-line(CRLH-TL) metamaterial. Particularly, the interdigital coupled(IDC) lines of the CRLH geometry are proposed to be separated by inserting open stubs to meet the specs on the passband. Also, there is another pair of stubs to complete the design in a limited space. The measurement is shown to be acceptable and agreeable with the circuit and Electromagnetic field simulations","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122690689","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058810
V. Mohtashami, A. A. Shishegar
Site-specific ultrawideband propagation modeling involves dealing with frequency variations of the propagation mechanisms and antenna patterns in the ray tracing program. Typically, electromagnetic field calculations have to be performed in a lot of frequencies to accurately construct the frequency response of the channel at a receiving point. This imposes a heavy computational burden on ray tracing specially in calculating the coverage map or finding the statistics of channel parameters where the number of receiving locations is large. In this paper, the computational complexity of ray tracing in ultrawideband propagation modeling is reduced by using cubic B-spline interpolation. The frequency response of the channel at each receiving point is obtained by calculating the electromagnetic fields at a limited number of frequencies and then interpolating the results using cubic B-splines. A speedup of about four times in simulating a typical residential environment is achieved. Besides, the accuracy of the results is maintained due to excellent characteristics of the cubic B-spline interpolation.
{"title":"Using cubic B-spline interpolation for efficient ray-tracing-based ultrawideband propagation modeling","authors":"V. Mohtashami, A. A. Shishegar","doi":"10.1109/ICUWB.2011.6058810","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058810","url":null,"abstract":"Site-specific ultrawideband propagation modeling involves dealing with frequency variations of the propagation mechanisms and antenna patterns in the ray tracing program. Typically, electromagnetic field calculations have to be performed in a lot of frequencies to accurately construct the frequency response of the channel at a receiving point. This imposes a heavy computational burden on ray tracing specially in calculating the coverage map or finding the statistics of channel parameters where the number of receiving locations is large. In this paper, the computational complexity of ray tracing in ultrawideband propagation modeling is reduced by using cubic B-spline interpolation. The frequency response of the channel at each receiving point is obtained by calculating the electromagnetic fields at a limited number of frequencies and then interpolating the results using cubic B-splines. A speedup of about four times in simulating a typical residential environment is achieved. Besides, the accuracy of the results is maintained due to excellent characteristics of the cubic B-spline interpolation.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129762154","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058835
Marco Hernandez, R. Kohno
The paper describes a survey of the physical layer (PHY) of UWB systems for body area networks (BANs) currently in development by the international standard IEEE 802.15.6 Task Group (TG6). The UWB PHY includes IR-UWB and FM-UWB technologies. IR-UWB transceivers for BANs are based on the transmission of a single and relative long pulse per symbol (new paradigm in UWB) or a concatenation or burst of short pulses per symbol (legacy). FM-UWB transceivers are based on the concatenation of a CP-2FSK signal and a wideband FM signal (FM with high modulation index). Such systems are optimized for low power consumption and reliable operation, especially in medical applications.
{"title":"UWB systems for body area networks in IEEE 802.15.6","authors":"Marco Hernandez, R. Kohno","doi":"10.1109/ICUWB.2011.6058835","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058835","url":null,"abstract":"The paper describes a survey of the physical layer (PHY) of UWB systems for body area networks (BANs) currently in development by the international standard IEEE 802.15.6 Task Group (TG6). The UWB PHY includes IR-UWB and FM-UWB technologies. IR-UWB transceivers for BANs are based on the transmission of a single and relative long pulse per symbol (new paradigm in UWB) or a concatenation or burst of short pulses per symbol (legacy). FM-UWB transceivers are based on the concatenation of a CP-2FSK signal and a wideband FM signal (FM with high modulation index). Such systems are optimized for low power consumption and reliable operation, especially in medical applications.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130153938","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058878
A. Costanzo, F. Mastri, D. Masotti, V. Rizzoli
The paper describes an efficient and accurate circuit-level approach to the co-design of UWB receivers integrated with broadband antennas. A full nonlinear simulation of the front end is integrated with the electromagnetically (EM)-based description of the antenna impedance and far-field performance. For each direction of incidence of the transmitted UWB pulse, a circuit description of the receiver excitation under the form of a set of Norton equivalent current sources is generated by EM theory. The source internal impedance is the antenna impedance determined by full-wave EM analysis. The receiver nonlinear analysis is carried out by a model-order reduction Harmonic Balance (HB) technique based on Krylov subspaces. The procedure allows the actual receiver sensitivity to be accurately evaluated by taking into account the amplitude and phase distortion introduced by the antenna, which may significantly change with the UWB pulse direction of incidence. It also allows an effective prediction of the link power budget, which is particularly critical in ultra-low power Impulse Radio (IR) -UWB applications.
{"title":"Circuit-level nonlinear/EM co-simulation and co-design of UWB receivers","authors":"A. Costanzo, F. Mastri, D. Masotti, V. Rizzoli","doi":"10.1109/ICUWB.2011.6058878","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058878","url":null,"abstract":"The paper describes an efficient and accurate circuit-level approach to the co-design of UWB receivers integrated with broadband antennas. A full nonlinear simulation of the front end is integrated with the electromagnetically (EM)-based description of the antenna impedance and far-field performance. For each direction of incidence of the transmitted UWB pulse, a circuit description of the receiver excitation under the form of a set of Norton equivalent current sources is generated by EM theory. The source internal impedance is the antenna impedance determined by full-wave EM analysis. The receiver nonlinear analysis is carried out by a model-order reduction Harmonic Balance (HB) technique based on Krylov subspaces. The procedure allows the actual receiver sensitivity to be accurately evaluated by taking into account the amplitude and phase distortion introduced by the antenna, which may significantly change with the UWB pulse direction of incidence. It also allows an effective prediction of the link power budget, which is particularly critical in ultra-low power Impulse Radio (IR) -UWB applications.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126876193","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058904
B. Rautio, M. E. El Sabbagh, J. Rautio
A broadband methodology for measurement of uniaxial dielectric anisotropy is described. Previous work is improved with reduced measurement error, enhanced automation, and additional material testing. Additionally, permittivity variation with temperature is explored.
{"title":"Broadband analysis and characterization of anisotropic dielectric temperature dependence","authors":"B. Rautio, M. E. El Sabbagh, J. Rautio","doi":"10.1109/ICUWB.2011.6058904","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058904","url":null,"abstract":"A broadband methodology for measurement of uniaxial dielectric anisotropy is described. Previous work is improved with reduced measurement error, enhanced automation, and additional material testing. Additionally, permittivity variation with temperature is explored.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"4169 3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127566144","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058863
SangHyun Chang, Ta-Shun Chu, J. Roderick, Chenliang Du, Timothy Mercer, J. Burdick, H. Hashemi
This paper presents a radio frequency (RF) CMOS chip and algorithm integrated solution of an Ultra-Wideband (UWB) Impulse-Radio (IR) radar system for human presence detection and tracking. UWB radar can complement other human detection and tracking technologies, as it works well in poor visibility conditions with high time/depth-resolution. UWB radar response provides the complex multipath scattering characteristics in each scan, as well as the high sensitive variation in dynamic observation patterns between scans to pose challenge in designing UWB radar hardware and signal processing algorithm. We develop a UWB IR CMOS human feature detection radar transceiver chip and human presence detection algorithm. Thereafter, we integrated the UWB CMOS radar chip and the algorithm through UWB sensor module, and tested the integrated system in a simple outdoor environment to validate the performance of the integrated system. We present experimental results in which the integrated UWB human detection radar system tracks human and non-human targets, and detects human presence by discerning human from moving non-human objects robustly using human feature extraction and likelihood ratio testing (LRT).
{"title":"UWB human detection radar system: A RF CMOS chip and algorithm integrated sensor","authors":"SangHyun Chang, Ta-Shun Chu, J. Roderick, Chenliang Du, Timothy Mercer, J. Burdick, H. Hashemi","doi":"10.1109/ICUWB.2011.6058863","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058863","url":null,"abstract":"This paper presents a radio frequency (RF) CMOS chip and algorithm integrated solution of an Ultra-Wideband (UWB) Impulse-Radio (IR) radar system for human presence detection and tracking. UWB radar can complement other human detection and tracking technologies, as it works well in poor visibility conditions with high time/depth-resolution. UWB radar response provides the complex multipath scattering characteristics in each scan, as well as the high sensitive variation in dynamic observation patterns between scans to pose challenge in designing UWB radar hardware and signal processing algorithm. We develop a UWB IR CMOS human feature detection radar transceiver chip and human presence detection algorithm. Thereafter, we integrated the UWB CMOS radar chip and the algorithm through UWB sensor module, and tested the integrated system in a simple outdoor environment to validate the performance of the integrated system. We present experimental results in which the integrated UWB human detection radar system tracks human and non-human targets, and detects human presence by discerning human from moving non-human objects robustly using human feature extraction and likelihood ratio testing (LRT).","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"108 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133630750","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 : 2011-10-24DOI: 10.1109/ICUWB.2011.6058827
H. Khani, H. Nie, Weidong Xiang, Z. Chen
Having adequate robustness to variations of both weight coefficient and integration interval, the weighted-transmitted reference (WTR) system can achieve a superior performance and support high data rate ultra-wideband (UWB) communications as well. To benefit from these excellent advantages without using ultra-wideband analog delay lines, in this paper, a finite-resolution digital receiver is proposed. The performance of the proposed receiver is evaluated at a data rate of 114Mbps averaged over 100 realizations of IEEE 802.15.3a channel model 1 (CM1) for different quantization levels of finite-resolution analog-to-digital converters (ADCs) operating at Nyquist rate, taking into account noise, inter-path/pulse interference (IPaI/IPI), and inter-symbol interference (ISI). The effects of sampling rates, number of reference pulses, and the ADC threshold(s), weight coefficient, and summation interval on the receiver performance are also investigated. The evaluation results show that the proposed receivers using finite-resolution ADCs only suffer a performance degradation of several dB as compared to the full-resolution ADC and analog receivers. Therefore, employing finite-resolution ADCs could be a promising approach to implement the WTR receivers without using ultra-wideband analog delay lines.
{"title":"Finite-resolution digital receiver for high rate ultra-wideband weighted-transmitted reference system","authors":"H. Khani, H. Nie, Weidong Xiang, Z. Chen","doi":"10.1109/ICUWB.2011.6058827","DOIUrl":"https://doi.org/10.1109/ICUWB.2011.6058827","url":null,"abstract":"Having adequate robustness to variations of both weight coefficient and integration interval, the weighted-transmitted reference (WTR) system can achieve a superior performance and support high data rate ultra-wideband (UWB) communications as well. To benefit from these excellent advantages without using ultra-wideband analog delay lines, in this paper, a finite-resolution digital receiver is proposed. The performance of the proposed receiver is evaluated at a data rate of 114Mbps averaged over 100 realizations of IEEE 802.15.3a channel model 1 (CM1) for different quantization levels of finite-resolution analog-to-digital converters (ADCs) operating at Nyquist rate, taking into account noise, inter-path/pulse interference (IPaI/IPI), and inter-symbol interference (ISI). The effects of sampling rates, number of reference pulses, and the ADC threshold(s), weight coefficient, and summation interval on the receiver performance are also investigated. The evaluation results show that the proposed receivers using finite-resolution ADCs only suffer a performance degradation of several dB as compared to the full-resolution ADC and analog receivers. Therefore, employing finite-resolution ADCs could be a promising approach to implement the WTR receivers without using ultra-wideband analog delay lines.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"76 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122193326","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 : 2011-10-24DOI: 10.1109/icuwb.2011.6058885
Markos Losada, Leticia Zamora-Cadenas, U. Alvarado, I. Vélez
This work presents an Impulse Radio Ultra-Wideband ranging system that is compliant with the IEEE802.15.4a standard. A novel Time-of-Arrival estimator is proposed for ranging purposes. This estimator is robust against multipath fading and presents a small ranging error. Measurement results show the good accuracy of the proposed ranging system.
{"title":"Performance of an IEEE 802.15.4a ranging system in multipath indoor environments","authors":"Markos Losada, Leticia Zamora-Cadenas, U. Alvarado, I. Vélez","doi":"10.1109/icuwb.2011.6058885","DOIUrl":"https://doi.org/10.1109/icuwb.2011.6058885","url":null,"abstract":"This work presents an Impulse Radio Ultra-Wideband ranging system that is compliant with the IEEE802.15.4a standard. A novel Time-of-Arrival estimator is proposed for ranging purposes. This estimator is robust against multipath fading and presents a small ranging error. Measurement results show the good accuracy of the proposed ranging system.","PeriodicalId":143107,"journal":{"name":"2011 IEEE International Conference on Ultra-Wideband (ICUWB)","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128603520","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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