In this paper we show how the capacity of the uplink of a multiuser system can be increased by a scheduling strategy, which pairs the transmission of users in different time/frequency/code slots according to the channel quality. The optimal scheduling strategy is equivalent to a combinatorial optimization problem. We show how this problem can be solved efficiently by using the Hungarian method. We then show that, by using the proposed scheduling scheme, the performance of minimum mean square error detection approaches the one of maximum likelihood detection, as the number of users increases.
{"title":"Optimal User Pairing for Multiuser MIMO","authors":"E. Viterbo, A. Hottinen","doi":"10.1109/ISSSTA.2008.50","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.50","url":null,"abstract":"In this paper we show how the capacity of the uplink of a multiuser system can be increased by a scheduling strategy, which pairs the transmission of users in different time/frequency/code slots according to the channel quality. The optimal scheduling strategy is equivalent to a combinatorial optimization problem. We show how this problem can be solved efficiently by using the Hungarian method. We then show that, by using the proposed scheduling scheme, the performance of minimum mean square error detection approaches the one of maximum likelihood detection, as the number of users increases.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"86 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123330465","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}
S. Persia, D. Cassioli, Francesco Vatalaro, Fulvio Ananasso
Low data rate location/tracking UWB sensors have both location/tracking and communication capabilities, calling for novel routing and MAC strategies, in order to efficiently manage ranging and data transfer. In this paper, a particular configuration is adopted for routing and MAC, that are strongly correlated, because both are tied to the ranging module. Hence, a cross-layer design approach appears as the most appropriate. The routing algorithm, the e-GPSR, is a novel energy-aware version of a geographic reactive multi-hop protocol, namely the greedy perimeter stateless routing (GPSR). The MAC scheme is a modified hybrid slotted-aloha time-hopping code division multiple access. Performance of the e-GPSR are evaluated as a function of design parameters of MAC and ranging module. Optimal values are provided for different degrees of network's mobility such that MAC and ranging are optimally designed to provide best performance of routing.
{"title":"Cross-Layer Design of a LDR-L/T UWB Sensor Network","authors":"S. Persia, D. Cassioli, Francesco Vatalaro, Fulvio Ananasso","doi":"10.1109/ISSSTA.2008.116","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.116","url":null,"abstract":"Low data rate location/tracking UWB sensors have both location/tracking and communication capabilities, calling for novel routing and MAC strategies, in order to efficiently manage ranging and data transfer. In this paper, a particular configuration is adopted for routing and MAC, that are strongly correlated, because both are tied to the ranging module. Hence, a cross-layer design approach appears as the most appropriate. The routing algorithm, the e-GPSR, is a novel energy-aware version of a geographic reactive multi-hop protocol, namely the greedy perimeter stateless routing (GPSR). The MAC scheme is a modified hybrid slotted-aloha time-hopping code division multiple access. Performance of the e-GPSR are evaluated as a function of design parameters of MAC and ranging module. Optimal values are provided for different degrees of network's mobility such that MAC and ranging are optimally designed to provide best performance of routing.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"112 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115815533","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}
Radio channel models intended for system performance assessment need to balance between accuracy and complexity. Computational complexity of channel realisation generation tend to grow due to increasing bandwidth, number of antennas, number of users, as well as with advanced network topologies. This paper investigates complexity related to radio channel parameterisation of a drop based MIMO simulation, where a number of user terminals are dropped into a network topology and short segments of the radio channel are simulated. The focus is on pre-processing associated with antenna embedding, e.g. interpolation of antenna field patterns, and stochastic propagations parameter determination, e.g. random delays, powers and azimuth angles. Complexities are calculated based on WINNER II channel model. Two modelling principles are compared, namely correlation matrix based and sum of rays based methods. Also variation of the bit error ratio (BER) performance on different drops was measured with a 2times2 MIMO hardware demonstrator. This study show that drop based simulation does not necessarily increase the complexity compared to the traditional fixed models. It also shows that geometry based simulation has lower pre-processing complexity than correlation based simulation.
{"title":"Computational Complexity of Drop Based Radio Channel Simulation","authors":"P. Kyosti, T. Jamsa, A. Byman, M. Narandzic","doi":"10.1109/ISSSTA.2008.58","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.58","url":null,"abstract":"Radio channel models intended for system performance assessment need to balance between accuracy and complexity. Computational complexity of channel realisation generation tend to grow due to increasing bandwidth, number of antennas, number of users, as well as with advanced network topologies. This paper investigates complexity related to radio channel parameterisation of a drop based MIMO simulation, where a number of user terminals are dropped into a network topology and short segments of the radio channel are simulated. The focus is on pre-processing associated with antenna embedding, e.g. interpolation of antenna field patterns, and stochastic propagations parameter determination, e.g. random delays, powers and azimuth angles. Complexities are calculated based on WINNER II channel model. Two modelling principles are compared, namely correlation matrix based and sum of rays based methods. Also variation of the bit error ratio (BER) performance on different drops was measured with a 2times2 MIMO hardware demonstrator. This study show that drop based simulation does not necessarily increase the complexity compared to the traditional fixed models. It also shows that geometry based simulation has lower pre-processing complexity than correlation based simulation.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116920970","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}
In this paper, we study the performance of wireless multiple-access communication systems, where two correlated sources communicate to an access point (AP). The communication links are affected by Rayleigh fading, and the source correlation is exploited only at the AP, which makes use of closed-loop power control (CLPC) to counter-act the effects of fading. We first propose an analytical framework to evaluate the theoretical performance limits in the presence of feedback (power control). Then, we consider coded communication schemes, where the sources make use of turbo codes and the AP performs joint source-channel decoding. A simple feedback power control strategy is considered and its performance is evaluated through simulations.
{"title":"Optimization of Closed-Loop Power Control for Wireless Multiple Orthogonal Access Schemes with Correlated Sources","authors":"A. Abrardo, F. Perna, G. Ferrari","doi":"10.1109/ISSSTA.2008.79","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.79","url":null,"abstract":"In this paper, we study the performance of wireless multiple-access communication systems, where two correlated sources communicate to an access point (AP). The communication links are affected by Rayleigh fading, and the source correlation is exploited only at the AP, which makes use of closed-loop power control (CLPC) to counter-act the effects of fading. We first propose an analytical framework to evaluate the theoretical performance limits in the presence of feedback (power control). Then, we consider coded communication schemes, where the sources make use of turbo codes and the AP performs joint source-channel decoding. A simple feedback power control strategy is considered and its performance is evaluated through simulations.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"58 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120986064","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}
This paper is concerned with a wireless access system with adaptive modulation and coding (AMC) at the physical layer (PHY), Type-Ill hybrid automatic repeat request (HARQ) at the data link layer (LL) and transport control protocol (TCP) at the transport layer. In order to evaluate the quality-of-service (QoS) of TCP, we analyze the queueing behavior induced by both AMC and Type-Ill HARQ with an embedded Markov chain and study the interaction between AMC, Type-Ill HARQ and TCP via a fixed-point procedure. To maximize the TCP throughput for QoS-guaranteed traffic, we propose a cross-layer design which optimizes the target packet error rate (PER) for AMC at the PHY as well as the maximum number of retransmission for Type-III HARQ at the LL.
{"title":"Cross-Layer Performance Analysis of TCP over Wireless Link with AMC and Type-III HARQ","authors":"Feijin Shi, D. Yuan","doi":"10.1109/ISSSTA.2008.97","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.97","url":null,"abstract":"This paper is concerned with a wireless access system with adaptive modulation and coding (AMC) at the physical layer (PHY), Type-Ill hybrid automatic repeat request (HARQ) at the data link layer (LL) and transport control protocol (TCP) at the transport layer. In order to evaluate the quality-of-service (QoS) of TCP, we analyze the queueing behavior induced by both AMC and Type-Ill HARQ with an embedded Markov chain and study the interaction between AMC, Type-Ill HARQ and TCP via a fixed-point procedure. To maximize the TCP throughput for QoS-guaranteed traffic, we propose a cross-layer design which optimizes the target packet error rate (PER) for AMC at the PHY as well as the maximum number of retransmission for Type-III HARQ at the LL.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125034551","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}
In this paper, two multiple access techniques for the uplink of next generation cellular mobile communication systems are investigated. The paper targets the optimum power allocation and link scheduling of the orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA) schemes. A heuristic relaxation is used to simplify the NP-hard problem of the joint optimization between power control and link scheduling into the power controlled random access (PCRA) problem. PCRA problem is transformed to convex optimization problem through the geometric programming. For a single cell uplink system with imperfect frequency synchronization, OFDMA outperforms CDMA significantly. OFDMA uplink system requires 22% less transmit power than CDMA for the proposed scheme. Furthermore it has been found that a high subcarrier granularity is advantageous and results in less Pareto optimum transmit power.
{"title":"Comparison of Pareto Optimum Transmit Power between CDMA and OFDMA Uplink","authors":"D. Kolyuzhnov, A. Mudesir, H. Haas","doi":"10.1109/ISSSTA.2008.19","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.19","url":null,"abstract":"In this paper, two multiple access techniques for the uplink of next generation cellular mobile communication systems are investigated. The paper targets the optimum power allocation and link scheduling of the orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA) schemes. A heuristic relaxation is used to simplify the NP-hard problem of the joint optimization between power control and link scheduling into the power controlled random access (PCRA) problem. PCRA problem is transformed to convex optimization problem through the geometric programming. For a single cell uplink system with imperfect frequency synchronization, OFDMA outperforms CDMA significantly. OFDMA uplink system requires 22% less transmit power than CDMA for the proposed scheme. Furthermore it has been found that a high subcarrier granularity is advantageous and results in less Pareto optimum transmit power.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"30 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125293781","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}
The need for accurate positioning has attracted significant interest in recent years, especially in cluttered environments where signals from satellite navigation systems are not reliable. Positioning systems based on ultrawide bandwidth (UWB) technology have been considered due to the property of UWB signals to resolve multipath and penetrate obstacles. However, range-based localization techniques typically lack accuracy in dense cluttered environments, due to line-of-sight blockage and excess propagation delay through material. In this paper, we consider positioning in a real indoor environment scenario, where anchor nodes are deployed in known locations, and one or more target nodes wish to determine the own position. A range measurement error models based on measured data from real ranging devices is considered and we propose a multilateration cooperative algorithm that, without the need of measurements between targets, exploit the estimated position of cooperative nodes to increase localization performance. We examine the case where multiple targets are present in the same environment and how the position accuracy is affected by the cooperative nodes positions and by the availability of priori information about the environment and network geometry. Using numerical results based on experimental data, we demonstrate the impact of cooperation on the positioning accuracy. It is shown that, depending on the geometric configuration of the nodes, cooperation is not always advantageous.
{"title":"Cooperative UWB-Based Positioning Systems: CDAP Algorithm and Experimental Results","authors":"A. Conti, D. Dardari, L. Zuari","doi":"10.1109/ISSSTA.2008.158","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.158","url":null,"abstract":"The need for accurate positioning has attracted significant interest in recent years, especially in cluttered environments where signals from satellite navigation systems are not reliable. Positioning systems based on ultrawide bandwidth (UWB) technology have been considered due to the property of UWB signals to resolve multipath and penetrate obstacles. However, range-based localization techniques typically lack accuracy in dense cluttered environments, due to line-of-sight blockage and excess propagation delay through material. In this paper, we consider positioning in a real indoor environment scenario, where anchor nodes are deployed in known locations, and one or more target nodes wish to determine the own position. A range measurement error models based on measured data from real ranging devices is considered and we propose a multilateration cooperative algorithm that, without the need of measurements between targets, exploit the estimated position of cooperative nodes to increase localization performance. We examine the case where multiple targets are present in the same environment and how the position accuracy is affected by the cooperative nodes positions and by the availability of priori information about the environment and network geometry. Using numerical results based on experimental data, we demonstrate the impact of cooperation on the positioning accuracy. It is shown that, depending on the geometric configuration of the nodes, cooperation is not always advantageous.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125476954","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}
Achieving consensus on common global parameters through totally decentralized algorithms is a topic that has attracted considerable attention in the last few years, in view of its potential application in sensor networks. Several algorithms, along with their convergence properties, have been studied in the literature, among which the most popular are the (weighted) average consensus based schemes. One of the most critical aspects of these algorithms is that they suffer from catastrophic noise propagation. In addition, the effect of additive interference is dramatic. In this work we propose a novel consensus algorithm which is effective in suppressing both noise and interference. In particular, the variance of the noise affecting the consensus values can be made arbitrarily low. Moreover, interferences of finite duration or periodic can be completely rejected. The proposed consensus algorithm subsumes, as a special cases, previously known algorithms. Finally, its ability in suppressing noise and interference holds regardless of the noise statistics and for arbitrary network topology.
{"title":"Novel Consensus Algorithm for Wireless Sensor Networks with Noise and Interference Suppression","authors":"A. Fasano","doi":"10.1109/ISSSTA.2008.83","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.83","url":null,"abstract":"Achieving consensus on common global parameters through totally decentralized algorithms is a topic that has attracted considerable attention in the last few years, in view of its potential application in sensor networks. Several algorithms, along with their convergence properties, have been studied in the literature, among which the most popular are the (weighted) average consensus based schemes. One of the most critical aspects of these algorithms is that they suffer from catastrophic noise propagation. In addition, the effect of additive interference is dramatic. In this work we propose a novel consensus algorithm which is effective in suppressing both noise and interference. In particular, the variance of the noise affecting the consensus values can be made arbitrarily low. Moreover, interferences of finite duration or periodic can be completely rejected. The proposed consensus algorithm subsumes, as a special cases, previously known algorithms. Finally, its ability in suppressing noise and interference holds regardless of the noise statistics and for arbitrary network topology.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114942368","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}
We derive expectation-maximization (EM) based iterative algorithms to estimate the impulse response of multipath channel with coded OFDM system. We compare two ways for choosing EM complete data: a complete data built from observations and transmitted symbols (CL-EM) and complete data chosen by decomposing noise and observation components (NCD-EM). We also derive the Cramer-Rao lower bound (CRB) for coded OFDM transmission. Simulation results show that CLEM has better convergence than NCD-EM and achieves the CRB.
{"title":"EM Channel Estimation for Coded OFDM Transmissions over Frequency-Selective Channel","authors":"Yang Liu, L. Brunel, J. Boutros","doi":"10.1109/ISSSTA.2008.107","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.107","url":null,"abstract":"We derive expectation-maximization (EM) based iterative algorithms to estimate the impulse response of multipath channel with coded OFDM system. We compare two ways for choosing EM complete data: a complete data built from observations and transmitted symbols (CL-EM) and complete data chosen by decomposing noise and observation components (NCD-EM). We also derive the Cramer-Rao lower bound (CRB) for coded OFDM transmission. Simulation results show that CLEM has better convergence than NCD-EM and achieves the CRB.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"70 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116448495","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}
To provide multimedia services in optical networks, 2 dimensional optical code division multiple access (2D OCDMA) system is considered as a potential solution. We focus here on a 2D OCDMA system using 2D multi-weight codes and parallel mapping technique to provide respectively quality of service (QoS) and data rate differentiation. To improve the performance of such a scheme, we investigate forward error correction (FEC) based on low density parity check (LDPC) codes known to have an efficient error correction power for Gaussian channels. We particularly propose an adaptation of the LDPC decoding scheme to the 2D OCDMA multimedia channel which has a specific noise distribution due to multiple access interference (MAI). We evaluate the system robustness to additive white Gaussian noise (AWGN) perturbation in addition to MAI and the gain provided in term of SNR. Finally, we show that the adapted FEC scheme we propose, not only permits improving the data rate per service but also the number of simultaneously communicating users.
{"title":"Adapted LDPC Error Correction Scheme for 2D Optical CDMA Multimedia System","authors":"S. Sahuguède, A. Julien-Vergonjanne, J. Cances","doi":"10.1109/ISSSTA.2008.151","DOIUrl":"https://doi.org/10.1109/ISSSTA.2008.151","url":null,"abstract":"To provide multimedia services in optical networks, 2 dimensional optical code division multiple access (2D OCDMA) system is considered as a potential solution. We focus here on a 2D OCDMA system using 2D multi-weight codes and parallel mapping technique to provide respectively quality of service (QoS) and data rate differentiation. To improve the performance of such a scheme, we investigate forward error correction (FEC) based on low density parity check (LDPC) codes known to have an efficient error correction power for Gaussian channels. We particularly propose an adaptation of the LDPC decoding scheme to the 2D OCDMA multimedia channel which has a specific noise distribution due to multiple access interference (MAI). We evaluate the system robustness to additive white Gaussian noise (AWGN) perturbation in addition to MAI and the gain provided in term of SNR. Finally, we show that the adapted FEC scheme we propose, not only permits improving the data rate per service but also the number of simultaneously communicating users.","PeriodicalId":334589,"journal":{"name":"2008 IEEE 10th International Symposium on Spread Spectrum Techniques and Applications","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122868997","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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