Pub Date : 2024-11-11DOI: 10.1109/LCOMM.2024.3495998
Abdollah Masoud Darya;Saeed Abdallah
This letter proposes decision-directed semi-blind channel estimation for massive multiple-input multiple-output low-Earth-orbit satellite communications. Two semi-blind estimators are proposed. The first utilizes detected data symbols in addition to pilot symbols. The second, a modified semi-blind estimator, is specially designed to mitigate the channel-aging effect caused by the highly dynamic nature of low-Earth-orbit satellite communication channels—an issue that adversely impacts the performance of pilot-based estimators. Consequently, this modified estimator outperforms an optimal pilot-based estimator in terms of normalized mean square error and achieves symbol error rate performance comparable to that of a Genie-aided (perfectly known channel) detector. The trade-offs between the proposed estimators are also examined.
{"title":"Semi-Blind Channel Estimation for Massive MIMO LEO Satellite Communications","authors":"Abdollah Masoud Darya;Saeed Abdallah","doi":"10.1109/LCOMM.2024.3495998","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3495998","url":null,"abstract":"This letter proposes decision-directed semi-blind channel estimation for massive multiple-input multiple-output low-Earth-orbit satellite communications. Two semi-blind estimators are proposed. The first utilizes detected data symbols in addition to pilot symbols. The second, a modified semi-blind estimator, is specially designed to mitigate the channel-aging effect caused by the highly dynamic nature of low-Earth-orbit satellite communication channels—an issue that adversely impacts the performance of pilot-based estimators. Consequently, this modified estimator outperforms an optimal pilot-based estimator in terms of normalized mean square error and achieves symbol error rate performance comparable to that of a Genie-aided (perfectly known channel) detector. The trade-offs between the proposed estimators are also examined.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"75-79"},"PeriodicalIF":3.7,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940871","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-08DOI: 10.1109/LCOMM.2024.3494030
Yi Wang;Junlei Zhi;Shaochuan Yang;Zheng Chu;Baofeng Ji;Hui Guo;Meng Hua;Chunguo Li
This letter explores an intelligent reflecting surface (IRS) enhanced wireless powered Internet of Things (WP-IoT) network, wherein massive IoT nodes are wirelessly charged by radio frequency signals and then transmit information by means of an IRS to promote the system performance. To evaluate the network performance, we aim at maximizing the total throughput while adhering to constraints pertaining to fairness-aware individual signal-to-noise ratio (SNR), the time allocations (TAs) as well as the unit-modulus IRS phase shifts. However, the intricate coupling of these variables renders the optimization problem nonconvex, thus posing a challenge for direct solution. To deal with this dilemma, we first resort to employing the Lagrange dual method and Karush-Kuhn–Tucker (KKT) conditions to transform the sum of logarithmic objective function into sum of fractional counterpart, and further derive the analytical solutions of TAs for downlink wireless energy transfer (WET) and uplink wireless information transfer (WIT). Then, the Riemannian manifold optimization (RMO) is utilized to iteratively derive the IRS phase shifts in term of semi-closed-form expression. Lastly, numerical simulations are conducted to examine the efficacy of the proposed algorithm in enhancing performance in comparison to the existing benchmark schemes.
{"title":"Enhancing Fairness-Aware Massive Wireless Powered IoT Connectivity by IRS","authors":"Yi Wang;Junlei Zhi;Shaochuan Yang;Zheng Chu;Baofeng Ji;Hui Guo;Meng Hua;Chunguo Li","doi":"10.1109/LCOMM.2024.3494030","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3494030","url":null,"abstract":"This letter explores an intelligent reflecting surface (IRS) enhanced wireless powered Internet of Things (WP-IoT) network, wherein massive IoT nodes are wirelessly charged by radio frequency signals and then transmit information by means of an IRS to promote the system performance. To evaluate the network performance, we aim at maximizing the total throughput while adhering to constraints pertaining to fairness-aware individual signal-to-noise ratio (SNR), the time allocations (TAs) as well as the unit-modulus IRS phase shifts. However, the intricate coupling of these variables renders the optimization problem nonconvex, thus posing a challenge for direct solution. To deal with this dilemma, we first resort to employing the Lagrange dual method and Karush-Kuhn–Tucker (KKT) conditions to transform the sum of logarithmic objective function into sum of fractional counterpart, and further derive the analytical solutions of TAs for downlink wireless energy transfer (WET) and uplink wireless information transfer (WIT). Then, the Riemannian manifold optimization (RMO) is utilized to iteratively derive the IRS phase shifts in term of semi-closed-form expression. Lastly, numerical simulations are conducted to examine the efficacy of the proposed algorithm in enhancing performance in comparison to the existing benchmark schemes.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"65-69"},"PeriodicalIF":3.7,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this letter, we investigate a distributed design integrating user-centric association with local sub-connected hybrid precoding in mmWave cell-free massive MIMO (CF-mMIMO) systems, aiming to maximize the long-term global energy efficiency (EE) under quality-of-service and power budget constraints. The joint optimization problem is formulated as a Markov Game problem and a novel weighted critic update multi-agent twin-delayed deep deterministic policy gradient (WCU-MATD3) algorithm is proposed to solve it, which promotes cooperation among access point agents and reduces power consumption in front-haul links. The results show that the proposed WCU-MATD3 algorithm significantly improves the global EE and the trade-off between spectral efficiency (SE) and EE, providing a practical and stable distributed collaboration framework for dynamic distributed environments.
{"title":"A Multi-Agent DRL Method for Distributed Energy-Efficient Association and Hybrid Precoding in mmWave Cell-Free Massive MIMO Systems","authors":"Huiting Li;Yanxiang Jiang;Yige Huang;Fu-Chun Zheng;Gang Wu","doi":"10.1109/LCOMM.2024.3494537","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3494537","url":null,"abstract":"In this letter, we investigate a distributed design integrating user-centric association with local sub-connected hybrid precoding in mmWave cell-free massive MIMO (CF-mMIMO) systems, aiming to maximize the long-term global energy efficiency (EE) under quality-of-service and power budget constraints. The joint optimization problem is formulated as a Markov Game problem and a novel weighted critic update multi-agent twin-delayed deep deterministic policy gradient (WCU-MATD3) algorithm is proposed to solve it, which promotes cooperation among access point agents and reduces power consumption in front-haul links. The results show that the proposed WCU-MATD3 algorithm significantly improves the global EE and the trade-off between spectral efficiency (SE) and EE, providing a practical and stable distributed collaboration framework for dynamic distributed environments.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"70-74"},"PeriodicalIF":3.7,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-08DOI: 10.1109/LCOMM.2024.3493962
Huihou Zhang;Lianyou Jing;Nan Zhao;Chengbing He;Yonghui Li
The orthogonal time-frequency space (OTFS) modulation has gained significant attention, due to its robust performance in high-speed mobile environment. In this correspondence, we develop a novel approach wherein delay-Doppler grid symbols into vectors are organized according to their Doppler index for OTFS. A novel detection algorithm is proposed in the Doppler transform domain, which offers lower complexity and better bit error rate (BER) performance compared to existing OTFS detection algorithms. In addition, considering the superior performance of short-block polar codes, we integrate them to further enhance the performance. Simulation results validate the performance advantages of the proposed algorithm over existing benchmarks in terms of BER for OTFS. Specifically, BER performance can be improved by at least 1 dB.
{"title":"Low-Complexity Polar-Coded Iterative OTFS Receiver","authors":"Huihou Zhang;Lianyou Jing;Nan Zhao;Chengbing He;Yonghui Li","doi":"10.1109/LCOMM.2024.3493962","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3493962","url":null,"abstract":"The orthogonal time-frequency space (OTFS) modulation has gained significant attention, due to its robust performance in high-speed mobile environment. In this correspondence, we develop a novel approach wherein delay-Doppler grid symbols into vectors are organized according to their Doppler index for OTFS. A novel detection algorithm is proposed in the Doppler transform domain, which offers lower complexity and better bit error rate (BER) performance compared to existing OTFS detection algorithms. In addition, considering the superior performance of short-block polar codes, we integrate them to further enhance the performance. Simulation results validate the performance advantages of the proposed algorithm over existing benchmarks in terms of BER for OTFS. Specifically, BER performance can be improved by at least 1 dB.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"60-64"},"PeriodicalIF":3.7,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-07DOI: 10.1109/LCOMM.2024.3493427
Honglei Jin;Zhe Li;Jide Yuan;Yili Xia
This letter investigates the physical layer security of a downlink non-orthogonal multiple access (NOMA) system aided by a reconfigurable intelligent surface (RIS), where artificial noise (AN) is introduced to confuse the eavesdropper. To enhance secrecy, we employ improper Gaussian signaling (IGS) to alleviate the influence of AN on legitimate users. This is formulated as a sum secrecy rate maximization problem, where the reflecting coefficients of RIS and transmit covariance matrices of legitimate users and eavesdroppers are jointly optimized. An alternating optimization framework aided by the minorization-maximization method is adopted to address this non-convex optimization problem. Numerical results show that IGS significantly outperforms proper Gaussian signaling in improving the secrecy performance of RIS-aided NOMA systems, and such a secrecy advantage is more pronounced in RIS-aided NOMA than in traditional NOMA.
{"title":"Improper Gaussian Signaling for Secrecy Transmission in RIS-Aided Downlink NOMA","authors":"Honglei Jin;Zhe Li;Jide Yuan;Yili Xia","doi":"10.1109/LCOMM.2024.3493427","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3493427","url":null,"abstract":"This letter investigates the physical layer security of a downlink non-orthogonal multiple access (NOMA) system aided by a reconfigurable intelligent surface (RIS), where artificial noise (AN) is introduced to confuse the eavesdropper. To enhance secrecy, we employ improper Gaussian signaling (IGS) to alleviate the influence of AN on legitimate users. This is formulated as a sum secrecy rate maximization problem, where the reflecting coefficients of RIS and transmit covariance matrices of legitimate users and eavesdroppers are jointly optimized. An alternating optimization framework aided by the minorization-maximization method is adopted to address this non-convex optimization problem. Numerical results show that IGS significantly outperforms proper Gaussian signaling in improving the secrecy performance of RIS-aided NOMA systems, and such a secrecy advantage is more pronounced in RIS-aided NOMA than in traditional NOMA.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"50-54"},"PeriodicalIF":3.7,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-07DOI: 10.1109/LCOMM.2024.3493457
Jie Zhang;Hao Gao;Shuangkui Xia;Jiahui Cheng;Baodong Zhao;Yapeng Liu;Bin Luo;Song Yu
A dual phase-locked loop structure for wireless stable radio frequency is proposed in this letter. The noise introduced by free space is suppressed by the phase-locked loop filtering function and phase conjugation module. Backscattering is avoided by regenerating different radio frequency signals at the local end and remote end via dual phase-locked loop. Furthermore, the influence of atmospheric conditions such as temperature, humidity and pressure on the performance of the system is analyzed. Experimental validation is performed in a 15 m outdoor wireless link with frequency instability of ${3.8} mathbf {times } {10}^{mathbf {-}{14}}$ at text {1}s and ${4.4} mathbf {times } {10}^{mathbf {-}{17}}$ at ${10}^{{4}}$ s. This design can provide a reference for the construction of wireless frequency synchronization networks.
{"title":"Dual Phase-Locked Loop Design for Wireless Stable Radio Frequency Transmission","authors":"Jie Zhang;Hao Gao;Shuangkui Xia;Jiahui Cheng;Baodong Zhao;Yapeng Liu;Bin Luo;Song Yu","doi":"10.1109/LCOMM.2024.3493457","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3493457","url":null,"abstract":"A dual phase-locked loop structure for wireless stable radio frequency is proposed in this letter. The noise introduced by free space is suppressed by the phase-locked loop filtering function and phase conjugation module. Backscattering is avoided by regenerating different radio frequency signals at the local end and remote end via dual phase-locked loop. Furthermore, the influence of atmospheric conditions such as temperature, humidity and pressure on the performance of the system is analyzed. Experimental validation is performed in a 15 m outdoor wireless link with frequency instability of \u0000<inline-formula> <tex-math>${3.8} mathbf {times } {10}^{mathbf {-}{14}}$ </tex-math></inline-formula>\u0000 at text {1}s and \u0000<inline-formula> <tex-math>${4.4} mathbf {times } {10}^{mathbf {-}{17}}$ </tex-math></inline-formula>\u0000 at \u0000<inline-formula> <tex-math>${10}^{{4}}$ </tex-math></inline-formula>\u0000s. This design can provide a reference for the construction of wireless frequency synchronization networks.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"55-59"},"PeriodicalIF":3.7,"publicationDate":"2024-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-06DOI: 10.1109/LCOMM.2024.3488195
Wenhan Li;Taijun Liu;Hua Chen;Gaoming Xu
Signal recognition plays a crucial role in wireless communications, with artificial neural network models being widely applied, and the success of these models largely depends on abundant labeled data. However, practical signal recognition scenarios often face a shortage of labeled samples and an abundance of unlabeled ones. Therefore, semi-supervised learning (SSL) methods have emerged as a solution. This letter proposes a novel signal-understanding semi-supervised learning (SUSSL) framework to enhance the performance of SSL further. SUSSL comprises a reconstruction and a metric module. The former module learns useful features by disrupting and reconstructing low-level features, and the latter utilizes similarity learning to process low-level features. A symmetric dual-branch neural network (SDNN) model is also designed to facilitate these two modules. Simulation experiments on the open-source datasets RadioML2016.10a and RadioML2016.10b demonstrate that the proposed method outperforms current SSL methods.
{"title":"A Signal-Understanding Semi-Supervised Learning Framework for Signal Recognition","authors":"Wenhan Li;Taijun Liu;Hua Chen;Gaoming Xu","doi":"10.1109/LCOMM.2024.3488195","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3488195","url":null,"abstract":"Signal recognition plays a crucial role in wireless communications, with artificial neural network models being widely applied, and the success of these models largely depends on abundant labeled data. However, practical signal recognition scenarios often face a shortage of labeled samples and an abundance of unlabeled ones. Therefore, semi-supervised learning (SSL) methods have emerged as a solution. This letter proposes a novel signal-understanding semi-supervised learning (SUSSL) framework to enhance the performance of SSL further. SUSSL comprises a reconstruction and a metric module. The former module learns useful features by disrupting and reconstructing low-level features, and the latter utilizes similarity learning to process low-level features. A symmetric dual-branch neural network (SDNN) model is also designed to facilitate these two modules. Simulation experiments on the open-source datasets RadioML2016.10a and RadioML2016.10b demonstrate that the proposed method outperforms current SSL methods.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"28 12","pages":"2789-2793"},"PeriodicalIF":3.7,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142810495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-06DOI: 10.1109/LCOMM.2024.3492282
Ying Lu;Zhiyong Luo
Integrating unmanned aerial vehicles (UAVs) with mobile edge computing (MEC) presents a viable approach to addressing challenges posed by computation-intensive tasks. Faced with scarce communication resources, this letter adopts non-orthogonal multiple access (NOMA) to enhance spectrum efficiency, aiming to minimize the sum maximum delay of processing tasks from wandering user equipment (UEs) in a multi-UAV-enabled MEC system by jointly optimizing user association, offloading strategy, resource allocation and UAV three-dimensional (3D) trajectories. We propose a K-means-based user association and multi-agent soft actor-critic (MSAC)-based algorithm, which utilizes entropy maximization for exploration and stable learning to address the non-convex problem. Simulation results show that our proposed algorithm outperforms other schemes.
{"title":"An Effective Scheme for Delay Minimization in a Multi-UAV-Enabled NOMA-MEC System","authors":"Ying Lu;Zhiyong Luo","doi":"10.1109/LCOMM.2024.3492282","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3492282","url":null,"abstract":"Integrating unmanned aerial vehicles (UAVs) with mobile edge computing (MEC) presents a viable approach to addressing challenges posed by computation-intensive tasks. Faced with scarce communication resources, this letter adopts non-orthogonal multiple access (NOMA) to enhance spectrum efficiency, aiming to minimize the sum maximum delay of processing tasks from wandering user equipment (UEs) in a multi-UAV-enabled MEC system by jointly optimizing user association, offloading strategy, resource allocation and UAV three-dimensional (3D) trajectories. We propose a K-means-based user association and multi-agent soft actor-critic (MSAC)-based algorithm, which utilizes entropy maximization for exploration and stable learning to address the non-convex problem. Simulation results show that our proposed algorithm outperforms other schemes.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"40-44"},"PeriodicalIF":3.7,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940866","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The multiple input multiple output (MIMO) system deployed in multicell multiuser scenario suffers from pilot contamination due to interference. The contaminated pilot used in the channel estimation leads to inaccurate estimates of the channel. In this letter, a multicell multiuser channel estimation technique based on the Amari alpha divergence based LMS algorithm (AALMS) is proposed for MIMO system. The mean stability analysis has been carried out, and the upper bound on the step size parameter of the AALMS algorithm is derived. The steady state mean square deviation (MSD) analysis is also presented. Monte-carlo simulations have been carried out considering a Rayleigh fading channel. The simulation results show that the proposed scheme provides better estimates of the channel as indicated by the lower mean square error (MSE) and MSD.
{"title":"Amari Alpha Divergence-Based Channel Estimator for Pilot Contaminated Multicell MIMO System","authors":"Shekhar Pratap Singh;Parth Sharma;Pyari Mohan Pradhan","doi":"10.1109/LCOMM.2024.3492280","DOIUrl":"https://doi.org/10.1109/LCOMM.2024.3492280","url":null,"abstract":"The multiple input multiple output (MIMO) system deployed in multicell multiuser scenario suffers from pilot contamination due to interference. The contaminated pilot used in the channel estimation leads to inaccurate estimates of the channel. In this letter, a multicell multiuser channel estimation technique based on the Amari alpha divergence based LMS algorithm (AALMS) is proposed for MIMO system. The mean stability analysis has been carried out, and the upper bound on the step size parameter of the AALMS algorithm is derived. The steady state mean square deviation (MSD) analysis is also presented. Monte-carlo simulations have been carried out considering a Rayleigh fading channel. The simulation results show that the proposed scheme provides better estimates of the channel as indicated by the lower mean square error (MSE) and MSD.","PeriodicalId":13197,"journal":{"name":"IEEE Communications Letters","volume":"29 1","pages":"35-39"},"PeriodicalIF":3.7,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142940709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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