The growth of the wireless and mobile communication data traffic has brought severe challenges to the present telecommu- nication systems. To meet the ever-increasing mobile traffic demand in the next 5th generation ...The growth of the wireless and mobile communication data traffic has brought severe challenges to the present telecommu- nication systems. To meet the ever-increasing mobile traffic demand in the next 5th generation (SG) communication systems, deploying 5G in the unlicensed spectrum (SG-U), has been regarded as a promising technology. The Third Generation Partnership Project (3GPP) has specified the standardization of the Li- censed Assisted Access (LAA) and its extension enhanced LAA (eLAA), to opportunistically transmit in the unlicensed spectrum. The LAA/eLAA systems share unlicensed spectrum resource with other networks, e.g., the Wi-Fi systems. In this article, we analyze the coexistence between the eLAA and the Wi-Fi systems in the unlicensed spectrum. We firstly establish the system model where the eLAA coexists with the Wi-Fi systems. Then, we theoretically derive and figure out the unfairness in the multi-channel occupancy rate between the eLAA and the Wi-Fi systems. After that, we propose a weight based channel selection method to improve the fairness of the coexistence. The numerical results demonstrate that by avoiding contentions and declining collisions, our method not only enhances the fairness, but also improves the overall unlicensed spectrum usage rate.展开更多
License assisted access(LAA) was proposed as a solution to the challenge of satisfying high throughput requirement in cellular network with limited licensed band. LAA uses long term evolution(LTE) carrier aggregation ...License assisted access(LAA) was proposed as a solution to the challenge of satisfying high throughput requirement in cellular network with limited licensed band. LAA uses long term evolution(LTE) carrier aggregation technique to combine licensed and unlicensed bands, specifically 5 GHz Wi Fi band, in order to achieve high data rates. However, LAA has several critical concerns for services provision on 5 GHz unlicensed band. In this article, an overview of the techniques concerning the coexistence of LTE and Wi Fi on the same unlicensed band is presented. We first present several general approaches including power control of LTE evolved Node B(e NB), carrier selection, LTE duty cycling, self clear to send(CTS) and request to send/CTS(RTS/CTS), and listen before talk(LBT). Then, we focus on LBT techniques for LAA-Wi Fi coexistence and discuss how LBT based coexistence solutions can dynamically respond to the variations in network load and ensure fair coexistence in a distributed manner. Based on the LBT mechanism, we also present a fairness-aware LAA-WiF i coexisting scheme with TXOP(transmitted in a single transmission opportunity) backoff for LAA e NB. Finally, the performances of various LBT solutions for LAA-Wi Fi coexistence are evaluated using Markov chain analytical model.展开更多
Utilizing the unlicensed spectrum as supplementary is being studied to meet the increasingly growing demand of user equipment for rate,traffic and bandwidth,and thus to mitigate the current spectrum scarcity crisis.In...Utilizing the unlicensed spectrum as supplementary is being studied to meet the increasingly growing demand of user equipment for rate,traffic and bandwidth,and thus to mitigate the current spectrum scarcity crisis.In this paper,we investigate the uplink multi-user multiple-input multiple-output(UL MU-MIMO) technique to achieve multiplexing gain in unlicensed spectrum.We first define a new parameter called channel busy radio(CBR) which is related to the probability of occupying the unlicensed channel,and find that the failure to occupy the unlicensed channel leads to the performance degradation in unlicensed spectrum.Then,according to the user-specific CBR of the unlicensed channel,we propose a flexible scheduling scheme for UL MU-MIMO in unlicensed spectrum,and formulate an optimization problem for the optimal scheduled user number.Furthermore,an adaptive scheduling algorithm is proposed to decide the optimal number of the scheduled users efficiently.The simulation results show that,based on statistical channel condition in unlicensed spectrum,adjusting the number of the scheduled user flexibly can offset the degraded throughput and form an optimal MU-MIMO transmission.展开更多
Currently,limited licensed frequency bands cannot meet the increasing demands for various wireless communication applications any more.It is necessary to extend wireless communication networks to unlicensed spectrum.I...Currently,limited licensed frequency bands cannot meet the increasing demands for various wireless communication applications any more.It is necessary to extend wireless communication networks to unlicensed spectrum.In this paper,we propose a new bargaining framework for unlicensed band access to achieve high spectrum efficiency,where one radio access technology(RAT)(such as macro cellular network)“competes”the unlicensed bands with multiple other RATs(such as small cellular networks or Wi-Fi)virtually.Considering that macro cell can share unlicensed frequencies with multiple small cells which are in the same coverage area for more freedom,we use bargaining game theory to fairly and effectively share the unlicensed spectrum between macro and multiple heterogeneous small cell networks,where bargaining loss and time dissipation loss for virtual“price”of unlicensed bands are mainly considered.In the oneto-many bargaining process,we also develop a multiple RAT alliance game strategy to reduce transmission loss in a joint manner.Simulation results show that the proposed unlicensed band sharing algorithm significantly improves the spectrum efficiency performance compared with the other practical schemes for heterogeneous networks.展开更多
<strong>Aim:</strong> To describe unlicensed personnel’s experience of digital signing lists via a smartphone application for the distribution of medication in municipal healthcare in Western Sweden.<s...<strong>Aim:</strong> To describe unlicensed personnel’s experience of digital signing lists via a smartphone application for the distribution of medication in municipal healthcare in Western Sweden.<strong> Design:</strong> A qualitative and quantitative design was used. <strong>Methods:</strong> The study included 48 unlicensed personnel, 28 of whom answered an open-ended questionnaire, while an additional 20 volunteered for individual interviews. The material was analysed by qualitative content analysis. <strong>Results:</strong> The results indicate that digital signing lists via a smartphone application are feasible, and efficient and facilitate the work. However, some aspects negatively affected the sense of security, meetings with patients and quality of care, such as an insufficient internet signal in some rural areas, difficulty remembering the password, as well as the change of focus from patient to smartphone. To improve quality of care and the meeting with the patient, it is crucial that the technology works and that unlicensed personnel develop technical skills.展开更多
By cognitive radio,the low Earth orbit(LEO) satellites may prefer to operate in the unlicensed spectrum which is open to all the users,and compete for the limited resources with terrestrial cognitive radio networks...By cognitive radio,the low Earth orbit(LEO) satellites may prefer to operate in the unlicensed spectrum which is open to all the users,and compete for the limited resources with terrestrial cognitive radio networks(CRNs).The competition can be regarded as a game and analyzed with game theory.This particular unlicensed spectrum sharing problem is modeled here,and the special properties of "spatially-distinguished-interference" and the short period of the interactions between satellites and terrestrial CRNs are explored.Then,the problem is formulated as a "partially-blind" finitely repeated prisoner's dilemma by game theory.Finally,we begin with two promising spectrum sharing schemes,which can be used to enforce the frequency reuse among the remotely located terrestrial CRN players as well as to overcome the observation noise.By analysis and comparison,it is proposed that the novel refreshing-contrite-tit-for-tat(R-CTFT) is the optimal spectrum sharing scheme.Simulation results verify that it can be used to utilize the spectrum most efficiently.展开更多
Background Off-label and unlicensed prescriptions pose a severe safety concern among the pediatric population.We aimed to summarize the up-to-date evidence on the extent,reasons,and consequences of off-label and unlic...Background Off-label and unlicensed prescriptions pose a severe safety concern among the pediatric population.We aimed to summarize the up-to-date evidence on the extent,reasons,and consequences of off-label and unlicensed drugs in hospitalized pediatric patients.Methods We systematically searched PubMed,EMBASE,SCOPUS,Web of Science and Google Scholar between 1990 and 2020 in which the last search was conducted on 12 February 2021.We included studies with the following inclusion criteria:(1)observational studies in design;(2)target population was hospitalized pediatric patients whether admitted in the intensive care unit or in the general ward;(3)study reporting the prevalence of off-label,unlicensed prescriptions or both;and(4)published in English.Results A total of 47 studies were eligible for inclusion.The proportion of off-label and unlicensed prescriptions ranged from 7.4%to 99.5%and 0.1%to 74.4%,respectively.The most frequent category of off-label prescriptions was prescription outside the age range,with the most commonly reported reason for off-label prescriptions being the lack of information specifically for pediatrics on the drug information leaflets.The consequences of off-label and unlicensed prescriptions ranged from minor and bearable skin reactions to debilitating renal failure,risking deaths.Conclusions Off-label and unlicensed prescriptions are extensive and require progressively meditative interventions.However,the pediatric population is currently a“therapeutic orphan”.Unless adequate pediatric clinical trials and licensed drugs become available,off-label and unlicensed drug prescription should not entirely be banned but rather promoted in an organized manner.展开更多
The rapid boosting in mobile traffic and the scarcity of available radio spectrum have hindered the improvement of capacity in cellular networks.It is necessary to discover an appropriate coexistence between cellular ...The rapid boosting in mobile traffic and the scarcity of available radio spectrum have hindered the improvement of capacity in cellular networks.It is necessary to discover an appropriate coexistence between cellular and other radio access technologies(mainly Wi-Fi)to offload the high traffic on to unlicensed bands.Dealing with joint time and power allocation to devices,a non-convex problem is modeled to maximize the throughput as well as guarantee the desired user satisfaction.A two-step traffic balancing scheme is proposed to derive the solution.We also focus on the inner competition among cellular users instead of traditional competition between cellular and Wi-Fi in the unlicensed bands.Finally,simulation results show the effectiveness of the proposed two-step traffic balancing scheme.展开更多
This paper investigates the data collection in an unmanned aerial vehicle(UAV)-aided Internet of Things(IoT) network, where a UAV is dispatched to collect data from ground sensors in a practical and accurate probabili...This paper investigates the data collection in an unmanned aerial vehicle(UAV)-aided Internet of Things(IoT) network, where a UAV is dispatched to collect data from ground sensors in a practical and accurate probabilistic line-of-sight(LoS) channel. Especially, access points(APs) are introduced to collect data from some sensors in the unlicensed band to improve data collection efficiency. We formulate a mixed-integer non-convex optimization problem to minimize the UAV flight time by jointly designing the UAV 3D trajectory and sensors’ scheduling, while ensuring the required amount of data can be collected under the limited UAV energy. To solve this nonconvex problem, we recast the objective problem into a tractable form. Then, the problem is further divided into several sub-problems to solve iteratively, and the successive convex approximation(SCA) scheme is applied to solve each non-convex subproblem. Finally,the bisection search is adopted to speed up the searching for the minimum UAV flight time. Simulation results verify that the UAV flight time can be shortened by the proposed method effectively.展开更多
Ultra-Dense Network (UDN) is considered to be the key enabler for realizing capacity goals set by 5G. The major concern in UDN deployment is the backhaul network, which should be scalable, cost-effective, and have s...Ultra-Dense Network (UDN) is considered to be the key enabler for realizing capacity goals set by 5G. The major concern in UDN deployment is the backhaul network, which should be scalable, cost-effective, and have sufficient capacity to support massive small cell traffic. Otherwise, the backhaul can become the bottleneck of the network. In this paper, we propose a wireless backhaul solution for UDN deployment by considering MultiPath-MultiHop (MPMH) backhaul architecture in mmWave frequency band. In addition, we propose a distributed routing scheme to forward the backhaul traffic over the multihop network. Backhaul capacity and line-of-sight probability of the proposed backhaul architecture for various picocell densities were compared with direct, multiple-association, and multihop backhaul schemes under interference limited scenarios in outdoor and indoor small cell deployments. The simulation results indicate that the MPMH mmWave backhaul is the most cost-effective and scalable solution for UDN deployment.展开更多
The rapid growth of mobile data traffic has caused great pressure on the limited spectrum resources,and there must be some better methods to deal with this problem.The innovative technology of Long-Term Evolution(LTE)u...The rapid growth of mobile data traffic has caused great pressure on the limited spectrum resources,and there must be some better methods to deal with this problem.The innovative technology of Long-Term Evolution(LTE)using the unlicensed spectrum,known as LTE-Unlicensed(LTE-U),has been proposed to effectively alleviate the shortage of authorized band resources.LTE-U has explored a lot of potential capacity in mobile communication systems with limited authorized spectrum resources,and improved the spectrum utilization of unauthorized frequency bands.However,LTE-U is still facing challenges in its application.In this paper,we summarize the key features of LTE-U and the coex-istence of LTE-U with Wi-Fi in the unlicensed Spectrum.We analyze the key technologies(including carrier aggregation,HARQ,interference cancelation,and centralized scheduling),the operating modes and deployment scenarios(including carrier aggregation LTE-U,duty cycle LTE-U,and standalone LTE-U),and the advantages(including anchored LTE-U and Standalone LTE-U scenarios),as well as main technical challenges.We then address the different management mechanisms of LTE-U and Wi-Fi(including the differences between the MAC layer and physical layer),the types of coexistence technology classification(including channel separation and channel sharing technologies),and directions for future work.We hope that this comprehensive survey spurs further research in this promising area.展开更多
基金partly supported by the National Science and Technology Major Project(grant no.16510711600)the National Natural Science Foundation of China(grant no.61631013)partly supported by the National Natural Science Foundation of China(grant no.61401440)
文摘The growth of the wireless and mobile communication data traffic has brought severe challenges to the present telecommu- nication systems. To meet the ever-increasing mobile traffic demand in the next 5th generation (SG) communication systems, deploying 5G in the unlicensed spectrum (SG-U), has been regarded as a promising technology. The Third Generation Partnership Project (3GPP) has specified the standardization of the Li- censed Assisted Access (LAA) and its extension enhanced LAA (eLAA), to opportunistically transmit in the unlicensed spectrum. The LAA/eLAA systems share unlicensed spectrum resource with other networks, e.g., the Wi-Fi systems. In this article, we analyze the coexistence between the eLAA and the Wi-Fi systems in the unlicensed spectrum. We firstly establish the system model where the eLAA coexists with the Wi-Fi systems. Then, we theoretically derive and figure out the unfairness in the multi-channel occupancy rate between the eLAA and the Wi-Fi systems. After that, we propose a weight based channel selection method to improve the fairness of the coexistence. The numerical results demonstrate that by avoiding contentions and declining collisions, our method not only enhances the fairness, but also improves the overall unlicensed spectrum usage rate.
基金supported in part by Joint Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP) and Research Grants Council Earmarked Research Grants (RGC ERG) with Grant 20130142140002National Science Foundation of China with Grants 61531011 and 61471163Major Program of National Natural Science Foundation of Hubei in China with Grant 2016CFA009
文摘License assisted access(LAA) was proposed as a solution to the challenge of satisfying high throughput requirement in cellular network with limited licensed band. LAA uses long term evolution(LTE) carrier aggregation technique to combine licensed and unlicensed bands, specifically 5 GHz Wi Fi band, in order to achieve high data rates. However, LAA has several critical concerns for services provision on 5 GHz unlicensed band. In this article, an overview of the techniques concerning the coexistence of LTE and Wi Fi on the same unlicensed band is presented. We first present several general approaches including power control of LTE evolved Node B(e NB), carrier selection, LTE duty cycling, self clear to send(CTS) and request to send/CTS(RTS/CTS), and listen before talk(LBT). Then, we focus on LBT techniques for LAA-Wi Fi coexistence and discuss how LBT based coexistence solutions can dynamically respond to the variations in network load and ensure fair coexistence in a distributed manner. Based on the LBT mechanism, we also present a fairness-aware LAA-WiF i coexisting scheme with TXOP(transmitted in a single transmission opportunity) backoff for LAA e NB. Finally, the performances of various LBT solutions for LAA-Wi Fi coexistence are evaluated using Markov chain analytical model.
基金partly supported by the NSFC International Cooperation and Exchange Program(Grant No.61461136001)partly supported by the Shanghai Rising-Star Program(grant no.17QA1403800)+2 种基金the NSFC International Cooperation and Exchange Program(Grant No.61461136004)partly supported by the ESEC project of Tekes and the National Natural Science Foundation of China(Grant No.61401440)partly supported by the NSFC International Cooperation and Exchange Program(Grant No.61461136003)
文摘Utilizing the unlicensed spectrum as supplementary is being studied to meet the increasingly growing demand of user equipment for rate,traffic and bandwidth,and thus to mitigate the current spectrum scarcity crisis.In this paper,we investigate the uplink multi-user multiple-input multiple-output(UL MU-MIMO) technique to achieve multiplexing gain in unlicensed spectrum.We first define a new parameter called channel busy radio(CBR) which is related to the probability of occupying the unlicensed channel,and find that the failure to occupy the unlicensed channel leads to the performance degradation in unlicensed spectrum.Then,according to the user-specific CBR of the unlicensed channel,we propose a flexible scheduling scheme for UL MU-MIMO in unlicensed spectrum,and formulate an optimization problem for the optimal scheduled user number.Furthermore,an adaptive scheduling algorithm is proposed to decide the optimal number of the scheduled users efficiently.The simulation results show that,based on statistical channel condition in unlicensed spectrum,adjusting the number of the scheduled user flexibly can offset the degraded throughput and form an optimal MU-MIMO transmission.
基金the National Natural Science Foundation of China under Grant 61871433,61828103in part by the Research Platform of South China Normal University and Foshan
文摘Currently,limited licensed frequency bands cannot meet the increasing demands for various wireless communication applications any more.It is necessary to extend wireless communication networks to unlicensed spectrum.In this paper,we propose a new bargaining framework for unlicensed band access to achieve high spectrum efficiency,where one radio access technology(RAT)(such as macro cellular network)“competes”the unlicensed bands with multiple other RATs(such as small cellular networks or Wi-Fi)virtually.Considering that macro cell can share unlicensed frequencies with multiple small cells which are in the same coverage area for more freedom,we use bargaining game theory to fairly and effectively share the unlicensed spectrum between macro and multiple heterogeneous small cell networks,where bargaining loss and time dissipation loss for virtual“price”of unlicensed bands are mainly considered.In the oneto-many bargaining process,we also develop a multiple RAT alliance game strategy to reduce transmission loss in a joint manner.Simulation results show that the proposed unlicensed band sharing algorithm significantly improves the spectrum efficiency performance compared with the other practical schemes for heterogeneous networks.
文摘<strong>Aim:</strong> To describe unlicensed personnel’s experience of digital signing lists via a smartphone application for the distribution of medication in municipal healthcare in Western Sweden.<strong> Design:</strong> A qualitative and quantitative design was used. <strong>Methods:</strong> The study included 48 unlicensed personnel, 28 of whom answered an open-ended questionnaire, while an additional 20 volunteered for individual interviews. The material was analysed by qualitative content analysis. <strong>Results:</strong> The results indicate that digital signing lists via a smartphone application are feasible, and efficient and facilitate the work. However, some aspects negatively affected the sense of security, meetings with patients and quality of care, such as an insufficient internet signal in some rural areas, difficulty remembering the password, as well as the change of focus from patient to smartphone. To improve quality of care and the meeting with the patient, it is crucial that the technology works and that unlicensed personnel develop technical skills.
文摘By cognitive radio,the low Earth orbit(LEO) satellites may prefer to operate in the unlicensed spectrum which is open to all the users,and compete for the limited resources with terrestrial cognitive radio networks(CRNs).The competition can be regarded as a game and analyzed with game theory.This particular unlicensed spectrum sharing problem is modeled here,and the special properties of "spatially-distinguished-interference" and the short period of the interactions between satellites and terrestrial CRNs are explored.Then,the problem is formulated as a "partially-blind" finitely repeated prisoner's dilemma by game theory.Finally,we begin with two promising spectrum sharing schemes,which can be used to enforce the frequency reuse among the remotely located terrestrial CRN players as well as to overcome the observation noise.By analysis and comparison,it is proposed that the novel refreshing-contrite-tit-for-tat(R-CTFT) is the optimal spectrum sharing scheme.Simulation results verify that it can be used to utilize the spectrum most efficiently.
文摘Background Off-label and unlicensed prescriptions pose a severe safety concern among the pediatric population.We aimed to summarize the up-to-date evidence on the extent,reasons,and consequences of off-label and unlicensed drugs in hospitalized pediatric patients.Methods We systematically searched PubMed,EMBASE,SCOPUS,Web of Science and Google Scholar between 1990 and 2020 in which the last search was conducted on 12 February 2021.We included studies with the following inclusion criteria:(1)observational studies in design;(2)target population was hospitalized pediatric patients whether admitted in the intensive care unit or in the general ward;(3)study reporting the prevalence of off-label,unlicensed prescriptions or both;and(4)published in English.Results A total of 47 studies were eligible for inclusion.The proportion of off-label and unlicensed prescriptions ranged from 7.4%to 99.5%and 0.1%to 74.4%,respectively.The most frequent category of off-label prescriptions was prescription outside the age range,with the most commonly reported reason for off-label prescriptions being the lack of information specifically for pediatrics on the drug information leaflets.The consequences of off-label and unlicensed prescriptions ranged from minor and bearable skin reactions to debilitating renal failure,risking deaths.Conclusions Off-label and unlicensed prescriptions are extensive and require progressively meditative interventions.However,the pediatric population is currently a“therapeutic orphan”.Unless adequate pediatric clinical trials and licensed drugs become available,off-label and unlicensed drug prescription should not entirely be banned but rather promoted in an organized manner.
基金supported by The National Natural Science Foundation of China(No.61471058)Beijing Nova Program(No.xx2012037).
文摘The rapid boosting in mobile traffic and the scarcity of available radio spectrum have hindered the improvement of capacity in cellular networks.It is necessary to discover an appropriate coexistence between cellular and other radio access technologies(mainly Wi-Fi)to offload the high traffic on to unlicensed bands.Dealing with joint time and power allocation to devices,a non-convex problem is modeled to maximize the throughput as well as guarantee the desired user satisfaction.A two-step traffic balancing scheme is proposed to derive the solution.We also focus on the inner competition among cellular users instead of traditional competition between cellular and Wi-Fi in the unlicensed bands.Finally,simulation results show the effectiveness of the proposed two-step traffic balancing scheme.
基金supported by the National Key Research and Development Program under Grant 2022YFB3303702the Key Program of National Natural Science Foundation of China under Grant 61931001+1 种基金supported by the National Natural Science Foundation of China under Grant No.62203368the Natural Science Foundation of Sichuan Province under Grant No.2023NSFSC1440。
文摘This paper investigates the data collection in an unmanned aerial vehicle(UAV)-aided Internet of Things(IoT) network, where a UAV is dispatched to collect data from ground sensors in a practical and accurate probabilistic line-of-sight(LoS) channel. Especially, access points(APs) are introduced to collect data from some sensors in the unlicensed band to improve data collection efficiency. We formulate a mixed-integer non-convex optimization problem to minimize the UAV flight time by jointly designing the UAV 3D trajectory and sensors’ scheduling, while ensuring the required amount of data can be collected under the limited UAV energy. To solve this nonconvex problem, we recast the objective problem into a tractable form. Then, the problem is further divided into several sub-problems to solve iteratively, and the successive convex approximation(SCA) scheme is applied to solve each non-convex subproblem. Finally,the bisection search is adopted to speed up the searching for the minimum UAV flight time. Simulation results verify that the UAV flight time can be shortened by the proposed method effectively.
基金This work was supported in part by the National Science Foundation for Distinguished Young Scholars of China with Grant number 61325004 as well as the National Science Foundation of China with Grants 61771216 and 61601191.
文摘Ultra-Dense Network (UDN) is considered to be the key enabler for realizing capacity goals set by 5G. The major concern in UDN deployment is the backhaul network, which should be scalable, cost-effective, and have sufficient capacity to support massive small cell traffic. Otherwise, the backhaul can become the bottleneck of the network. In this paper, we propose a wireless backhaul solution for UDN deployment by considering MultiPath-MultiHop (MPMH) backhaul architecture in mmWave frequency band. In addition, we propose a distributed routing scheme to forward the backhaul traffic over the multihop network. Backhaul capacity and line-of-sight probability of the proposed backhaul architecture for various picocell densities were compared with direct, multiple-association, and multihop backhaul schemes under interference limited scenarios in outdoor and indoor small cell deployments. The simulation results indicate that the MPMH mmWave backhaul is the most cost-effective and scalable solution for UDN deployment.
文摘The rapid growth of mobile data traffic has caused great pressure on the limited spectrum resources,and there must be some better methods to deal with this problem.The innovative technology of Long-Term Evolution(LTE)using the unlicensed spectrum,known as LTE-Unlicensed(LTE-U),has been proposed to effectively alleviate the shortage of authorized band resources.LTE-U has explored a lot of potential capacity in mobile communication systems with limited authorized spectrum resources,and improved the spectrum utilization of unauthorized frequency bands.However,LTE-U is still facing challenges in its application.In this paper,we summarize the key features of LTE-U and the coex-istence of LTE-U with Wi-Fi in the unlicensed Spectrum.We analyze the key technologies(including carrier aggregation,HARQ,interference cancelation,and centralized scheduling),the operating modes and deployment scenarios(including carrier aggregation LTE-U,duty cycle LTE-U,and standalone LTE-U),and the advantages(including anchored LTE-U and Standalone LTE-U scenarios),as well as main technical challenges.We then address the different management mechanisms of LTE-U and Wi-Fi(including the differences between the MAC layer and physical layer),the types of coexistence technology classification(including channel separation and channel sharing technologies),and directions for future work.We hope that this comprehensive survey spurs further research in this promising area.