Due to its high mobility and flexible deployment,unmanned aerial vehicle(UAV)is drawing unprecedented interest in both military and civil applications to enable agile and ubiquitous connectivity.Mainly operating in an...Due to its high mobility and flexible deployment,unmanned aerial vehicle(UAV)is drawing unprecedented interest in both military and civil applications to enable agile and ubiquitous connectivity.Mainly operating in an open environment,UAV communications benefit from dominant line-of-sight links;however,this on the other hand renders the communications more vulnerable to malicious attacks.Recently,physical layer security(PLS)has been introduced to UAV systems as an important complement to the conventional cryptography-based approaches.In this paper,a comprehensive survey on the current achievements of UAV-PLS is conducted.We first introduce the basic concepts including typical static/-mobile UAV deployment scenarios,the unique air-toground channel and aerial nodes distribution models,as well as various roles that a UAV may act when PLS is concerned.Then,we start by reviewing the secrecy performance analysis and enhancing techniques for statically deployed UAV systems,and extend the discussion to the more general scenario where the UAVs’mobility is further exploited.For both cases,respectively,we summarize the commonly adopted methodologies,then describe important works in the litera ture in detail.Finally,potential research directions and challenges are discussed to provide an outlook for future works in the area of UAV-PLS.展开更多
Root-associated bacteria play a vital role in the growth and adaptation of host plants to drought stress.These bacteria can be classified as rhizoplane and rhizosphere bacteria based on their distance from the root su...Root-associated bacteria play a vital role in the growth and adaptation of host plants to drought stress.These bacteria can be classified as rhizoplane and rhizosphere bacteria based on their distance from the root surface.Tomato plants are often exposed to periodic drought and nitrogen(N)addition throughout their life cycle,but the impacts of these factors on the plant and root-associated bacteria are not well understood.To gain insight into this relationship,we conducted an experiment to monitor the effects of periodic drought and N addition on rhizoplane and rhizosphere bacteria of tomato plants.Drought and N addition had interactive effects on plant and soil properties,which varied with the timing of drought.There were clear divergences in community traits such as alpha diversity,beta diversity,and network topological features between the two types of bacteria.The rhizoplane bacteria showed lower alpha diversity but higher beta diversity and were more sensitive to drought and N addition than the rhizosphere bacteria.Nitrogen addition could downsize the effects of drought on rhizoplane bacterial community compositions.The higher proximity to the root might induce a community to develop more cooperation between different members to cope with plant metabolites,as revealed by the more connected and modularized community network of the rhizoplane bacteria.Drought at the seedling stage had great legacy effects on plant and soil properties.It may enhance selection,cause the dominance of deterministic processes in the assembly of rhizoplane bacteria,and reduce bacterial community network complexity.In conclusion,N addition could interact with drought in affecting tomato plants and their root-associated bacteria,depending on the timing of drought and the fineness of root niches.The higher sensitivity of rhizoplane bacteria to drought and N addition calls for more research due to their higher proximity and importance to plants in future environmental changes.展开更多
Channel training in reconfigurable intelligent surface(RIS)-assisted communications is usually conducted in an on-off manner,resulting in unaffordable training time overhead when the number of RIS elements is large.In...Channel training in reconfigurable intelligent surface(RIS)-assisted communications is usually conducted in an on-off manner,resulting in unaffordable training time overhead when the number of RIS elements is large.In this paper,for correlated Rayleigh channels,we compare three typical training overhead reduction schemes,namely RIS element selection(Scheme 1),element grouping(Scheme 2),and statistical CSI-based phase shifts design(Scheme3).For Scheme 1 and Scheme 2,we propose two algorithms to select RIS elements(or form element groups) and determine the optimal number of activated elements(or formed groups),based on the channel correlation information only;for Scheme 3,we consider a semi-definite programming-based approach in the literature,and propose an alternative dominant eigenvector-based method for determining the RIS phase shifts vector.Via extensive simulations,we compare the achievable ergodic rates of these schemes versus the signal-to-noise ratio,the channel correlation level,and the element number-to-coherent time ratio,respectively,and discuss possible switching of the three schemes over these system parameters.At last,operation regions of the considered training overhead reduction schemes are shown in the plane characterized by the system parameters,which provides useful guidelines for practical scheme determination.展开更多
This study addresses the joint state and fault fusion estimation problem for mobile robot localization under the energy-harvesting sensors.Under such a circumstance,the sensors can harvest energy from the external env...This study addresses the joint state and fault fusion estimation problem for mobile robot localization under the energy-harvesting sensors.Under such a circumstance,the sensors can harvest energy from the external environment and then consume an amount of energy when transmitting measurements to the corresponding estimator.Based on the energy harvesting mechanism's probability distribution,the probability of measurement loss is computed at each step.The main objective of this study is to tackle the mobile robot localization problem by designing local estimators for each sensor node,where the upper bound of the local estimation error covariance is guaranteed and then minimized by appropriately tuning the estimator parameters.Furthermore,the local estimates are fused using the covariance intersection(CI)fusion approach.Finally,a numerical experiment is presented to demonstrate the effectiveness of the proposed fusion estimation algorithm.展开更多
基金supported in part by the National Key Research and Development Program of China under Grant 2020YFA0711301in part by the National Natural Science Foundation of China under Grant 61922049,61941104,61921004,62171240,61771264,62001254,61801248,61971467+2 种基金the Key Research and Development Program of Shandong Province under Grant 2020CXGC010108the Key Research and Development Program of Jiangsu Province of China under Grant BE2021013-1the Science and Technology Program of Nantong under Grants JC2021121,JC2021017。
文摘Due to its high mobility and flexible deployment,unmanned aerial vehicle(UAV)is drawing unprecedented interest in both military and civil applications to enable agile and ubiquitous connectivity.Mainly operating in an open environment,UAV communications benefit from dominant line-of-sight links;however,this on the other hand renders the communications more vulnerable to malicious attacks.Recently,physical layer security(PLS)has been introduced to UAV systems as an important complement to the conventional cryptography-based approaches.In this paper,a comprehensive survey on the current achievements of UAV-PLS is conducted.We first introduce the basic concepts including typical static/-mobile UAV deployment scenarios,the unique air-toground channel and aerial nodes distribution models,as well as various roles that a UAV may act when PLS is concerned.Then,we start by reviewing the secrecy performance analysis and enhancing techniques for statically deployed UAV systems,and extend the discussion to the more general scenario where the UAVs’mobility is further exploited.For both cases,respectively,we summarize the commonly adopted methodologies,then describe important works in the litera ture in detail.Finally,potential research directions and challenges are discussed to provide an outlook for future works in the area of UAV-PLS.
基金supported by the National Natural Science Foundation of China(Nos.31800439 and 32171517)the GDAS’Special Project of Science and Technology Development,China(No.2021GDASYL-20210103023)+1 种基金the Guangdong Special Support Program of China(No.2021JC06N628)the Talent Support Program of Sourthem Marine Science and Engineering Guangdong Laboratory(Guangzhou),China(No.GML20220017)。
文摘Root-associated bacteria play a vital role in the growth and adaptation of host plants to drought stress.These bacteria can be classified as rhizoplane and rhizosphere bacteria based on their distance from the root surface.Tomato plants are often exposed to periodic drought and nitrogen(N)addition throughout their life cycle,but the impacts of these factors on the plant and root-associated bacteria are not well understood.To gain insight into this relationship,we conducted an experiment to monitor the effects of periodic drought and N addition on rhizoplane and rhizosphere bacteria of tomato plants.Drought and N addition had interactive effects on plant and soil properties,which varied with the timing of drought.There were clear divergences in community traits such as alpha diversity,beta diversity,and network topological features between the two types of bacteria.The rhizoplane bacteria showed lower alpha diversity but higher beta diversity and were more sensitive to drought and N addition than the rhizosphere bacteria.Nitrogen addition could downsize the effects of drought on rhizoplane bacterial community compositions.The higher proximity to the root might induce a community to develop more cooperation between different members to cope with plant metabolites,as revealed by the more connected and modularized community network of the rhizoplane bacteria.Drought at the seedling stage had great legacy effects on plant and soil properties.It may enhance selection,cause the dominance of deterministic processes in the assembly of rhizoplane bacteria,and reduce bacterial community network complexity.In conclusion,N addition could interact with drought in affecting tomato plants and their root-associated bacteria,depending on the timing of drought and the fineness of root niches.The higher sensitivity of rhizoplane bacteria to drought and N addition calls for more research due to their higher proximity and importance to plants in future environmental changes.
基金the National Natural Science Foundation of China under Grants 62171240,61771264,62001254,61971467,the Key Research and Development Program of Jiangsu Province of China under Grant BE2021013-1the Science and Technology Program of Nantong under Grants JC2021121,JC2021017.
文摘Channel training in reconfigurable intelligent surface(RIS)-assisted communications is usually conducted in an on-off manner,resulting in unaffordable training time overhead when the number of RIS elements is large.In this paper,for correlated Rayleigh channels,we compare three typical training overhead reduction schemes,namely RIS element selection(Scheme 1),element grouping(Scheme 2),and statistical CSI-based phase shifts design(Scheme3).For Scheme 1 and Scheme 2,we propose two algorithms to select RIS elements(or form element groups) and determine the optimal number of activated elements(or formed groups),based on the channel correlation information only;for Scheme 3,we consider a semi-definite programming-based approach in the literature,and propose an alternative dominant eigenvector-based method for determining the RIS phase shifts vector.Via extensive simulations,we compare the achievable ergodic rates of these schemes versus the signal-to-noise ratio,the channel correlation level,and the element number-to-coherent time ratio,respectively,and discuss possible switching of the three schemes over these system parameters.At last,operation regions of the considered training overhead reduction schemes are shown in the plane characterized by the system parameters,which provides useful guidelines for practical scheme determination.
基金supported in part by the National Natural Science Foundation of China(Nos.62403259,62431014,and 62001254)the Natural Science Foundation of Jiangsu Province(No.BK20240945)+1 种基金Fujian Province Special Fund Project for Promoting High-Quality Development of Marine and Fisheries Industries(No.FJHYF-ZH-2023-03)the Natural Science Foundation of Nantong(No.JC2023074).
文摘This study addresses the joint state and fault fusion estimation problem for mobile robot localization under the energy-harvesting sensors.Under such a circumstance,the sensors can harvest energy from the external environment and then consume an amount of energy when transmitting measurements to the corresponding estimator.Based on the energy harvesting mechanism's probability distribution,the probability of measurement loss is computed at each step.The main objective of this study is to tackle the mobile robot localization problem by designing local estimators for each sensor node,where the upper bound of the local estimation error covariance is guaranteed and then minimized by appropriately tuning the estimator parameters.Furthermore,the local estimates are fused using the covariance intersection(CI)fusion approach.Finally,a numerical experiment is presented to demonstrate the effectiveness of the proposed fusion estimation algorithm.
