Security-Reliability Tradeoff Analysis for Jamming Aided Decode-and-Forward Relay Networks

In this paper,we explore a cooperative decode-and-forward(DF)relay network comprised of a source,a relay,and a destination in the presence of an eavesdropper.To improve physical-layer security of the relay system,we propose a jamming aided decodeand-forward relay(JDFR)scheme combining the use of artificial noise and DF relaying which requires two stages to transmit a packet.Specifically,in stage one,the source sends confidential message to the relay while the destination acts as a friendly jammer and transmits artificial noise to confound the eavesdropper.In stage two,the relay forwards its re-encoded message to the destination while the source emits artificial noise to confuse the eavesdropper.In addition,we analyze the security-reliability tradeoff(SRT)performance of the proposed JDFR scheme,where security and reliability are evaluated by deriving intercept probability(IP)and outage probability(OP),respectively.For the purpose of comparison,SRT of the traditional decode-and-forward relay(TDFR)scheme is also analyzed.Numerical results show that the SRT performance of the proposed JDFR scheme is better than that of the TDFR scheme.Also,it is shown that for the JDFR scheme,a better SRT performance can be obtained by the optimal power allocation(OPA)between the friendly jammer and user.

Simplifying the Nonlinear Continuous Time-Cost Tradeoff Problem

Equivalent simplification is an effective method for solving large-scale complex problems. In this paper, the authors simplify a classic project scheduling problem, which is the nonlinear continuous time-cost tradeoff problem(TCTP). Simplifying TCTP is a simple path problem in a critical path method(CPM) network. The authors transform TCTP into a simple activity float problem and design a complex polynomial algorithm for its solution. First, the authors discover relationships between activity floats and path lengths by studying activity floats from the perspective of path instead of time.Second, the authors perform simplification and improve the efficiency and accuracy of the solution by deleting redundant activities and narrowing the duration intervals of non-redundant activities. Finally,the authors compare our method with current methods. The relationships between activity floats and path lengths provide new approaches for other path and correlative project problems.

辽宁太子河流域生态系统服务权衡/协同关系时空变化与情景预测

研究生态系统服务权衡与协同关系为制定合理的区域社会-生态系统管理方案提供依据,促进区域可持续发展。太子河是维护辽宁中部城市群生态安全和用水安全的重要保障,以重工业为主的产业布局使得该区生态安全受到威胁,严重影响社会经济的可持续发展。综合气象、土地利用等多源数据,借助InVEST模型,探究太子河流域固碳、土壤保持、生境质量的时空特征;采用Pearson相关分析法,探讨不同样点尺度、不同地类上权衡与协同关系的时空变化,并对2030年不同土地利用情景进行预测。结果表明:①三种生态系统服务在各尺度上(除100m尺度)均为协同关系,且样点尺度越大,相关系数越高。②在不同地类中,耕地、林地、草地三种地类生态系统服务功能类似,以土壤保持功能为主,碳储功能其次;生态系统服务的热点区分布在流域的东部,冷点区集中在流域西部。③不同预测情景下三种生态系统服务间仍为协同关系,在保护情景下生境质量最好、水域面积最多,生态系统服务能力最高;开发情景下建设用地面积增加最多,但生境质量最差。

基于多模型和权衡矩阵法的乡村生态-游憩景观安全格局重构

【目的】乡村旅游地的突出矛盾是人类旅游活动对生态环境的干扰,景观规划时需要权衡游憩功能与生态功能。探究乡村生态-游憩景观安全格局(landscape security pattern, LSP)重构路径,旨在促进乡村旅游与生态环境和谐、可持续发展,为乡村旅游地景观规划提供参考思路。【方法】以江苏省无锡市马山为例,综合运用InVEST、ArcSWAT、最小累积阻力(minimum cumulative resistance, MCR)多模型,分别模拟生态、游憩空间格局以及生态、游憩廊道,并划分景观单元;基于“权衡矩阵法”,比较各单元生态、游憩功能重要性,实现景观功能分区,识别权衡问题突出的区域及战略点,进而为各类景观功能区提出针对性的规划、建设及管控策略。【结果】将马山景观功能区划分为生态核心区、生态重要区、生态-游憩重点权衡区、生态-游憩次级权衡区、游憩核心区、游憩重要区、游憩协调区及弹性发展区8类,构建生态-游憩景观网络并识别出32处战略点。【结论】重构乡村生态-游憩LSP有利于区分不同类型景观功能区的建设侧重点与优先级,科学、精细化地管理、利用乡村景观资源,促进多功能景观的协调与增效。

多项目环境下time-cost置换问题建模与求解

针对多项目环境下的time-cost置换问题,以活动资源为决策变量,建立了以各项目总延迟最小与总成本最小的双目标time-cost置换模型。在总结前人对于多目标优化求解方法的基础上,针对多项目的特点,提出了基于NSGA-II非劣排序的局部直接搜索改进遗传算法,并考虑资源为连续与离散两种情况进行求解。与NSGA-II相比,算法可以较快地收敛到最优解,并且具有较好的离散变量搜索能力,与ZDT系列测试函数的比较也体现了算法的优越性。

基于土地利用和地形的生态系统服务空间分布及权衡-协同-独立关系——以安塞区为例

[目的]生态系统退化问题日益突出,开展生态系统服务空间分布及其相关关系研究对区域生态文明建设具有重要意义。[方法]基于InVEST和CASA模型,在10 m空间分辨率下定量评估安塞区2020年土壤保持、固碳释氧、水源涵养和生境质量及其随地形和土地利用变化趋势,分析生态系统服务间权衡—协同—独立关系。[结果](1)林地和草地生态系统服务较强,未利用地和建设用地较弱;耕地、林地和草地生态系统服务间协同作用明显,而未利用地表现为权衡作用,水域表现为独立作用。(2)土壤保持量最高值在中低海拔、急悬坡和半阴坡,固碳释氧量最高值在中低海拔、陡峭坡和阴坡,涵养水源量最高值在低海拔和阳坡,生境质量最高值在高海拔、急悬坡和阳坡。(3)地形和土地利用视角下,生态系统服务整体表现为协同度>独立度>权衡度,协同作用常发生在土壤保持、固碳释氧和水源涵养之间,生境质量与其他生态系统服务权衡作用明显。(4)协同作用随着海拔升高和坡向向阳程度加强而提升,随着坡度增加呈先升高后降低变化趋势,权衡则与之相反。[结论]土地利用和地形对生态系统服务影响较大,应因地制宜开展土地规划和生态管理,基本证明了退耕还林还草生态恢复措施与其地形气候的适应性和决策的正确性。

金沙江下游梯级水电工程库区生态系统服务价值演化及权衡协同关系

基于生态系统服务变化指数、相关分析及空间自相关等方法,对金沙江下游梯级水电工程库区2005—2018年生态系统服务价值进行定量分析,探索库区生态系统服务权衡协同关系的时空演变规律。结果表明:(1)2018年库区生态系统服务价值达到940亿元,研究期间生态系统服务价值总量增加42亿元。(2)库区生态系统服务价值空间分布较为稳定,呈现南高北低格局,空间相关类型均为正相关,生态系统服务价值增益地区集聚于金沙江沿岸。(3)库区生态系统支持服务与供给、调节、文化服务之间表现为权衡关系,供给、调节、文化服务两两之间表现为协同关系,各乡镇生态系统服务的相关关系以协同关系为主。研究结果进一步证明水电工程的实施能改善库区生态系统服务功能,为库区环境保护和土地资源可持续利用提供技术支撑。

无人机无线网络中基于队列稳定的无线与计算资源分配优化

无人机(UAV)无线网络中,UAV承载基站设备,可灵活提供无线通信服务,支持在高质量的无线信道状态下进行数据传输;另一方面,将边缘计算服务器部署到基站侧,计算资源更靠近用户,通过任务卸载,能够直接在基站侧进行计算处理,缓解无线网络的去程链路压力;但是,考虑到能耗受限问题,如何通过资源优化来降低网络能耗并保证用户到基站的数据传输和任务处理的稳定性依然是研究的难题;针对UAV无线网络中用户向UAV基站发送数据并卸载计算任务的场景,研究了在数据传输和任务处理稳定性约束下进行无线与计算资源优化的能耗最小化问题,构建数据队列与任务队列,采用李雅普诺夫优化理论对问题进行转化和分解,获得能耗与队列的折中关系,并通过仿真分析评估了所提解决方案的有效性。

非完美CSI下的全双工中继网络的能效谱效均衡

为优化非完美信道状态信息下的解码转发全双工中继网络的能效和谱效,提出了一种基于该网络模型的能效谱效均衡策略。通过构建能量效率和频谱效率的折中优化函数,将一个非凸的多目标优化问题转换为一个凸的单目标优化问题,利用求导法和拉格朗日乘子法求解在不同折中因子下的最优中继发射功率。仿真结果表明,可以通过改变折中因子来优化系统的能效和谱效值,获得最优能效和谱效的性能折中。

基于GTWR模型的济南都市圈生态系统服务价值对城市扩张时空响应

【目的】随着我国城镇化发展进入到以中心城市引领都市圈、城市群的发展阶段,如何促进都市圈城镇化与生态环境协调发展成为高质量城镇发展的重要议题。生态系统服务价值对城市扩张的时空响应研究有助于把脉城市发展与生态系统服务的时空演进特征,推动城市与生态系统的协同发展,助力可持续规划以及建设策略的拟定与实施。【方法】本文以济南都市圈为研究对象,基于城镇扩展指数的计算,定量描述各城市扩张的时空特征。采用生态系统服务当量因子法,从多个角度刻画研究区生态系统服务的时空分异特征,并分析生态系统权衡与协同效应。在此基础上,运用时空地理加权回归(GTWR)模型,探究城市扩张对生态系统服务功能变化的驱动方向与驱动强度。【结果】(1)1980—2020年间济南都市圈内城市扩张显著,具有时序阶段性与区域分异性两方面特征,城市空间扩展速率与强度由高到低依次为小城市、大城市、特大城市、中等城市。(2)都市圈内整体生态服务价值量呈逐年下降趋势,黄河干流、东平湖及周边区域与鲁中山区等地区是重要的生态系统服务价值高值聚集区,都市圈内协同关系占比略低于权衡关系,其中特大城市协同关系占比最高。(3)济南都市圈内城市扩张对生态系统服务价值整体具有负面影响,随着时间的推进,影响强度有所下降。城市扩张对各亚类生态系统服务功能的影响作用具有显著差异,对供给服务与支持服务价值量变化具有负面影响,其中对供给服务变化的驱动强度不断增强,对调节服务价值量变化具有正向作用且影响力整体变化不大,对文化服务价值量变化的影响具有两面性,在不同地区的驱动方向与强度差异性较大。【结论】本研究明确了研究期限内济南都市圈中不同等级城市空间扩展的时空分异规律以及生态系统服务逐渐劣化的发展状态,所构建的GTWR模型在空间层面上量化了城市扩张对生态系统服务总量及各亚类变化量的不同驱动特征与驱动强度,研究成果可为都市圈高质量可持续发展提供决策依据。

基于InVEST模型的渭河流域生境质量评估

基于生态系统服务评估与权衡模型和ArcGIS软件探索2000-2020年渭河流域生境质量的时空变化,利用地形分布指数分析生境质量的地形梯度效应.结果表明, 20 a间,研究区土地利用变化主要包括耕地向建设用地和草地的转移,以及草地向耕地和林地的转移,不同类型之间的转移是影响局部生境质量变化的主要因素;生境质量的空间分布以中等生境为主,占比约57%,主要分布在关中城市群外围和西北部.低等生境占比约5%,但面积增长最快,增幅达到105.80%,原因是关中城市群的大面积扩张;研究区生境质量空间分布存在一定的正相关性,且聚集程度增加1.15%,局部自相关类型以高-高和低-低集聚为主,高-高集聚分布在研究区东北部黄土高原和南部秦岭北坡,低-低集聚分布在关中城市群;2020年生境质量具有显著的地形梯度效应,表现在生境质量等级随着地形梯度级别的增加而增加.

Response of ecosystem carbon storage to land use change from 1985 to 2050 in the Ningxia Section of Yellow River Basin,China

Regional sustainable development necessitates a holistic understanding of spatiotemporal variations in ecosystem carbon storage(ECS),particularly in ecologically sensitive areas with arid and semi-arid climate.In this study,we calculated the ECS in the Ningxia Section of Yellow River Basin,China from 1985 to 2020 using the Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)model based on land use data.We further predicted the spatial distribution of ECS in 2050 under four land use scenarios:natural development scenario(NDS),ecological protection scenario(EPS),cultivated land protection scenario(CPS),and urban development scenario(UDS)using the patch-generating land use simulation(PLUS)model,and quantified the influences of natural and human factors on the spatial differentiation of ECS using the geographical detector(Geodetector).Results showed that the total ECS of the study area initially increased from 1985 until reaching a peak at 402.36×10^(6) t in 2010,followed by a decreasing trend to 2050.The spatial distribution of ECS was characterized by high values in the eastern and southern parts of the study area,and low values in the western and northern parts.Between 1985 and 2020,land use changes occurred mainly through the expansion of cultivated land,woodland,and construction land at the expense of unused land.The total ECS in 2050 under different land use scenarios(ranked as EPS>CPS>NDS>UDS)would be lower than that in 2020.Nighttime light was the largest contributor to the spatial differentiation of ECS,with soil type and annual mean temperature being the major natural driving factors.Findings of this study could provide guidance on the ecological construction and high-quality development in arid and semi-arid areas.

基于RIS辅助的通信感知一体化技术研究

随着更大带宽、更高频段和更大规模天线阵列的使用,现代无线通信系统展现出了越来越强的空间辨识能力,表明了通信与感知融合的巨大潜力。立足于智能超表面(Reconfigurable Intelligent Surface, RIS)辅助通信感知一体化(Integrated Sensing and Communication, ISAC)技术,考虑通信感知性能边界,从信息论角度提出通感性能权衡方法,并结合多种通信、感知性能指标,构建ISAC网络完备的性能权衡理论体系。结合RIS辅助通信硬件结构特征,设计高精度、低复杂度的通信感知传输技术。设计通信感知多载波发射波束,采用RIS实现高低频协作大规模多输入多输出(Multiple-Input Multiple-Output, MIMO)通信感知波束优化,协同控制功率和调度无线资源,实现通信感知资源最优部署。旨在形成新型的RIS辅助通信感知增强框架,提升网络整体性能。

Potential tradeoffs between intraspecific and interspecific trait variations along an environmental gradient in a subtropical forest

There has been growing attention to intraspecific variation in trait-based plant ecology. However, studies on these changes across ontogenetic stages and the potential trade-offs with interspecific traits along environmental gradients are rare. In this study, we measured six wood and bark traits of 1030 trees of six species(Castanopsis nigrescens; C. carlesii; Lithocarpus polystachyus; L. synbalanos; Ormosia glaberrima; O. pachycarpa) from a10-ha plot in a subtropical forest. Mean intraspecific variation in bark thickness and bark percentage to DBH was more than twice that for wood density and bark density.Bark thickness and bark percentage showed a consistent trend with increasing tree size. Small-tree traits were more variable than the same traits in larger trees. Altitude,convexity and soil nutrients explained the majority of the variations in the six traits, while sibling species had similar relationships between traits and environmental variables.Trees with dense wood and thin bark were usually found on steep slopes at lower altitudes. Our findings show intraspecific trait variability has different spatial patterns compared with interspecific variabilities along an environmental gradient.

Tradeoffs and synergies between ecosystem services : A comparison of the karst and non-karst area

Under the influence of various natural and human factors, the relationship between the ecosystem services provided for human beings by a karst ecosystem is becoming increasingly complex, profoundly limiting the effective and sustainable development of the social economy and ecosystem protection in karst areas. Taking Guizhou, China as an example, which includes both karst(including five different landforms) and non-karst area, the study explored and compared the tradeoff and synergy between ecosystem services in both terrain types. The results showed higher change rates of water yield and soil retention in karst areas than those in non-karst areas, with only small differences in the carbon storage and crop production change. The ecosystem service relationships in the karst area from 1995 to 2005 were consistent with the relationships in the non-karst area. However, differences were observed in most of these relationships from 2005 to 2015. The relationships between ecosystem services in different karst landforms from 1995 to 2005 remained the same, but there are differences found in the relationships of ecosystem services from 2005 to 2015. The trade-off and synergistic relationships between ecosystem services in the different landforms were closely related to the changes of climate and land use, particularly related to rainfall, rainfall erosivity, farmland, and forestland.

DIVERSITY-AND-MULTIPLEXING TRADEOFF AND THROUGHPUT OF SUPERPOSITION CODING RELAYING STRATEGY

While the Network Coding cooperative relaying (NC-relaying) has the merit of high spectral efficiency,Superposition Coding relaying (SC-relaying) has the merit of high throughput. In this paper,a novel concept,coded cooperative relaying,is presented,which is a unified scheme of the NC-relaying and SC-relaying. For the SC-relaying strategy which can be considered one-way coded relaying scheme with multi-access channel,the close-form solution of the outage probabilities of the basic signal and additional signal are obtained firstly. Secondly,the Diversity-and-Multiplexing Tradeoff (DMT) characteristics of basic signal and additional signal are investigated entirely as well as the optimal close-form solutions. The compared numerical analysis shows the evaluation error of throughput based on the close-form solution is about 0.15 nats,which is within the acceptable error range. Due to the mutual effect between the both source signals,the available maximal values of the two multiplexing gains are less than 1.

GIS-based Analysis for Hotspot Identification of Tradeoff Between Ecosystem Services： A Case Study in Yanhe Basin, China

Although the quantification and valuation of ecosystem services have been studied for a long time, few studies have specifically focused on the quantification of tradeoffs between ecosystem services and tradeoff hotspots. Based on previous studies of ecosystem service assessment, we proposed a feasible method to analyze the tradeoffs between ecosystem services, including determination of their relationship, quantification of tradeoffs, and identification of tradeoff hotspots. Potential influencing factors were then further analyzed. The Yanhe Basin in the Loess Plateau was selected as an example to demonstrate the application process. Firstly, the amounts of net primary production(NPP) and water yield(WY) in 2000 and 2008 were estimated by using biophysical models. Secondly, correlation analysis was used to indicate the tradeoffs between NPP and WY. Thirdly, tradeoff index(TI_(NPP/WY)) was established to quantify the extent of tradeoffs between NPP and WY, and the average value of TI_(NPP/WY) is 24.4 g/(mm·m^2) for the Yanhe Basin between 2000 and 2008. Finally, the tradeoff hotspots were identified. The results indicated that the area of lowest tradeoff index concentrated in the middle part of the Yanhe Basin and marginal areas of the southern basin. Map overlapping was used for preliminary analysis to seek potential influencing factors, and the results showed that shrub was the best suited for growing in the Yanhe Basin, but also was a potential influencing factor for formulation of the tradeoff hotspots. The concept of tradeoff index could also be used to quantify the degree of synergy between different ecosystem services. The method to identify the tradeoff hotspots could help us to narrow the scope of study area for further research on the relationship among ecosystem services and concentrate on the potential factors for formation of tradeoff between ecosystem services, enhance the capacity to maintain the sustainability of ecosystem.

Delay-Throughput Tradeoff in Satellite Data Relay Networks with Prioritized User Satellites

The efficient antenna scheduling strategy for data relay satellites(DRSs)is essential to optimize the throughput or delay of the satellite data relay network.However,these two objectives conflict with each other since the user satellites(USs)with higher priorities take up more transmission time of DRSs’antennas for greater throughput but the USs storing more packets cause a severer waiting delay to the whole network.To balance the conflicting metrics for meeting the delay-throughput integrated requirements,we formulate the antenna scheduling as a stochastic non-convex fractional programming,which is challenging to be solved.For the tractability,we equivalently transform the fractional programming to a parametric problem and implement the Lyapunov drift to guarantee the constraint of mean rate stability.By proposing a delay and throughput tradeoff based antenna scheduling algorithm,we further transform the parametric problem to a solvable weight matching problem.Simulation results reveal the feasible region of the preference control parameter for integrated QoS cases and its variation relationship with network delay and throughput.

Grain production space reconstruction and land system function tradeoffs in China

Grain production space reconstruction referred to the changes in the quantity,quality and pattern of grain produc-tion space caused by functional tradeoffs and conflicts between grain production space,urban-rural development space,and ecological service space.Exploring tradeoffs between land system functions caused by grain produc-tion space reconstruction was particularly important for ensuring food security,promoting the construction of ecological civilization,and achieving sustainable development.Therefore,this study identified four relationships of land system functions during the process of grain production space reconstruction(1980-2018)in China by using Set Pair Analysis.Research results showed that the reconstruction of grain production space was achieved mainly through three pathways:Grain for Green,deforestation and reclamation,and urban expansion.Generally,ecological service had spatial negative correlation with grain production,economic development and population carrying capacity(P<0.01),but grain production,economic development and population carrying capacity were positively correlated with each other(P<0.01).In the process of grain production space reconstruction,eco-logical services and economic development,ecological services and population carrying capacity had all shown inverse synergies;there was a tradeoffbetween grain production and ecological services,a codirectional tradeoffbetween grain production and economic development,but a strong synergy between economic development and population carrying capacity.However,the functions of land systems only appeared as synergies or tradeoffs,and there were no inverse synergies and codirectional tradeoffs in the separate processes of Grain for Green,deforestation and reclamation,and urban expansion.It can be concluded that the relationships between land system functions were relatively simple in a single process,but it became complex and diverse when multiple processes were integrated for system analysis.

Dynamic Tradeoff of Forced Steering Motor Trucks

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