Diversity-multiplexing tradeoff of half-duplex multi-input multi-output two-way relay channel with decode-and-forward protocol

A multi-input multi-output(MIMO) separated two-way relay channel(STWRC) is considered,where two users exchange their messages via a relay node.When each link is quasi-static Rayleigh fading,the achievable diversity-multiplexing tradeoff(DMT) of the half-duplex STWRC is analyzed.Firstly,the achievable DMT of the STWRC with static decode-and-forward(DF) protocol is obtained.Then,a dynamic decode-and-forward(DDF) protocol for the STWRC is proposed,where the relay listening time varies dynamically with the channel qualities of the links between two users and the relay.Finally,the achievable DMT of the proposed DDF protocol is derived in a case-bycase manner.Numerical examples are also provided to verify the theoretical analysis of both protocols.

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.

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.

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 specifi- cally focused on the quantification of tradeoffs between ecosystem services and tradeoff hotspots, Based on previous studies of ecosys- tem 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 ana- lyzed. 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, correla- tion analysis was used to indicate the tradeoffs between NPP and WY. Thirdly, tradeoff index （TINpp/wy） was established to quantify the extent of tradeoffs between NPP and WY, and the average value of TINpp/wy is 24.4 g/（mm·m2） 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 mid- dle part of the Yanhe Basin and marginal areas of the southern basin. Map overlapping was used for preliminary analysis to seek poten- tial influencing factors, and the results showed that shrub was the best suited for growing in the Yanhe Basin, but also was a potential irtfluencing factor for formulatiort 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.

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.

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.

Physical mechanism of mind changes and tradeoffs among speed,accuracy, and energy cost in brain decision making:Landscape, flux,and path perspectives

Cognitive behaviors are determined by underlying neural networks. Many brain functions, such as learning and memory, have been successfully described by attractor dynamics. For decision making in the brain, a quantitative description of global attractor landscapes has not yet been completely given. Here, we developed a theoretical framework to quantify the landscape associated with the steady state probability distributions and associated steady state curl flux, measuring the degree of non-equilibrium through the degree of detailed balance breaking for decision making. We quantified the decision-making processes with optimal paths from the undecided attractor states to the decided attractor states, which are identified as basins of attractions, on the landscape. Both landscape and flux determine the kinetic paths and speed. The kinetics and global stability of decision making are explored by quantifying the landscape topography through the barrier heights and the mean first passage time. Our theoretical predictions are in agreement with experimental observations： more errors occur under time pressure. We quantitatively explored two mechanisms of the speed-accuracy tradeoff with speed emphasis and further uncovered the tradeoffs among speed, accuracy, and energy cost. Our results imply that there is an optimal balance among speed, accuracy, and the energy cost in decision making. We uncovered the possible mechanisms of changes of mind and how mind changes improve performance in decision processes. Our landscape approach can help facilitate an understanding of the underlying physical mechanisms of cognitive processes and identify the key factors in the corresponding neural networks.

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

In this paper, the dynamic tradeoff of forced steering motor trucks is analyzed in detail. Some dynamic models are developed to analyze the nonlinear curving, lateral stability and stick slip vibration stability. The computed results show that forced steering motor trucks successfully solve the tradeoff problem among traction, steering and stability. Its comprehensive dynamic performance is excellent.

Secure Spectral-Energy Efficiency Tradeoff in RandomCognitive Relay Networks

Spectral efficiency(SE) and energy efficiency(EE) in secure communications is of primary importance due to the fact that 5 G wireless networks aim to achieve high throughput,low power consumption and high level of security.Nevertheless,maximizing SE and EE are not achievable simultaneously.In this paper,we investigate the SE and EE tradeoff for secure transmission in cognitive relay networks where all nodes are randomly distributed.We first introduce the opportunistic relay selection policy,where each primary transmitter communicates with the primary receiver with the help of a secondary user as a relay.Then,we evaluate the secure SE and secure EE of the primary network based on the outage probabilities analysis.Thirdly,by applying a unified SE-EE tradeoff metric,the secure SE and EE tradeoff problem is formulated as the joint secure SE and EE maximization problem.Considering the non-concave feature of the objective function,an iterative algorithm is proposed to improve secure SE and EE tradeoff.Numerical results show that the opportunistic relay selection policy is always superior to random relay selection policy.Furthermore,the opportunistic relay selection policy outperforms conventional direct transmission policy when faced with small security threat(i.e.,for smaller eavesdropper density).

An Approach to Developing a Performance Test Based on the Tradeoffs from SW Architectures

In a performance test, the standards for assessing its test results are not sufficiently determined due to the lack of a well-structured test developing methods which are found in a functionality test. By extending the established workflow structure, this approach will concentrate on tradeoffs within T-workflow and further develop tests based on T-workflow. The monitoring and tuning point have also been investigated to understand the validity and performance of software. Finally through a case study, it has been shown that better assessment of software performance can be obtained with the suggested tests developed based on T-workflow and by locating its monitoring point and tuning point.

Architecture-level performance/power tradeoff in network processor design

Network processors are used in the core node of network to flexibly process packet streams. With the increase of performance, the power of network processor increases fast, and power and cooling become a bottleneck. Architecture-level power conscious design must go beyond low-level circuit design. Architectural power and performance tradeoff should be considered at the same time. Simulation is an efficient method to design modem network processor before making chip. In order to achieve the tradeoff between performance and power, the processor simulator is used to design the architecture of network processor. Using Netbeneh, Commubench benchmark and processor simulator-SimpleScalar, the performance and power of network processor are quantitatively evaluated. New performance tradeoff evaluation metric is proposed to analyze the architecture of network processor. Based on the high performance lnteI IXP 2800 Network processor eonfignration, optimized instruction fetch width and speed ,instruction issue width, instruction window size are analyzed and selected. Simulation resuits show that the tradeoff design method makes the usage of network processor more effectively. The optimal key parameters of network processor are important in architecture-level design. It is meaningful for the next generation network processor design.

Tradeoff between the number of firefighting resources and the level of fire ignition prevention efforts in the Republic of Korea

This study explores the tradeoff relationship between the number of initial attack firefighting resources and the level of fire ignition prevention efforts mitigating the probability of human-made fires in the Republic of Korea,where most fires are caused by human activities.To examine this tradeoff relationship,we develop a hybrid model that combines a robust optimization model with a stochastic simulation model.The robust optimization minimizes the expected number of fires not receiving a pre-defined response,such as the number of firefighting resources that must arrive at the fire within half an hour,subject to budget constraints and uncertainty about the daily number and location of fires.The simulation model produces a set of fire scenarios in which a combination of number,location,ignition time,and intensity of fires occur.Results show that fire ignition prevention is as cost-effective as initial attack firefighting resources given the current budget in the Republic of Korea for reducing the expected number of fires not covered by the predefined response.The mixed policy of fire suppression and fire prevention may produce some gains in efficiency relative to the dominant policy of strong fire suppression strategies.

Aircraft Combat Survivability Estimation and Synthetic Tradeoff Methods

A new concept is proposed that susceptibility, vulnerability, reliability, maintainability and supportability should be essential factors of aircraft combat survivability. A weight coefficient method and a synthetic method are proposed to estimate aircraft combat survivability based on the essential factors. Considering that it takes cost to enhance aircraft combat survivability, a synthetic tradeoff model between aircraft combat survivability and life cycle cost is built. The aircraft combat survivability estimation methods and synthetic tradeoff with a life cycle cost model will be helpful for aircraft combat survivability design and enhancement.

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。

森林生态系统服务多功能性:概念、指标和经营模拟模型

森林生态系统同时提供多种功能和服务的能力,被称为森林生态系统多功能性,可分为生态系统功能多功能性和生态系统服务多功能性。近年来,生态学领域对生物多样性与多功能性关系机理、多功能性驱动因子等进行了大量研究,这些研究持续成为热点。然而,这些研究成果在实际应用,尤其是在指导森林经营实践方面,尚显不足。森林经营一直以实现多种功能或服务的最大化为目标,但目前还缺乏与生态学中多功能性理论研究的有机联系,迫切需要将二者结合。本文对国际国内森林生态系统服务多功能性的概念、指标、评价方法、经营模拟和优化模型进行了综述,认为预测森林生态系统服务及多功能性、在森林经营单位层面实现多功能性最大化是将来的研究方向。因此,需要加强森林经营模型模拟研究,寻找减少不同服务间冲突、增加协同(即增加多功能性)的经营策略,回答森林经营和气候变化如何影响生态系统服务间的权衡和协调关系及其时空变化等理论和实际问题。

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。

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。

草地植物生殖分配研究进展

植物生殖分配调控着植物营养生长与生殖生长的平衡,从而影响种群的更新速度,最终改变群落结构及演替方向。因此,研究植物生殖分配对草地生态系统稳定和可持续发展至关重要。本文通过文献综述方法,系统地梳理了草地生态系统植物生殖分配的相关研究理论及影响因素,学者们先后基于最优控制理论、生活史理论和生物量分配理论提出光合补偿机制、养分循环假说、时间限制假说、r/k策略、资源可用性假说等,以解释自然环境因素、植物自身因素和人为干扰因素等调控植物生殖分配的机制。然而,草地植物对诸多因素(植株形态性状、自然灾害、放牧、刈割、外源养分添加等)的生殖分配响应仍存在争议,且复杂因素(气候变化、生境条件、植物间竞争等)及多因素协作的过程和驱动机制不清晰。基于此,建议从多维度解析草地植物生殖分配策略及驱动机制,以期为促进草地生态系统更新及正向演替、提高草地资源利用率的研究提供理论依据。