信息类专业英语翻译.doc

Dynamic topology:As the channel of communicationchanges, some of the neighbors who were reachable on theprevious channel might not be reachable on the currentchannel and vice versa. As a result the topology of the network changes with the change in frequency of operation resulting in route failures and packet loss.Heterogeneity: Different channels may support differenttransmission ranges, data rates and delay characteristics.Spectrum-Handoff delay: For each transition from onechannel to another channel due to the PUs activity, thereis a delay involved in the transition called Spectrum-Handoff delay.All these factors decrease the predictability of the cause oftransit-delay and subsequent packet loss on the network. Thetime latency during channel hand-off in cognitive networksmight cause the TCP round trip timer to time out. TCP willwrongly recognize the delays and losses due to the abovefactors as network congestion and immediately take steps toreduce the congestion window size knowing not the cause ofpacket delay. This reduces the efficiency of the protocol insuch environments.动态技术：随着信道通信的变化，一些邻进信道的用户在原信道没有发生变化而在新信道发生变化，或者相反。随着操作频段的变化，网络的拓扑结构发生变化导致路由失败和丢包。异构：不同的信道支持不同的传输范围，传输速率，延迟特点。频谱切换延迟：由于主用户的出现，每个从一个信道切换到另一个信道，在过渡中，一种延迟被包括叫做频谱切换延迟。所有因素减少了在网络中，传输延迟和随后丢包的原因的预测性。在认知网络的信道切换过程中潜在的时间引起TCP的RTT的超时。TCP错误的认为延迟和丢包由于以上因素比如网络拥塞和立刻采取减少拥塞窗口大小，而不知道包延迟的原因。这些降低协议在这样环境的效率。Throughput maximization is one of the main challengesin cognitive radio ad hoc networks, where the availability oflocal spectrum resources may change from time to time and hop byhop. For this reason, a cross-layer opportunistic spectrum accessand dynamic routing algorithm for cognitive radio networks isproposed, which is called the routing and dynamic spectrum allocation(ROSA) algorithm. Through local control actions,ROSA aims to maximize the network throughput by performingjoint routing, dynamic spectrum allocation, scheduling, and transmitpower control. Specifically, the algorithm dynamically allocatesspectrum resources to maximize the capacity of links withoutgenerating harmful interference to other users while guaranteeinga bounded bit error rate (BER) for the receiver. In addition, thealgorithm aims to maximize the weighted sum of differential backlogsto stabilize the system by giving priority to higher capacitylinks with a high differential backlog. The proposed algorithmis distributed, computationally efficient, and has bounded BERguarantees. ROSA is shown through numerical model-based evaluationand discrete-event packet-level simulations to outperformbaseline solutions, leading to a high throughput, low delay, andfair bandwidth allocation在认知ad hoc网络中，吞吐量最大化是重要挑战之一，随着时间和跳数的变化当地的频谱资源的可用性发生变化。考虑这些原因，提出了认知网络的跨层机会频谱接入和动态路由算法，叫做路由动态频谱分配算法ROSA。通过当地的控制作用，ROSA通过实行共同路由、动态频谱分配、时序安排传输功率控制，目的在于最大化网络吞吐量。具体的就是，没有产生有害的干扰对其他用户保证接收方在一定限制的无比特率，动态算法分配频谱资源来最大化链路容量。另外，算法通过认为带有高不同的累积有比较高的链路容量，目的在于最大化不同累积的加权和来稳定系统。提出的算法是分布式的，计算效率高，保证限定误比特率。通过基于模型的数值估计展示ROSA和时间分离包数量仿真胜过基本解决方法，得到一个高吞吐量，低时延，公平的带宽分配。Cognitive radio is considered as one of the mainenablers for provisioning dynamic and flexiblespectrum/channel allocation in wireless communications. Onthe other hand several physical layer mechanisms such asadaptive modulation, multiple-input multiple output systems,advanced channel coding and/or combinations of themenhance the capacity of wireless networks. However little efforthas been put till now in studying the performance gains ofphysical layer mechanisms with the presence of cognitioncapabilities. The incorporation of cognitive mechanismsdemands more detailed studies for assessing the impact on thespectral efficiency. To this direction, cross-layer combinationof such a physical layer with upper layers should be alsoconsidered as a case study in a cognitive wireless environment.In this work we present a study on the spectral efficiency ofadaptive modulation and coding which is one of the mostpromising schemes of applying cognitive radio at the physicallayer. Besides, we study a cross-layer combination of adaptivemodulation with upper layers in the same cognitive context.We prove that the performance gain of cognitive radio oversuch a physical layer is not negligible.认知无线电所能提供的主要能力之一是在无线通信中，提供动态的灵活的频谱信道分配。另一方面几种物理层机制像适应性调制，多输入多输出系统，先进的信道译码和结合他们增强无线网络容量。然而直到现在，在研究带有存在认知能力的物理层机制增加的性能当中，提出很少的成果。认知机制的结合要求较多的详细的研究对频谱效率的影响。朝着这个方向，和上层的物理层的跨层结合可以被看作个案研究在认知无线环境。在这个工作中，我们提出一个研究适应性的调制解调的频谱效率，他是在物理层应用认知无线电最有希望的策略之一。并且我们研究带有上层的适应性调制解调的跨层结合在相同认知背景。我们证明了在这些的物理层上的认知无线电增加的性能不是忽略不计的。AbstractCongestion control in wireless multi-hop networksis challenging and complicated because of two reasons. First,interference is ubiquitous and causes loss in the shared medium.Second, wireless multihop networks are characterized by the useof diverse and dynamically changing routing paths. Traditionalend point based congestion control protocols are ineffectivein such a setting resulting in unfairness and starvation. Thispaper adapts the optimal theoretical work of Tassiulas andEphremedes 33 on cross-layer optimization of wireless networksinvolving congestion control, routing and scheduling, for practicalsolutions to congestion control in multi-hop wireless networks.This work is the first that implements in real off-shelf radios, adifferential backlog based MAC scheduling and router-assistedbackpressure congestion control for multi-hop wireless networks.Our adaptation, called DiffQ, is implemented between transportand IP and supports legacy TCP and UDP applications. In anetwork of 46 IEEE 802.11 wireless nodes, we demonstrate thatDiffQ far outperforms many previously proposed “practical”solutions for congestion control.在无线多跳网络中，拥塞控制是有挑战的和复杂的。原因有两点如下：第一，干扰是普遍的和丢包的原因是共享媒介。第二，无线多跳网络的特征是多用户，动态改变路由路径。传统的以指向终端为基础的拥塞控制协议在这样的设施导致不公平和饥饿是无效的。AbstractCognitive radio (CR) technology can achieve higherspectrum efficiency by exploring the unused spectrum in licensedband. Most of the existing work focuses on maximizing thespectrum utilization but ignores the immediate influence fromprimary users to network throughput. In this paper, we investigatethe importance of planned link restoration in cognitiveradio networks. We formulate the link restoration problem asan integer programming problem. By considering both channelassignment and interference between links, the link throughputcan be guaranteed even when primary users appear, andtherefore can provide the needed reliability for real-time wirelessapplications. We consider a link failure model which captures theinduced link failures from multiple primary users operating onone frequency channel. Under this failure model, our algorithmexplores the sharing of backup capacity. We compare ouralgorithm to two baseline restoration schemes. Our algorithmperforms very well in terms of capacity usage and throughputreliability.通过在受权频段中扫描空闲频段，cr技术可以到达比较高的频谱效率。大部分的工作在于最大化频谱利用率而忽视了立即的从主用户的影响对网络吞吐量。在本文，我们调查cr网络中计划链路恢复的重要性。我们系统阐述链路恢复问题作为整体规划问题。通过分析信道分配和链路之间的干扰，即使主用户出现，链路的吞吐量可以被保证，因此能够提供可靠地实时的无线应用。我们认为链路失败模型，它可以从多个主用户使用在频段上捕获诱发的链路故障。在这个失败模型下，我们的算法探索共享备用容量。In this paper, we investigated the end-to-endthroughput of a chain in Cognitive Radio Networks (CRNs). Wefound that, the end-to-end throughput is dependant on both theprimary usage patterns and the transmission scheduling schemebeing used. In addition, to increase the end-to-end throughput ofa Cognitive Radio (CR) chain, the scheduling scheme should beadjusted according to the primary usage patterns of the CR linksin the chain. In the paper, firstly, we proposed an algorithm toapproximate the achievable end-to-end throughput consideringthe primary usage patterns by abstraction and iteration. Then,a novel layered packets transmission scheduling scheme wasproposed in attempt to realize the approximated end-to-endthroughput. Finally, extensive simulations were conducted andresults showed that, using proposed transmission schedulingscheme, the achievable end-to-end throughput of a CR chainis increased by considering the primary usage patterns and thefinal end-to-end throughput is close to the approximation在本文，我们调查了CRNs链中，点对点的吞吐量。我们发现对对点的吞吐量取决去主用户的使用方式和所采用的传输时序安排策略。另外，为了增加cr链的点对点的吞吐量。根据cr链的主用户的使用方式，时序安排策略被调整。在本文，首先，我们通过提取和反复考虑考虑主用户的方式，提出一个算法来接近可到达的点对点的吞吐量。Spectrum Handoff in Cognitive Radio Networks:Opportunistic and Negotiated SituationsSpectrum handoff is an indispensable componentin cognitive radio networks to provide resilient service forthe secondary users. In this paper, we explore the spectrumhandoff procedure and then propose four metrics to characterizeboth short-term and long-term spectrum handoff performance:link maintenance probability, the number of spectrum handoff,switching delay, and non-completion probability. In particular,the probability mass function (pmf) and the average numberof spectrum handoff are developed. The tele-traffic parametersare relaxed to follow a general distribution function, which willenable a wide applicability and theoretical significance of thederived formulae. Both opportunistic and negotiated spectrumaccess strategies are investigated. Results show that these twomechanisms will generate significantly different performance.Numerical examples are presented to demonstrate the performancetrade-off and the interaction between the primary usersand the secondary users. The impact of key parameters onspectrum handoff is also discussed. The techniques as well asthe results are important for evaluating the primary and secondusers co-existence, and hence helpful for design and optimizationof cognitive radio networks.在CR网络中，频谱切换是必不可少的组成来提供适应性的服务为次用户。在本文中，我们探索频谱切换过程和提出四个公制的为特性分短期长期频谱切换性能：；链路维持概率，频谱切换数量，切换延时，切换失败概率。具体的，发展了概率分布函数和平均切换函数。tele-traffic参数是随机的服从一般分布函数，它提供广泛的应用性的和推导出系统阐述的理论上的重大意义。调查机会主义的和协商的频谱接入策略。结果显示两个机制会产生董大不同的性能。In cognitive radio networks (CRNs), the traditionalnotion is to terminate the secondary communication upon thereturn of the primary users. Even though the spectrumhandoff technology is adopted, a long time delay to thecognitive communication is unavoidable. And the problem ofthe hand off delay is not to be solved without the innovation ofthe hardware in communication systems. In our paper, we aimat the real-time spectrum handoff in the view of the spectrumsensing. We proposed two distinguished modules, the secondreceiver and the spectrum pool, to support the real-timehandoff. In the sensing selection, we propose the necessity ofre-sensing (sensing again) to determine the sensing band. Andthe model-based prediction is also adopted in the paper. Fromthe computer simulation under different SNR and differentprimary traffic rate, we can see that the proposed spectrumhandoff scheme outperforms the non-real time scheme.在CRNs中，传统的观念是终止次用户的通信在主用户返回时。即使频谱切换技术被采纳，认知网络的长期的延迟是不可避免的。没有通信系统硬件的革新，切换延迟是不可能被解决的。在本文中，从频谱感知的角度看，我们的目的在于实时的频谱切换。我们提出两个不同的模型，次用户接收方和频谱池，来支持实时切换，在感知的选择上，我们提出再次感知的必要性来决定感知带宽。在本文，基本的模型预测被提出。在不同的SNR和主用户传输速率从仿真结果看，提出提出的频谱切换策略优于非实时的策略。TP-CRAHN: A Transport Protocol for CognitiveRadio Ad-hoc NetworksExisting research in transport protocols for wirelessad-hoc networks has focused on reliable end-to-end packetdelivery under uncertain channel conditions, route failures dueto node mobility and link congestion. In a cognitive radio(CR) environment, there are several key challenges that mustbe addressed apart from the above concerns. The intermittentspectrum sensing undertaken by the CR users, the activity of thelicensed users of the spectrum, large-scale bandwidth variationbased on spectrum availability, and the channel switching processneed to be considered in the transport protocol design. Inthis paper, a window-based Transport Protocol for CR Ad-HocNetworks, TP-CRAHN, is proposed that distinguishes each ofthese events by a combination of explicit feedback from theintermediate nodes and the destination. This is achieved byadapting the classical TCP rate control algorithm running atthe source to closely interact with the physical layer channelinformation, the link layer functions of spectrum sensing andbuffer management, and a predictive mobility framework that isdeveloped at the network layer. To the best of our knowledge,this is the first work on the transport layer to specifically addressthe concerns of the CR ad-hoc networks and our approach isthoroughly validated by simulation experiments.目前的研究在无线ad-hoc网络的传输层集中在于点对点的包传递在不确定的信道条件路由失败由于节点移动和链路拥塞。在cr网络环境下，除了以上的几个还有几个关键的挑战，次用户进行间隔的频谱感知，主用户在频谱的活跃程度，基于频谱可用性的大范围的带宽变化 ，信道转变过程需要被考虑在设计传输层协议。在本文基于窗口的CR Ad-Hoc网络的传输层协议TP-CRAHN,，被提出：通过结合准确的反馈从中间节点和目的节点，它可以区别每个事件，这是高度完美的通过经典TCP速率控制算法运行在原节点相互作用在物理层信道信息，频谱感知的链路层函数和缓冲管理，一个预言性的移动框架：是发展的在网络层。A Markov chain analysis for spectrum access inlicensed bands for cognitive radios is presented and forcedtermination probability, blocking probability and traffic throughputare derived. In addition, a channel reservation scheme forcognitive radio spectrum handoff is proposed. This scheme allowsthe tradeoff between forced termination and blocking accordingto QoS requirements. Numerical results show that the proposedscheme can greatly reduce forced termination probability at aslight increase in blocking probability.在认知无线电的授权频段Markov链分析频谱接入被提到，影响终止概率，阻塞概率和传输吞吐量。另外信道预留策略用在认知无线电的频谱切换被提出。根据服务质量，这些策略权衡强制中断和阻塞，数字的结果展示提出的策略大大减少强制中断的概率，微微增加阻塞概率。On the Performance of Spectrum Handoff for LinkMaintenance in Cognitive RadioCognitive radio (CR) has the potential for resolvingthe spectrum scarcity issue in wireless communications. A CRdevice can establish unharmful links in the spectrum of thelegacy system. Among many enabling functions for CR, spectrumhandoff can restore CRs connection when the primary userappears in the occupied channel. In this paper, we study threetypes of spectrum handoff for the link maintenance: (1) nonspectrumhandoff method, (2) the pre-determined channel listspectrum handoff, and (3) the spectrum handoff based on radiosensing scheme. We examine the performances of the threemechanisms in terms of the link maintenance probability andthe effective data rate of the secondary users transmission.Our numerical results show that erroneous channel selectionprobability, radio sensing time and the number of handoff trialsare important for spectrum handoff schemes. We also providethe design guideline for these parametersCR能够解决无线通信中的频谱稀缺问题。一个CR设备能建立无害的链路在合法系统的频谱。他们当中许多能够提供CR功能。当主用户返回授权频段时，频谱切换可以恢复cr链接。在本文，我们研究三种频谱切换策略为了链路维护1无频谱切换方法2预先决定的信道切换列表3频谱切换基于无线电感知策略。从链路维持的可能性和次用户传输的有效速率，我们检验三种机制的性能。我们的数字结果显示错误的信道选择的，无线感知时间，切换次数的检验时是重要的对频谱切换Fuzzy-based Spectrum Handoff in CognitiveRadio NetworksThis paper focuses on spectrum handoffs in acognitive radio network where secondary (unlisenced) u