认知无线电网络一种自适应切换机制的Markov建模分析

为了提高认知无线电网络(CRN)的利用率和吞吐量性能,提出了一种新的主用户优先的自适应频谱切换机制。强调主用户的优先地位,并考虑主用户到达率对次用户的通信影响和限制次用户对主用户的干扰功率,次用户以此自适应地决定执行主动切换机制或被动切换机制。在此自适应切换机制下建立了主次用户之间的Markov链,求出了相应的稳态概率,由稳态概率和不同状态下的吞吐量推导出系统吞吐量和信道利用率的解析表达式。又对次用户之间的通信建立了一个Markov链,推导出次用户之间传递控制信息的时间。数值结果表明提出的新的自适应切换机制比基于CSMA的接入方法具有更高的系统吞吐量和信道利用率,并且可以求出次用户之间的传递时间。     

RAC: Range Adaptive Cognitive Radio Networks

In recent years, cognitive radio has received a great attention due to tremendous potential to improve the utilization of the radio spectrum by efficiently reusing and sharing the licensed spectrum bands, as long as the interference power inflicted on the primary users of the band remains below a predefined threshold level. Cognitive radio allows the secondary users in the cognitive radio network to access the licensed spectrum of the primary users opportunistically. In this paper, an autonomous distributed adaptive transmission range control scheme for cognitive radio networks which is called the RAC is proposed. The RAC considers the QoS requirements of both the primary and the secondary users simultaneously. The cognitive user's maximization of its achievable throughput without interfering the primary user by adapting transmission range of the secondary users dynamically is the key feature of the RAC. One of the advantages of using the proposed scheme is its implementation simplicity. The RAC is compared to other cognitive radio schemes in a simulation environment by using ns2. Simulations indicate that, the RAC can well fit into the mobile cognitive radio ad hoc networks and improve the network performance. Having compared to the other schemes utilizing contemporary cognitive radio technology, the RAC provides better adaptability to the environment and maximizes throughput and minimizes data delivery latency.     

基于频谱池的认知无线电频谱切换分析

为了解决认知无线网络中认知用户频繁切换的问题,最大程度上降低认知用户的切换次数,在已建频谱池的基础上,提出了频谱空穴空闲时间由长到短的排队时间模型,并对该模型下的频谱切换概率问题进行对比研究.推导了一次认知业务请求服务时间内发生频谱切换的概率公式,研究了授权用户到达率与认知用户到达率对频谱切换概率的影响,给出了频谱切换的概率仿真,仿真证明该模型比随机信道选择的效果更优越.     

A cross-layer protocol of spectrum mobility and handover in cognitive LTE networks

Cognitive radio technique is the next step toward efficient wireless bandwidth utilization. While some of the spectrum bands (unlicensed band) have been increasingly used, most of the other spectrum resources (licensed band) are underutilized. This drives the challenges of open spectrum and dynamic spectrum access concepts, which allows unlicensed users (or called secondary users, SUs) equipped with cognitive radios to opportunistically access the spectrum not used by licensed users (or called primary users, PUs). Most existing results mainly focus on designing the lower-layer cognitive radio problems. In the literature, this is the first result to investigate the higher-layer solution for cognitive radio networks. In this paper, we present a cross-layer protocol of spectrum mobility (layer-2) and handover (layer-3) in cognitive LTE networks. With the consideration of the Poisson distribution model of spectrum resources, a cross-layer handoff protocol with the minimum expected transmission time is developed in cognitive LTE networks. Performance analysis of the proposed handoff protocol is investigated. Finally, simulation results illustrates the proposed handoff protocol significantly reduces the expected transmission time and the spectrum mobility ratio.     

认知无线Mesh网络中基于概率的贪婪频谱决策技术研究

认知无线电网络传统的频谱决策方法中次用户根据不同的判据选择信道,会引起信道竞争和拥塞。针对认知无线Mesh网络中基于概率的频谱决策方法,提出一种贪婪信道选择算法,当发生频谱切换时,其结合改进的抢占优先(相似文献   

认知无线电频谱切换的高效信道选择机制

针对认知无线电系统中,频谱切换效率低这个难点,采用分组匹配的思想,基于业务类型对用户进行分组,将用户分组与一种全面可靠的信道评估机制匹配。这种先分组后分配信道的切换算法能有效提高多个用户的复杂场景中频谱切换的效率。仿真结果表明,该算法能够减少认知用户拥塞概率、频谱切换次数以及切换延迟,提高频谱切换效率,有效保证系统服务质量。     

Operating point selection for primary and secondary users in cognitive radio networks

This paper addresses the problem of opportunistic access of secondary users to licensed spectrum in cognitive radio networks. In order to avoid interference to the licensed primary users, efficient spectrum detection methods need to be developed. For this purpose, in recent years several sensing techniques have been proposed to monitor and regulate the spectrum access to the shared spectrum resources. However, spectrum sensing may be affected by errors in the form of missed-detections (i.e., an occupied spectrum is erroneously detected as free) or false-alarms (i.e., a free spectrum is erroneously detected as occupied). These two magnitudes pose a tradeoff on the design of the spectrum sensing mechanisms meaning that low missed-detection can only be achieved at the expense of high false-alarm and vice versa. Thus, the network designers should adaptively tune the sensing techniques such that the highest perceived Quality of Service (QoS) is achieved by both primary and secondary users. In this paper, a framework is introduced for determining the sensing operating points. Also the definition of Grade-of-Service (GoS) metrics is adopted to the case of primary/secondary users spectrum sharing. It is shown that the operating points of the sensing mechanisms can be easily adjusted according to the current traffic load of both primary and secondary users so that the perceived GoS is maximized. In addition, the Erlang Capacity of the spectrum sharing system for both primary and secondary users is also evaluated considering the effects of erroneous sensing.     

基于Ad Hoc无线网的多跳交换算法分析及其仿真结果

论文对基于多跳无线局域网并应用多接入点技术(APs)进行通信的交换性能进行了分析。当一个移动终端不能跟任何接入点进行通信时,它就会用其他移动终端作为终端转发器(TRs)。这种交换标准是建立在绝对和相对信号强度基础上的,其性能指标即平均交换量和平均交换延迟。论文研究了当移动终端和终端转发器均处于移动状态下的交换标准及性能指标之间的联系。多次结果表明当终端转发器移动速度增大时平均交握延迟减小但平均交换量增大。     

认知无线网络中动态频谱接入性能分析

认知无线电技术利用频谱空洞进行通信,有效缓解了频谱资源紧缺问题,动态频谱接入是其核心技术。网络中主用户对授权频谱的使用效率较高时,次用户接入网络无法完成符合QoS要求的通信,只有当主用户频谱效率在一定门限值下时网络才适合次用户接入。有限频谱空洞资源只能满足有限次用户的通信需求,为了保证通信质量,网络在固定的主用户频谱效率下只能接入适量的次用户。提出用强制优先排队理论对认知无线网络中的动态频谱接入过程进行模拟,通过仿真对次用户的切换概率、阻塞概率两个QoS因子进行分析,在给定的QoS条件下,得到了网络适合次用户接入的主用户频谱效率门限值,以及在固定的主用户频谱效率下网络适合接入次用户的量。     

基于分级的频谱切换技术研究

为解决认知无线电网络中频谱切换机制问题,以提高连接保持概率和频谱利用率,降低频谱切换延迟,综合考虑了频谱质量和次用户的业务差异性,将可用频谱资源进行分类并建立起两种使用模型;结合主用户出现概率、信道选择机制和冲突避免算法等因素,提出了一个完整的基于分级的频谱切换机制。仿真结果表明,该机制使得用户在切换时能够快速且无冲突地找到目标信道,有效地保证了主用户和次用户的服务质量。     

地铁环境中双网卡软切换机制的研究与应用

高速移动的无线节点在接入点间切换时,切换延迟较大、丢包率较高.在单网卡切换环境中,不可避免地存在网络中断的现象.该文结合地铁无线通信环境对切换延迟和丢包问题进行研究,为移动节点配备两块无线网卡,控制两块网卡协同工作,共同完成无线切换和数据传输.测试结果表明,双网卡软切换机制无需修改网络层及上层协议栈,在特定环境中可以实现低延迟和零丢包.该切换机制已经在地铁信号系统国产化预研项目中得到应用.     

高铁旅客认知频谱共享算法研究

针对高铁环境中包含多个主用户的主服务和多个次用户的频谱分配问题,提出一种认知博弈频谱共享算法。引入次用户优先级和用户传输业务等级,满足不同优先级用户的不同业务频谱使用需求,并根据主基站和次用户的距离变化更新主服务向次用户提出的价格函数,获得静态博弈下的纳什均衡解,同时分析不完全信息和完全信息的动态博弈,确定不完全信息动态博弈的稳定区间。分别对静态博弈和动态博弈进行仿真,结果表明,在该算法下,当次用户优先级相同时,不同业务等级租借不同的带宽,业务等级越高,租借的带宽也越多,随着距离的变化,较高的业务等级频谱变化较为迅速,而在同一业务等级下,用户优先级越高,则会租借到更多的频谱。     

Markov-based vertical handoff decision algorithms in heterogeneous wireless networks

In this paper, we propose a received signal strength (RSS)-based single-attribute handoff decision algorithm at first, and investigate handoff decision model based on connection lifetime, which can keep mobile terminals (MTs) staying long enough in the preferred network. Since the preferred quality of service (QoS) parameters may be distinct among different MTs, we then formulate the vertical handoff decision problem as a Markov decision process, with the objectives of maximizing the expected total reward and minimizing average number of handoffs. A reward function is constructed to assess the QoS during each connection, and the G1 and entropy methods are applied in an iterative way, by which we can work out a stationary deterministic handoff decision policy. Numerical results demonstrate the superiority of our proposed schemes compared with other existing algorithms.     

基于SIP无线IP网络移动管理的研究

IETF组织提出的SIP是建立、修改和终止多媒体会话的端到端应用层协议,能够满足移动性的要求。但是在会话切换的过程中会丢失数据包,产生不能忍受的延迟。该文分析了延迟产生的原因,并在此基础上提出了充分利用网络资源、由用户终端发起的BS服务器来完成软切换的解决方法。并证明这种方法能够解决切换延迟问题,有效地提高了通话质量。     

全IP移动网络中基于信令预测优先级排队的动态资源预留排序

无线移动网络中的QoS是最近的研究热点之一,其中资源预留协议(ResourceReserVationProtocol,RSVP)是一个关键技术.为了提供更多的服务,蜂窝在变小,这样切换更频繁了.因此为了保证切换时的QoS,需要进行资源预留.当有多个移动主机需要进行预留时,就需要对它们进行优先级排序.本文提出一种在全IP移动网络中基于信令预测优先级排队的动态排序算法,以有效地对多个移动主机进行资源预留.仿真结果表明本文提出的算法既保证了快速切换,又实现了资源的有效预留,有效地分配了有限的资源.     

Mobility management in ubiquitous environments

Ubiquitous computing is aiming at providing users with intelligent human-centric context-aware services at anytime anywhere. However, mobility increases dynamism and uncertainty conditions. This study therefore explores the management and uses of various contexts for automatically providing appropriate services to individual users. This issue is explored from an open framework perspective referred to as ubiquitous gate (U-gate). In this framework, a distributed context management architecture and a communication model based on standard protocols are proposed. To fit user requirements and to achieve complete mobility management, a context-aware path planning mechanism (UbiPaPaGo) and a context-aware handoff mechanism (UbiHandoff) are proposed based on context stored in an open and distributed context management server U-gate. Based on the path planning results of UbiPaPaGo, UbiHandoff derives a minimum access point (AP) handoff plan that satisfies multiple QoS requirements for individual users and services. The UbiHandoff mechanism includes multiple-attribute decision making method (MADM)–based handoff planning, referred to as MADM-based UbiHandoff, and genetic algorithm (GA)–based handoff planning, referred to as GA-based UbiHandoff. In the proposed MADM-based UbiHandoff, analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) provide efficient and seamless AP handoff to gain higher QoS performance. In GA-based UbiHandoff, genetic algorithm is employed to minimize handoff by finding appropriate APs along the path under QoS constraints. Finally, the effectiveness of the proposed mechanisms is evaluated through simulations. Numerical results demonstrate that both mechanisms minimize handoffs and ensure compliance with QoS requirements.     

Distributed cooperative spectrum sensing in cognitive radio for ad hoc networks

Cognitive radio refers to an intelligent radio with the capability of sensing the radio environment and dynamically reconfiguring the operating parameters. Recent research has focused on using cognitive radios in ad hoc environments. Spectrum sensing is the most important aspect of successful cognitive radio ad hoc network deployment to overcome spectrum scarcity. Multiple cognitive radio users can cooperate to sense the primary user and improve sensing performance. Cognitive radio ad hoc networks are dynamic in nature and have no central point for data fusion. In this paper, gradient-based fully distributed cooperative spectrum sensing in cognitive radio is proposed for ad hoc networks. The licensed band used for TV transmission is considered the primary user. The gradient field changes with the energy sensed by cognitive radios, and the gradient is calculated based on the components, which include energy sensed by secondary users and received from neighbors. The proposed scheme was evaluated from the perspective of reliable sensing, convergence time, and energy consumption. Simulation results demonstrated the effectiveness of the proposed scheme.     

基于模糊多目标决策的两跳中继蜂窝网络切换算法

简要介绍了在集成两跳Ad Hoc和蜂窝网络的结构下,触发网络进行切换的一些因素和两种路由代理发现算法,并且提出了一种新的基于模糊多目标决策方法的切换决定算法。算法从层次分析和模糊综合评价理论的思想出发,结合用户、终端、业务和网络信息,对网络链路的性能进行综合评价,选择出最适合用户业务请求的路径。仿真显示在用户可感知业务QoS下降的情况下,算法可以通过增加QoS的权重而切换到更好的网络链路上,从而为用户提供了“总是最好连接”的服务。     

A network flow based approach for network selection in dynamic spectrum access networks

In this paper, we present a network flow based approach for dynamic network and channel selection for secondary users in dynamic spectrum access networks. Most approaches in the current literature on dynamic spectrum access networks do not consider dynamic network and channel selection. We present a network flow framework for network selection. We show that our approach can enable re-assignment of networks to secondary users and also re-assignment of channels to secondary users within the same network. The assignments and re-assignments take into account, the interference caused to primary users, the price each secondary user is willing to pay and the quality of service (QoS) obtained by each secondary user. We obtain a bound for the maximum number of re-assignments.     

Context-aware handoff middleware for transparent service continuity in wireless networks

Advances in wireless networking and content delivery are enabling new challenging provisioning scenarios where a growing number of users access continuous services, e.g., audio/video streaming, while moving among different points of attachment to the Internet, possibly with different connectivity technologies, e.g., Wi-Fi, Bluetooth, and cellular 3G. That calls for novel middlewares capable of dynamically personalizing service provisioning to the characteristics of client environments, in particular to discontinuities in wireless resource availability due to handoffs. The paper proposes a novel middleware solution, called Mobile agent-based Ubiquitous multimedia Middleware (MUM), that performs effective and context-aware handoff management to transparently avoid service interruptions during both horizontal and vertical handoffs. MUM exploits the full visibility of wireless connections available and their handoff implementations (handoff awareness), of service quality requirements and handoff-related quality degradations (QoS awareness), and of network topology and local resource availability (location awareness); that visibility enables MUM to provide original solutions for handoff prediction, multimedia continuity via adaptive data buffering/pre-fetching, and proactive re-addressing/rebinding.