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   

认知无线电网络中基于排队论的集中式频谱分配策略

传统的基于图着色模型和基于博弈论模型的动态频谱分配算法因存在计算复杂度高、收敛速度慢等缺陷,在实际网络环境中会造成很大的时延和能耗开销。针对主次用户共存,主用户交替转移忙闲状态的网络环境下,基于排队论模型提出了一种高效、低能耗的集中式频谱分配方案,并给出了该方案下次要用户的平均阻塞率和强制中断率的解析表达式。理论分析和仿真结果表明,所提的方案能够大幅度降低节点能耗。     

OFDMA认知无线电网络中面向功率控制的频谱定价与分配

针对OFDMA认知无线电网络,提出一种基于Stackelberg博弈的频谱定价和分配模型.对于次基站控制次网络传输功率来保护主网络通信的场景,主基站可通过该模型获得最优的频谱定价方案.从功率控制的角度,重新设计次用户的效用函数,运用Stackelberg博弈对单个主基站和多个次用户在频谱租赁市场中的交易行为进行建模.通过逆向归纳法,求解市场均衡下的最优频谱定价,使得主基站在考虑主网络QoS降级的同时获得最大收益.此外,对于主基站只能获取本地信息的情形,提出了基于动态Stackelberg博弈的分布式频谱定价和分配模型.仿真实验表明,该模型能够在控制次网络传输功率的基础上,提供最优频谱定价和频谱分配方案.     

基于Markov的频谱切换研究

为了进一步提高认知无线电网络中认知用户的切换性能,有效降低认知用户切换中的阻塞率和强制中断率,提出了频谱池与预留信道相结合的解决方案,并且借助马尔科夫链和排队理论对认知切换系统关键指标进行分析.仿真结果显示,该方案能够有效保障和提高认知用户的服务质量.     

基于能量和频谱共享的传感器网络时延性能分析

采用协同频谱共享和射频能量采集技术后,传感器网络的可用频谱资源和可用能量均受主用户行为约束。为了刻画主用户对传感器网络性能的影响,利用排队理论对基于能量和频谱共享的无线传感器网络时延性能进行建模和分析。首先,通过分析主用户的服务过程和传感器节点的服务过程,推导出了主用户的时延性能。然后,分析了主用户参数对传感器节点服务时间的影响,得到了传感器节点的时延性能,并推导出了Nakagami衰落信道下传感器节点平均时延与系统参数关系的表达式。最后,比较了仿真结果和理论结果,验证了理论分析的正确性,并揭示了网络时延性能与到达率、节点间距离等参数的关系。     

带有认知用户预留信道的双信道分配策略研究

在传统的双信道认知无线网络频谱分配策略下，双信道上均可发生认知用户传输被授权用户抢占的情况，极大地影响到认知用户的传输性能。为了有效保证认知用户传输，提出一种带有认知用户预留信道的双信道分配策略，假设双信道中一条信道为认知用户所预留，在该信道上传输的认知用户不会被中断；另一条信道为传统的普通信道，授权用户能够中断正在使用该信道的认知用户的传输。通过建立一种带有两类服务台的双服务台马尔可夫排队模型，在MATLAB环境下进行实验，数值实验结果表明：较于传统双信道机制，所提出的带有认知用户预留信道的频谱策略能提高认知用户吞吐量，降低认知用户平均延迟时间，大幅提升认知用户综合传输性能。     

基于排队论的车辆动态频谱接入系统研究

将动态频谱接入技术引入到车辆通信网络中,提出了一种使用空闲广播电视信道进行车辆动态频谱接入的模型。该模型将用户通信需求分为紧急和普通服务请求,构建马尔科夫链分析其服务过程,得到了能够满足不同需求的分析模型。仿真结果表明,该模型能准确分析车辆动态频谱接入的过程,当空闲信道数增加时平均等待时间减少,紧急服务请求的平均等待时间和平均队列长度都远小于普通服务请求。     

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。     

动态频谱接入无线传输性能分析*

动态频谱接入技术允许非授权用户利用已授权分配频谱信道的空闲空隙完成数据传输,但是要求不能对授权用户的信道传输造成严重影响。在两种不同的频谱信道共享策略下,利用排队分析模型,对采用动态频谱接入技术的非授权用户的链路传输性能以及对授权用户的传输影响进行了分析,并讨论了非授权用户性能的优化。尽管增加可利用的授权频谱信道的数量可以改善非授权用户的传输性能,但是其传输吞吐量的增加只能趋近于一个上界值。     

服务切换模型及其性能研究

由于通过无线网络可以很方便地使用网络服务,因此无线网络用户越来越多。与此同时,随着无线网络服务的快速发展,人们对无线网络提供的通信容量提出了很高的要求。如何分析和设定网络参数,提高当前网络的运行效率已成为解决网络服务质量优化的一个重要问题。论文提出了一种描述和分析服务切换策略的概率模型,利用生灭过程来分析基站通信信道在不同使用方式下的状态转移概率模型。通过分析不同信道分配策略所对应的队列模型性能,给出了各种队列使用方法的优缺点,并讨论了无线基站预留信道的使用方式以及预留信道的数量对无线基站运行性能的影响。     

Analytical modeling for spectrum handoff decision in cognitive radio networks

Cognitive Radio (CR) is an emerging technology used to significantly improve the efficiency of spectrum utilization. Although some spectrum bands in the primary user’s licensed spectrum are intensively used, most of the spectrum bands remain underutilized. The introduction of open spectrum and dynamic spectrum access lets the secondary (unlicensed) users, supported by cognitive radios; opportunistically utilize the unused spectrum bands. However, if a primary user returns to a band occupied by a secondary user, the occupied spectrum band is vacated immediately by handing off the secondary user’s call to another idle spectrum band. Multiple spectrum handoffs can severely degrade quality of service (QoS) for the interrupted users. To avoid multiple handoffs, when a licensed primary user appears at the engaged licensed band utilized by a secondary user, an effective spectrum handoff procedure should be initiated to maintain a required level of QoS for secondary users. In other words, it enables the channel clearing while searching for target vacant channel(s) for completing unfinished transmission. This paper proposes prioritized proactive spectrum handoff decision schemes to reduce the handoff delay and the total service time. The proposed schemes have been modeled using a preemptive resume priority (PRP) M/G/1 queue to give a high priority to interrupted users to resume their transmission ahead of any other uninterrupted secondary user. The performance of proposed handoff schemes has been evaluated and compared against the existing spectrum handoff schemes. Experimental results show that the schemes developed here outperform the existing schemes in terms of average handoff delay and total service time under various traffic arrival rates as well as service rates.     

保护信道和排队相结合的信道分配策略

提出了一种适用于语音、数据呼叫的蜂窝移动通信系统的信道分配策略。该策略为数据呼叫提供保护信道,降低数据呼叫的阻塞率。同时,采取语音呼叫排队策略抑制数据保护信道引起的语音呼叫阻塞率的恶化。为了进一步提高系统的性能,在策略中引入了不耐烦顾客,并建立了带有不耐烦顾客的排队模型。仿真结果表明该策略能够有效地降低语音呼叫和数据呼叫阻塞率,改善系统性能。     

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。     

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.     

动态频谱访问无线网络的连通性分析

与传统无线网络不同,在动态频谱访问无线网络中,授权用户对分配的频段具有优先使用权,非授权用户网络的连通性受授权用户的分布和授权用户对频段的使用行为的影响.基于连续渗流理论,证明当授权用户较为稀疏或者负载较轻时,非授权用户可以构成部分连通的网络;反之,当授权用户较为密集并且负载较重时,无法部署部分连通的非授权用户网络.此外,在授权用户和非授权用户共享1个信道的情况下,给出了非授权用户网络存在部分连通性的必要条件.仿真实验数据验证了理论分析的正确性.     

Queuing-Based Dynamic Channel Selection for Heterogeneous Multimedia Applications Over Cognitive Radio Networks

In this paper, we propose a dynamic channel-selection solution for autonomous wireless users transmitting delay-sensitive multimedia applications over cognitive radio networks. Unlike prior works that seldom consider the requirement of the application layer, our solution explicitly considers various rate requirements and delay deadlines of heterogeneous multimedia users. Note that the users usually possess private utility functions, application requirements, and distinct channel conditions in different frequency channels. To efficiently manage available spectrum resources in a decentralized manner, information exchange among users is necessary. Hence, we propose a novel priority virtual queue interface that determines the required information exchanges and evaluates the expected delays experienced by various priority traffics. Such expected delays are important for multimedia users due to their delay-sensitivity nature. Based on the exchanged information, the interface evaluates the expected delays using priority queuing analysis that considers the wireless environment, traffic characteristics, and the competing users' behaviors in the same frequency channel. We propose a dynamic strategy learning (DSL) algorithm deployed at each user that exploits the expected delay and dynamically adapts the channel selection strategies to maximize the user's utility function. We simulate multiple video users sharing the cognitive radio network and show that our proposed solution significantly reduces the packet loss rate and outperforms the conventional single-channel dynamic resource allocation by almost 2 dB in terms of video quality.      

基于最佳中继选择的异构多媒体自适应协作分集算法

本文提出一种自适应协作分集方案,以保证异构多媒体业务中主用户传输的服务质量(QoS),并改善次级用户的数据传输性能。采用基于功率控制的系统模型,使得主用户的平均信道增益相对稳定,并且能够在次用户中进行估计,可以节省在反馈信道上的资源。根据次级用户传输过程中的中断概率提出次级中断概率的闭式表达式 ,在满足主用户传输过程中所需要的中断概率约束的条件下,针对主用户和次用户的协作性和瑞利衰落信道的适应性提出了最佳中继选择的自适应协作分集,尽可能地次级中断概率,并获得的分集增益。实验仿真结果表明,该算法可以减少次级用户的中断概率并提高频谱效率,有助于提升次级用户的数据传输性能。     

Optimal user scheduling and power control in multi-user cognitive broadcast systems

Cognitive radio systems should not only have the ability to sense and exploit "frequency spectrum holes",but also the ability to sense and utilize "spatial spectrum holes".In this paper,we consider the issue of maximizing the throughput of the cognitive systems by fully utilizing "spatial spectrum holes" brought in by multiple cognitive users,in the scenario where a pair of licensed users and a cognitive broadcast system share multiple spectrum bands.By exploiting the channel reciprocity under the premise that the licensed system adopts the time-division-duplexing (TDD) mode,we propose a more practical cognitive access scheme that can sense the interference at the licensed user caused by the cognitive transmitter,based on the existing feedback signals from the licensed user to the licensed base station.Taking both interferences from the licensed base station to the cognitive receiver and from the cognitive transmitter to the licensed user into consideration,we investigate the optimal user scheduling and power allocation scheme that can maximize the ergodic sum rate of the cognitive system.We show that scheduling the user whose channel gain to interference and noise ratio (CGINR) is the largest for each frequency band is optimal.We also derive the dynamic power allocation scheme meeting the three practical constraints,i.e.,the transmitter’s average transmission power constraint,the power amplifier’s instantaneous transmission power constraint,and the interference power constraint at the licensed user.The result shows that in different coherent time intervals and different frequency bands,the power allocation has a multi-level waterfilling structure.Theoretical analysis shows that the strategy scheduling user with the largest CGINR introduces significant performance improvement compared with the traditional strategy scheduling user with the largest channel gain to noise ratio (CGNR).We also illustrate the impact of power constraints and the number of users on system performance by simulation.     

QoS enhancements and performance analysis for delay sensitive applications

This paper presents a comprehensive system modeling and analysis approach for both predicting queuing delay and controlling average queuing delay of a single buffer to a required value in a multiple traffic source network environment. This approach could effectively enhance the QoS performance of delay sensitive applications. A discrete-time analytical model that approximates the multi-source arrival process with a binomial distribution has been developed to analyze the relationship between the queuing threshold and average queuing delay. A control strategy with dynamic queue thresholds based on the analytical result is then used to control the average queuing delay to a required value within the buffer. Packet dropping is treated as implicit congestion feedback to the arrival process for rate adjustment. The feasibility of the system has been validated by comparing theoretical analysis with a diverse set of simulation results. Following from the simulation results, a set of statistical analyses has been performed to evaluate the efficiency and accuracy of the proposed scheme. In addition, a user-friendly graphical user interface has been developed to allow user-configuration of the simulation process and display simulation results.