首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   41篇
  国内免费   5篇
  完全免费   34篇
  自动化技术   80篇
  2019年   2篇
  2018年   1篇
  2017年   7篇
  2016年   5篇
  2015年   12篇
  2014年   12篇
  2013年   11篇
  2012年   11篇
  2011年   13篇
  2010年   4篇
  2009年   2篇
排序方式: 共有80条查询结果,搜索用时 31 毫秒
1.
协作感知技术可提高认知无线电网络中的频谱资源利用率,但网络节点在形成协作感知联盟的同时也不可避免地引入了额外开销,联盟内节点总希望用较少的额外能量开销达到较大的吞吐量期望.为此,文中提出了协作感知系统的多目标非线性优化问题,然后基于联盟博弈理论为该问题构建了一个不可转移支付的联盟构造博弈模型,在其核心的支付函数的设计中,采用线性加权和的方法同时考虑了节点吞吐最期望和能量消耗两个优化目标.基于该函数,提出了一种分布式多目标联盟构造算法DMCF,其核心是根据优超算子所定义的联盟的帕累托顺序,循环地对联盟进行合并和分裂操作.此外,还证明了DMCF的收敛性和最终联盟划分的稳定性.仿真实验的结果表明,DMCF可有效解决提出的多目标优化问题,与一种分布式随机联盟构造算法DRCF相比,DMCF总能使节点消耗较少能量却达到相对较大的吞吐量期望.在不同网络规模下,DMCF可获得的节点平均吞吐量期望可提升约7.5%,而节点平均能量消耗却可降低约70%.  相似文献
2.
In wireless networks, context awareness and intelligence are capabilities that enable each host to observe, learn, and respond to its complex and dynamic operating environment in an efficient manner. These capabilities contrast with traditional approaches where each host adheres to a predefined set of rules, and responds accordingly. In recent years, context awareness and intelligence have gained tremendous popularity due to the substantial network-wide performance enhancement they have to offer. In this article, we advocate the use of reinforcement learning (RL) to achieve context awareness and intelligence. The RL approach has been applied in a variety of schemes such as routing, resource management and dynamic channel selection in wireless networks. Examples of wireless networks are mobile ad hoc networks, wireless sensor networks, cellular networks and cognitive radio networks. This article presents an overview of classical RL and three extensions, including events, rules and agent interaction and coordination, to wireless networks. We discuss how several wireless network schemes have been approached using RL to provide network performance enhancement, and also open issues associated with this approach. Throughout the paper, discussions are presented in a tutorial manner, and are related to existing work in order to establish a foundation for further research in this field, specifically, for the improvement of the RL approach in the context of wireless networking, for the improvement of the RL approach through the use of the extensions in existing schemes, as well as for the design and implementation of RL in new schemes.  相似文献
3.
We investigate a distributed contention-based spectrum access scheme in cognitive radio networks where ON/OFF periods of the channel by primary users follow discrete phase (PH) type distributions. The main motivation for ON/OFF having PH distributions is that the channel activity has a more general behavior depending on the primary users’ traffic. In the past most other researchers assumed that ON/OFF periods of a channel follow a geometric distribution for the purpose of mathematical tractability even though this assumption is restrictive.We propose a distributed medium access control (MAC) scheme for the secondary users (SUs) which is characterized by a constant contention window size and a method to decide whether for each SU to participate in competition or not depending on the queueing delay of a head-of-line (HoL) packet. In order to investigate the performance of our proposed MAC protocol, we construct a two-dimensional Markov chain which incorporates both the proposed MAC scheme and the general channel activity. The resulting one-step transition probability matrix of the Markov chain has a very special structure. With the help of the censored Markov chain method, we provide a computationally efficient method to obtain the stationary distribution of the Markov chain. We then obtain the system capacity, which is defined as the maximum number of SUs that can be accommodated with a quality of service (QoS) guarantee on the packet dropping probability and the packet delay. Numerical examples show that the system capacity considerably depends on the distributions of ON/OFF periods and our proposed MAC scheme achieves a higher capacity than the existing one.  相似文献
4.
一种多信道Ad hoc认知无线电网络密钥交互协议*   总被引:1,自引:0,他引:1       下载免费PDF全文
针对现有密钥协商协议没有考虑Ad hoc认知无线电网络多信道这一缺陷,提出一种多信道密钥协商协议(multi channels key agreement protocol,MCKAP),通过建立多重图和替换广播操作减少信道冲突,优化协商路径提高共享密钥协商效率,利用信道属性为节点间选择合理位置,避免主用户干扰。该方案能有效地利用多信道提高共享密钥协商效率。最后通过理论分析和仿真实验证明该协议适用于Ad hoc认知无线电网络,具有较好的执行效率。  相似文献
5.
Cognitive radio ad hoc networks (CRAHNs) constitute a viable solution to solve the current problems of inefficiency in the spectrum allocation, and to deploy highly reconfigurable and self-organizing wireless networks. Cognitive radio (CR) devices are envisaged to utilize the spectrum in an opportunistic way by dynamically accessing different licensed portions of the spectrum. To this aim, most of the recent research has mainly focused on devising spectrum sensing and sharing algorithms at the link layer, so that CR devices can operate without interfering with the transmissions of other licensed users, also called primary users (PUs). However, it is also important to consider the impact of such schemes on the higher layers of the protocol stack, in order to provide efficient end-to-end data delivery. At present, routing and transport layer protocols constitute an important yet not deeply investigated area of research over CRAHNs. This paper provides three main contributions on the modeling and performance evaluation of end-to-end protocols (e.g. routing and transport layer protocols) for CRAHNs. First, we describe NS2-CRAHN, an extension of the NS-2 simulator, which is designed to support realistic simulation of CRAHNs. NS2-CRAHN contains an accurate yet flexible modeling of the activities of PUs and of the cognitive cycle implemented by each CR user. Second, we analyze the impact of CRAHNs characteristics over the route formation process, by considering different routing metrics and route discovery algorithms. Finally, we study TCP performance over CRAHNs, by considering the impact of three factors on different TCP variants: (i) spectrum sensing cycle, (ii) interference from PUs and (iii) channel heterogeneity. Simulation results highlight the differences of CRAHNs with traditional ad hoc networks and provide useful directions for the design of novel end-to-end protocols for CRAHNs.  相似文献
6.
提出了两个Ad hoc认知无线电网络中基于能量优化的组播路由启发式算法。一个是基于经典的最短路径树的组播算法(shortest path tree algorithm,SPTA),另一个是基于能量函数的组播启发式算法(energy function based heuristic algorithm,EFHA)。这两个算法都在考虑了认知无线电网络特性的基础上建立能量优化的组播树,从应用例子可以看出, EFHA算法明显优于SPTA算法,并且复杂度较低。  相似文献
7.
基于最短时延的认知无线电网络安全路由算法   总被引:1,自引:0,他引:1       下载免费PDF全文
针对认知无线电网络可用频谱动态变化和路由过程中出现的安全问题,提出将最短数据传输时延和高安全等级路由作为选路标准,设计了一种跨层路由选择算法。算法通过优化转发节点个数和各转发节点接收、发送数据信道来减少数据传输时延。通过选择具有高安全级别的转发节点来保证路由的安全性。理论分析表明算法是高效和可行的。它的时间复杂度是O(N2),其中N是拓扑图中节点的个数。  相似文献
8.
Cognitive radio networks are envisioned to drive the next generation wireless networks that can dynamically optimize spectrum use. However, the deployment of such networks is hindered by the vulnerabilities that these networks are exposed to. Securing communications while exploiting the flexibilities offered by cognitive radios still remains a daunting challenge. In this survey, we put forward the security concerns and the vulnerabilities that threaten to plague the deployment of cognitive radio networks. We classify various types of vulnerabilities and provide an overview of the research challenges. We also discuss the various techniques that have been devised and analyze the research developments accomplished in this area. Finally, we discuss the open research challenges that must be addressed if cognitive radio networks were to become a commercially viable technology.  相似文献
9.
We propose a new priority discipline called the T-preemptive priority discipline. Under this discipline, during the service of a customer, at every T time units the server periodically reviews the queue states of each class with different queue-review processing times. If the server finds any customers with higher priorities than the customer being serviced during the queue-review process, then the service of the customer being serviced is preempted and the service for customers with higher priorities is started immediately. We derive the waiting-time distributions of each class in the M/G/1 priority queue with multiple classes of customers under the proposed T-preemptive priority discipline. We also present lower and upper bounds on the offered loads and the mean waiting time of each class, which hold regardless of the arrival processes and service-time distributions of lower-class customers. To demonstrate the utility of the T-preemptive priority queueing model, we take as an example an opportunistic spectrum access in cognitive radio networks, where one primary (licensed) user and multiple (unlicensed) users with distinct priorities can share a communication channel. We analyze the queueing delays of the primary and secondary users in the proposed opportunistic spectrum access model, and present numerical results of the queueing analysis.  相似文献
10.
针对认知无线电网络中协作频谱感知使能耗增加而降低网络寿命的问题,提出了一种双阈值能量检测的协作频谱感知方案.利用基于双阈值的能量检测方法最大化网络吞吐量,使能耗低于一个阈值同时保护主用户不受次用户的干扰.利用凸优化分析来获得感知时间和检测阈值的最佳值.仿真结果表明,方法能有效权衡网络吞吐量与能量效率之间的关系,相比传统的频谱感知方法,具有明显的优越性.  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号