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认知无线电频谱切换目标信道访问机制 总被引:1,自引:0,他引:1
针对认知无线电先应式决策频谱切换,该文提出按照信道平均空闲时间递减的顺序对目标信道进行访问的机制,证明了该机制在主用户信道空闲时间服从均匀分布、Rayleigh分布以及Weibull分布下均能够保证频谱切换失败概率最小。仿真结果表明所提机制得到的频谱切换失败概率要远远小于随机访问机制的切换失败概率。另外,当能够获得数十次信道空闲时间观测样本情况下,虽然存在估计误差,但所得频谱切换失败概率与理想最优频谱切换失败概率非常接近。 相似文献
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为了简化分析认知无线电系统中授权用户享有更高优先级对认知用户造成的影响,该文将2维生灭排队过程等效为1维非占先排队模型进行分析;并在多信道情景下,提出了一种基于信道收益的阶梯式排队接入方案,给出了由队列结构系数决定的系统性能参数阻塞概率及强制中断率的解析结果。仿真与数值计算验证了等效1维非占先排队模型的有效性;同时比较几种排队机制的性能参数,该文接入方案有较低的阻塞率,并且可根据系统环境自适应调整队列结构将强制中断率控制在较低范围内,不会随系统负荷率增高而增高。 相似文献
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无线局域网MAC层信道利用效率分析 总被引:1,自引:1,他引:1
基于IEEE802·11g的WLAN的标称速率高达54Mb/s,而实际数据传输速率只有20Mb/s左右。从成帧效率、信道共享效率和冲突避免效率的角度对IEEE802·11g的MAC层信道利用效率进行了分析,得出这种基于CSMA/CA机制的MAC层信道利用效率较低。实测结果验证了分析结论的有效性。 相似文献
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针对认知无线电网络可用信道资源随时间和空间环境变化的特点,分析了认知无线电网络MAC协议面临的问题,提出了一种基于全局控制信道的MAC协议方案,在此基础上阐述了两种接入方式及相应适用场合,实现了认知无线电节点对可用信道资源变化的感知,可为认知无线电MAC协议研究及应用提供参考. 相似文献
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基于信道分类和自适应调制编码的认知无线电决策引擎 总被引:1,自引:0,他引:1
在多径信道条件下,针对单载波频域均衡(SC-FDE)认知系统不能通过多目标优化策略进行决策的问题,该文提出一种基于信道分类和自适应调制编码(AMC)的认知无线电决策引擎。该决策引擎首先对当前信道进行分类,确定当前信道状态;然后根据当前信道状态下的策略切换表选取最优传输策略(MCS),并计算该策略的使用时长(MCSD)。一旦当前策略的持续时间超过了其使用时长,认知决策引擎就会对最优策略进行更新。仿真结果表明,该决策引擎能够提供最优的传输策略以提高频谱效率,使SC-FDE认知系统更好地适应无线信道复杂的电磁环境。 相似文献
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传统的认知无线电技术采用机会频谱接入,认知用户的通信质量难以得到保证。通过利用多天线技术提供的空间信号处理能力,该文提出一种基于空分复用的机会频谱接入方法,当存在频谱空洞时,采用传统的机会频谱接入;无空闲频率资源可用时,认知系统利用空域信息完成发射预编码与接收滤波,从而以空分复用的方式实现通信。文中对认知系统天线配置要求进行了分析,当满足该要求时,认知系统能够与授权系统在同一授权频道实现无互扰共存。仿真结果表明,与传统的机会频谱接入相比,所提方法能够在不影响授权系统性能的情况下有效改善认知系统的通信性能。 相似文献
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Cognitive radio and dynamic spectrum sharing systems use innovative spectrum management techniques that allow different systems to share the same frequency band to utilize the radio spectrum in an efficient way. In this paper, we propose a novel cognitive media access control protocol for cognitive radio networks under the property‐rights model, in which secondary users are divided into several nonoverlapping groups, and each group uses the proposed auction algorithm to bid for required channels from the auctioneer appointed by primary users. Simulations indicate that our proposed media access control protocol can effectively utilize spectrum resources, achieve high system efficiency, and guarantee the fairness of channel allocation among groups. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Contention-based medium access control (MAC) protocol is a key component for the success of wireless data networks. Conventional random access protocols like ALOHA and Carrier Sense Multiple Access (CSMA) suffer from packet collision which leads to low throughput. Aimed at improving the throughput performance, we propose to integrate erasure coding with contention-based MAC protocols for recovering collided packets. To demonstrate the effectiveness of this approach, we focus on combining erasure coding with slotted ALOHA and slotted non-persistent CSMA in this paper. The performances of the resulting protocols are evaluated by both analytical model and simulation. Simulation results match very well with analytical results and show that the system throughput is increased for low to medium traffic loading. Packet loss ratio is also improved considerably with our scheme when the maximum number of packet retransmission times is limited. However, the delay for our scheme is higher due to the longer waiting time in our scheme for recovering collided packets. It is also shown that delay can be significantly reduced if we choose appropriate coding parameters though throughput will be sacrificed. 相似文献
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无线传感器网络及其MAC层协议 总被引:5,自引:0,他引:5
无线传感器网络(WSN)是当今信息领域的一大研究热点,在军事、环境、医疗护理和智能家居等方面有着广阔的应用前景,引起了世界各国的广泛关注。首先介绍了无线传感器网络的相关理论知识,然后对无线传感器网络目前所采用的典型的MAC协议按类型进行了介绍。 相似文献
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O. León J. Hernández‐Serrano M. Soriano 《International Journal of Communication Systems》2010,23(5):633-652
Cognitive radio is a promising technology aiming to improve the utilization of the radio electromagnetic spectrum. A cognitive radio device uses general purpose computer processors that run radio applications software to perform signal processing. The use of this software enables the device to sense and understand its environment and actively change its mode of operation based on its observations. Unfortunately, this solution entails new security challenges. Our objective in this paper is to analyze the security issues of the main recent developments and architectures of cognitive radio networks. We present vulnerabilities inherent to those systems, identify novel types of abuse, classify attacks, and analyze their impact on the operation of cognitive radio‐based systems. Moreover, we discuss and propose security solutions to mitigate such threats. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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针对具有连续性接入需求的业务,论文融合时分多址接入技术和竞争窗口差分服务机制,提出了具有连续性保障的无线接入协议:CP-MAC(MAC with Continuity Provisioning)协议.通过对业务等级划分,保障了连续用户的接入概率.并基于Markov模型,给出了非饱和认知无线电网络的系统容量,接入时延和被阻塞概率的数学解析式.最后,通过与现存的MAC接入协议比较,CP-MAC协议在不降低系统容量的同时,提高了连续用户的接入概率,并降低了其接入时延. 相似文献
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The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR‐MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR‐MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR‐MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Zhijin Zhao Shiyu Xu Shilian Zheng Junna Shang 《Wireless Communications and Mobile Computing》2009,9(7):875-881
One of the basic capabilities of cognitive radio is to adapt the radio parameters according to the changing environment and user needs. This paper proposes a new adaptation method which uses particle swarm optimization (PSO) to optimize cognitive radio parameters given a set of objectives. The procedure of the proposed method is presented and multicarrier system is used for simulation analysis. Experimental results show that the proposed method performs far better than genetic algorithm (GA)‐based adaptation method in terms of convergence speed, converged fitness values, and stability. The proposed method can also provide the tradeoffs of the objective functions, and the resulting parameter configuration is consistent with the weights of the objective functions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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针对认知无线多跳网中频谱资源具有较大时变性及差异性的问题,设计了一种结合QoS查找的跨层多信道MAC协议。该协议将按需QoS查找与动态频谱分配跨层相结合,仅让参与传输的节点执行频谱分配并按QoS要求获取频谱资源。此外,协议使用频分双工收发机实现了对公共控制信道的不间断监听,并设计了一套支持不同数量收发机节点间混合通信的接入算法。大量仿真结果表明,该协议能有效保证对端到端传输的QoS要求的满足,并显著提高端到端吞吐量及时延。 相似文献