一种支持服务区分的动态频谱接入机制

动态频谱接入技术是实现认知无线电(CR)网络的重要技术之一,其可以灵活地对频谱空洞加以利用并能够有效地缓解频谱紧缺的窘境。文章设计了一种支持服务区分的动态频谱接入机制,将次用户分为高优先级次用户和低优先级次用户;然后利用强制优先排队理论对认知无线电网络中有服务区分的动态频谱接入过程进行模拟建模,并对高优先级次用户和低优先级次用户的切换率、接入失败率进行了仿真分析,这些因子对于用户的接入性能起着关键性作用。     

基于认知无线电技术的动态频谱接入

文章介绍了基于认知无线电的动态频谱接入技术,并对其网络架构、关键技术以及目前的研究现状进行了详细分析。在此基础上探讨了动态频谱接入网络中采用跨层协议设计方法的必要性。     

动态自适应频谱的接入策略研究

认知无线电技术利用非授权频谱资源进行业务传输,缓和了目前通信业务飞速发展与频谱资源稀缺的矛盾。动态频谱接入技术通过感知频带,使认知用户能够伺机接入未被主用户占用的频谱空洞。但是在接入过程中,特别是在多个认知用户竞争接入相同的可用频谱资源时,往往面临认知用户间的冲突和各认知用户的QoS得不到保证的问题。文章重点介绍了目前国内外在多个认知用户接入策略上的一些研究成果,并对这些成果进行分析,提出了今后需要进一步研究的方向。     

动态频谱技术接入研究

目前认知无线电技术受到了极大的关注,其中的动态频谱分配问题是不得不面对的一个问题.讨论了动态频谱接入的分类,尤其是讨论了机会式频谱接入,包括其基本组成以及各组成部分的功能,并提出了实现这些功能的过程中遇到的挑战.将对今后动态频谱接入的进一步研究起到积极的促进作用.     

认知无线电中的频谱接入技术

认知无线电是一种基于软件无线电的智能通信系统,它能够认知周围环境,并能通过一定的方法相应地改变某些工作参数来实时地适应环境,从而达到提高频谱利用率、缓解频谱资源紧张的目的.授权频段的频谱利用问题是认知无线电实现的关键技术之一.研究了授权频段的两种频谱利用方法:动态频谱接入和基于动态频谱接入模型之一的机会频谱接入.     

一种基于认知无线电的动态频谱接入MAC方案

在传统的无线通信系统中,频谱的分配是固定的。但是由于通信过程的突发性,这些频谱的使用率很低。另一方面,随着无线通信和多媒体的高速发展和广泛应用,无线频谱资源日趋紧张。如何提高频谱利用率已经成为迫切需要解决的问题。一种可行的思路是把这些授权频谱向未授权用户开放,未授权用户采用动态频谱接入技术,在不对授权用户造成干扰的前提下使用频谱。本文以认知无线电技术(Cognitive Radio,CR)为基础,提出了一种基于CR的动态频谱接入MAC方案(CR-Ad Hoc-MAC)。该方案允许未授权用户自适应地选取可用带宽,实现了动态频谱接入,有效地提高了频谱利用率。     

动态频谱接入技术的分类和研究现状

动态频谱接入是认知无线电技术的一种重要应用,它利用通信过程中出现的频谱空洞机会式地接入频谱,能极大地提高频谱的利用效率.文章介绍了动态频谱接入的一种分类方法,重点分析了该分类中三个模型的特征、关键技术,以及在美国下一代(XG)无线通信计划、IEEE 802.22标准和欧洲端到端效率(E3)项目中对于动态频谱接入技术的研究现状,最后探讨了动态频谱接入技术的应用前景.     

一种短波动态频谱接入系统的设计

为了有效利用空闲频谱,提高短波频段频谱资源的利用率,采用TMS320VC5502为信号处理核心,TLV320AIC10为输入模拟信号滤波和A/D转换芯片的一种短波动态频谱接入系统的设计,并完成了相应的软件开发。实验结果表明:所设计系统的平均建链时间小于10 s,建链概率大于92%。当数据传输速率为600 baud时,报文的正确接收概率大于90%;数据传输速率为1200 baud时,报文的正确接收概率大于80%。而且平均错误字符的概率达到10-4数量级,能够充分满足短波普通通信业务的需求。     

基于动态频谱接入的应急移动通信系统

新兴的动态频谱接入(DSA)技术可以解决频谱稀缺问题.本文在研究荷兰典型的下一代应急网络xGEN的基础上,分析了DSA在应急通信网络中的应用需求,设计了分级混合网络架构的DSA应急移动专用通信网络及其基于软件无线电(SDR)平台的快速可重配置的应急终端结构,并探讨了DSA设备特有的动态频谱管理功能实现的关键技术.     

应急通信网络的动态频谱接入方案研究

利用认知无线电的动态频谱接入技术,提高应急通信网络在突发事件中的反应效率已成为无线通信领域的研究热点。对认知无线电的几种动态频谱接入方案进行了探索及研究。由分析可知,选择合适的接入方案,将会形成认知用户间的良性竞争,降低CR业务的通信中断率,从而增大系统的吞吐量,提升整个系统的性能。     

Initial spectrum access control with QoS protection for active users in cognitive wireless networks

In this paper, an initial spectrum access control algorithm for cognitive wireless networks was studied. The objective was to maximize the number of admitted secondary users (SUs) under the constraints of interference temperature at multiple measurement points (MPs), while providing active SUs' QoS protection (AQP). Here, AQP means that the signal‐to‐interference‐plus‐noise ratios (SINRs) of all active SUs will not fluctuate below some predefined thresholds during a new SU's initial spectrum access process. To this end, we proposed a new distributive power control algorithm in conjunction with a simple alarm mechanism that ensures the interference temperatures at multiple MPs to be always below their thresholds during the initial spectrum access process. Then, two realizations of the spectrum access algorithms, namely, D‐AQP and C‐AQP, according to whether the MPs can act as local controllers or not, were presented. In the D‐AQP algorithm, each SU updates its transmit power distributively based on the local information including the current SINR, the QoS requirement, and the indicator from the MPs so that the resultant SINRs of the active SUs are able to stay above the predefined thresholds. Whereas in the C‐AQP algorithm, apart from the same procedure as mentioned, each MP is supposed to be able to decide which new SU should quit the initial spectrum access process so as to protect the communication quality of the primary system. Finally, the performances of the proposed algorithms were validated by extensive simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

支持紧急通信的无线认知网络频谱接入方法

提出了支持应急通信的无线认知网络机会频谱接入模型。首先按照离散时间完全和限定(k=1)服务两级轮询策略实现主用户和次用户对频谱的共享。其次,通过在数据确认中捎带轮询列表信息方式实现数据传输和用户调度的并行处理,减少用户切换造成的时延浪费。通过建模分析得出网络吞吐量及用户平均等待时延的精确解析,结果表明本方案能有效抑制次用户对主用户通信质量的影响,又能增加网络吞吐量并为通信业务提供时延保障。     

无线网格网

无线网格网是一种新型的分布式网络，它融合了WLAN和AdHoc网络两者的优势，成为无线宽带接入的一种有效手段。详细介绍了无线网格网的概念、特点、应用需求、与其他无线宽带接入的区别和关键技术方案等方面的问题。     

一种改进的认知无线电频谱接入策略

认知无线电（Cognitive Radio）网络中,次用户在不干扰主用户的情况下即时接入检测到的空闲频谱以提高频谱资源的利用率。基于部分可观测马尔科夫决策过程的最优频谱接入算法计算复杂度较高,而基于贪婪算法的次优接入策略具有自私性,都不能有效的提高频谱利用率。本文提出一种新的频谱接入算法,该算法对贪婪算法的自私性进行了改进。由于贪婪算法只关注信道当前时隙的瞬时奖励值,导致最大奖励值相同的信道可能会有多个,因此给瞬时奖励值加上这些信道下一时隙的奖励值后重新选择,直至次用户选择出奖励值最大的一个信道。仿真结果表明,相比于传统的贪婪算法,改进算法虽然增加了一些计算复杂度,但有效提高了系统的吞吐量。     

Multi-channel transmission strategy for dynamic spectrum access

Cognitive radio is a promising technology that deals with the scarcity of radio spectrum. In this paper, we propose a new multi-channel transmission strategy for dynamic spectrum access in cognitive radio network. Starting with the model of spectrum activities, we present the multi-channel transmission strategy which has primary user’s protection mechanism to improve the spectrum efficiency and study its performance under perfect and imperfect sensing. Numerical example results reveal that the performance of the proposed strategy has the superiority with respect to capacity performance of cognitive users and the protection of primary users.     

MaxDiv: an optimal randomized spectrum access with maximum diversity scheme for cognitive radio networks

Cognitive radio network (CRN) is an emerging technology that can increase the utilization of spectrum underutilized by primary users (PUs). In the literature, most exiting investigations on CRNs have focused on how secondary users (SUs) can coexist harmlessly with the PUs. Despite the importance of such a coexistence issue, it is also crucial to investigate the coexistence of SUs because (i) the PUs usually rarely use the licensed spectrum and (ii) the advantages of CRN will significantly increase the number of SUs in the future. To address this challenging issue, we propose, in this paper, an optimal randomized spectrum access scheme, whose main ideas include the following: (i) an SU shares its sensing results with neighboring SUs and (ii) with the regional sensing results, an SU will access available channels with a non‐uniform probability distribution. We first formulate a multichannel optimal randomized multiple access (MC‐ORMA) problem that aims to maximize the throughput of the CRN; we then develop efficient distributed algorithms to solve the MC‐ORMA problem; we derive the closed‐form value of collision probability for each SU; and finally, we conduct extensive numerical experiments and compare our theoretical analysis with simulation results to demonstrate the advantages of our scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

ATMAC: adaptive token‐based medium access control protocol for cognitive radio wireless mesh network

In next generation wireless communication, cognitive radio technology facilitates to utilize underutilized licensed frequency bands that help to enhance the spectrum utilization. Cognitive radio wireless mesh network (CRWMN) is a promising and reliable technology to experience high throughput with low cost. Existing IEEE 802.11 based medium access control (MAC) protocols offer high data rates with decreasing efficiency at the MAC layer. Hence, most of the researchers applied aggregation mechanisms to provide the solution to bandwidth craving applications. In CRWMN, MAC design is significant because stability, efficient resource utilization, and scalability are predominating problems; however, the specified MAC issues are not yet resolved. The proposed MAC is novel, which aims to ensure reliability and scalability for CRWMN. The common control channel is used to exchange handshaking frames between the transmitter and receiver. It helps us to schedule the data transmission as well as reserve the channel in a discrete time interval. It introduces a token‐based channel accessing mechanism with resource‐aware channel assignment, which resolves the problems of efficiency and stability. The proposed MAC simulated using the network simulator (ns‐2), and the simulation results demonstrate that the proposed protocol improved the performance compared with the existing protocols.     

Spectrum resource allocation method of maximizing transmission rate in cognitive heterogeneous wireless networks

Aiming at the problem that it is difficult to allocate spectrum resources to secondary users efficiently in cognitive heterogeneous wireless networks with heterogeneous spectrum attributes,dynamic channel conditions and diverse service requirements,a spectrum resource allocation strategy with maximum transmission rate was proposed.Firstly,the strategy aimed at maximizing the total transmission rate,and constrained the limited spectrum resources and user service requirements to construct a non-linear multi-constrained spectrum resource allocation 0-1 planning model.Then a polynomial time complexity simplification method was designed.According to idle spectrum information,channel conditions,business requirements and allocation decision history information,and the benefit matrix was constructed and modified to achieve constraint simplification,and the execution efficiency was improved by improving the coefficient matrix transformation strategy of the traditional Hungarian algorithm.Finally,the performance of the method was compared and analyzed by experiments.Experimental results show that the proposed method has higher transmission rate and execution efficiency.     

认知无线Mesh网络中基于马氏决策模型的MAC协议

为解决认知无线Mesh网络中专用控制信道较难获得的问题,提出一种基于POMDP的机会式频谱接入MAC协议,在不需要中心控制器和专用控制信道的协调下,实现动态频谱感知和接入。仿真结果表明,基于POMDP的接入策略能够有效提高网络频谱利用率和吞吐量,性能最优,而基于贪心算法的接入策略,在降低计算复杂度的同时,获得了较好的性能,实用性较强。