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。     

基于信道获益和业务实时性的频谱切换策略

为了尽可能地降低认知无线电频谱切换的次数,更加全面地考虑通信环境里的因素,引入模糊控制技术,提出一个可行的频谱切换策略。首先,认知用户接收方根据信噪比和主用户活动性估计信道获益,再通过信道反馈机制将结果值告知认知用户发送方;最后,认知用户发送方将业务分成两类：实时业务与非实时业务,并将信道获益与业务实时性作为两个新参数纳入频谱切换策略。仿真结果显示,与随机选择策略相比,根据信道获益选择信道可以明显降低认知用户的切换率。另外,将业务进行分类,非实时用户与实时用户相比有更低的切换可能性,这种差距可以达到32%。     

QoS保证的多信道混合接入CRN频谱共享策略设计

根据既不对主用户(Primary Radio user,PR)产生干扰,又对认知无线电用户(Cognitive Radio user,CR)提供QoS保证的原则,将认知无线电网络(Cognitive Radio Network,CRN)中多信道接入频谱共享问题建模为混合整数非线性规划。采用多级功率限制保证PR不被干扰,以CR物理层能够提供的速率作为信道和功率分配的依据,提出将能够为CR提供最大传输速率的信道分配给该CR的分配策略,将混合整数非线性规划转化为整数线性规划,并给出集中式启发算法和基于功率速率比(Power Rate Ratio,PRR)最小的分布式启发算法求解该整数线性规划。仿真结果表明,文中给出的算法能够提供较高的CRN吞吐量和较好的CR用户QoS保证。     

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。     

认知mesh网络服务区分的动态频谱接入策略

动态频谱接入策略是实现认知无线电网络高效利用频谱的关键。与传统认知无线电网络不同,认知mesh网络中不同QoS需求的多类型业务共同接入,为适应这一特点,提出服务区分的动态频谱接入策略。策略依据业务的QoS需求确立优先级,针对不同优先级业务采取不同的信道接入方案,实时业务依据最优传输延迟期望选择接入信道集合,在减小传输延迟的同时降低数据传输过程授权用户出现的概率,普通业务选择最优理想传输成功概率的信道,降低信道切换概率。理论与实验结果表明,与传统的认知网络频谱接入策略相比,提出的策略能提供不同业务的服务区分,满足实时业务的低延迟需求,降低数据传输的中断率,同时在授权信道空闲率与网络负载较大时吞吐量性能较优。     

异构频谱环境下基于协商的机会频谱接入策略

文章在异构频谱环境下的分布式认知无线网络中,提出了一种基于协商（可用频谱信息交互）的机会频谱接入策略,对该策略的原理作了详细阐述。仿真结果表明,相比于随机信道选择接入机制,该频谱接入策略在吞吐量性能上有明显提升。     

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。     

浅谈基于认知无线电的机会频谱的接入技术

目前,宽带无线业务正在不断增多,其中,影响无线通信发展的一大问题就是频谱资源非常稀少。但是,在某段频谱资源上具有很多的业务,而其他频段的使用效率却比较低。因此,我们就提出了认知无线电技术,进一步改善了无线环境,使频谱资源提高了利用率。     

Q学习算法在机会频谱接入信道选择中的应用

针对“先听后传”的机会频谱接入中认知用户的信道选择问题,本文提出了一种基于Q学习的信道选择算法。在非理想感知的条件下,通过建立认知用户的信道选择模型并设计恰当的奖励函数,使智能体能够与未知环境不断交互和学习,进而选择长期累积回报最大的信道接入。在学习过程中,本文引入了Boltzmann实验策略,运用模拟退火思想实现了资源探索与资源利用之间的折衷。仿真结果表明,所提算法能够在未知环境先验知识条件下可以快速选择性能较好的信道接入,有效提高认知用户的接入吞吐量和系统的平均容量。      

基于Q-Learning的机会频谱接入算法

针对认知无线电在动态信道业务特征场景下的机会频谱接入问题进行研究。将Q-Learning理论应用于频谱接入问题,提出一种基于Q-Learning的适用于动态信道业务特征的机会频谱接入算法。该算法中认知用户通过与外部环境进行交互和迭代来获取信息,从而选择适当的接入策略来降低频谱冲突率。通过将Q-Learning中学习速率设置为动态变化值,使得算法可以在外部环境特征发生改变后快速地再次收敛。仿真结果表明,该算法可以使认知用户在频谱环境未知的情况下选择更加空闲的频段,有效降低频谱冲突率,同时明显提高了动态信道业务特征场景下的收敛速度。     

The BMAP/G/1 Queue with Level-Dependent Arrivals – An Overview

The BMAP/G/1 queue is a field of intensive research since several years. We generalize the BMAP/G/1 queue by allowing the arrival process to depend on the state (level) of the queue, i.e., on the number of customers in the system. This will be called a BMAP/G/1 queueing system with level-dependent arrivals. A suitable arrival process is defined by nesting a countable number of BMAPs.We give conditions for the level-dependent BMAP/G/1 queue to be stable, i.e., in equilibrium. By analysing the fundamental periods, which now depend on their starting level, we determine the stationary queue length at service completion times and at an arbitrary time.     

Spectrum Co-existence of IEEE 802.11b and 802.16a Networks Using Reactive and Proactive Etiquette Policies

This paper presents an investigation of spectrum co-existence between IEEE 802.11b and 802.16a networks in the same shared frequency band using cognitive radio techniques with different levels of complexity. Simple reactive interference avoidance algorithms as well as proactive spectrum coordination policies based on etiquette protocols are proposed and compared in terms of achievable spectrum efficiency in a shared Wi-Fi/Wi-Max scenario. In reactive interference avoidance methods, radio nodes coordinate spectrum usage without exchange of explicit control information—this is done by adaptively adjusting transmit PHY parameters such as frequency, power and time occupancy based on local observations of the radio band. Because local observations provide information only about transmitters, they may not be sufficient for resolving spectrum contention in scenarios with “hidden receivers”. Proactive coordination techniques solve the hidden-receiver problem by utilizing a common spectrum coordination channel (CSCC) for exchange of transmitter and receiver parameters. Radio nodes can cooperatively select key PHY-layer variables such as frequency and power by broadcasting messages in the CSCC channel and then following specified spectrum etiquette policies. An ns2 simulation model is developed to evaluate both reactive and proactive etiquette policies in scenarios with co-existing IEEE 802.11b and 802.16a networks. The density of radio nodes in the coverage region, and their degree of spatial clustering are key parameters in the system evaluation. Detailed simulation studies were carried out for a variety of scenarios including both single and multiple 802.11b hotspots per 802.16a cell with and without spatial clustering. Our results show that simple reactive algorithms can improve system throughput when sufficient “free space” (in frequency, power or time) is available for PHY adaptation. In more congested scenarios with spatially clustered nodes and hidden receivers, the proposed CSCC etiquette can significantly improve overall system performance over reactive schemes. Research supported by NSF grant # CNS-0435370 and #0205362. Paper submitted for publication after presentation in part at IEEE DySpan 2005, Nov. 8–11, 2005, Baltimore, MD. Xiangpeng Jing received the B.S. degree in Electrical Engineering from Peking University, Beijing, P. R. China in 2000 and the M.E. degree in Electrical Engineering from City College of City University of New York, New York in 2002. He is currently a Ph. D. candidate in the WINLAB (Wireless Information Network Laboratory), Rutgers University, NJ. He has been with the MobiNet Group since 2002. His research interests include spectrum etiquette protocols, co-existence between wireless communication systems, cognitive radio technologies, and adaptive wireless ad hoc networks. Dipankar Raychaudhuri is Professor, Electrical & Computer Engineering Department and Director, WINLAB (Wireless Information Network Lab) at Rutgers University. As WINLAB’s Director, he is responsible for a cooperative industry-university research center with focus on next-generation wireless technologies. WINLAB’s current research scope includes topics such as RF/sensor devices, UWB, spectrum management, future 3G and WLAN systems, ad-hoc networks and pervasive computing. He has previously held progressively responsible corporate R&D positions in the telecom/networking area including: Chief Scientist, Iospan Wireless (2000-01), Assistant General Manager & Dept. Head-Systems Architecture, NEC USA C&C Research Laboratories (1993–99) and Head, Broadband Communications Research, Sarnoff Corp (1990–92). Dr. Raychaudhuri obtained his B.Tech (Hons) from the Indian Institute of Technology, Kharagpur in 1976 and the M.S. and Ph.D. degrees from SUNY, Stony Brook in 1978, 79. He is a Fellow of the IEEE.     

基于分形盒维数的频谱感知技术研究

为了降低频谱感知的计算复杂度,提高感知性能,该文提出基于分形盒维数的频谱感知方法。由于噪声与信号盒维数值存在差异,将分形盒维数作为检验统计量。仿真结果表明,该方法在高斯白噪声环境下,具有良好的检测性能,对噪声不敏感。并且计算复杂度低,易工程实现。     

Cyclo-energy detector for spectrum sensing in cognitive radio

In this paper, a cyclo-energy detector is proposed for the spectrum sensing problem based on the cyclostationary signal analysis. The proposed detector can determine the existence of primary user by estimating the primary user's received power according to the cyclostationarity features of the secondary user. By using this detector, the secondary user does not need to stop transmitting signals when sensing the frequency spectrum. Simulation results are presented to confirm the performance of the proposed detector.     

On the M/G/1 queueing system with multiclass customers and fixed feedback

The M/G/1 queueing system with multiclass customer arrivals, fixed feedback, and first come first served policy is considered, where different classes of customers have different arrival rates, service-time distributions, and feedback numbers. The joint probabifity generation function of queue size of each class and the Laplace-Stieltjes transform of the total sojourn time of a customer in each class are presented, which extended the results obtained by Choi B D. The mean queue size of each class and mean total sojourn time of a customer in each class are obtained with this result. The results can be used in computer and communication networks for their performance analysis.     

一种基于博弈论的认知CDMA频谱分配机制

针对认知无线电的频谱资源分配问题,提出了一种考虑认知用户间相互干扰行为的完全信息博弈模型。在最大化认知用户传输速率的条件下为其分配子载波以及功率,并且证明了纳什均衡的存在。仿真结果表明,该算法合理地对认知用户的效用函数进行了设计,算法能够很好地满足不同认知用户的速率需求,符合实际通信环境。提高了通信系统容量,并且能够较快地达到均衡状态以及具有较好的收敛性。     

Particle swarm optimization applied to a spectrum sharing problem

It is recognized that the centralized approach to spectrum management currently used in most countries has led to highly inefficient allocations. It means available spectrum regulated by Static Spectrum Allocation Policy is underutilized over certain bands while in others remain scarce. In this context, spectrum sharing techniques are proposed to recycle bands in order to solve the problem of spectrum scarcity and use the limited spectrum resource as effectively as possible. Due to spectrum sharing is a complex issue; in this work we proposed a heuristic optimization approach applying particle swarm optimization (PSO) to maximize the sum throughput for the maximum number of secondary links that can be admitted to the network under interference constraints.     

基于OFDM符号宽度的循环平稳频谱感知方法

该文提出一种新的基于OFDM符号宽度的感知方法。该方法首先对接收到的每个OFDM符号在其符号周期内进行循环自相关函数的估计,然后利用多元统计理论计算判决量和判决门限,最后将判决量和判决门限进行比较从而得到判决结果。该方法是非参数化的,因而能够在噪声不确定的情况下有效工作,并且该方法能够极大简化目前循环平稳感知类算法的复杂度而只有细微的性能损失。此外,该文接着又提出一个非参数化多天线线性加权合并感知方法。仿真结果表明,所提合并方法通过合理地非参数化优化加权系数,与传统循环平稳感知方法相比,在复杂度显著降低的同时,性能几乎与传统循环平稳感知方法一致。