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。     

Optimal Transmission Strategies for Dynamic Spectrum Access in Cognitive Radio Networks

Cognitive radio offers a promising technology to mitigate spectrum shortage in wireless communications. It enables secondary users (SUs) to opportunistically access low-occupancy primary spectral bands as long as their negative effect on the primary user (PU) access is constrained. This PU protection requirement is particularly challenging for multiple SUs over a wide geographical area. In this paper, we study the fundamental performance limit on the throughput of cognitive radio networks under the PU packet collision constraint. With perfect sensing, we develop an optimum spectrum access strategy under generic PU traffic patterns. Without perfect sensing, we quantify the impact of missed detection and false alarm, and propose a modified threshold-based spectrum access strategy that achieves close-to-optimal performance. Moreover, we develop and evaluate a distributed access scheme that enables multiple SUs to collectively protect the PU while adapting to behavioral changes in PU usage patterns. Our results provide useful insight on the trade-off between the protection of the primary user and the throughput performance of cognitive radios.     

基于预留最优信道机制的CR动态频谱接入研究

在认知无线电网络中,如何提高次用户的性能是当前研究的热点。针对等级覆盖式频谱接入模型进行研究分析,考虑了动态频谱切换过程,建立三维的持续时间马尔可夫链模型,计算出切换概率、阻塞概率、掉线概率,并综合分析各个参数对这些概率的影响。同时提出为主用户预留最优信道数的方案,数值结果表明此方案能有效降低次用户的切换概率和掉线概率,使次系统的切换概率、阻塞概率、掉线概率更加均衡,且提高了次用户系统的接入容量。     

Modified 802.11‐Based Opportunistic Spectrum Access in Cognitive Radio Networks

In this letter, a modified 802.11‐based opportunistic spectrum access is proposed for single‐channel cognitive radio networks where primary users operate on a slot‐by‐slot basis. In our opportunistic spectrum access, control frames are used to reduce the slot‐boundary impact and achieve channel reservation to improve throughput of secondary users. An absorbing Markov chain model is used to analyze the throughput of secondary users. Simulation results show that the analysis accurately predicts the saturation throughput.     

基于认知无线电技术的动态频谱管理构想

本文介绍了认知无线电的感知、分配及共享等相关技术,并针对其技术特点提出了一种以无线电管理机构为感知主体,基于认知无线电技术进行统筹分配的动态频谱管理构想。     

Secondary Spectrum Access in Cognitive Radio Networks Using Rateless Codes over Rayleigh Fading Channels

In this paper, we propose secondary relaying schemes in cognitive spectrum leasing. In the proposed protocols, a primary transmitter uses rateless code to transmit its data to a primary receiver. In the secondary network, \(M\) secondary transmitters are ready to help the primary transmitter forward the data to a primary receiver so that they can find opportunities to transmit their data. For performance evaluation, we derive the average outage probability, the average number of encoded packets transmitted by the primary transmitter, the average number of remaining time slots for secondary network and the average capacity of the secondary network over Rayleigh fading channels. Various Monte-Carlo simulations are presented to verify the derivations.     

动态频谱接入网络的路由技术研究

新一代宽带无线通信网络迫切需要引入认知无线电技术以提升系统性能。针对动态频谱接入(DSA)的无线网络环境,首先探讨了其路由技术研究所面临的新挑战,然后以体现动态频谱管理特征的独特分类方式,分析了其路由技术研究的最新进展,最后展望了路由技术研究的未来发展方向。     

基于主动频谱感知接入的认知无线电台研究

讨论了所研制的工作于30-512 MHz的基于主动频谱感知接入的认知无线电台。该电台实现了认知无线电动态频谱接入最为关键的几大功能：频谱感知、频谱会合、频谱监视,以及频谱切换。试验结果表明,该电台具备在不依赖于公共控制信道的情况下自动寻找空闲信道建立链路的能力,也具备在当前通信信道上出现主用户信号或其他干扰信号时自动切换到其他空闲信道上继续通信的能力,为认知无线电技术的实用化提供了很好的借鉴。     

Energy-Based Collaborative Spectrum Sensing for Cognitive UWB Impulse Radio

This paper focuses on the issue of collaborative spectrum sensing in cognitive ultra wideband (CUWB) impulse radio. We employ energy-based signal detection method and apply the Neyman-Pearson (NP) deci...     

Variable Persistence Sensing Schemes for Opportunistic Spectrum Access

Cognition technologies can significantly enhance spectrum utilization through secondary usage. Secondary users （SUs） search for spectrum holes which are not used by Primary users （PUs） and communicate through them. The design and analysis of simple opportunistic spectrum access schemes for maximizing utilization efficiency and minimizing delay of SUs under limited sensing bandwidth and energy is still at infancy. In this work, we consider PU＇s frequency occupancy patterns and propose three simple variable persistence sensing schemes for maximum exploitation of idle spectrum chunks by SUs, and perform their theoretical analysis. Numerical case studies are presented to verify the theoretical analysis and illustrate the performance of the schemes proposed.     

CVANET中基于POMDP模型的频谱接入算法

针对认知车载Ad Hoc网络(CVANET)信道的动态特性,以部分可观测马尔科夫决策过程(POMDP)为模型对认知车辆用户的频谱感知和频谱接入过程进行研究,提出基于POMDP模型的分布式机会频谱接入算法,并通过贪心算法降低POMDP算法计算量,最后通过仿真研究影响认知车辆用户吞吐量的主要因素,并验证算法的可行性。仿真分析结果表明,认知车辆用户通过本算法接入吞吐量得到有效提高,降低了交通中广播风暴的可能,并且降低了计算量。     

认知无线电跨层传输的建模与仿真

将认知无线电(CR)中的跨层传输建模为约束马尔可夫决策过程(MDP),考虑了频谱可用性的变化规律、上层数据的到达过程和信道衰落,提出一种满足掉包率约束的前提下最小化平均功率消耗的方案。采用拉格朗日乘子法对此过程求解,并用2种简化的方法,即状态聚合和行动集缩来解决因状态空间、行动集规模过大引起的收敛速度慢的问题。计算机仿真结果表明,简化方法对该方案的性能影响很小,且该方案的平均功耗最低。     

一种认知无线Adhoc网络跨层最优频谱共享方案

针对由认知无线电组成的Adhoc网络中的频谱共享提出了一个跨层方案。通过综合考虑认知用户之间的干扰约束和流量需求,特别考虑到用户双向连接以及信道的非均匀性,以BFP（bandwidth—footprint-product）值最小为目,建立了一个二进制整数线性规划（BILP）模型。仿真结果给出了最优的频带分配和路由选择方案。     

Soft Combination Schemes for Cooperative Spectrum Sensing in Cognitive Radio Networks

This paper investigates linear soft combination schemes for cooperative spectrum sensing in cognitive radio networks. We propose two weight-setting strategies under different basic optimality criteria to improve the overall sensing performance in the network. The corresponding optimal weights are derived, which are determined by the noise power levels and the received primary user signal energies of multiple cooperative secondary users in the network. However, to obtain the instantaneous measurement of these noise power levels and primary user signal energies with high accuracy is extremely challenging. It can even be infeasible in practical implementations under a low signal-to-noise ratio regime. We therefore propose reference data matrices to scavenge the indispensable information of primary user signal energies and noise power levels for setting the proposed combining weights adaptively by keeping records of the most recent spectrum observations. Analyses and simulation results demonstrate that the proposed linear soft combination schemes outperform the conventional maximal ratio combination and equal gain combination schemes and yield significant performance improvements in spectrum sensing.     

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.     

认知超宽带无线电波形设计和频谱整形技术

认知超宽带无线电（CUWBR）系统实现的关键问题是当CUWBR感知到频谱空洞时,怎样设计合适的发送波形和频谱整形使其对合法用户造成的干扰最小。针对这一问题,文中简要介绍了CUWBR系统中基于检测与躲避的抗干扰原理,综述了CUWBR抗干扰发送波形设计和频谱整形技术的研究状况和最新进展,并对未来的发展动态进行了分析。解决这一问题能够提高现有频谱的利用率,缓和频谱供需矛盾,对UWB的实用化和CR的实现有积极的推动意义。     

A Cell Based Dynamic Spectrum Management Scheme with Interference Mitigation for Cognitive Networks

Future wireless systems are expected to be characterized by the coexistence of different radio access technologies (RATs) resulting in complex heterogeneous wireless environments. In parallel with this, the tremendous demand for spectrum has inspired the requirement of dynamic spectrum management (DSM). This paper aims at designing a cell based dynamic spectrum management (CBDSM) scheme to enhance the spectrum utilization and maximize the profit of operators in wireless heterogeneous networks. The system architecture and the functional modules supporting the CBDSM scheme are designed. As a fundamental issue in spectrum management, the inter-system interference issue is solved in the proposed CBDSM scheme. Furthermore, game theory, which is a potential tool for studying the distributed autonomous resource optimization algorithms, is applied to design a spectrum trading algorithm enabling the heterogeneous wireless networks to dynamically trade spectrum and to share the profit. In the algorithm, we take into account the economic value of the spectrum of wireless systems in order to guarantee the rationality for the spectrum trading. The simulation results show that the proposed CBDSM scheme effectively improves the spectrum utilization and the profit of operators while it reduces the mutual interference between wireless networks to a tolerable level.

Handoff and Optimal Channel Assignment in Wireless Networks

In this paper, a non-preemptive prioritization scheme for access control in cellular networks is analyzed. Two kinds of users are assumed to compete for the access to the limited number of frequency channels available in each cell: the high priority users represent handoff requests, while the low priority users correspond to initial access requests originated within the same cell. Queueing of handoff requests is also considered. The research for the best access policy is carried out by means of a Markov decision model which allows us to study a very wide class of policies which includes some well known pure stationary policies, as well as randomized ones. The cutoff priority policy, consisting in reserving a certain number of channels to the high priority stream of requests, is proved to be optimal within this class while using an objective function in the form of a linear combination of some quality of service parameters, when no queueing device is considered. Numerical results confirm the optimality of the cutoff priority policy when queueing of handoff requests is allowed.     

On co-channel and adjacent channel interference mitigation in cognitive radio networks

Cognitive radio (CR) is an emerging wireless communications paradigm of sharing spectrum among licensed (or, primary) and unlicensed (or, CR) users. In CR networks, interference mitigation is crucial not only for primary user protection, but also for the quality of service of CR user themselves. In this paper, we consider the problem of interference mitigation via channel assignment and power allocation for CR users. A cross-layer optimization framework for minimizing both co-channel and adjacent channel interference is developed; the latter has been shown to have considerable impact in practical systems. Cooperative spectrum sensing, opportunistic spectrum access, channel assignment, and power allocation are considered in the problem formulation. We propose a reformulation–linearization technique (RLT) based centralized algorithm, as well as a distributed greedy algorithm that uses local information for near-optimal solutions. Both algorithms are evaluated with simulations and are shown quite effective for mitigating both types of interference and achieving high CR network capacity.