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.     

认知无线电技术

随着无线通信技术的发展。无线用户的数量急剧增加，使得频谱资源变得越来越紧张，如何充分提高无线频谱的利用率成为亟待解决的技术问题。认知无线电技术提出了一种新的解决思路。其核心思想就是使无线通信设备具有发现“频谱空洞”并合理利用所发现的“空洞”的能力。虽然认知无线电技术能以更为灵活的方式来管理有限的频谱资源，但要真正将其应用于实际通信系统还需解决包括频谱检测、自适应频谱资源分配和无线频谱管理等关键技术问题。     

Unlicensed cognitive sharing of TV spectrum: the controversy at the Federal Communications Commission

As societies become increasingly mobile and more dependent on information technologies, their radio spectrum also needs change. The basic spectrum management structure in all countries was developed over a long period, and much of the basic framework has remained stable for decades. The FCC is interested in making more spectrum available to unlicensed devices because of the explosive growth of IEEE 802.11/Wi-Fi unlicensed wireless LAN technology, and because the FCC recognizes that there is a great deal of "white space" that could be exploited by unlicensed devices. The FCC proposal selected the TV bands as an initial home for cognitive radio based on several factors. First, the frequencies used for TV can give greater range in rural areas than the microwave frequencies used for Wi-Fi, and can also give better building penetration than Wi-Fi in all areas. Second, TV broadcast systems usually use high antennas, and the intended receivers need greater than 10 dB signal-to-noise ratio (SNR) to function. A variety of controversial issues have emerged from public comments. One concern is that the confusion resulting from the proposal might discourage purchase of new digital televisions and hence delay the transition from analog to digital televisions. This would also delay the transfer of some current TV spectrum to new mobile uses, including public safety.     

Pre-reservation based spectrum allocation for cognitive radio network

Studies on the current usage of the radio spectrum by several agencies have already revealed that a large fraction of the radio spectrum is inadequately utilized. This basic finding has led to numerous research initiatives. Cognitive radio technology is one of the key candidate technologies to solve the problems of spectrum scarcity and low spectrum utilization. However, random behavior of the primary user (PU) appears to be an enormous challenge. In this paper, a Pre-reservation based spectrum allocation method for cognitive radio network is proposed to apply a PU behavior aware joint spectrum band (SB) selection and allocation scheme. In the first step, the SB is observed in terms of PU usage statistics whereas in the second phase, a network operator (NO) using a spectrum allocation scheme is employed to allocate SBs among secondary users (SUs). We also introduce the concept of reservation and exchange functionality under the priority serving strategy in a time-varying framing process. Simulation results show that the proposed scheme outperforms existing schemes in terms of the spectrum utilization and network revenue. In addition, it helps NO to manage the spectrum on a planned basis with a systematical spectrum reservation management where the NO has the status of time slots. Moreover, SUs have an opportunity to reserve or instantly request a SB that maximizes the SUs satisfaction in terms of quality of experience.     

Analysis of cognitive radio spectrum access with finite user population

A new loss model for cognitive radio spectrum access with finite user population are presented, and exact solution for the model and its approximation for computation scalability are given. Our model provides the investigation of the delay performance of a cognitive radio system. We study the delay performance of a cognitive radio system under various primary traffic loads and spectrum band allocations.     

Secure centralized spectrum sensing for cognitive radio networks

Spectrum utilization becomes more and more important while new communication techniques keep increasing and the spectrum bands remain finite. Cognitive radio is a revolutionary technology to make use of the spectrum more effectively. In order to avoid the interference to the primary user, spectrum sensing must be sensitive and reliable. Cooperative spectrum sensing (CSS) is one of the ways to increase the reliability of spectrum sensing. The information fusion technique is a key component of CSS. In this paper, we proposed a novel fusion scheme based on spatial correlation technique. We utilize geographical information with reputational weights to propose a two-level fusion scheme called secure centralized spectrum sensing (SCSS). The simulation results show that as the attackers present high density aggregation at some areas, the correct sensing ratio of SCSS is increasing as well even when the number of attackers is very large.     

Future trends in radio resource management for wireless communications

Recent growth in wirelessly connected devices shows no signs of slowing, and indeed with new services and new technologies waiting in the wings, usage of wireless terminals looks set to continue increasing rapidly. However, radio spectrum is finite and in a wirelessly connected future, new approaches to ensuring connectivity and quality of service are going to be needed. Radio resource management has an important part to play in ensuring that the very best is obtained from the finite resources available for radio communications in the future. This paper considers the characteristics of current end emerging wireless networks, and aspects of radio resource management that may offer the performance gains needed to ensure end-to-end quality of service is met.     

Radio Spectrum Management for Tetherless Communications

For any new radio technology, spectrum management is an essential part of the development process, to identify the best frequency band for operation of the system. This has to take account of the many other users and applications of the radio spectrum, so that systems neither cause, nor receive, harmful interference from other radio systems. It is a process that is sometimes considered to be unnecessarily restrictive and slow; however, that is because it is often a difficult balancing act between the technical, commercial and political pressures on the (finite) radio spectrum. This paper describes the underlying principles and processes of radio spectrum management, explaining the relationships between the organisations which are responsible for spectrum management at the national, regional and international levels. It also describes the current work on the identification of frequency bands for the new tetherless communications technologies, and in particular the 2.4 and 5 GHz bands. This revised version was published online in July 2006 with corrections to the Cover Date.     

动态频谱分配的连通分支并行处理

关键词快速无干扰的动态频谱分配是实现认知无线电的关键技术之一。针对现有图论频谱分配算法均存在时间开销过大这一瓶颈问题,引入并行原理和连通分量理论,提出了一种连通分支并行处理新方法。该方法可应用于目前所有基于图论着色模型的分配算法,在保证算法原有效益的基础上,能够显著降低频谱分配过程的时间。研究了连通分支并行处理方法的应用实例,结果验证了该方法是快速有效的,更加适应时变的认知无线电环境。     

Future management of spectrum

As the heterogeneity of wireless access technologies increases, dynamic allocation and utilisation of spectrum become ever more important. The traditional rigid allocation of spectrum for technology-specific usage is not suitable for the increasingly dynamic demand driven by the continuous emergence of technologies providing new services with different quality of service requirements. New spectrum management techniques and increasingly flexible spectrum usage rights are therefore called for. We discuss the limitations of present spectrum management techniques and explore some new alternatives including spectrum trading and opportunistic spectrum access.     

Joint power and spectrum allocation in multi-hop cognitive radio networks

Various cognitive network technologies are developed rapidly. In the article, the power and spectrum allocation in multi-hop cognitive radio network （CRN） with linear topology is investigated. The overall goal is to minimize outage probability and promote spectrum utility, including total reward and fairness, while meeting the limits of total transmit power and interference threshold to primary user simultaneously. The problem is solved with convex optimization and artificial bee colony （ABC） algorithm jointly. Simulation shows that the proposed scheme not only minimizes outage probability, but also realizes a better use of spectrum.     

Approaches to spectrum sharing

Many complain about severe spectrum shortage. The shortage comes from outdated spectrum policies that allows for little sharing. Regulators have granted licenses that offer exclusive access to the spectrum. When these licensees are not transmitting, the spectrum sits idle. A new technology regarding spectrum shortage enables more spectrum sharing that unleashes innovative products and services, provided that we adopt the appropriate spectrum policies. Two camps are pushing for extreme reform, one for "property rights" and the other for "spectrum commons". This article presents concepts underlying the "property" and "commons" debate, clarifies options for spectrum reform, and describes the trade-offs of spectrum sharing     

我国频谱共享的可行性研究与推进建议

目前,我国工业和信息化领域一系列战略稳步推进,5G、移动互联网等信息技术快速发展,无线电频谱资源的稀缺性再次凸显。频谱共享为解决频谱资源的稀缺问题提供了解决方案,并被国际主流国家积极推行。在分析国内外频谱共享研究与应用现状的基础之上,进一步讨论了我国推行频谱共享的意义和挑战,给出了频谱共享可行性评估和分析框架,并提出了频谱共享的推进建议。     

A dynamic spectrum access network based on cognitive radio

Dynamic spectrum access technologies based on Cognitive Radio (CR) is under intensive research carried out by the wireless communication society and is expected to solve the problem of spectrum scarcity. However, most enabling technologies related to dynamic spectrum access are considered individually. In this paper, we consider these key technologies jointly and introduce a new implementation scheme for a Dynamic Spectrum Access Network Based on Cognitive Radio (DSAN-BCR). We start with a flexible hardware platform for DSAN-BCR, as well as a flexible protocol structure that dominates the operation of DSAN-BCR. We then focus on the state of the art of key technologies such as spectrum sensing, spectrum resources management, dynamic spectrum access, and routing that are below the network layer in DSAN-BCR, as well as the development of technologies related to higher layers. Last but not the least, we analyze the challenges confronted by these mentioned technologies in DSAN-BCR, and give the perspectives on the future development of these technologies. The DSAN-BCR introduced is expected to provide a system level guidance to alleviate the problem of spectrum scarcity.     

基于无线电环境地图的频谱共享网络研究

现有的频谱分配模式限制了频谱高效利用,束缚了无线电技术创新发展.频谱共享被认为是有效解决频谱供需矛盾、提高频谱使用效率的技术方案之一.在综合论述欧美等国家关于频谱共享研究进展的基础上,提出了一种基于无线电环境地图和用户分级的智能频谱共享网络架构.该网络可获得完整准确、及时可靠的频谱信息,通过对用户实行分级接入,实现不同用户高效动态地共享频谱资源.重点介绍了架构中各个网络单元的组成和功能,阐述了架构中不同网络单元之间的信息交互过程,最后剖析了架构实现上待解决的关键技术问题.相关内容为我国建设频谱共享网络提供了借鉴和参考.     

A survey of spectrum sensing algorithms for cognitive radio applications

The spectrum sensing problem has gained new aspects with cognitive radio and opportunistic spectrum access concepts. It is one of the most challenging issues in cognitive radio systems. In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented. Various aspects of spectrum sensing problem are studied from a cognitive radio perspective and multi-dimensional spectrum sensing concept is introduced. Challenges associated with spectrum sensing are given and enabling spectrum sensing methods are reviewed. The paper explains the cooperative sensing concept and its various forms. External sensing algorithms and other alternative sensing methods are discussed. Furthermore, statistical modeling of network traffic and utilization of these models for prediction of primary user behavior is studied. Finally, sensing features of some current wireless standards are given.     

New concepts in spectrum usage

The author alleges that there is no shortage of radio spectrum, but rather, a shortage of new concepts in spectrum usage. The recent reallocation of additional frequencies to land mobile radio uses (FCC Dockets 18 261 and 18 262) provides new opportunities for innovative approaches, approaches that are free of the constraints of existing rules and regulations, existing manufacturing and engineering processes and concepts. Intending to be provocative and to initiate action and dialogue, the author challenges the technologists of this industry to come forward with innovative approaches based upon thorough, objective engineering analyses. The FCC, he contends, sorely needs factual, objective data from industry technologists in order to make the best decisions possible.     

Compressive spectrum sensing in the cognitive radio networks by exploiting the sparsity of active radios

Spectrum sensing is a key technology to detect spectrum holes in cognitive network. It has been demonstrated that collaboration among cognitive users can improve the probability of detecting the primary users, but the fusion center is the bottleneck when a lot of collaborative information is transmitted. In this paper, we consider the cognitive radio users only transmit part of sensing information to relieve the transmission load. Besides, the sensing information will be inevitably influenced by various noise in the process of transmission. Therefore, the challenge is how we can detect spectrum holes successfully from these incomplete and inexact measurements. Most recently, there are some research results on this but the detection performance is not satisfactory. In this paper, we firstly formulate the collaborative spectrum sensing as an optimization model and then present a novel adaptive orthogonal matching pursuit algorithm by exploiting the sparsity of active primary users. Statistical property of the sensing data plays a crucial role in spectrum sensing. Theoretical analysis shows the presented scheme can detect active primary users rapidly and efficiently. Simulation results verify that the proposed method can obtain better detection performance with stronger noise background, which is more attractive in real applications.     

Potential effects of broadband wireline telecommunications on the HF spectrum

Power line telecommunications and various forms of digital subscriber line transmissions are recent and rapidly evolving technologies using the existing electricity power or telephone lines for data transmission at rates higher than 1 Mb/s. As these lines were not designed for transmission of high data rates, they produce noiselike interferences in the HF range. The intensity depends on the electrical characteristics of the lines (balance, match, screening) as well as on the density and area coverage of these new systems. Exact calculations are impossible at this time because of missing models for the new wirebound communication systems with respect to emission of radio noise in the HF band. Early measurements and estimations showed that radio noise from PLT and xDSL has the potential to cause problems for military HF radio communications and communication intelligence. A Research Task Group under NATO was assigned to study the issue and determine possible solutions. Briefly, the findings of the RTG do indicate that PLT emissions have the potential to cause appreciable degradation in the exploitation of the HF spectrum by military users.