认知无线电在宽带无线通信系统中的应用

认知无线电技术（CR）是软件无线电技术的演化，是一种新的智能无线通信技术。认知无线电技术的主要特点，就是根据环境不断调整参数以适应通讯的需求从而提高通讯质量。目前宽带无线通讯系统有正交频分复用（OFDM），多输入多输出（MIMO）等关键技术。将CR引进OFDM系统中，采用特殊的导频设计，感知宽带的传输特征，从空间、时间、频率、调制方式等多维度共享无线频谱，能提高频谱利用的灵活性，有效抑制窄带干扰。LTE是由3GPP定义的下一个移动宽带网络标准，基于OFDM、MIMO等关键技术，论述了实现CR的过程。     

认知无线电研究综述

认知无线电是一种智能频谱共享技术。它通过感知频谱环境、智能学习并实时调整其传输参数,实现频谱的再利用,可显著地提高频谱的利用率,特别是可让未授权用户使用授权用户的频谱。本文在概述了认知无线电技术的发展之后,重点介绍了认知无线电技术及其应用的研究现状,包括认知无线电的总体概念、相关频谱政策和标准化工作进展、相关关键技术和安全技术的研究,以及它在UWB、Mesh、WRAN中的应用现状。最后对认知无线电技术的发展进行了展望。     

二维空间谱的频谱感知技术研究

认知无线电的提出,能够有效的解决目前频谱资源匮乏的问题,频谱感知是认知无线电中必不可少的关键技术之一.着重对低功率复杂无线场景的频谱感知技术进行研究,在待测区域布置大量传感器或阵列天线,对授权用户的信息进行估计,得出区域性的干扰温度估计.     

二维空间谱的频谱感知技术研究

认知无线电的提出,能够有效地解决目前频谱资源匮乏的问题,频谱感知是认知无线电中必不可少的关键技术之一.着重对低功率复杂无线场景的频谱感知技术进行研究,在待测区域布置大量传感器或阵列天线,对授权用户的信息进行估计,得出区域性的干扰温度估计.     

认知无线电系统中的关键技术研究

深入研究了当前认知无线电中的关键技术,讨论了认知无线电系统的体系结构,分析了主流频谱感知技术并对比了其特点。同时给出了当前动态频谱管理研究的新进展。     

认知无线电关键技术研究

认知无线电技术是一种崭新的提高频谱利用率的解决方法,而自适应OFDM技术则以其具有频谱利用率高、抗多径性能强、可自适应地改变传输参数等特点而非常适合于认知无线电系统的应用。文中在研究了认知无线电系统关键技术的基础上,将认知无线电系统分类为分布式系统以及集中式系统两种应用场景,然后着重对分布式场景中的功率控制和频谱资源管理问题进行了深入研究,并在假设的认知无线电网络环境中对系统性能进行了仿真分析。     

随机共振在认知无线电频谱感知中应用的最新研究进展

频谱感知是认知无线电网络的一项关键技术.低信噪比(SNR)环境下频谱检测的性能会大幅降低,而随机共振(SR)能有效提高信号信噪比,所以将其应用到频谱感知中,能增强认知用户对主用户(PU)的检测性能.首先介绍了随机共振在认知无线电频谱感知中应用的最新研究进展,包括随机共振在本地感知中(如能量检测、协方差矩阵频谱感知、循环平稳特征检测)及协作感知中的应用,然后指出了随机共振在认知无线电频谱感知中还有待解决的问题,并提出了下一步的研究方向.     

认知无线电中一种循环特征检测方法研究

认知无线电是一种能感知周围通信环境从而改变发射机在特定的参数上实时改变的智能通信系统。它采用动态频谱管理来提高频谱利用率,高可靠性的频谱感知是实现频谱共享的关键技术。文中利用通信系统中调制信号的二阶循环平稳性对频谱感知技术的循环特征检测法进行了较深入的研究,并与能量检测法做了比较。最后由仿真结果可得出该检测方法的优越性。     

认知无线电的频谱感知技术研究

认知无线电技术接入灵活,能够大大提高频谱的利用率,被认为是当前解决频带使用拥挤的最佳方案。认知无线电是一种可以感知周围通信环境来改变发射机在特定的参数上实时改变的智能通信系统。它采用动态频谱管理来提高频谱利用率,高可靠性的频谱感知是实现频谱共享的关键技术,对频谱感知技术的匹配滤波器检测、能量检测、静态循环特征检测和合作检测等进行了讨论,并分析了各种方法的特点和性能。     

基于认知无线电技术的IEEE 802.22

随着无线通信技术的发展,无线频谱资源越来越贫乏。同时,认知无线电技术以其灵活高效的利用频谱受到广泛的关注。文章结合认知无线电技术的特点,介绍了IEEE802.22系统中的关键技术。从无线区域网实现的频谱感知技术、共存技术、正交频分多址(OFDMA)、信道管理和多信道绑定等关键技术入手,理解认知无线电技术的核心思想。     

Cognitive radios for dynamic spectrum access - polyphase multipath radio circuits for dynamic spectrum access

Dynamic access of unused spectrum via a cognitive radio asks for flexible radio circuits that can work at an arbitrary radio frequency. This article reviews techniques to realize radios without resorting to frequency selective dedicated filters. In particular, a recently proposed polyphase multipath technique canceling harmonics and sidebands is discussed. Using this technique, a wideband and flexible power upconverter with a clean output spectrum has been realized on a CMOS chip, aiming at flexible radio transmitter application. Prototype chips can transmit at an arbitrary frequency between DC and 2.4 GHz. Unwanted harmonics and sidebands are more than 40 dB lower than the desired signal up to the 17th harmonic of the transmit frequency     

一种通用数字中频正交扩频调制器的实现

提出了一种适应于宽带扩频通信系统的数字中频调制的实现方案,它基于正交调制、DDS、数字上变频和数字内插等技术,采用通用硬件平台,可以生成多种中频调制信号,可广泛用于数字化扩频通信电台、宽带CDMA、软件无线电、遥控遥测等通信系统中。     

基于软件无线电的抗干扰数字通信系统研究

各种自然干扰和人为干扰使得通信环境日益恶劣,采用数字扩频通信和软件无线电技术可以有效解决通信系统中的抗干扰和兼容性问题。首先讨论了软件无线电中的宽带/多频段天线、高速ADC以及高速DSP等关键技术;其次分析了扩频技术对于通信抗干扰的意义;最后结合数字扩频通信和软件无线电这两种技术的特点,提出一种采用可编程数字器件的实现方案。实验表明该系统具有安全可靠的传输性能,而且具有良好的抗干扰以及兼容性,具有较好的发展前景。     

Spectrum sharing radios

A major shift in radio design is now just beginning which attempts to share spectrum in a fundamentally new way. These radios are addressing the fact that spectrum is actually poorly utilized in many bands, in spite of the increasing demand for wireless connectivity. The new approaches to spectrum sharing make use of the advances in technology to implement new wireless systems that can share previously allocated spectra in such a way that the primary users of these spectra are not affected. Additionally, the allowed use of this band is on an unlicensed basis. Two methods that are being investigated to accomplish this task are the use of ultra wideband transmission and cognitive techniques. Ultra wideband transmission relies on the fact that if the bandwidth is increased, that reliable data transmission can occur even at power levels so low that primary radios in the same spectral bands are not affected. On the other hand the cognitive approach does not necessarily limit the transmission power, but rather attempts to share the spectra through a dynamic avoidance strategy. The opportunities and challenges of this new era in radio design are described along with the open questions in their implementation.     

采用压缩采样匹配追踪算法的频谱感知

频谱资源的匮乏成为无线电发展的瓶颈,解决频率匮乏有两类方法:一是提高频谱利用率;二是扩大可利用的频率范围。频谱感知技术能提高频谱利用率,但在高频的应用中会面对过高的采样速率、较大的数据量,这对硬件实现提出了艰巨的挑战。本文根据无线电频谱稀疏性介绍一种基于调制宽带转换器的压缩采样匹配追踪（CoSaMP）算法。本文利用调制宽带转换器对无线电信号进行亚奈奎斯特采样,再利用CoSaMP算法对采样后的自相关矩阵求解。本文的方法不仅能应用在更高的频谱,且能提高频谱利用率。仿真结果表明:该方法能在能以一个较低的采样速率对信号进行采样,且CoSaMP算法的恢复误差要小于OMP和ROMP算法。      

基于压缩采样和DWPT的认知无线电频谱感知方案

认知无线电频谱感知技术要求能够快速、准确地对高达上千兆赫兹的带宽进行频谱感知,它需要很高速率的模数转换器（A/D）,这对传统的工作在Nyquist采样率下的频谱估计方法提出了很大的挑战。利用实际信号频谱在开放式频谱接入环境中的稀巯性,提出了基于压缩采样和小波包分解的宽带频谱感知方案。通过SIMULINK仿真表明,该方法对宽带信号能以远远低于Nyquist采样率的速率采样,并且能够精确地估计出可用信道列表。     

基于DSCS的宽带频谱感知新算法

频谱感知是认知无线电技术的基础,随着通信技术不断发展,越来越高的采样速率成为一大瓶颈.实际应用中频谱占用通常具有稀疏性,根据这一特点并结合频谱检测要求,本文提出一种基于差分信号压缩感知(Differential SignalCompressed Sensing,DSCS)的宽带频谱感知方法.该方法在能量检测法的基础上引入压缩感知理论(compressed sensing,CS),使系统能以远低于奈奎斯特采样速率的速率无损采样,降低对硬件的要求;为降低计算量、提高算法稳定性,采用检测差分信号代替检测信号本身作为判断频谱占用变更的依据;引入精度作为算法的迭代停止条件,可根据需要灵调整算法准确度、降低计算复杂度.仿真表明,适当精度下DSCS法能大幅降低迭代次数、减少计算量,并获得更好的检测性能.     

A novel signal separation algorithm based on compressed sensing for wideband spectrum sensing in cognitive radio networks

In cognitive radio networks, since cognitive terminals use a shared wideband frequency spectrum for data transmissions, they are susceptible to malicious denial‐of‐service attacks, where adversaries try to corrupt communication by actively transmitting interference signals. To address this issue, in this paper, we propose a novel signal separation algorithm based on compressed sensing, which can not only recover the entire spectrum but also separate mixed occupying signals. Specifically, the proposed algorithm is executed following three steps: (i) each cognitive terminal attempts to recover all signals over an entire wideband spectrum employing the compressed sensing technique; (ii) all cognitive terminals send their recovered signals to the fusion center where a wavelet edge detection method is adopted to locate the spectrum edges of these signals and then divide the entire spectrum into several sub‐bands; (iii) the fusion center separates its received signals on each spectrum sub‐band into different categories according to their features. Both analytical and simulation results indicate that this novel compressed‐sensing‐based algorithm can effectively separate wideband signals at a low cost and combat interference of the malicious terminals in cognitive radio networks as well. Copyright © 2013 John Wiley & Sons, Ltd.     

软件无线电关键技术分析与实现设想

给出了第三代移动通信系统的核心技术之一－软件无线电的概念、组成体系和功能结构,讨论了软件无线电的宽带Ａ／Ｄ变换器、高速ＤＳＰ和宽带射频前端等三个关键技术,对模糊变换的性能进行了计算机模拟分析,指出了设计软件无线电时存在的问题并提出实现的设想。     

Cognitive Wireless Communication Networks (Hossian, E. and Bhargava, V.; 2007) [Book Review]

?Cognitive radio? is emerging as a promising technology to cope with the spectrum scarcity as well as the spectrum underutilization problem in the next generation wireless communications systems. This book, Cognitive Wireless Communication Networks, edited by Ekram Hossain and Vijay Bhargava, puts together a rich set of research articles featuring recent advances in theory, design, and analysis of cognitive wireless communication networks. The book consists of 15 invited articles from distinguished researchers in this area, which cover a wide range of topics related to the cognitive radio technology. In particular, the topics covered in this book include fundamental challenges and issues in designing cognitive radio systems, information-theoretic analysis of cognitive radio systems, spectrum sensing and co-existence issues, adaptive physical layer protocols and link adaptation techniques for cognitive radio, orthogonal frequency division multiple access (OFDM) and ultra wide band (UWB)- based cognitive radio, different techniques for spectrum access by distributed cognitive radio, cognitive medium access control (MAC) protocols, decentralized learning-based dynamic spectrum access methods, and microeconomic models for spectrum management in cognitive radio.