毕业设计英文翻译认知无线电频谱感知算法仿真Word文件下载.docx

1、班 级 学 生 学 号 Implementation Issues in Spectrum Sensing for Cognitive Radios认知无线电频谱感知的实现问题Abstract:There are new system implementation challenges involved in the design of cognitive radios, which have both the ability to sense the spectral environment and the flexibility to adapt transmission paramete

2、rs to maximize system capacity while co-existing with legacy wireless networks. The critical design problem is the need to process multi-gigahertz wide bandwidth and reliably detect presence of primary users. This places severe requirements on sensitivity, linearity, and dynamic range of the circuit

3、ry in the RF front-end. To improve radio sensitivity of the sensing function through processing gain we investigated three digital signal processing techniques: matched filtering, energy detection, and cyclostationary feature detection. Our analysis shows that cyclostationary feature detection has a

4、dvantages due to its ability to differentiate modulated signals, interference and noise in low signal to noise ratios. In addition, to further improve the sensing reliability, the advantage of a MAC protocol that exploits cooperation among many cognitive users is investigated. 摘要：出现了一些新系统的实施挑战，其涉及认知

5、无线电具有感知频谱环境下的传输参数既适应能力和灵活性，以最大限度地提高系统容量，同时并存于传统无线网络。关键设计问题是需要处理多千兆赫宽的带宽，可靠地检测主用户的存在。这对灵敏度，线性度和在RF前端电路的动态范围有严格要求。为了通过处理增益而提高无线电灵敏度，我们调查了三种数字信号处理技术的感测功能：匹配滤波，能量检测和循环平稳特征检测。我们的分析表明：由于能够区分调制信号，干扰和噪声在低信噪比，循环平稳特征检测更有优势。此外，为了进一步提高检测的可靠性，MAC协议，它利用在许多认知用户合作的优势已经在这一块研究很久了。I. INTRODUCTION一、介绍1. It is commonly

6、believed that there is a spectrum scarcity at frequencies that can be economically used for wireless communications. This concern has arisen from the intense competition for use of spectra at frequencies below 3 GHz. The Federal Communications Commissions （FCC） frequency allocation chart indicates o

7、verlapping allocations over all of the frequency bands, which reinforces the scarcity mindset. On the other hand, actual measurements taken in downtown Berkeley are believed to be typical and indicate low utilization, especially in the 3-6 MHz bands. Figure 1 shows the power spectral density （PSD） o

8、f the received 6 GHz wide signal collected for a span of 50s sampled at 20 GS/s 12. This view is supported by recent studies of the FCCs Spectrum Policy Task Force who reported 1 vast temporal and geographic variations in the usage of allocated spectrum with utilization ranging from 15% to 85%. In o

9、rder to utilize these spectrum white spaces, the FCC has issued a Notice of Proposed Rule Making （NPRM FCC 03-322 2） advancing Cognitive Radio （CR） technology as a candidate to implement negotiated or opportunistic spectrum sharing.人们普遍认为，有一个频谱稀缺的频率，可以经济地用于无线通信。从使用3 GHz以下频率光谱的激烈竞争开始，它就越来越受到关注。美国联邦通信

10、委员会（FCC）的频率分配图表显示所有频段都有重叠的分配，这加强了稀缺的现状。另一方面，在伯克利市中心采取的实际测量被认为是典型的实验结果，从中指出频谱利用率低，特别是在3-6 MHz频段。图1显示接收到的6千兆赫的功率谱密度（PSD）宽信号，50s的采样在20 GS / s的的一个跨度。这种观点是最近FCC的频谱政策任务组的研究报告，报告称浩瀚时空和地域变化在分配的频谱利用率介乎15至85的使用。为了利用这些频谱空白，FCC已发出建议规则制定的通知（NPRM - FCC03-3222）推进认知无线电（CR）技术，以实现协商或伺机频谱共享的候选人。2.Wireless systems toda

11、y are characterized by wasteful static spectrum allocations, fixed radio functions, and limited network coordination. Some systems in unlicensed frequency bands have achieved great spectrum efficiency, but are faced with increasing interference that limits network capacity and scalability. Cognitive

12、 radio systems offer the opportunity to use dynamic spectrum management techniques to help prevent interference, adapt to immediate local spectrum availability by creating time and location dependent in “virtual unlicensed bands”, i.e. bands that are shared with primary users. Unique to cognitive ra

13、dio operation is the requirement that the radio is able to sense the environment over huge swaths of spectrum and adapt to it since the radio does not have primary rights to any pre-assigned frequencies. This new radio functionality will involve the design of various analog, digital, and network pro

14、cessing techniques in order to meet challenging radio sensitivity requirements and wideband frequency agility.现在无线系统的特点是浪费的静态频谱分配，固定无线功能，以及有限的网络协调。在未经许可的频带一些系统已经取得了很大的频谱效率，但都面临着限制的网络容量和可扩展性增加的干扰。认知无线电系统提供使用动态频谱管理技术，以帮助防止干扰，通过创建时间和位置相关的“虚拟免授权频段”，适应当地的即时频谱可用性的机会，例如与主要用户共享频段。独特的认知无线电操作是有需要的，它使无线电能够通过频谱

15、巨大的大片感知环境，并适应它，纵然无线电对任何预指配频率没有基本权利。这种新的无线功能将涉及各种模拟设计，数字化和网络处理技术，以满足具有挑战性的射频灵敏度的要求和宽带频率捷变。3.Spectrum sensing is best addressed as a cross-layer design problem. Cognitive radio sensitivity can be improved by enhancing radio RF front-end sensitivity, exploiting digital signal processing gain for specif

16、ic primary user signal, and network cooperation where users share their spectrum sensing measurements. 频谱感知在跨层设计问题上是最好的方法。认知无线电的灵敏度可以通过增强无线电射频前端的灵敏度，利用数字信号处理增益为特定主用户信号，以及网络合作，用户共享他们的频谱感测的测量得到改善。4.The paper is organized as follows; Section II defines spectrum sensing function and proposes a cross-lay

17、er approach for its implementation. Section III considers RF front-end and A/D requirements for spectrum sensing and analog techniques for feasible implementations. In section IV we investigate digital signal processing techniques that can improve radio sensitivity and detect primary userspresence.

18、Section V presents the results from a cooperative sensing scheme, achievable gains and implementation issues. Finally, conclusions are presented in Section VI.本文结构如下，第二部分定义频谱感知功能，并提出了实施一个跨层的方法。第三部分讨论频谱感知的射频前端，后端和A / D的要求，与可实现的模拟技术。在第四部分中，我们研究，可以提高无线电灵敏度和检测主用户的存在的数字信号处理技术。第五部分提出了从协作感知方案，可实现收益和实施问题的结果

19、。最后，结论载于第六部分。II. SPECTRUM SENSING2、 频谱感知1.A “Cognitive Radio” is a radio that is able to sense the spectral environment over a wide frequency band and exploit this information to opportunistically provide wireless links that best meet the user communications requirements 2. While many other characte

20、ristics have also been discussed as possible additional capabilities, we will use this more restricted definition and consider physical （PHY） and medium access control （MAC） functions that are linked to spectrum sensing as illustrated in Figure 2认知无线电是一种无线电，它能够感觉到在很宽的频带内的频谱环境，并利用这些信息来投机提供最能满足用户的通信需求

21、的无线链路。在许多其他特性也已讨论过作为可能的附加功能时，我们将使用这个更受限制的定义，并考虑物理层（PHY）和介质访问控制（MAC）功能链接到频谱感测，如图2Since cognitive radios are considered lower priority or secondary users of spectrum allocated to a primary user, a fundamental requirement is to avoid interference to potential primary users in their vicinity. On the oth

22、er hand, primary user networks have no requirement to change their infrastructure for spectrum sharing with cognitive networks. Therefore, cognitive radios should be able to independently detect primary user presence through continuous spectrum sensing. For example, TV broadcast signals are much eas

23、er to detect than GPS signals, since the TV receivers sensitivity is tens of dBs worse than GPS receiver. 由于认知无线电被认为是低优先级或分配给主用户频谱的二级用户，一个基本要求是，避免附近的有潜力的主要用户的干扰。另一方面，主用户网络具有不要求改变他们与认知网络频谱共享的基础设施。因此，认知无线电应该能够通过不断的频谱感知独立检测主用户的存在。例如，广播电视信号更容易比GPS信号来检测，因为电视接收器的灵敏度是几十分贝比GPS接收器差。In general, cognitive radi

24、o sensitivity should outperform primary user receiver by a large margin in order to prevent what is essentially a hidden terminal problem. This is the key issue that makes spectrum sensing very challenging research problem. Meeting the sensitivity requirement of each primary receiver with a wideband

25、 radio would be difficult enough, but the problem becomes even more challenging if the sensitivity requirement is raised by additional 30-40 dB. This margin is required because cognitive radio does not have a direct measurement of a channel between primary user receiver and transmitter and must base

26、 its decision on its local channel measurement to a primary user transmitter. This type of detection is referred to as local spectrum sensing and the worst case hidden terminal problem would occur when the cognitive radio is shadowed, in severe multipath fading, or inside buildings with high penetra

27、tion loss while in a close neighborhood there is a primary user whose is at the marginal reception, due to its more favorable channel conditions. Even though the probability of this scenario is low, cognitive radio should not cause interference to such primary user. 一般情况下，认知无线电灵敏度应远远胜过主用户接收器，为的是防止出现

28、隐藏终端问题。这是使频谱感知非常具有挑战性的研究课题的关键问题。满足每个主接收器的灵敏度要求，宽带无线电将难以足够了，但如果灵敏度的要求是提出额外的30-40分贝的问题就变得更加具有挑战性。这个利润率是必需的，因为认知无线电没有直接测量主用户接收机和发射机之间的信道，并且必须立足其上的本地信道测量决定主要用户发送。这种类型的检测被称为本地频谱检测和当认知无线电是阴影，在严重的多径衰落会发生隐藏终端问题的最坏的情况下，在严重的多径衰落，或内部具有高穿透损耗的物体，而在一个近邻域有一个主要用户，其是在边缘接收，由于其更有利的信道条件。即使这种情况的概率较低，认知无线电应该不会对这样的主用户造成干扰

29、。The implementation of the spectrum sensing function also requires a high degree of flexibility since the radio environment is highly variable, both because of different types of primary user systems, propagation losses, and interference. The main design challenge is to define RF and analog architec

30、ture with right trade-offs between linearity, sampling rate, accuracy and power, so that digital signal processing techniques can be utilized for spectrum sensing, cognition, and adaptation. This also motivates research of signal processing techniques that can relax challenging requirements for anal

31、og, specifically wideband amplification, mixing and A/D conversion of over a GHz or more of bandwidth, and enhance overall radio sensitivity.频谱检测功能的实现也需要高度灵活性，由于无线环境是高度可变，另一个原因是不同类型的主用户系统中存在传播损耗和干扰。主要的设计挑战是定义射频和模拟结构与线性，采样率，精度和功率之间权利权衡，以使数字信号处理技术可被用于频谱感知，认知和适应。这也促使了可以放宽对模拟的，特别宽频带放大，混合和超过带宽的GHz或多个A/ D

32、转换的挑战性的要求，提高整体的无线电灵敏度的信号处理技术的研究。III. COGNITIVE RADIO FRONTEND3、认知无线电前端There are two frequency bands where the cognitive radios might operate in a near future: 400-800 MHz （UHF TV bands） and 3-10 GHz. The FCC has noted that in the lower UHF bands almost every geographical area has several unused 6 MHz wide TV channels. This frequency band is particularly appealing due to good propagation properties for long-range communications. Furthermore, given the static TV channe