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<html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8"> <meta name="generator" content="pdf2htmlEX"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"> <link rel="stylesheet" href="https://static.pudn.com/base/css/base.min.css"> <link rel="stylesheet" href="https://static.pudn.com/base/css/fancy.min.css"> <link rel="stylesheet" href="https://static.pudn.com/prod/directory_preview_static/6255e9b6b744eb386feed92b/raw.css"> <script src="https://static.pudn.com/base/js/compatibility.min.js"></script> <script src="https://static.pudn.com/base/js/pdf2htmlEX.min.js"></script> <script> try{ pdf2htmlEX.defaultViewer = new pdf2htmlEX.Viewer({}); }catch(e){} </script> <title></title> </head> <body> <div id="sidebar" style="display: none"> <div id="outline"> </div> </div> <div id="pf1" class="pf w0 h0" data-page-no="1"><div class="pc pc1 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/6255e9b6b744eb386feed92b/bg1.jpg"><div class="t m0 x1 h2 y1 ff1 fs0 fc0 sc0 ls0 ws0">IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING, VOL. 5, NO. 1, FEBRUARY 2011 5</div><div class="t m0 x2 h3 y2 ff1 fs1 fc0 sc0 ls1 ws0">Advances in Cognitive Radio Networks: A Survey</div><div class="t m0 x3 h4 y3 ff1 fs2 fc0 sc0 ls1 ws0">Beibei Wang and K. J. Ray Liu</div><div class="t m0 x4 h5 y4 ff2 fs3 fc0 sc0 ls1 ws0">Abstract—With the rapid deployment of new wireless devices</div><div class="t m0 x1 h6 y5 ff3 fs3 fc0 sc0 ls1 ws0">and applications, the last decade has witnessed a growing demand</div><div class="t m0 x1 h6 y6 ff3 fs3 fc0 sc0 ls1 ws0">for wireless radio spectrum. However, the ﬁxed spectrum assign-</div><div class="t m0 x1 h6 y7 ff3 fs3 fc0 sc0 ls1 ws0">ment policy becomes a bottleneck for more efﬁcient spectrum uti-</div><div class="t m0 x1 h6 y8 ff3 fs3 fc0 sc0 ls1 ws0">lization, under which a great portion of the licensed spectrum is</div><div class="t m0 x1 h6 y9 ff3 fs3 fc0 sc0 ls1 ws0">severely under-utilized. The inefﬁcient usage of the limited spec-</div><div class="t m0 x1 h6 ya ff3 fs3 fc0 sc0 ls1 ws0">trum resources urges the spectrum regulatory bodies to review</div><div class="t m0 x1 h6 yb ff3 fs3 fc0 sc0 ls1 ws0">their policy and start to seek for innovative communication tech-</div><div class="t m0 x1 h6 yc ff3 fs3 fc0 sc0 ls1 ws0">nology that can exploit the wireless spectrum in a more intelligent</div><div class="t m0 x1 h6 yd ff3 fs3 fc0 sc0 ls1 ws0">and ﬂexible way. The concept of cognitive radio is proposed to ad-</div><div class="t m0 x1 h6 ye ff3 fs3 fc0 sc0 ls1 ws0">dress the issue of spectrum efﬁciency and has been receiving an in-</div><div class="t m0 x1 h6 yf ff3 fs3 fc0 sc0 ls1 ws0">creasing attention in recent years, since it equips wireless users the</div><div class="t m0 x1 h6 y10 ff3 fs3 fc0 sc0 ls1 ws0">capability to optimally adapt their operating parameters according</div><div class="t m0 x1 h6 y11 ff3 fs3 fc0 sc0 ls1 ws0">to the interactions with the surrounding radio environment. There</div><div class="t m0 x1 h6 y12 ff3 fs3 fc0 sc0 ls1 ws0">have been many signiﬁcant developments in the past few years on</div><div class="t m0 x1 h6 y13 ff3 fs3 fc0 sc0 ls1 ws0">cognitive radios. This paper surveys recent advances in research</div><div class="t m0 x1 h6 y14 ff3 fs3 fc0 sc0 ls1 ws0">related to cognitive radios. The fundamentals of cognitive radio</div><div class="t m0 x1 h6 y15 ff3 fs3 fc0 sc0 ls1 ws0">technology, architecture of a cognitive radio network and its appli-</div><div class="t m0 x1 h6 y16 ff3 fs3 fc0 sc0 ls1 ws0">cations are ﬁrst introduced. The existing works in spectrum sensing</div><div class="t m0 x1 h6 y17 ff3 fs3 fc0 sc0 ls1 ws0">are reviewed, and important issues in dynamic spectrum allocation</div><div class="t m0 x1 h6 y18 ff3 fs3 fc0 sc0 ls1 ws0">and sharing are investigated in detail.</div><div class="t m0 x4 h5 y19 ff2 fs3 fc0 sc0 ls1 ws0">Index Terms—Cognitive radio (CR), platforms and standards,</div><div class="t m0 x1 h6 y1a ff3 fs3 fc0 sc0 ls1 ws0">radio spectrum management, software radio, spectrum sensing,</div><div class="t m0 x1 h6 y1b ff3 fs3 fc0 sc0 ls1 ws0">wireless communication.</div><div class="t m0 x5 h7 y1c ff1 fs4 fc0 sc0 ls1 ws0">I. INTRODUCTION</div><div class="t m0 x1 h8 y1d ff3 fs6 fc0 sc0 ls1 ws0">T</div><div class="t m0 x6 h7 y1e ff1 fs4 fc0 sc0 ls1 ws0">HE usage of radio spectrum resources and the regulation</div><div class="t m0 x6 h7 y1f ff1 fs4 fc0 sc0 ls1 ws0">of radio emissions are coordinated by national regulatory</div><div class="t m0 x1 h7 y20 ff1 fs4 fc0 sc0 ls1 ws0">bodies like the Federal Communications Commission (FCC).</div><div class="t m0 x1 h7 y21 ff1 fs4 fc0 sc0 ls1 ws0">The FCC assigns spectrum to licensed holders, also known as</div><div class="t m0 x1 h7 y22 ff4 fs4 fc0 sc0 ls1 ws0">primary users, on a long-term basis for large geographical re-</div><div class="t m0 x1 h7 y23 ff1 fs4 fc0 sc0 ls1 ws0">gions. However, a large portion of the assigned spectrum re-</div><div class="t m0 x1 h7 y24 ff1 fs4 fc0 sc0 ls1 ws0">mains under utilized as illustrated in Fig. 1. The inefﬁcient usage</div><div class="t m0 x1 h7 y25 ff1 fs4 fc0 sc0 ls1 ws0">of the limited spectrum necessitates the development of dy-</div><div class="t m0 x1 h7 y26 ff1 fs4 fc0 sc0 ls1 ws0">namic spectrum access techniques, where users who have no</div><div class="t m0 x1 h7 y27 ff1 fs4 fc0 sc0 ls1 ws0">spectrum licenses, also known as secondary users, are allowed</div><div class="t m0 x1 h7 y28 ff1 fs4 fc0 sc0 ls1 ws0">to use the temporarily unused licensed spectrum. In recent years,</div><div class="t m0 x1 h7 y29 ff1 fs4 fc0 sc0 ls1 ws0">the FCC has been considering more ﬂexible and comprehensive</div><div class="t m0 x1 h7 y2a ff1 fs4 fc0 sc0 ls1 ws0">uses of the available spectrum [1], through the use of cognitive</div><div class="t m0 x1 h7 y2b ff4 fs4 fc0 sc0 ls1 ws0">radio technology [2].</div><div class="t m0 x7 h7 y2c ff1 fs4 fc0 sc0 ls1 ws0">Cognitive radio is the key enabling technology that enables</div><div class="t m0 x1 h7 y2d ff1 fs4 fc0 sc0 ls1 ws0">next generation communication networks, also known as dy-</div><div class="t m0 x8 h9 y2e ff1 fs5 fc0 sc0 ls1 ws0">Manuscript received October 30, 2009 accepted October 24, 2010. Date of</div><div class="t m0 x1 h9 y2f ff1 fs5 fc0 sc0 ls1 ws0">publication November 18, 2010; date of current version January 19, 2011. The</div><div class="t m0 x1 h9 y30 ff1 fs5 fc0 sc0 ls1 ws0">associate editor coordinating the review of this manuscript and approving it for</div><div class="t m0 x1 h9 y31 ff1 fs5 fc0 sc0 ls1 ws0">publication was Dr. Sastri Kota.</div><div class="t m0 x8 h9 y32 ff1 fs5 fc0 sc0 ls1 ws0">B. Wang is with Corporate Research and Development, Qualcomm, Inc., San</div><div class="t m0 x1 h9 y33 ff1 fs5 fc0 sc0 ls1 ws0">Diego, CA 92121 USA (e-mail: beibeiw@qualcomm.com).</div><div class="t m0 x8 h9 y34 ff1 fs5 fc0 sc0 ls1 ws0">K. J. R. Liu is with the Department of Electrical and Computer Engi-</div><div class="t m0 x1 h9 y35 ff1 fs5 fc0 sc0 ls1 ws0">neering, University of Maryland, College Park, MD 20742 USA (e-mail:</div><div class="t m0 x1 h9 y36 ff1 fs5 fc0 sc0 ls1 ws0">bebewang@umd.edu; kjrliu@umd.edu).</div><div class="t m0 x8 h9 y37 ff1 fs5 fc0 sc0 ls1 ws0">Color versions of one or more of the ﬁgures in this paper are available online</div><div class="t m0 x1 h9 y38 ff1 fs5 fc0 sc0 ls1 ws0">at http://ieeexplore.ieee.org.</div><div class="t m0 x8 h9 y39 ff1 fs5 fc0 sc0 ls1 ws0">Digital Object Identiﬁer 10.1109/JSTSP.2010.2093210</div><div class="t m0 x9 h9 y3a ff1 fs5 fc0 sc0 ls1 ws0">Fig. 1. Spectrum usage [5].</div><div class="t m0 xa h7 y3b ff1 fs4 fc0 sc0 ls1 ws0">namic spectrum access (DSA) networks, to utilize the spec-</div><div class="t m0 xa h7 y3c ff1 fs4 fc0 sc0 ls1 ws0">trum more efﬁciently in an opportunistic fashion without inter-</div><div class="t m0 xa h7 y3d ff1 fs4 fc0 sc0 ls1 ws0">fering with the primary users. It is deﬁned as a radio that can</div><div class="t m0 xa h7 y3e ff1 fs4 fc0 sc0 ls1 ws0">change its transmitter parameters according to the interactions</div><div class="t m0 xa h7 y3f ff1 fs4 fc0 sc0 ls1 ws0">with the environment in which it operates [3]. It differs from</div><div class="t m0 xa h7 y40 ff1 fs4 fc0 sc0 ls1 ws0">conventional radio devices in that a cognitive radio can equip</div><div class="t m0 xa h7 y41 ff1 fs4 fc0 sc0 ls1 ws0">users with cognitive capability and reconﬁgurability [4], [5].</div><div class="t m0 xa h7 y42 ff1 fs4 fc0 sc0 ls1 ws0">Cognitive capability refers to the ability to sense and gather in-</div><div class="t m0 xa h7 y43 ff1 fs4 fc0 sc0 ls1 ws0">formation from the surrounding environment, such as informa-</div><div class="t m0 xa h7 y44 ff1 fs4 fc0 sc0 ls1 ws0">tion about transmission frequency, bandwidth, power, modula-</div><div class="t m0 xa h7 y45 ff1 fs4 fc0 sc0 ls1 ws0">tion, etc. With this capability, secondary users can identify the</div><div class="t m0 xa h7 y46 ff1 fs4 fc0 sc0 ls1 ws0">best available spectrum. Reconﬁgurability refers to the ability</div><div class="t m0 xa h7 y47 ff1 fs4 fc0 sc0 ls1 ws0">to rapidly adapt the operational parameters according to the</div><div class="t m0 xa h7 y48 ff1 fs4 fc0 sc0 ls1 ws0">sensed information in order to achieve the optimal performance.</div><div class="t m0 xa h7 y49 ff1 fs4 fc0 sc0 ls1 ws0">By exploiting the spectrum in an opportunistic fashion, cogni-</div><div class="t m0 xa h7 y4a ff1 fs4 fc0 sc0 ls1 ws0">tive radio enables secondary users to sense which portion of the</div><div class="t m0 xa h7 y4b ff1 fs4 fc0 sc0 ls1 ws0">spectrum are available, select the best available channel, coor-</div><div class="t m0 xa h7 y4c ff1 fs4 fc0 sc0 ls1 ws0">dinate spectrum access with other users, and vacate the channel</div><div class="t m0 xa h7 y4d ff1 fs4 fc0 sc0 ls1 ws0">when a primary user reclaims the spectrum usage right.</div><div class="t m0 xb h7 y4e ff1 fs4 fc0 sc0 ls1 ws0">Considering the more ﬂexible and comprehensive use of the</div><div class="t m0 xa h7 y4f ff1 fs4 fc0 sc0 ls1 ws0">spectrum resources, especially when secondary users coexist</div><div class="t m0 xa h7 y50 ff1 fs4 fc0 sc0 ls1 ws0">with primary users, traditional spectrum allocation schemes [6]</div><div class="t m0 xa h7 y51 ff1 fs4 fc0 sc0 ls1 ws0">and spectrum access protocols may no longer be applicable.</div><div class="t m0 xa h7 y52 ff1 fs4 fc0 sc0 ls1 ws0">New spectrum management approaches need to be developed</div><div class="t m0 xa h7 y53 ff1 fs4 fc0 sc0 ls1 ws0">to solve new challenges in research related to cognitive radio,</div><div class="t m0 xa h7 y54 ff1 fs4 fc0 sc0 ls1 ws0">speciﬁcally, in spectrum sensing and dynamic spectrum sharing.</div><div class="t m0 xb h7 y55 ff1 fs4 fc0 sc0 ls1 ws0">As primary users have priority in using the spectrum, when</div><div class="t m0 xa h7 y56 ff1 fs4 fc0 sc0 ls1 ws0">secondary users coexist with primary users, they have to per-</div><div class="t m0 xa h7 y57 ff1 fs4 fc0 sc0 ls1 ws0">form real-time wideband monitoring of the licensed spectrum</div><div class="t m0 xa h7 y58 ff1 fs4 fc0 sc0 ls1 ws0">to be used. When secondary users are allowed to transmit data</div><div class="t m0 xa h7 y59 ff1 fs4 fc0 sc0 ls1 ws0">simultaneously with a primary user, interference temperature</div><div class="t m0 xa h7 y5a ff1 fs4 fc0 sc0 ls1 ws0">limit should not be violated [7]. If secondary users are only al-</div><div class="t m0 xa h7 y5b ff1 fs4 fc0 sc0 ls1 ws0">lowed to transmit when the primary users are not using the spec-</div><div class="t m0 xa h7 y5c ff1 fs4 fc0 sc0 ls1 ws0">trum, they need to be aware of the primary users’ reappearance</div><div class="t m0 xa h7 y5d ff1 fs4 fc0 sc0 ls1 ws0">through various detection techniques, such as energy detection,</div><div class="t m0 xa h7 y5e ff1 fs4 fc0 sc0 ls1 ws0">feature detection, matched ﬁltering and coherent detection. Due</div><div class="t m0 xa h7 y5f ff1 fs4 fc0 sc0 ls1 ws0">to noise uncertainty, shadowing, and multipath effect, detection</div><div class="t m0 xa h7 y60 ff1 fs4 fc0 sc0 ls1 ws0">performance of single user sensing is pretty limited. Coopera-</div><div class="t m0 xa h7 y61 ff1 fs4 fc0 sc0 ls1 ws0">tive sensing has been considered effective in improving detec-</div><div class="t m0 xc h9 y62 ff1 fs5 fc0 sc0 ls1 ws0">1932-4553/$26.00 © 2011 IEEE</div><div class="t m0 xd ha y63 ff5 fs7 fc0 sc0 ls1 ws0">Downloaded from https://iranpaper.ir</div><div class="t m0 xe hb y64 ff6 fs8 fc0 sc0 ls1 ws0">https://www.tarjomano.com/order</div></div><div class="pi" data-data='{"ctm":[1.616162,0.000000,0.000000,1.616162,0.000000,0.000000]}'></div></div> </body> </html>

<div id="pf2" class="pf w0 h0" data-page-no="2"><div class="pc pc2 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/6255e9b6b744eb386feed92b/bg2.jpg"><div class="t m0 xf h2 y1 ff1 fs0 fc0 sc0 ls0 ws0">6 IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING, VOL. 5, NO. 1, FEBRUARY 2011</div><div class="t m0 xf h7 y65 ff1 fs4 fc0 sc0 ls1 ws0">tion accuracy by taking advantage of the spatial and multi-user</div><div class="t m0 xf h7 y66 ff1 fs4 fc0 sc0 ls1 ws0">diversity. In cooperative spectrum sensing, how to select proper</div><div class="t m0 xf h7 y67 ff1 fs4 fc0 sc0 ls1 ws0">users for sensing, how to fuse individual user’s decision and ex-</div><div class="t m0 xf h7 y68 ff1 fs4 fc0 sc0 ls1 ws0">change information, and how to perform distributed spectrum</div><div class="t m0 xf h7 y69 ff1 fs4 fc0 sc0 ls1 ws0">sensing are issues worth studying.</div><div class="t m0 x10 h7 y6a ff1 fs4 fc0 sc0 ls1 ws0">In order to fully utilize the spectrum resources, efﬁcient dy-</div><div class="t m0 xf h7 y6b ff1 fs4 fc0 sc0 ls1 ws0">namic spectrum allocation and sharing schemes are very im-</div><div class="t m0 xf h7 y6c ff1 fs4 fc0 sc0 ls1 ws0">portant. Novel spectrum access control protocols and control</div><div class="t m0 xf h7 y6d ff1 fs4 fc0 sc0 ls1 ws0">channel management should be designed to accommodate the</div><div class="t m0 xf h7 y6e ff1 fs4 fc0 sc0 ls1 ws0">dynamic spectrum environment while avoid collision with a pri-</div><div class="t m0 xf h7 y6f ff1 fs4 fc0 sc0 ls1 ws0">mary user. When a primary user re-appears in a licensed band,</div><div class="t m0 xf h7 y70 ff1 fs4 fc0 sc0 ls1 ws0">a good spectrum handoff mechanism is required to provide sec-</div><div class="t m0 xf h7 y71 ff1 fs4 fc0 sc0 ls1 ws0">ondary users with smooth frequency transition with low latency.</div><div class="t m0 xf h7 y72 ff1 fs4 fc0 sc0 ls1 ws0">In multi-hop cognitive wireless networks, intermediate cogni-</div><div class="t m0 xf h7 y73 ff1 fs4 fc0 sc0 ls1 ws0">tive nodes should intelligently support relaying information and</div><div class="t m0 xf h7 y74 ff1 fs4 fc0 sc0 ls1 ws0">routing through using a set of dynamically changing channels.</div><div class="t m0 xf h7 y75 ff1 fs4 fc0 sc0 ls1 ws0">In order to manage the interference to the primary users and the</div><div class="t m0 xf h7 y76 ff1 fs4 fc0 sc0 ls1 ws0">mutual interference among themselves, secondary users’ trans-</div><div class="t m0 xf h7 y77 ff1 fs4 fc0 sc0 ls1 ws0">mission power should be carefully controlled, and their compe-</div><div class="t m0 xf h7 y78 ff1 fs4 fc0 sc0 ls1 ws0">tition for the spectrum resources should also be addressed.</div><div class="t m0 x10 h7 y79 ff1 fs4 fc0 sc0 ls1 ws0">There have been many signiﬁcant developments in the past</div><div class="t m0 xf h7 y7a ff1 fs4 fc0 sc0 ls1 ws0">few years on cognitive radios. This article surveys recent ad-</div><div class="t m0 xf h7 y7b ff1 fs4 fc0 sc0 ls1 ws0">vances in research related to cognitive radios. In Section II, we</div><div class="t m0 xf h7 y7c ff1 fs4 fc0 sc0 ls1 ws0">overview the fundamentals of cognitive radio technology, ar-</div><div class="t m0 xf h7 y7d ff1 fs4 fc0 sc0 ls1 ws0">chitecture of a cognitive radio network and its applications. In</div><div class="t m0 xf h7 y7e ff1 fs4 fc0 sc0 ls1 ws0">Section III, we review existing works in spectrum sensing, in-</div><div class="t m0 xf h7 y7f ff1 fs4 fc0 sc0 ls1 ws0">cluding interference temperature, different types of detection</div><div class="t m0 xf h7 y80 ff1 fs4 fc0 sc0 ls1 ws0">techniques, and cooperative spectrum sensing. In Section IV,</div><div class="t m0 xf h7 y81 ff1 fs4 fc0 sc0 ls1 ws0">we discuss several important issues in dynamic spectrum allo-</div><div class="t m0 xf h7 y82 ff1 fs4 fc0 sc0 ls1 ws0">cation and sharing.</div><div class="t m0 x11 h7 y83 ff1 fs4 fc0 sc0 ls1 ws0">II. F</div><div class="t m0 x12 h9 y84 ff1 fs5 fc0 sc0 ls1 ws0">UNDAMENTALS</div><div class="t m0 xf hc y85 ff4 fs4 fc0 sc0 ls1 ws0">A. Cognitive Radio Characteristics</div><div class="t m0 x10 h7 y86 ff1 fs4 fc0 sc0 ls1 ws0">The dramatic increase of service quality and channel capacity</div><div class="t m0 xf h7 y87 ff1 fs4 fc0 sc0 ls1 ws0">in wireless networks is severely limited by the scarcity of en-</div><div class="t m0 xf h7 y88 ff1 fs4 fc0 sc0 ls1 ws0">ergy and bandwidth, which are the two fundamental resources</div><div class="t m0 xf h7 y89 ff1 fs4 fc0 sc0 ls1 ws0">for communications. Therefore, researchers are currently fo-</div><div class="t m0 xf h7 y8a ff1 fs4 fc0 sc0 ls1 ws0">cusing their attention on new communications and networking</div><div class="t m0 xf h7 y8b ff1 fs4 fc0 sc0 ls1 ws0">paradigms that can intelligently and efﬁciently utilize these</div><div class="t m0 xf h7 y8c ff1 fs4 fc0 sc0 ls1 ws0">scarce resources. Cognitive radio (CR) is one critical enabling</div><div class="t m0 xf h7 y8d ff1 fs4 fc0 sc0 ls1 ws0">technology for future communications and networking that</div><div class="t m0 xf h7 y8e ff1 fs4 fc0 sc0 ls1 ws0">can utilize the limited network resources in a more efﬁcient</div><div class="t m0 xf h7 y8f ff1 fs4 fc0 sc0 ls1 ws0">and ﬂexible way. It differs from traditional communication</div><div class="t m0 xf h7 y90 ff1 fs4 fc0 sc0 ls1 ws0">paradigms in that the radios/devices can adapt their operating</div><div class="t m0 xf h7 y91 ff1 fs4 fc0 sc0 ls1 ws0">parameters, such as transmission power, frequency, modulation</div><div class="t m0 xf h7 y92 ff1 fs4 fc0 sc0 ls1 ws0">type, etc., to the variations of the surrounding radio environment</div><div class="t m0 xf h7 y93 ff1 fs4 fc0 sc0 ls1 ws0">[3]. Before CRs adjust their operating mode to environment</div><div class="t m0 xf h7 y94 ff1 fs4 fc0 sc0 ls1 ws0">variations, they must ﬁrst gain necessary information from the</div><div class="t m0 xf h7 y95 ff1 fs4 fc0 sc0 ls1 ws0">radio environment. This kind of characteristics is referred to as</div><div class="t m0 xf h7 y96 ff4 fs4 fc0 sc0 ls1 ws0">cognitive capability [4], which enables CR devices to be aware</div><div class="t m0 xf h7 y97 ff1 fs4 fc0 sc0 ls1 ws0">of the transmitted waveform, radio frequency (RF) spectrum,</div><div class="t m0 xf h7 y98 ff1 fs4 fc0 sc0 ls1 ws0">communication network type/protocol, geographical infor-</div><div class="t m0 xf h7 y99 ff1 fs4 fc0 sc0 ls1 ws0">mation, locally available resources and services, user needs,</div><div class="t m0 xf h7 y9a ff1 fs4 fc0 sc0 ls1 ws0">security policy, and so on. After CR devices gather their needed</div><div class="t m0 xf h7 y9b ff1 fs4 fc0 sc0 ls1 ws0">information from the radio environment, they can dynamically</div><div class="t m0 xf h7 y9c ff1 fs4 fc0 sc0 ls1 ws0">change their transmission parameters according to the sensed</div><div class="t m0 x13 h9 y9d ff1 fs5 fc0 sc0 ls1 ws0">Fig. 2. Cognitive cycle.</div><div class="t m0 x14 h9 y9e ff1 fs5 fc0 sc0 ls1 ws0">Fig. 3. Illustration of spectrum white space [5].</div><div class="t m0 x15 h7 y9f ff1 fs4 fc0 sc0 ls1 ws0">environment variations and achieve optimal performance,</div><div class="t m0 x15 h7 ya0 ff1 fs4 fc0 sc0 ls1 ws0">which is referred to as reconﬁgurability [4].</div><div class="t m0 x15 hc ya1 ff4 fs4 fc0 sc0 ls1 ws0">B. Cognitive Radio Functions</div><div class="t m0 x16 h7 ya2 ff1 fs4 fc0 sc0 ls1 ws0">A typical duty cycle of CR, as illustrated in Fig. 2, includes</div><div class="t m0 x15 h7 ya3 ff1 fs4 fc0 sc0 ls1 ws0">detecting spectrum white space, selecting the best frequency</div><div class="t m0 x15 h7 ya4 ff1 fs4 fc0 sc0 ls1 ws0">bands, coordinating spectrum access with other users and va-</div><div class="t m0 x15 h7 ya5 ff1 fs4 fc0 sc0 ls1 ws0">cating the frequency when a primary user appears. Such a cog-</div><div class="t m0 x15 h7 ya6 ff1 fs4 fc0 sc0 ls1 ws0">nitive cycle is supported by the following functions:</div><div class="t m0 xb h7 ya7 ff1 fs4 fc0 sc0 ls1 ws0">• spectrum sensing and analysis;</div><div class="t m0 xb h7 ya8 ff1 fs4 fc0 sc0 ls1 ws0">• spectrum management and handoff;</div><div class="t m0 xb h7 ya9 ff1 fs4 fc0 sc0 ls1 ws0">• spectrum allocation and sharing.</div><div class="t m0 x16 h7 yaa ff1 fs4 fc0 sc0 ls1 ws0">Through spectrum sensing and analysis, CR can detect the</div><div class="t m0 x15 h7 yab ff1 fs4 fc0 sc0 ls1 ws0">spectrum white space (see Fig. 3), i.e., a portion of frequency</div><div class="t m0 x15 h7 yac ff1 fs4 fc0 sc0 ls1 ws0">band that is not being used by the primary users, and utilize the</div><div class="t m0 x15 h7 yad ff1 fs4 fc0 sc0 ls1 ws0">spectrum. On the other hand, when primary users start using the</div><div class="t m0 x15 h7 yae ff1 fs4 fc0 sc0 ls1 ws0">licensed spectrum again, CR can detect their activity through</div><div class="t m0 x15 h7 yaf ff1 fs4 fc0 sc0 ls1 ws0">sensing, so that no harmful interference is generated due to sec-</div><div class="t m0 x15 h7 yb0 ff1 fs4 fc0 sc0 ls1 ws0">ondary users’ transmission.</div><div class="t m0 x16 h7 yb1 ff1 fs4 fc0 sc0 ls1 ws0">After recognizing the spectrum white space by sensing,</div><div class="t m0 x15 h7 yb2 ff1 fs4 fc0 sc0 ls1 ws0">spectrum management and handoff function of CR enables</div><div class="t m0 x15 h7 yb3 ff1 fs4 fc0 sc0 ls1 ws0">secondary users to choose the best frequency band and hop</div><div class="t m0 x15 h7 yb4 ff1 fs4 fc0 sc0 ls1 ws0">among multiple bands according to the time varying channel</div><div class="t m0 x15 h7 yb5 ff1 fs4 fc0 sc0 ls1 ws0">characteristics to meet various Quality of Service (QoS) re-</div><div class="t m0 x15 h7 yb6 ff1 fs4 fc0 sc0 ls1 ws0">quirements [5]. For instance, when a primary user reclaims</div><div class="t m0 x15 h7 yb7 ff1 fs4 fc0 sc0 ls1 ws0">his/her frequency band, the secondary user that is using the</div><div class="t m0 x15 h7 yb8 ff1 fs4 fc0 sc0 ls1 ws0">licensed band can direct his/her transmission to other available</div><div class="t m0 x15 h7 yb9 ff1 fs4 fc0 sc0 ls1 ws0">frequencies, according to the channel capacity determined by</div><div class="t m0 x15 h7 yba ff1 fs4 fc0 sc0 ls1 ws0">the noise and interference levels, path loss, channel error rate,</div><div class="t m0 x15 h7 ybb ff1 fs4 fc0 sc0 ls1 ws0">holding time, and etc.</div><div class="t m0 x16 h7 ybc ff1 fs4 fc0 sc0 ls1 ws0">In dynamic spectrum access, a secondary user may share</div><div class="t m0 x15 h7 ybd ff1 fs4 fc0 sc0 ls1 ws0">the spectrum resources with primary users, other secondary</div><div class="t m0 x15 h7 ybe ff1 fs4 fc0 sc0 ls1 ws0">users, or both. Hence, a good spectrum allocation and sharing</div><div class="t m0 xd ha y63 ff5 fs7 fc0 sc0 ls1 ws0">Downloaded from https://iranpaper.ir</div><div class="t m0 xe hb y64 ff6 fs8 fc0 sc0 ls1 ws0">https://www.tarjomano.com/order</div></div><div class="pi" data-data='{"ctm":[1.616162,0.000000,0.000000,1.616162,0.000000,0.000000]}'></div></div>

<div id="pf3" class="pf w0 h0" data-page-no="3"><div class="pc pc3 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/6255e9b6b744eb386feed92b/bg3.jpg"><div class="t m0 x1 h2 y1 ff1 fs0 fc0 sc0 ls0 ws0">WANG AND LIU: ADVANCES IN COGNITIVE RADIO NETWORKS: A SURVEY 7</div><div class="t m0 x17 h9 ybf ff1 fs5 fc0 sc0 ls1 ws0">Fig. 4. Network architecture of dynamic spectrum sharing.</div><div class="t m0 x1 h7 yc0 ff1 fs4 fc0 sc0 ls1 ws0">mechanism is critical to achieve high spectrum efﬁciency. Since</div><div class="t m0 x1 h7 yc1 ff1 fs4 fc0 sc0 ls1 ws0">primary users own the spectrum rights, when secondary users</div><div class="t m0 x1 h7 yc2 ff1 fs4 fc0 sc0 ls1 ws0">co-exist in a licensed band with primary users, the interference</div><div class="t m0 x1 h7 yc3 ff1 fs4 fc0 sc0 ls1 ws0">level due to secondary spectrum usage should be limited by</div><div class="t m0 x1 h7 yc4 ff1 fs4 fc0 sc0 ls1 ws0">a certain threshold. When multiple secondary users share a</div><div class="t m0 x1 h7 yc5 ff1 fs4 fc0 sc0 ls1 ws0">frequency band, their access should be coordinated to alleviate</div><div class="t m0 x1 h7 yc6 ff1 fs4 fc0 sc0 ls1 ws0">collisions and interference.</div><div class="t m0 x1 hc yc7 ff4 fs4 fc0 sc0 ls1 ws0">C. Network Architecture and Applications</div><div class="t m0 x7 h7 yc8 ff1 fs4 fc0 sc0 ls1 ws0">With the development of CR technologies, secondary users</div><div class="t m0 x1 h7 yc9 ff1 fs4 fc0 sc0 ls1 ws0">who are not authorized with spectrum usage rights can utilize</div><div class="t m0 x1 h7 yca ff1 fs4 fc0 sc0 ls1 ws0">the temporally unused licensed bands owned by the primary</div><div class="t m0 x1 h7 ycb ff1 fs4 fc0 sc0 ls1 ws0">users. Therefore, in a CR network architecture, the components</div><div class="t m0 x1 h7 ycc ff1 fs4 fc0 sc0 ls1 ws0">include both a secondary network and a primary network, as</div><div class="t m0 x1 h7 ycd ff1 fs4 fc0 sc0 ls1 ws0">shown in Fig. 4.</div><div class="t m0 x7 h7 yce ff1 fs4 fc0 sc0 ls1 ws0">A secondary network refers to a network composed of a</div><div class="t m0 x1 h7 ycf ff1 fs4 fc0 sc0 ls1 ws0">set of secondary users with/without a secondary base station.</div><div class="t m0 x1 h7 yd0 ff1 fs4 fc0 sc0 ls1 ws0">Secondary users can only access the licensed spectrum when it</div><div class="t m0 x1 h7 yd1 ff1 fs4 fc0 sc0 ls1 ws0">is not occupied by a primary user. The opportunistic spectrum</div><div class="t m0 x1 h7 yd2 ff1 fs4 fc0 sc0 ls1 ws0">access of secondary users is usually coordinated by a secondary</div><div class="t m0 x1 h7 yd3 ff1 fs4 fc0 sc0 ls1 ws0">base station, which is a ﬁxed infrastructure component serving</div><div class="t m0 x1 h7 yd4 ff1 fs4 fc0 sc0 ls1 ws0">as a hub of the secondary network. Both secondary users and</div><div class="t m0 x1 h7 yd5 ff1 fs4 fc0 sc0 ls1 ws0">secondary base stations are equipped with CR functions. If</div><div class="t m0 x1 h7 yd6 ff1 fs4 fc0 sc0 ls1 ws0">several secondary networks share one common spectrum band,</div><div class="t m0 x1 h7 yd7 ff1 fs4 fc0 sc0 ls1 ws0">their spectrum usage may be coordinated by a central network</div><div class="t m0 xa h7 yd8 ff1 fs4 fc0 sc0 ls1 ws0">entity, called spectrum broker [8]. The spectrum broker col-</div><div class="t m0 xa h7 yd9 ff1 fs4 fc0 sc0 ls1 ws0">lects operation information from each secondary network, and</div><div class="t m0 xa h7 yda ff1 fs4 fc0 sc0 ls1 ws0">allocates the network resources to achieve efﬁcient and fair</div><div class="t m0 xa h7 ydb ff1 fs4 fc0 sc0 ls1 ws0">spectrum sharing.</div><div class="t m0 xb h7 ydc ff1 fs4 fc0 sc0 ls1 ws0">A primary network is composed of a set of primary users and</div><div class="t m0 xa h7 ydd ff1 fs4 fc0 sc0 ls1 ws0">one or more primary base stations. Primary users are authorized</div><div class="t m0 xa h7 yde ff1 fs4 fc0 sc0 ls1 ws0">to use certain licensed spectrum bands under the coordination of</div><div class="t m0 xa h7 ydf ff1 fs4 fc0 sc0 ls1 ws0">primary base stations. Their transmission should not be inter-</div><div class="t m0 xa h7 ye0 ff1 fs4 fc0 sc0 ls1 ws0">fered by secondary networks. Primary users and primary base</div><div class="t m0 xa h7 ye1 ff1 fs4 fc0 sc0 ls1 ws0">stations are in general not equipped with CR functions. There-</div><div class="t m0 xa h7 ye2 ff1 fs4 fc0 sc0 ls1 ws0">fore, if a secondary network share a licensed spectrum band with</div><div class="t m0 xa h7 ye3 ff1 fs4 fc0 sc0 ls1 ws0">a primary network, besides detecting the spectrum white space</div><div class="t m0 xa h7 ye4 ff1 fs4 fc0 sc0 ls1 ws0">and utilizing the best spectrum band, the secondary network is</div><div class="t m0 xa h7 ye5 ff1 fs4 fc0 sc0 ls1 ws0">required to immediately detect the presence of a primary user</div><div class="t m0 xa h7 ye6 ff1 fs4 fc0 sc0 ls1 ws0">and direct the secondary transmission to another available band</div><div class="t m0 xa h7 ye7 ff1 fs4 fc0 sc0 ls1 ws0">so as to avoid interfering with primary transmission.</div><div class="t m0 xb h7 ye8 ff1 fs4 fc0 sc0 ls1 ws0">Because CRs are able to sense, detect, and monitor the sur-</div><div class="t m0 xa h7 ye9 ff1 fs4 fc0 sc0 ls1 ws0">rounding RF environment such as interference and access avail-</div><div class="t m0 xa h7 yea ff1 fs4 fc0 sc0 ls1 ws0">ability, and reconﬁgure their own operating characteristics to</div><div class="t m0 xa h7 yeb ff1 fs4 fc0 sc0 ls1 ws0">best match outside situations, cognitive communications can in-</div><div class="t m0 xa h7 yec ff1 fs4 fc0 sc0 ls1 ws0">crease spectrum efﬁciency and support higher bandwidth ser-</div><div class="t m0 xa h7 yed ff1 fs4 fc0 sc0 ls1 ws0">vice. Moreover, the capability of real-time autonomous deci-</div><div class="t m0 xa h7 yee ff1 fs4 fc0 sc0 ls1 ws0">sions for efﬁcient spectrum sharing also reduces the burdens of</div><div class="t m0 xa h7 yef ff1 fs4 fc0 sc0 ls1 ws0">centralized spectrum management. As a result, CRs can be em-</div><div class="t m0 xa h7 yf0 ff1 fs4 fc0 sc0 ls1 ws0">ployed in many applications.</div><div class="t m0 xd ha y63 ff5 fs7 fc0 sc0 ls1 ws0">Downloaded from https://iranpaper.ir</div><div class="t m0 xe hb y64 ff6 fs8 fc0 sc0 ls1 ws0">https://www.tarjomano.com/order</div></div><div class="pi" data-data='{"ctm":[1.616162,0.000000,0.000000,1.616162,0.000000,0.000000]}'></div></div>

<div id="pf4" class="pf w0 h0" data-page-no="4"><div class="pc pc4 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/6255e9b6b744eb386feed92b/bg4.jpg"><div class="t m0 xf h2 y1 ff1 fs0 fc0 sc0 ls0 ws0">8 IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL PROCESSING, VOL. 5, NO. 1, FEBRUARY 2011</div><div class="t m0 x10 h7 y65 ff1 fs4 fc0 sc0 ls1 ws0">First, the capacity of military communications is limited by</div><div class="t m0 xf h7 y66 ff1 fs4 fc0 sc0 ls1 ws0">radio spectrum scarcity because static frequency assignments</div><div class="t m0 xf h7 y67 ff1 fs4 fc0 sc0 ls1 ws0">freeze bandwidth into unproductive applications, where a large</div><div class="t m0 xf h7 yf1 ff1 fs4 fc0 sc0 ls1 ws0">amount of spectrum is idle. CR using dynamic spectrum access</div><div class="t m0 xf h7 yf2 ff1 fs4 fc0 sc0 ls1 ws0">can alleviate the spectrum congestion through efﬁcient alloca-</div><div class="t m0 xf h7 yf3 ff1 fs4 fc0 sc0 ls1 ws0">tion of bandwidth and ﬂexible spectrum access [2]. Therefore,</div><div class="t m0 xf h7 yf4 ff1 fs4 fc0 sc0 ls1 ws0">CR can provide military with adaptive, seamless, and secure</div><div class="t m0 xf h7 yf5 ff1 fs4 fc0 sc0 ls1 ws0">communications.</div><div class="t m0 x10 h7 yf6 ff1 fs4 fc0 sc0 ls1 ws0">Moreover, a CR network can also be implemented to en-</div><div class="t m0 xf h7 yf7 ff1 fs4 fc0 sc0 ls1 ws0">hance public safety and homeland security. A natural disaster or</div><div class="t m0 xf h7 yf8 ff1 fs4 fc0 sc0 ls1 ws0">terrorist attack can destroy existing communication infrastruc-</div><div class="t m0 xf h7 yf9 ff1 fs4 fc0 sc0 ls1 ws0">ture, so an emergency network becomes indispensable to aid the</div><div class="t m0 xf h7 yfa ff1 fs4 fc0 sc0 ls1 ws0">search and rescue. As a CR can recognize spectrum availability</div><div class="t m0 xf h7 yfb ff1 fs4 fc0 sc0 ls1 ws0">and reconﬁgure itself for much more efﬁcient communication,</div><div class="t m0 xf h7 yfc ff1 fs4 fc0 sc0 ls1 ws0">this provides public safety personnel with dynamic spectrum</div><div class="t m0 xf h7 yfd ff1 fs4 fc0 sc0 ls1 ws0">selectivity and reliable broadband communication to minimize</div><div class="t m0 xf h7 yfe ff1 fs4 fc0 sc0 ls1 ws0">information delay. Moreover, CR can facilitate interoperability</div><div class="t m0 xf h7 yff ff1 fs4 fc0 sc0 ls1 ws0">between various communication systems. Through adapting to</div><div class="t m0 xf h7 y100 ff1 fs4 fc0 sc0 ls1 ws0">the requirements and conditions of another network, the CR de-</div><div class="t m0 xf h7 y101 ff1 fs4 fc0 sc0 ls1 ws0">vices can support multiple service types, such as voice, data,</div><div class="t m0 xf h7 y102 ff1 fs4 fc0 sc0 ls1 ws0">video, and etc.</div><div class="t m0 x10 h7 y103 ff1 fs4 fc0 sc0 ls1 ws0">Another very promising application of CR is in the com-</div><div class="t m0 xf h7 y104 ff1 fs4 fc0 sc0 ls1 ws0">mercial markets for wireless technologies. Since CR can intel-</div><div class="t m0 xf h7 y105 ff1 fs4 fc0 sc0 ls1 ws0">ligently determine which communication channels are in use</div><div class="t m0 xf h7 y106 ff1 fs4 fc0 sc0 ls1 ws0">and automatically switches to an unoccupied channel, it pro-</div><div class="t m0 xf h7 y107 ff1 fs4 fc0 sc0 ls1 ws0">vides additional bandwidth and versatility for rapidly growing</div><div class="t m0 xf h7 y108 ff1 fs4 fc0 sc0 ls1 ws0">data applications. Moreover, the adaptive and dynamic channel</div><div class="t m0 xf h7 y109 ff1 fs4 fc0 sc0 ls1 ws0">switching can help avoid spectrum conﬂict and expensive re-</div><div class="t m0 xf h7 y10a ff1 fs4 fc0 sc0 ls1 ws0">deployment. As CR can utilize a wide range of frequencies,</div><div class="t m0 xf h7 y10b ff1 fs4 fc0 sc0 ls1 ws0">some of which has excellent propagation characteristics, CR</div><div class="t m0 xf h7 y10c ff1 fs4 fc0 sc0 ls1 ws0">devices are less susceptible to fading related to growing fo-</div><div class="t m0 xf h7 y10d ff1 fs4 fc0 sc0 ls1 ws0">liage, buildings, terrain and weather. When frequency changes</div><div class="t m0 xf h7 y10e ff1 fs4 fc0 sc0 ls1 ws0">are needed due to conﬂict or interference, the CR frequency</div><div class="t m0 xf h7 y10f ff1 fs4 fc0 sc0 ls1 ws0">management software will change the operating frequency au-</div><div class="t m0 xf h7 y110 ff1 fs4 fc0 sc0 ls1 ws0">tomatically even without human intervention. Additionally, the</div><div class="t m0 xf h7 y111 ff1 fs4 fc0 sc0 ls1 ws0">radio software can change the service bandwidth remotely to ac-</div><div class="t m0 xf h7 y112 ff1 fs4 fc0 sc0 ls1 ws0">commodate new applications. As long as no end-user hardware</div><div class="t m0 xf h7 y113 ff1 fs4 fc0 sc0 ls1 ws0">needs to be updated, product upgrades or conﬁguration changes</div><div class="t m0 xf h7 y114 ff1 fs4 fc0 sc0 ls1 ws0">can be completed simply by downloading newly released radio</div><div class="t m0 xf h7 y115 ff1 fs4 fc0 sc0 ls1 ws0">management software. Thus, CR is viewed as the key enabling</div><div class="t m0 xf h7 y116 ff1 fs4 fc0 sc0 ls1 ws0">technology for future mobile wireless services anywhere, any-</div><div class="t m0 xf h7 y117 ff1 fs4 fc0 sc0 ls1 ws0">time and with any device.</div><div class="t m0 x18 h7 y118 ff1 fs4 fc0 sc0 ls1 ws0">III. S</div><div class="t m0 x19 h7 y119 ff1 fs5 fc0 sc0 ls1 ws0">PECTRUM SENSING AND ANALYSIS</div><div class="t m0 x10 h7 y11a ff1 fs4 fc0 sc0 ls1 ws0">Through spectrum sensing, CR can obtain necessary obser-</div><div class="t m0 xf h7 y11b ff1 fs4 fc0 sc0 ls1 ws0">vations about its surrounding radio environment, such as the</div><div class="t m0 xf h7 y11c ff1 fs4 fc0 sc0 ls1 ws0">presence of primary users and appearance of spectrum holes.</div><div class="t m0 xf h7 y11d ff1 fs4 fc0 sc0 ls1 ws0">Only with this information can CR adapt its transmitting and</div><div class="t m0 xf h7 y11e ff1 fs4 fc0 sc0 ls1 ws0">receiving parameters, like transmission power, frequency, mod-</div><div class="t m0 xf h7 y11f ff1 fs4 fc0 sc0 ls1 ws0">ulation schemes, and etc., in order to achieve efﬁcient spec-</div><div class="t m0 xf h7 y120 ff1 fs4 fc0 sc0 ls1 ws0">trum utilization. Therefore, spectrum sensing and analysis is</div><div class="t m0 xf h7 y121 ff1 fs4 fc0 sc0 ls1 ws0">the ﬁrst critical step towards dynamic spectrum management. In</div><div class="t m0 xf h7 y122 ff1 fs4 fc0 sc0 ls1 ws0">this section, we will discuss three different aspects of spectrum</div><div class="t m0 xf h7 y123 ff1 fs4 fc0 sc0 ls1 ws0">sensing. First is the interference temperature model, which mea-</div><div class="t m0 xf h7 y124 ff1 fs4 fc0 sc0 ls1 ws0">sures the interference level observed at a receiver and is used to</div><div class="t m0 xf h7 y125 ff1 fs4 fc0 sc0 ls1 ws0">protect licensed primary users from harmful interference due to</div><div class="t m0 xf h7 y126 ff1 fs4 fc0 sc0 ls1 ws0">unlicensed secondary users. Then we will talk about the spec-</div><div class="t m0 xf h7 y127 ff1 fs4 fc0 sc0 ls1 ws0">trum hole detection to determine additional available spectrum</div><div class="t m0 x15 h7 y128 ff1 fs4 fc0 sc0 ls1 ws0">resources and compare several detection techniques. Finally, we</div><div class="t m0 x15 h7 y129 ff1 fs4 fc0 sc0 ls1 ws0">will discuss cooperative sensing with multiple users’ help.</div><div class="t m0 x15 hc y12a ff4 fs4 fc0 sc0 ls1 ws0">A. Interference Temperature</div><div class="t m0 x16 h7 y12b ff1 fs4 fc0 sc0 ls1 ws0">In opportunistic spectrum access, secondary users need to de-</div><div class="t m0 x15 h7 y12c ff1 fs4 fc0 sc0 ls1 ws0">tect primary users’ appearance and decide which portion of the</div><div class="t m0 x15 h7 y12d ff1 fs4 fc0 sc0 ls1 ws0">spectrum is available. Such a decision can be made according to</div><div class="t m0 x15 h7 y12e ff1 fs4 fc0 sc0 ls1 ws0">different metrics. Traditional approach is to limit the transmitter</div><div class="t m0 x15 h7 y12f ff1 fs4 fc0 sc0 ls1 ws0">power of interfering devices, i.e., the transmitted power should</div><div class="t m0 x15 h7 y130 ff1 fs4 fc0 sc0 ls1 ws0">be no more than a prescribed noise ﬂoor at a certain distance</div><div class="t m0 x15 h7 y131 ff1 fs4 fc0 sc0 ls1 ws0">from the transmitter. However, due to the increased mobility</div><div class="t m0 x15 h7 y132 ff1 fs4 fc0 sc0 ls1 ws0">and variability of radio frequency (RF) emitters, constraining</div><div class="t m0 x15 h7 y133 ff1 fs4 fc0 sc0 ls1 ws0">the transmitter power becomes more problematic, since unpre-</div><div class="t m0 x15 h7 y134 ff1 fs4 fc0 sc0 ls1 ws0">dictable new source of interference may appear. To address this</div><div class="t m0 x15 h7 y135 ff1 fs4 fc0 sc0 ls1 ws0">issue, FCC Spectrum Policy Task Force [9] has proposed a new</div><div class="t m0 x15 h7 y136 ff1 fs4 fc0 sc0 ls1 ws0">metric on interference assessment, the interference temperature,</div><div class="t m0 x15 h7 y137 ff1 fs4 fc0 sc0 ls1 ws0">to enforce an interference limit perceived by receivers. The in-</div><div class="t m0 x15 h7 y138 ff1 fs4 fc0 sc0 ls1 ws0">terference temperature is a measure of the RF power available</div><div class="t m0 x15 h7 y139 ff1 fs4 fc0 sc0 ls1 ws0">at a receiving antenna to be delivered to a receiver, reﬂecting the</div><div class="t m0 x15 h7 y13a ff1 fs4 fc0 sc0 ls1 ws0">power generated by other emitters and noise sources [10]. More</div><div class="t m0 x15 h7 y13b ff1 fs4 fc0 sc0 ls1 ws0">speciﬁcally, it is deﬁned as the temperature equivalent to the RF</div><div class="t m0 x15 h7 y13c ff1 fs4 fc0 sc0 ls1 ws0">power available at a receiving antenna per unit bandwidth [11],</div><div class="t m0 x15 h7 y13d ff1 fs4 fc0 sc0 ls1 ws0">i.e.,</div><div class="t m0 x1a h7 y13e ff1 fs4 fc0 sc0 ls1 ws0">(1)</div><div class="t m0 x15 h7 y13f ff1 fs4 fc0 sc0 ls1 ws0">where</div><div class="t m0 x1b h7 y140 ff1 fs4 fc0 sc0 ls1 ws0">is the average interference power in Watts cen-</div><div class="t m0 x15 h7 y141 ff1 fs4 fc0 sc0 ls1 ws0">tered at</div><div class="t m0 x1c h7 y142 ff1 fs4 fc0 sc0 ls1 ws0">, covering bandwidth measured in Hertz, and Boltz-</div><div class="t m0 x15 h7 y143 ff1 fs4 fc0 sc0 ls1 ws0">mann’s constant</div><div class="t m0 x1d h7 y144 ff1 fs4 fc0 sc0 ls1 ws0">is 1.38 Joules per degree Kelvin.</div><div class="t m0 x16 h7 y145 ff1 fs4 fc0 sc0 ls1 ws0">With the concept of interference temperature, FCC further</div><div class="t m0 x15 h7 y146 ff1 fs4 fc0 sc0 ls1 ws0">established an interference temperature limit, which provides</div><div class="t m0 x15 h7 y147 ff1 fs4 fc0 sc0 ls1 ws0">a maximum amount of tolerable interference for a given fre-</div><div class="t m0 x15 h7 y148 ff1 fs4 fc0 sc0 ls1 ws0">quency band at a particular location. Any unlicensed secondary</div><div class="t m0 x15 h7 y149 ff1 fs4 fc0 sc0 ls1 ws0">transmitter using this band must guarantee that their transmis-</div><div class="t m0 x15 h7 y14a ff1 fs4 fc0 sc0 ls1 ws0">sion plus the existing noise and interference must not exceed the</div><div class="t m0 x15 h7 y14b ff1 fs4 fc0 sc0 ls1 ws0">interference temperature limit at a licensed receiver.</div><div class="t m0 x16 h7 y14c ff1 fs4 fc0 sc0 ls1 ws0">Since any transmission in the licensed band is viewed to be</div><div class="t m0 x15 h7 y14d ff1 fs4 fc0 sc0 ls1 ws0">harmful if it would increase the noise ﬂoor above the interfer-</div><div class="t m0 x15 h7 y14e ff1 fs4 fc0 sc0 ls1 ws0">ence temperature limit, it is necessary that the receiver have a re-</div><div class="t m0 x15 h7 y14f ff1 fs4 fc0 sc0 ls1 ws0">liable spectral estimate of the interference temperature. This re-</div><div class="t m0 x15 h7 y150 ff1 fs4 fc0 sc0 ls1 ws0">quirement can be fulﬁlled by using the multitaper method to es-</div><div class="t m0 x15 h7 y151 ff1 fs4 fc0 sc0 ls1 ws0">timate the power spectrum of the interference temperature with</div><div class="t m0 x15 h7 y152 ff1 fs4 fc0 sc0 ls1 ws0">a large number of sensors [4]. The multitaper method can solve</div><div class="t m0 x15 h7 y153 ff1 fs4 fc0 sc0 ls1 ws0">the tradeoff between bias and variance of an estimator and pro-</div><div class="t m0 x15 h7 y154 ff1 fs4 fc0 sc0 ls1 ws0">vide a near-optimal estimation performance. The large number</div><div class="t m0 x15 h7 y155 ff1 fs4 fc0 sc0 ls1 ws0">of sensors can account for the spatial variation of the RF energy</div><div class="t m0 x15 h7 y156 ff1 fs4 fc0 sc0 ls1 ws0">from one location to another. Subspace-based method has also</div><div class="t m0 x15 h7 y157 ff1 fs4 fc0 sc0 ls1 ws0">been proposed to gain knowledge of the quality and usage of a</div><div class="t m0 x15 h7 y158 ff1 fs4 fc0 sc0 ls1 ws0">spectrum band [12], where information about the interference</div><div class="t m0 x15 h7 y159 ff1 fs4 fc0 sc0 ls1 ws0">temperature is obtained by eigenvalue decomposition.</div><div class="t m0 x16 h7 y15a ff1 fs4 fc0 sc0 ls1 ws0">If a regulatory body sets an interference temperature limit</div><div class="t m0 x15 h7 y15b ff1 fs4 fc0 sc0 ls1 ws0">for a particular frequency band with bandwidth , then the sec-</div><div class="t m0 x15 h7 y15c ff1 fs4 fc0 sc0 ls1 ws0">ondary transmitters has to keep the average interference below</div><div class="t m0 x1e h7 y15d ff1 fs4 fc0 sc0 ls1 ws0">. Therefore, the interference temperature serves as a cap</div><div class="t m0 x15 h7 y15e ff1 fs4 fc0 sc0 ls1 ws0">placed on potential RF energy that could appear on that band,</div><div class="t m0 x15 h7 y15f ff1 fs4 fc0 sc0 ls1 ws0">and there are some previous efforts about how to implement</div><div class="t m0 x15 h7 y160 ff1 fs4 fc0 sc0 ls1 ws0">efﬁcient spectrum allocation with the interference temperature</div><div class="t m0 x15 h7 y161 ff1 fs4 fc0 sc0 ls1 ws0">limit.</div><div class="t m0 xd ha y63 ff5 fs7 fc0 sc0 ls1 ws0">Downloaded from https://iranpaper.ir</div><div class="t m0 xe hb y64 ff6 fs8 fc0 sc0 ls1 ws0">https://www.tarjomano.com/order</div></div><div class="pi" data-data='{"ctm":[1.616162,0.000000,0.000000,1.616162,0.000000,0.000000]}'></div></div>