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1、,Cognitive Radio:Next Big Thing,Presented by:Huifang Li,May.26,2008,China Telecom Corporation Ltd.,2,OutlineBasic ConceptsApplications and MarketsKey IssuesEmerging StandardsChallenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,3,Background-current usage of radio resourceAccording to sc
2、anning portionsof the radio spectrum below3GHzsome frequency bands in thespectrum are largely;unoccupiedmost of the timesome other frequency bands areonly partially occupiedremaining frequency bands areheavily usedFCC reportutilization of the assigned spectrumrange from 15%to 85%the licensed bands a
3、re abundantbut poorly utilizedFig.1 Measurements of spectrum occupancy below 3GHz,China Telecom Corporation Ltd.,4,Background-improvements of spectrum utilizationShortage of spectrum management in traditional wayspectrum usage is very low in certain licensed bandsthe scarcity of radio resources is b
4、ecoming a crisis hindering thedevelopment of many wireless applicationsSpectrum holeband of frequencies assigned to a primary user and is not being utilizedby that user at a particular time and specific geographic locationWays to improve spectrum utilizationmaking it possible for a secondary user(wh
5、o is not being serviced)toaccess a spectrum hole unoccupied by the primary user at the rightlocation and timeCognitive Radio is seen as the solution to the currentlow usage of the radio spectrum,China Telecom Corporation Ltd.,5,Definition and function of Cognitive RadioCognitive radio(CR)a radio tha
6、t can change its transmitter parameters based on interactionwith the environment in which it operatesFunction of CR:spectrum sensingdetermine which portions of the spectrum is availabledetect the presence of licensed usersspectrum managementselect the best available channelspectrum sharingcoordinate
7、 access to this channel with other usersspectrum mobilityvacate the channel when a licensed user is detected,China Telecom Corporation Ltd.,6,Spectrum hole access with CRFig.2 usage of spectrum hole with CRCR enables the useraccess a spectrum hole unoccupied by the licensed userIf this band is furth
8、er used by a licensed usermoves to another spectrum holestays in the same band,altering its transmission power level or modulation schemeto avoid interference,China Telecom Corporation Ltd.,7,awareness,adaptability,intelligence,learning,efficiency,Characteristics of CRCognitive Radio,China Telecom C
9、orporation Ltd.,8,OutlineBasic ConceptsApplications and MarketsKey IssuesEmerging StandardsChallenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,9,Prominent target applicationCore application with initial trial deployments of CRwireless broadband access in rural and remote areasperforma
10、nce comparable to those of existing fixed broadband accesstechnologiesFCC selected the TV bands for providing CR service duetolower spectrum of frequencies features is favorable for propagationcharacteristicsmany TV channels are largely unoccupiedmost households and businesses rely on cable and sate
11、llite TV servicesunlicensed bands lower costs of electronic devices,China Telecom Corporation Ltd.,10,Other key marketsCR can be used in other settingssingle-family residentialmulti-dwelling unitssmall office/home office(SOHO)small businessesmulti-tenant buildingspublic and private campusesType of s
12、ervices provided by CRdatavoiceaudio and video traffic with appropriate Quality-of-Service(QoS)support,China Telecom Corporation Ltd.,11,OutlineBasic ConceptsApplications and MarketsKey IssuesEmerging StandardsChallenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,12,Physical architectur
13、e of CR-transceiverMain components:radio front-end and the baseband processing unitComponent can be reconfigured to adapt to the time-varying RFenvironmentBaseband processing unit is essentially similar to existingtransceiversRF front-end is a novelty of the CRFig.3 transceiver of CR,China Telecom C
14、orporation Ltd.,13,Physical architecture of CR-RF front-end of transceiverNovel characteristicwideband sensing capabilityRF hardware technologieswideband antenna,power amplifier,adaptive filterSpectrum sensing enables real-time measurements of spectruminformation from radio environmentFig.4 RF front
15、-end of transceiver,14,Fig.5 Basic cognitive cycle,bandwidth of the transmissionChina Telecom Corporation Ltd.,Cognitive capability-cognitive cycleThree cognitive tasks:1.Radio-scene analysisestimation of interference temperaturedetection of spectrum holes2.Channel identificationestimation of channe
16、l-state informationprediction of channel capacity3.Transmit-power control and dynamicspectrum managementdata ratetransmission mode,China Telecom Corporation Ltd.,15,Cognitive capability-cognitive stepsThree main stepsSpectrum sensingmonitors the available spectrum bands,captures their information,de
17、tects thespectrum holes.Spectrum analysisestimate the characteristics of the spectrum holes which are detected throughspectrum sensingSpectrum decisionappropriate spectrum band is chosen according to the spectrum characteristicsand user requirementsFig.6 Classification of spectrum sensing techniques
18、,China Telecom Corporation Ltd.,16,ReconfigurabilityCapability of adjusting operating parameters for the transmissionOperating frequencyModulationTransmission powerCommunication technologyCharacteristics of reconfigurabilityParameters can be reconfigured at any time of a transmissionEnables CR to ad
19、apt easily to the dynamic radio environmentEnables CR to switch to a different spectrum band,China Telecom Corporation Ltd.,17,OutlineBasic ConceptsApplications and MarketsKey IssuesEmerging StandardsChallenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,18,Standard work overviewSDR(soft
20、ware defined radio)Forum chartered two groups on CRCR Working Groupstandardizing a definition of CRidentifying the enabling technologiesCR Special Interest Groupidentifying attractive commercial applicationsIEEE 1900 group with three subgroups1900.1standardize definitions and terminology1900.2standa
21、rdizing a process for testing and verifying the operation1900.3standardizing approaches for qualifying software modulesIEEE 802 community is currently developing two standards802.22intending to provide high bandwidth access in rural areas802.11hfocusing on dynamic frequency selection in WLAN,China T
22、elecom Corporation Ltd.,19,IEEE 802.22 SYSTEM-Topology,Entities and RelationshipsSpecifies a fixed point-to-multipoint wireless air interface:Base Station(BS)Consumer Premise Equipments(CPEs)BS controls the medium access anddownstream transmits to CPEsSystem follows a strictmasters/slave relationshi
23、pBS controls RF characteristics of CPEsCPE is not allowed to transmit beforereceiving authorization from BSDistributed sensingBS instructs CPEs to perform distributedmeasurement activitiesFig.7 802.22 deployment configuration,China Telecom Corporation Ltd.,20,IEEE 802.22 SYSTEM-Service Coverage and
24、CapacityService coveragelarger coverage range,up to 100 Kmhigher powerfavorable propagation characteristicsof TV frequency bandsService capacitybroad bandoperation frequency 54-862 MHzextended range to 41-910 MHzaccommodate various TV channelbandwidths of 6,7,8 MHz0.5 bit/(sec/Hz)up to 5 bit/(sec/Hz
25、)Fig.8 802.22 compared to other standards,China Telecom Corporation Ltd.,21,IEEE 802.11h-wlan with cognitive functionCognitive tasksObservationestimate channel characteristics such as path loss and link marginOrientationdetermine if it is operating in the presence of a radar installation,in abad cha
26、nnel,in band with satellites,or in the presence of other wlansDecisiondecide to change frequency(Dynamic Frequency Selection),adjust thetransmit power(Transmit Power Control),or in the case of encounteringActionbe able to implement decisions,China Telecom Corporation Ltd.,22,OutlineBasic ConceptsApp
27、lications and MarketsKey IssuesEmerging StandardsChallenges to Wide-Scale Deployment,China Telecom Corporation Ltd.,23,Spectrum sensing challengesSpectrum sensing enables CR to be aware of changes inits surrounding by detecting spectrum holesChallenges for development of spectrum sensinginterference
28、 measurementno practical way to measure the interference at nearby primaryreceiversspectrum sensing in multi-user networksmulti-user environment makes it more difficult to sense theprimary users and to estimate the actual interferencedetection capabilitydesign complexity increases by using of a larg
29、e number ofcarriers in order to reduce overall detection time,China Telecom Corporation Ltd.,24,Spectrum decision challengesSpectrum decision choose appropriate spectrum bandaccording to the spectrum characteristics and userrequirementsChallenges for development of spectrum decision:decision modelho
30、w to combine the spectrum characterization parameters for thespectrum decision modelmultiple spectrum band decisionhow to determine the number of spectrum bandshow to select the set of appropriate bandsspectrum decision over heterogenous spectrum bandshow to support spectrum decision on both license
31、d andunlicensed bands over the heterogeneous environment,China Telecom Corporation Ltd.,25,Spectrum mobility challengesSpectrum mobility enables changing of frequency to getthe best available channelChallenges for development of spectrum mobilitymobility modelhow to decide the best available spectru
32、m based on the channelcharacteristics and the requirements of applicationsspectrum mobility in time domainhow to maintain QoS with changing of available channels overtimespectrum mobility in spacehow to continuous allocate spectrum with changing of availablebands when a user moves from one place to another,Thanks for your attention!,
