IEEE 802.22 - The First Cognitive Radio Wireless Regional Area Network Standard

IEEE Communications Magazine • January 2009130 0163-6804/09/$25.00 © 2009 IEEE

INTRODUCTION

With relatively low levels of industrial noise andionospheric reflections, reasonable antennasizes, and good non-line-of-sight (NLOS) propa-gation characteristics, the TV broadcast bands inthe high-VHF/low-UHF range are ideal for cov-ering large areas in sparsely populated ruralenvironments. Starting with a Notice of Inquiryby the U.S. FCC in December 2002 [1] exploringthe possibility of allowing access to the TVbroadcast bands for license-exempt devices on anoninterfering basis, and subsequently, a goldenopportunity was created to develop a systemcapable of using these frequency bands on anoninterfering basis to bring broadband accessto rural areas — the very areas where there area large number of vacant TV channels and thepopulation density is less than the typical 60 per-sons/km2 for which cabled media such as digitalsubscriber line (DSL) and coaxial cable tech-nologies make economic sense.

In its Notice of Proposed Rulemaking,released in May 2004 [2], and its latest R&O,released in November 2008 [3], the FCC indicat-ed that TV channels 5–13 in the VHF band and14–51 in the UHF band could be used for fixedbroadband access systems.

Canada has also taken steps in this directionby opening a subset of TV channels for broad-band access in remote rural areas in the UHF

band under licensed operation [4] Other regionsof the world will almost certainly evaluate theuse of this spectrum for broadband access, topromote both economic growth and more effi-cient use of this highly valuable and useful spec-tral resource.

The development of the IEEE 802.22 WRANstandard [5] (802.22 or 802.22 WRAN herein) isaimed at using cognitive radio techniques toallow sharing of geographically unused spectrumallocated to the television broadcast service, on anoninterfering basis, to bring broadband accessto hard-to-reach low-population-density areastypical of rural environments, and is thereforetimely and has the potential for wide applicabili-ty worldwide. IEEE 802.22 WRANs are designedto operate in the TV broadcast bands whileensuring that no harmful interference is causedto the incumbent operation (i.e., digital TV andanalog TV broadcasting) and low-power licenseddevices such as wireless microphones.

DYNAMIC SPECTRUM ACCESSA cognitive radio observes its environment andmodifies its transmission characteristics accord-ingly. The cognitive radio concept was initiallyintroduced in the software defined radioresearch community [6] but has since become itsown field of study. These cognitive radio net-works use a cognition cycle that includes radioscene analysis, channel state estimation and pre-dictive modeling, and transmit power controland spectrum management commands [7]. In2005 the IEEE began holding the annual Con-ference on Dynamic Spectrum Access Networks(DySPAN) [8].

A specific area of the cognitive radio field isthe area of dynamic spectrum access in which acognitive radio network dynamically identifies

ABSTRACT

This article presents a high-level overview of theIEEE 802.22 standard for cognitive wirelessregional area networks (WRANs) that is underdevelopment in the IEEE 802 LAN/MAN Stan-dards Committee.

IEEE STANDARDS IN COMMUNICATIONSAND NETWORKING

Carl R. Stevenson, WK3C Wireless

Gerald Chouinard, Communications Research Centre, Canada

Zhongding Lei, Institute for Infocomm Research, Singapore

Wendong Hu, STMicroelectronics, Inc.

Stephen J. Shellhammer, Qualcomm Inc.

Winston Caldwell, Fox Technology Group

IEEE 802.22: The First Cognitive Radio Wireless Regional Area Network Standard

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IEEE Communications Magazine • January 2009 131

and uses portions of the spectrum that are notbeing used by other systems. These unused por-tions of the spectrum are often referred to aswhite space in the literature. The white spacemay consist of unused frequencies or unusedfragments of time in a given location. In IEEE802.22, since the white space is unused televisionchannels over a given area, it is primarily fre-quency white space; however, there is a timecomponent, since if the spectrum availabilitychanges, the 802.22 network must adapt quicklyso as not to cause harmful interference to thelicensed transmissions. This is particularly so forprotecting licensed wireless microphone opera-tions.

There are several methods that can be usedby a cognitive radio network to be aware of itsspectral environment. The two methods usedwith IEEE 802.22 for spectral awareness aregeo-location/database and spectrum sensing. Inthe first method, knowledge of the location ofthe cognitive radio devices combined with adatabase of licensed transmitters can be used todetermine which channels are locally availablefor reuse by the cognitive radio network. Spec-trum sensing consists of observing the spectrumand identifying which channels are occupied bylicensed transmission.

The 802.22 network quickly modifies its oper-ating frequency so as to only operate on chan-nels unused by licensed transmissions. Thus, the802.22 network must both quickly identify whichchannels are allowed for use and move to a newunused channel, if the current operating channelbecomes occupied by a licensed transmission.

SYSTEM ASPECTSFigure 1 illustrates the place 802.22 WRANs areintended to occupy in the family and evolutionof the various wireless data communication stan-dards developed by the IEEE 802 LAN/MANStandard Committee (LMSC).

The application for the IEEE 802.22 WRANstandard will be providing wireless broadbandaccess to a rural area of typically 17–30 km ormore in radius (up to a maximum of 100 km)from a base station (BS) and serving up to 255fixed units of customer premises equipment(CPE) with outdoor directional antennas locatedat nominally 10 m above ground level, similar toa typical VHF/UHF TV receiving installation.The minimum peak throughput delivered toCPE at the edge of coverage will be equivalentto a T1 rate (1.5 Mb/s) in the downstream (DS)direction (BS to CPE) and 384 kb/s in theupstream (US) direction (CPE to BS), allowingfor videoconferencing service.

Due to the extended coverage afforded bythe use of these lower frequencies, the physicallayer (PHY) parameters must be optimized toabsorb longer multipath excess delays thanaccommodated by other 802 wireless standards.An excess delay of up to 37 µs can be absorbedby the orthogonal frequency-division multiplex-ing (OFDM) modulation used.

Beyond the 30 km for which the PHY layerhas been designed, the medium access control(MAC) layer will absorb additional propagationdelays for coverage distances of up to 100 km

through intelligent scheduling to cover caseswhere advantageous topography allows coverageto such distances.

As shown in Fig. 2, the reference architecture

n Figure 1. The IEEE 802.22 standard relative to other IEEE 802 wireless datatransmission standards.

0.8µs

Range

30 km

1–2 km(5 GHz)

33 m20 m

20-50m

Network type

RANRegional area network

10m

Maximumdata rate

2.4 GHz

2.4 GHz

2.4 GHz

< 2.4 GHz

54-862 MHz

Frequency

23, 27, 31 Mb/sBW = 6, 7, 8 MHz

5 GHz

IEEE802.15

0.25µs

2.2µs

37µs

PAN IEEE802.11a

IEEE802.11b

IEEE802.16

Industrystandards

IEEE 802.22

1Mb/s

10Mb/s

54Mb/s

54Mb/s

11Mb/s

LAN

MAN

Multipath absoprtion w

indow

(cyclic prefix)

n Figure 2. The IEEE 802.22 reference architecture.

Higher layers: IP, ATM,1394, etc.

MAC SAP

PHY SAP

MAC

SME

PHY

SSF

Geo-location

PLME

MLME

MLME-PLME SAP

SME-M

LME SA

PSM

E-PLME SA

P

Spectrummanager(BS)/spectrumautomaton(CPE)

Convergence sub-layerbridge (e.g., 802.1d)



IEEE Communications Magazine • January 2009132

for IEEE 802.22 systems addresses the PHY andMAC layers, and the interfaces to a station man-agement entity (SME) through PHY and MAClayer management entities (MLMEs), as well asto higher layers such as IP, asynchronous trans-fer mode (ATM), and IEEE 1394 through anIEEE 802.1d compliant convergence sublayer.

At the PHY layer there are three primaryfunctions: the main data communications, thespectrum sensing function (SSF), and the geolo-cation function, with the latter two providingnecessary functionality to support the cognitiveabilities of the system.

The PHY interfaces with the MAC throughthe PHY service access point (SAP), as well asto the MLME and the SME through the PHYlayer management entity (PLME) and its SAPs.

REFERENCE ARCHITECTUREAs shown, a functional entity known as the spec-trum manager (SM) exists in the MLME at theBS and a “lightweight” version of the SM, knownas a spectrum automaton (SA), exists in theMLME at the CPE. The SM at the BS controlsuse of and access to spectral resources for theentire cell and all associated CPEs served by theBS. The SA at each CPE provides theautonomous behaviors necessary to ensure prop-er noninterfering operation of CPE in all cases,including during startup/initialization, duringchannel changes, and in case of temporary lossof communications with the BS.

PHYSICAL LAYERIEEE 802.22 compliant WRANs will providebroadband access similar to asymmetrical DSL(ADSL) and cable modems, but will supportmore economical deployment over sparsely pop-ulated areas. The frequency range used in the

VHF/UHF TV broadcast bands extends from 54to 862 MHz depending on the various regulatorydomains around the world.

PHY FEATURESTable 1 tabulates the typical IEEE 802.22 fea-tures compared to IEEE 802.16e, its closest “rel-ative” among the IEEE 802 family. IEEE 802.22will define a single air interface based on 2048-carrier orthogonal frequency-division multipleaccess (OFDMA) to provide a reliable end-to-end link suitable for NLOS operation. A generaldescription of OFDMA is easily found in the lit-erature [9].

Since it is not always possible to have pairedTV channels available, IEEE 802.22 is initiallydefining a single time-domain duplex (TDD)mode, with plans to define a frequency-divisionduplex (FDD) mode as a future amendment tothe standard.

The granularity of frequency spectrum forWRAN is a TV channel as shown in Table 1. Tosupport the various TV channel bandwidths inuse in the world (6, 7, and 8 MHz channels), thesampling frequency, carrier spacing, symbolduration, signal bandwidth, and data rates willbe scaled by the channel bandwidth for world-wide operation. IEEE 802.22 systems will use acommon oversampling factor and the sameframe/symbol structure, coding schemes, inter-leaving, and so on.

Four different lengths of cyclic prefix aredefined as 1/4, 1/8, 1/16, and 1/32 of symbolduration to allow for different channel delayspreads while utilizing the spectrum efficiently.Due to the physical size of antenna structures atthese lower frequencies, IEEE 802.22 will notsupport multiple-antenna techniques such asmultiple-input multiple-output (MIMO) orbeamforming.

nn

Table 1. IEEE 802.22 features compared to IEEE 802.16.

IEEE 802.22 IEEE 802.16e

Air interface OFDMA OFDMA, OFDM, Single Carriers

Fast Fourier transform Single mode (2048) Multiple modes (2048, 1024, 512, 128)

OFDMA channel profile (MHz) 6, 7, or 8 (according to regulatory domain) 28, 20, 17.5, 14, 10, 8.75, 7, 3.5, 1.25

Burst allocation Linear Two dimensional

Subcarrier permutation Distributed with enhanced interleaver Adjacent or distributed

Multiple-antenna techniques Not supported Support multiplexing, space time coding,and beamforming

Superframe/frame structure Support a superframe structure based on groups of 16frames. Frame size: 10 ms

Superframe is not supported. Supportedframe sizes: 2, 5, 10, or 20 ms.

Coexistence with incumbentsSpectrum sensing management,geolocationmanagement, incumbent database query, andchannel management.

Not supported.

Self-coexistence Dynamic spectrum sharing Master frame assignment

Internetwork communications Over-the-air coexistence beacon or over-the-IP-network. Over-the-IP-network (primarily)




Since WRAN systems are for fixed operation,transmission channels are expected to changevery slowly, so there is little time diversity gainto be achieved through burst allocation acrossdifferent symbols. Therefore, the downstreambursts in IEEE 802.22 will be allocated progres-sively across subchannels in the frequencydomain, as depicted in Fig. 3, to minimize over-head by simplifying the downstream map. Thiswill also contribute to reducing decoding latency.The upstream bursts will be allocated progres-sively across symbols to minimize the number ofsubchannels used by CPE, hence reducing theinstantaneous effective isotropic radiated power(EIRP) to mitigate interference to incumbentsystems. The upstream bursts can also bemapped on a 7-symbol column basis, as shown inFig. 3.

The physical subcarriers in each subchannelin IEEE 802.22 are distributed across the chan-nel to increase frequency diversity. Transmittinga cluster of adjacent subcarriers is not supported

in the IEEE 802.22 standard because it wouldincrease the potential for harmful interferenceto narrowband wireless microphones.

ADAPTIVE MODULATION AND CODINGIEEE 802.22 defines 12 combinations of threemodulations (quaternary phase shift keying[QPSK], 16-quadrature amplitude modulaion[QAM], 64-QAM) and four coding rates (1/2,2/3, 3/4, 5/6) for data communications that canbe flexibly chosen among to achieve varioustrade-offs of data rate and robustness, depend-ing on channel and interference conditions. Asshown in Table 2, a total of 14 transmissionmodes are supported in IEEE 802.22. Modes3–14 are used for data communications; mode 1is used for transmission of code-division multipleaccess (CDMA) ranging/bandwidth (BW)request message/urgent coexistence situation(UCS) notification; and mode 2 is used for thecoexistence beacon protocol (CBP). The peakdata rate and spectrum efficiency shown are for

n Figure 3. Superframe and frame structure.

Fram

e pr

eam

ble

US

MA

PD

S M

AP

FCH

US

MA

PD

CD

Burs

t 1

Burs

t 2

Burs

t m

Burs

ts

UCD

Superframe n – 1••• •••Superframe n

160 ms

Superframe n + 1Time

Frame 0

Superframepreamble

Framepreamble

Framepreamble

26 to 42 symbols corresponding to bandwidths from 6 MHz to 8 MHz and cyclic prefixes from 1/4 to 1/32

FramepreambleSCH

Frame 1

10 ms10 ms

Frame 15

10 ms

Ranging/BW request/UCS notification

Burst 1

More than 7 PFDMA symbolsBurst 3

Burst 2

Tim

e bu

ffer

Tim

e bu

ffer

RTG

TT

60 s

ubch

anne

lsBursts

Burst

Burst

Burst

DS subframe

Burst

Burst n

US subframe(smallest US burst portion on a given

subchannel = 7 symbols)

•••

•••

Self-

coex

iste

nce

win

dow

(4 o

r 5 s

ymbo

ls w

hen

sche

dule

d)

Transmitting a cluster

of adjacent

subcarriers is not

supported in the

IEEE 802.22 standard

because it would

increase the

potential for harmful

interference to

narrowband wireless

microphones.




a single TV channel with BW = 6 MHz. Forother BWs such as 7 MHz or 8 MHz, the num-bers will scale up proportionally.

Convolutional coding is the only mandatorymode of forward error control (FEC) codingdefined in IEEE 802.22. The data burst is encod-ed using a rate 1/2 binary convolutional encoderwith constraint length 7. Different coding ratesare obtained by puncturing the output of theconvolutional coder.

Three optional advanced FEC modes areincluded to provide better performance, but atthe price of increased decoding latency and com-plexity: two variants of turbo codes, duo-binaryconvolutional turbo code (CTC) and shortenedblock turbo codes (SBTC), and low density pari-ty check (LDPC) codes.

It is worthwhile mentioning that the bit inter-leaving process after FEC is a departure fromother IEEE standards such as 802.16 or 802.11.The block interleaving algorithm is a turbo-based structure using an interleaving unit inte-grated in an iterative structure. Interleavingparameters are selected to optimize the inter-leaving spreading between adjacent samples andseparated samples in order to achieve better fre-quency diversity.

PREAMBLE, PILOT PATTERN, ANDCHANNELIZATION

There are three types of preamble defined inWRAN:, superframe preamble, frame preamble,and CBP preamble, in order to facilitate burst

detection, synchronization, and channel estima-tion. All three preambles are one OFDM symbollong in time with 1/4 cyclic prefix.

All CPEs synchronize to a BS, in time andfrequency, using the superframe preamble, whichconsists of four repetitions of a short trainingsequence (STS) following the cyclic prefix. Theframe preamble is used for synchronization,channel estimation, frequency offset estimation,and received power estimation. It consists of tworepetitions of a long training sequence (LTS).The CBP preamble is used for CBP detection,synchronization, frequency offset estimation, andCBP channel estimation. It has the same struc-ture as the superframe preamble but uses a dif-ferent STS to be distinct from the superframepreamble with low cross-correlation.

In order to obtain robust channel estimationand good tracking ability for frequency offsetand phase noise, one pilot is placed on everyseventh useful subcarrier in the frequencydomain, and the pilot positions are changedfrom symbol to symbol to ensure that every sub-carrier has been used as a pilot over the periodof seven OFDM symbols. The basic tiling is onesubcarrier by seven symbols for both down-stream and upstream.

The elementary unit for resource allocation isthe subchannel, which consists of 28 subcarrierswith 24 data subcarriers and 4 pilot subcarriers.There are a total of 60 subchannels in eachOFDM symbol.

In the downstream, all data subcarriers in the60 subchannels will be interleaved with block

nn

Table 2. Modulation and coding rates for IEEE 802.22.

PHY mode Modulation Coding rate Peak data rate in 6MHz (Mb/s)

Spectral efficiency(BW = 6 MHz)

1 BPSK Uncoded 4.54 0.76

2 QPSK 1/2 and repeat: 3 1.51 0.25

3 QPSK 1/2 4.54 0.76

4 QPSK 2/3 6.05 1.01

5 QPSK 3/4 6.81 1.13

6 QPSK 5/6 7.56 1.26

7 16-QAM 1/2 9.08 1.51

8 16-QAM 2/3 12.10 2.02

9 16-QAM 3/4 13.61 2.27

10 16-QAM 5/6 15.13 2.52

11 64-QAM 1/2 13.61 2.27

12 64-QAM 2/3 18.15 3.03

13 64-QAM 3/4 20.42 3.40

14 64-QAM 5/6 22.69 3.78

There are three types

of preamble defined

in WRAN:

superframe

preamble, frame

preamble, and CBP

preamble, in order

to facilitate burst

detection,

synchronization, and

channel estimation.

All three preambles

are one OFDM

symbol long in time

with 1/4 cyclic prefix.




size 1440 (24 × 60) before transmission to exploitfrequency diversity. In the upstream, two sub-channels will be reserved for ranging, bandwidthrequest message, or UCS notification. Theremaining subchannels will be interleaved withblock size 1624 (28 × 58), including both pilotand data. The frequency interleaving algorithmsfor upstream and downstream are the same asthe bit interleaving algorithm, but with differentparameters. The inclusion of pilots in the inter-leaving process in the upstream direction is toensure that every CPE burst that arrives at theBS will have one pilot on each subcarrier overthe period of seven OFDMA symbols, which isthe minimum upstream burst length. On theother hand, the exclusion of pilots in the inter-leaving process in the downstream is to allowfast channel estimation (using fewer than sevenOFDM symbols) at CPEs to allow for delay-sen-sitive applications

MAC LAYERThe IEEE 802.22 MAC provides mechanismsfor flexible and efficient data transmission, andsupports cognitive capabilities for both reliableprotection of incumbent services in the TV bandand self-coexistence among 802.22 systems. TheIEEE 802.22 MAC is applicable to any region inthe world and does not require country-specificparameter sets. Table 1 shows the major featuresprovided in IEEE 802.22 as compared to IEEE802.16e.

DATA TRANSMISSIONAn IEEE 802.22 system is a point-to-multipointnetwork in which a central BS controls the medi-um access of a number of associated CPE unitsfor broadband wireless access applications. Inthe downstream direction data are scheduledover consecutive MAC slots, while in theupstream direction the channel capacity is sharedby the CPE units based on a demand-assignedmultiple access (DAMA) scheduling scheme.The concept of a connection plays a key role inthe 802.22 MAC. The mapping of all services toconnections, as performed in the convergencesublayer, facilitates bandwidth allocation, QoSand traffic parameter association, and data deliv-ery between the corresponding convergence sub-layers. While each 802.22 station has a 48-bituniversal MAC address that serves as the stationidentification, the 12-bit connection identifica-tions (CIDs) are primarily used for data trans-missions within an 802.22 system.

SUPERFRAME AND FRAME STRUCTUREThe 802.22 MAC employs a superframe struc-ture in order to efficiently manage data commu-nication and facilitate a number of cognitivefunctions for licensed incumbent protection,WRAN synchronization, and self-coexistence. Asdepicted in Fig. 3, a superframe transmitted by aBS on its operating channel begins with a specialpreamble, and contains a superframe controlheader (SCH) and 16 MAC frames.

Each MAC frame, with a 10 ms frame size,comprises a downstream subframe and anupstream subframe with an adaptive boundary inbetween. While the DS subframe only contains a

single PHY protocol data unit (PDU), the USsubframe may have a number of PHY PDUsscheduled from different CPE units, as well ascontention intervals for initialization, bandwidthrequest, UCS notification, and self-coexistence.Because the DS traffic for CPE located far fromthe BS can be scheduled early in the DS sub-frame, such a data layout allows the MAC toabsorb the round-trip delay for large distances.In order to absorb the propagation delay for adistance of up to 100 km, a time buffer of onesymbol is included before and after the self-coexistence window. Similarly, in order to absorbthe round-trip delay in the initial ranging pro-cess, a time buffer of two symbols is includedbefore and after the ranging burst.

NETWORK ENTRY AND INITIALIZATIONUnlike other existing wireless access technolo-gies, the network entry and initialization proce-dures in the 802.22 MAC not only defineprocesses such as synchronization, ranging,capacity negotiation, authorization, registration,and connection setup, but also explicitly specifythe operations of geolocation, channel databaseaccess, initial spectrum sensing, internetworksynchronization, and discovery.

BSs and CPE will be required to use satellite-based geolocation technology, which will alsofacilitate synchronization among neighboringnetworks by providing a global time source. Thelist of available TV channels is obtained byreferring to an up-to-date TV channel usagedatabase and augmented by spectrum sensingperformed both by BSs and CPE.

SELF-COEXISTENCEIn a typical deployment scenario, multiple 802.22systems may operate in the same vicinity. Mutualinterference among these collocated WRAN sys-tems due to co-channel operation could degradethe system performance significantly. To addressthis issue, the 802.22 MAC specifies a self-coex-istence mechanism based on the CBP and con-sisting of spectrum sharing schemes that addressdifferent coexistence needs in a coherent man-ner.

The CBP is a communication protocol basedon beacon transmissions among the coexistingWRAN cells. A CBP packet, delivered in theoperating channel through the beacon transmis-sion in a dedicated self-coexistence window(SCW) at the end of some frames, comprises apreamble, an SCH, and a CBP MAC PDU. Itspurpose is to convey all necessary informationacross TV channels to facilitate network discov-ery, coordination, and spectrum sharing. Notethat the beacon transmissions which deliver CBPpackets are integral to IEEE 802.22 OFDMAtransmissions and therefore different from theIEEE 802.22.1 beacon transmissions that needto be transmitted continuously by the 802.22.1devices to signal the presence of licensed wire-less microphone operations.

During a SCW that is synchronized across theTV channels of interest, a WRAN station (BS orCPE) can either transmit CBP packets on itsoperating channel or receive CBP packets onany channel For efficient intercell communica-tions, each WRAN system is required to main-

The IEEE 802.22

MAC provides

mechanisms for

flexible and efficient

data transmission

and supports

cognitive capabilities

for both reliable

protection of

incumbent services

in the TV band and

self-coexistence

among 802.22

systems.




tain a minimum repeating pattern of SCWs intransmit (or active) mode, although the SCWscan also be scheduled on an on-demand basis.Each WRAN system can reserve its own SCWson the operating channel for exclusive CBPtransmission or share the active SCWs withother co-channel neighbors through contention-based access. By knowing the SCW patterns ofits neighbors, a WRAN system can schedulereceiving operation at the appropriate momentto capture the CBP packets transmitted from theneighboring systems of interest.

COGNITIVE FUNCTIONSIn order to operate in TV broadcast bands with-out affecting digital TV, analog TV, and licensedwireless microphones operated by TV broadcast-ers and other eligible licensees, 802.22 systemswill have to be cognizant of all incumbent opera-tions in their vicinity.

The necessary tools are being included in thestandard to fulfill these cognitive functions. First,the location of each BS and CPE unit will beaccurately established. This is described in detailin the geolocation section below. The secondtool is access to a channel availability databasethat will provide reliable information on channelavailability for WRAN use at any given location.The third tool is the sensing capability included

in the standard to sense the presence and identi-fy the type of incumbent signals in channels ofinterest.

These capabilities will, by allowing the BS tocontrol channel usage and CPE maximum EIRP,constitute the set of cognitive functions neededto allow operation of 802.22 systems in the TVbroadcast bands on a noninterference basis withthe incumbents.

SPECTRUM MANAGERThe spectrum manager is the cognitive functionat the BS that will use the inputs from the spec-trum sensing function (SSF), geolocation, andthe incumbent database to decide on the TVchannel to be used by the WRAN cell as well asthe EIRP limits imposed on the specific WRANdevices. This entity is to be conceptually locatedat the MAC sublayer in the BS, as illustrated inFig. 2, and will work closely with the data pathMAC to communicate with the CPE, and willinterface with the PLME to control the localsensing and geolocation functions, and with theSME to access the incumbent database and forany local override. The relationships between thespectrum manager, spectrum automaton, andvarious cognitive entities are depicted in Fig. 4.

Various steps need to be taken by the SM todeclare that a channel may be used for opera-tion. Sensing has to be done on the operating

n Figure 4. Relationship between the spectrum manager and other cognitive function entities.

Sensingreports

Locationinformation

Channelinformation

BS

CPE

Incumbentdatabase

Availablechannels& EIRP

Locationinformation

Locationinformation

Occupiedchannels

Sensingcontrol

Spectrum manager

Channel managementCoexistence management

Sensing managementTransmit power control limits

GEO

Transmit antennacharacteristics

SSF

Locationinformation

Occupiedchannels

Sensingcontrol

GEO SSF

Spectrum automaton

Sensing automaton

The spectrum

manager is the

cognitive function at

the BS that will use

the inputs from the

spectrum sensing

function (SSF),

geolocation and the

incumbent database

to decide on the TV

channel to be used

by the WRAN cell as

well as the EIRP

limits imposed to the

specific WRAN

devices.




channel (N) and adjacent channels (N ± 1) tomake sure that no incumbent (digital or analogTV or licensed wireless microphone) is present.Verification of the distance to the protected con-tour will need to be done through access to theTV incumbent database.

If it is established that WRAN operation onchannel N may create interference to a broad-cast incumbent operating on a related channel,the SM will have the following four options:• Reduce the EIRP of the CPE by placing a

limit on the transmit power control (TPC)range to eliminate the interference in theirlocal area.

• If such a decrease in CPE EIRP renders theservice unsustainable, disallow these CPEunits (i.e., these CPE units need to seekservice on another channel from the sameor a different service provider).

• Reduce the EIRP of the BS transmission toeliminate the potential interference.

• In many cases a reduction in the BS EIRPwill no longer allow proper WRAN opera-tion with distant CPE, and the SM will needto initiate a channel move (to its first back-up channel) involving the BS and all of itsassociated CPE.There will always be a manual override at the

BS in the unlikely event that an unexpectedinterference situation occurs. It is assumed thatthe WRAN operator will have the ultimateresponsibility for avoiding interference to incum-bents. Any special event will be handled on acase-by-case basis to avoid interference.

GEOLOCATION AND DATABASEThe IEEE 802.22 draft standard requires alldevices in the network to be installed in a fixedlocation and the BS is required to know its loca-tion and the location of all of its associated CPE.The location of the BS must be known to withina 15 m radius while the location of CPE must beknown to within a 100 m radius.

In order to meet this location requirement,all devices in the network are equipped withsatellite-based geolocation technology (GPS,Galileo, etc.). During the initialization proce-dure of any new CPE on the network, the geolo-cation unit in the CPE must successfully lock tothe necessary number of satellites; and, in doingso, the CPE must accurately determine its loca-tion before it can transmit. After the CPE deter-mines its own location, it can then attempt toassociate to the BS.

Another requirement of the 802.22 draft stan-dard is that the BS must have access to anincumbent database service. This service pro-vides accurate and up-to-date informationdescribing protected broadcast operation in thearea.

It is expected that the BS accesses throughthe incumbent database service not only adatabase detailing protected television opera-tions and a database detailing low-power licensedauxiliary operations in the area, but also adatabase detailing other IEEE 802.22 operationsin the area.

When a new CPE attempts to associate witha BS during initialization, the CPE sends itslocation coordinates to the BS. The BS then uses

the location information for the new CPE toquery the database. The latitude and longitudefor the CPE gets passed to the higher layers atthe BS. Other parameters for the CPE, inputfrom the higher layers, such as antenna pattern,height, and EIRP, can be provided along withthese coordinates so that the incumbent databaseservice can determine the expected area overwhich the CPE could potentially interfere. A listof available channels and their respective maxi-mum EIRP at which the CPE can operate with-out potentially causing interference to theprotected incumbent service is generated andreturned to the BS. An 802.22 network is pro-hibited from operating on any channel not onthis resultant list of available channels or abovethe maximum EIRP level specified for any avail-able channel.

SPECTRUM SENSINGSpectrum sensing involves observing the radiofrequency spectrum and processing the observa-tions to determine if a channel is occupied by alicensed transmission. Spectrum sensing isincluded as a mandatory feature within IEEE802.22.

In IEEE 802.22, both the BS and CPE sensethe spectrum for three different licensed trans-missions: analog television, digital television, andlicensed low-power auxiliary devices such aswireless microphones. In addition to these sig-nals, the Working Group is developing a stan-dard for a self-organizing network of beacondevices (being standardized as IEEE 802.22.1)which is intended to give additional protectionfor low-power licensed uses. The sensing require-ments are summarized in terms of four parame-ters: sensing receiver sensitivity, channeldetection time, probability of detection, andprobability of false alarm. All nodes in the 802.22network will sense licensed transmissions usingan antenna with a gain of at least 0 dBi in alldirections. The sensing antenna must be out-doors, clear of obstructions as much as possible,and at a minimum height of 10 m above groundlevel. The sensing receiver reference sensitivity isspecified for this 0 dBi antenna gain, and afterall losses between the antenna and the input tothe receiver have been included. For digital TV,the sensing receiver sensitivity is –116 dBm. Foranalog TV the sensitivity is –94 dBm, while forwireless microphones the sensitivity is –107 dBm.The channel detection time for all signal types is2 s. The probability of detection is 0.9, while theprobability of false alarm is 0.1 for all signaltypes.

The 802.22 spectrum sensing framework isbuilt on four pillars:• Per-channel sensing• Quiet periods• Standardized reporting• Implementation independence

Each television channel is sensed indepen-dently. However, the standard will not precludean implementation that senses multiple channelssimultaneously. This architecture was selected toallow a low-cost design that tunes the sensingreceiver to a single channel at a time. The sec-ond component of the sensing framework is theuse of quiet periods. The MAC supports schedul-

The IEEE 802.22

draft standard

requires all devices in

the network to be

installed in a fixed

location and the BS

is required to know

its location and the

location of all of its

associated CPEs. The

location of the BS

must be known to

within a 15 m radius

while the location of

a CPE must be

known to within a

100 m radius.




ing of quiet periods during which the BS and allCPE temporarily cease transmission. The MACalso includes signaling between nearby BSs thatenables these BSs to synchronize their quietperiods. Sensing is performed during thesescheduled quiet periods to minimize any inter-ference from the WRAN systems to the sensingreceiver. The third component of the sensingframework is standardized reporting of spectrumsensing. Sensing is performed in both the BSand the CPE, but the final decision on whether agiven channel is available for use by the WRANis made at the BS. Therefore, the results of thespectrum sensing performed at the CPE must bereported to the BS in a standardized way. Also,the spectrum sensing in CPE is controlled byMAC management messages sent from the BSindicating the prioritized lists of channels to besensed during CPE idle time or specific alternatesensing tasks. The fourth and final pillar in thespectrum sensing framework is spectrum sensingimplementation independence. No specific spec-trum sensing technique will be mandatory in thestandard. Designers will be free to implementwhatever spectrum sensing technique theychoose as long as it meets the specified sensingrequirements and reports the results in the stan-dardized format. However, descriptions of anumber of spectrum sensing techniques thatmight be used are included as examples in aninformative annex within the IEEE 802.22 draftstandard. Additional details on spectrum sensingin IEEE 802.22 can be found in [10].

A BRIEF OVERVIEW OF THEIEEE 802.22.1 BEACON

Beyond sensing the incumbent signals (i.e., digi-tal and analog TV, and licensed wireless micro-phones operated by broadcasters), WRANdevices must be able to sense the 802.22.1 bea-con [11], developed to signal the presence ofwireless microphones from a distance larger thanthe interference distance of WRAN CPE. Thisbeacon will occupy a bandwidth of 77 kHz in the6 MHz TV channel at the nominal digital TVpilot frequency and be transmitted in the sameTV channel as that occupied by the microphonesat a maximum power of 250 mW in the UHFTV band (50 mW at VHF) using a more effi-cient antenna than typical wireless microphoneantennas to achieve better coverage.

The beacon symbol is QPSK modulated andspread with an 8-chip pseudo-noise sequence.The in-phase component of the beacon symbolscarries a repetition of 3 ms sync bursts, includingan index that decrements to localize the start ofa longer payload carried by the other orthogonal

component, which contains information aboutthe location of these microphones, and a signa-ture and certificate to prove that it is legitimateand that protection is needed. Since this burst isasynchronous with WRAN operation, the cap-ture of an entire sync burst needs a sensing win-dow of 5.1 ms, which has become the basic widthof the WRAN intraframe sensing window. Thecapture of an entire beacon payload, which lastssome 100 ms, will need an interframe sensingwindow that spans one or two superframesdepending on the timing alignment.

CONCLUSIONSThe developing IEEE 802.22 standard will allowbroadband access to be provided in sparselypopulated areas that cannot be economicallyserved by wireline means, or other wireless solu-tions at higher frequencies, by using cognitiveradio techniques to allow operation on a nonin-terfering basis in the VHF/UHF TV broadcastbands. This will increase the efficiency of utiliza-tion of that spectrum, and provide large eco-nomic and societal benefits.

REFERENCES[1] U.S. FCC, ET Docket 02-380, “Notice of Inquiry, in the

matter of Additional Spectrum for Unlicensed DevicesBelow 900MHz and in the 3GHz Band,” Dec. 20, 2002.

[2] U.S. FCC, ET Docket 04-186, “Notice of Proposed RuleMaking, in the matter of Unlicensed Operation in theTV Broadcast Bands,” May 25, 2004.

[3] U.S. FCC, ET Docket 08-260, “Second Report and Orderand Memorandum Opinion and Order, in the Matter ofUnlicensed Operation in the TV Broadcast Bands Addi-tional Spectrum for Unlicensed Devices Below 900 MHzand in the 3 GHz Band,” Oct. 18, 2006.

[4] Industry Canada, Radio Systems Policy RP-06, “WhereInitially TV channels 25, 34, 35, and 43 are Open forLicensing for Remote Rural Broadband Systems (RRBS),”June 2006.

[5] “IEEE P802.22/D1.0 Draft Standard for Wireless Region-al Area Networks Part 22: Cognitive Wireless RAN Medi-um Access Control (MAC) and Physical Layer (PHY)Specifications: Policies and Procedures for Operation inthe TV Bands,” Apr. 2008.

[6] J. Mitolla and G. Q. MaGuire, Jr., “Cognitive Radio:Making Software Radios More Personal,” IEEE Pers.Commun., Aug. 1999, pp. 13–18.

[7] S. Haykin, “Cognitive Radio: Brain-Empowered WirelessCommunications,” IEEE JSAC, Feb. 2005, pp. 201–20.

[8] IEEE Dynamic Spectrum Access Networks Conference;http://www.ieee-dyspan.org/

[9] R. van Nee and R. Prasad, OFDM for Wireless Multime-dia Communications, Artech House, 2000.

[10] S. J. Shellhammer, “Spectrum Sensing in IEEE 802.22,”IAPR Wksp. Cognitive Info. Processing, June 2008.

[11] “IEEE P802.22.1/D2.0 Draft Standard for InformationTechnology — Telecommunications and InformationExchange Between Systems — Local and MetropolitanArea Networks – Specific Requirements — Part 22.1:Enhanced Protection for Low-Power, Licensed DevicesOperating in Television Broadcast Bands,” Oct. 2007.

The developing

IEEE 802.22 standard

will allow broadband

access to be

provided in sparsely

populated areas by

using cognitive radio

techniques to allow

operation on a

non-interfering basis

in the VHF/UHF

Television Broadcast

bands.



Documents

IEEE 802.22 - The First Cognitive Radio Wireless Regional Area Network Standard