IEEE 802 22 WRAN OverviewIEEE 802.22 WRAN Overview

Yun Hee Kim * School of Electronics and Information School of Electronics and Information

Kyung Hee UniversityKOREA

ContentsContentsMotivationsCognitive Radio Requirements of IEEE 802.22Main Features of PHYMain Features of PHYConclusion

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MotivationsMotivationsSpectrum Usage Today Average 5.2%

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MotivationsMotivationsTV Bands for Unlicensed Use

FCC TV b d fFCC opens TV bands for unlicensed useTV bands only sparsely used today 33% in 1994–33% in 1994

–15% in 2004 –Among these, on average only a

few channels watchedfew channels watched–0% in 2015

TV bands very suitable for long range low power wirelessrange, low power wireless networks

More “open spectrum” More opportunities

O i th TV b d i l th fi t t !

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Opening up the TV bands is only the first step!

Cognitive radio (Spectrum agile radio)Cognitive radio (Spectrum agile radio)Characteristics

Flexible reconfigurable radio

Quickly adapts transmission characteristics

SmartSmart

AwareAware of spectrum usage in vicinity,MakesMakes intelligent decisions decisions on that basis, and ReactsReacts to evolving FCC policies

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Cognitive radio (Spectrum agile radio)Cognitive radio (Spectrum agile radio)Key goals

Dynamic spectrum access (DSA) for primary usersDynamic spectrum sharing (DSS) for other secondary usersDynamic spectrum multi-channel usage y p g

• Provide operation over multiple non-contiguous channels

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IEEE 802 22 WRANIEEE 802.22 WRANIEEE 802.22 is the first worldwide cognitive radio based standard

Wireless broadband accessReuse of TV broadcast bands on a non-interfering basis

PHY layers are determinedDownlink OFDMA parameters are determined

OUplink OFDMA parameters will be determined soonExpected to become an official IEEE standard in January/2008

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Functional RequirementsFunctional RequirementsGeneral

Items Requirements

C i f UHF, VHF band ( < 1 GHz )Carrier frequency UHF, VHF band ( < 1 GHz )54~862 MHz (PAR), 54~698 MHz (USA)

Bandwidth 6 (7, 8) MHz, Possible use of a smaller band or multiple bands p

Service subscribers

Fixed location customers• Residential• Small & Medium Enterprise• SOHO (Small office/Home office)

Service type Packet-oriented (data, voice, video)

Similar to ADSL & cable MODEM over lessService model

Similar to ADSL & cable MODEM over less populated rural areas

Wireless Regional Area Network (WRAN)

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Functional RequirementsFunctional RequirementsTarget performance

Items Requirements

Service Coverage Typical 33 km ~ Max 100 km

Active subscribers Minimum 12 users

Minimum PeakThroughput at CellEdge

Forward link : 1.5 Mbps / subscriber(18 Mbps in total)

Reverse link : 384 kbps / subscriber

Spectral Efficiency Minimum : 0.5 bps/Hz Typical : 3 bps/Hz 18 Mbps for 6 MHz BW

Service Availability 50% of locations & 99.9% of time

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F ti l R i tFunctional RequirementsProtection of incumbent services

Broadcast TV (NTSC, DTV)Part 74 Subpart H Low Power Auxiliary Stations (i.e., wireless microphones)microphones)

Mechanisms for incumbent awareness and avoidance should b b ilt i t th MAC d PHYbe built into the MAC and PHY

Proper modulation Distributed spectrum sensingp gQuiet period and fast/fine sensing managementMeasurementsDetection algorithmsDetection algorithmsSpectrum management

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WRAN HierarchyWRAN Hierarchy

Public IP Network

S D

Service Provider IP Network

HAAAA

ACR ACR

WRANBS

CPE

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• AAA : Authentication, Authorization and Account Server • ACR : Access Control Router HA : Home Agent

Deployment ScenarioDeployment Scenario

WRANBase Station

WirelessMIC

TV Transmitter

WRANRepeater

WRANBase Station

WirelessMIC

: CPE

: WRAN Base Station

Typical ~33kmMax. 100km

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: CPE

System ParametersSystem ParametersParameters Specification Remark

F 54 862 MHFrequency range 54~862 MHz

Service coverage Typical range 33 km

B d idth M d t 6 7 8 MHOptional fractional use of TV channel and h l b di t 3 ti TV h lBandwidth Mandatory: 6, 7, 8 MHz channel bonding up to 3 contiguous TV channels.

Channel aggregation of discontiguous channels.

Data rate Maximum: 72.6 MbpsMinimum: 4.8 Mbps Maximum of 23 Mbps for 6 MHzp

Spectral Efficiency Maximum: 4.03 bits/s/HzMinimum: 0.81 bits/s/Hz Single TV channel BW of 6 MHz

Modulation QPSK, 16QAM, 64QAM mandatory

Transmit power Default 4W EIRP

Multiple Access Adaptive OFDMA Partial bandwidth allocation

FFT Mode 2K mandatory 1K / 4K optional, 2K / 4K / 6K for channel b diFFT Mode 2K mandatory bonding

Cyclic Prefix Mode 1/4, 1/8, 1/16, 1/32

Duplex TDD mandatory FDD supported

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Network topology Point-to-Multipoint Network

Adaptive OFDMAAdaptive OFDMA Flexible Bandwidth Allocation using FFT

Channel bondingFractional bandwidth usage

Adaptive resource allocation according to user environmentsAdaptive resource allocation according to user environmentsChannel selectivity

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Channel BondingChannel BondingMake opportunistic and simultaneous use of multiple

ti TV h lcontiguous TV channels

Benefits:Benefits:More data rate or range

• Initial link-budget analysis showed that single-TV channel can not s pport f ll data rate (e g 18Mbps) pto 30 Km rangesupport full data rate (e.g., 18Mbps) upto 30 Km range

Multi-path Diversityp y• Small BW signal can have deep fade or flat fade• Wider-bandwidth signal provides more frequency/multipath diversity

Interference• Wider-band reduces the amount of interference

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Channel Bonding StructureChannel Bonding Structure

6K FFT over 3 TV channels Fixed inter-carrier spacing2K per TV channelNull out the outer carriers for

1 or 2 TV channels

Several implementation possibilities

1 or 2 TV channels

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Fractional Bandwidth UsageFractional Bandwidth UsageConsidering the location, bandwidth and type of the narrowband incumbent users we can use the fractionally vacant bandwidth of a single channelusers, we can use the fractionally vacant bandwidth of a single channelThe number of used sub-carriers is proportional to the fractional bandwidthIf the wireless microphones are operating co-channel, the WRAN systems shall clear the entire channelThe fractional BW mode is identified by using a PreambleExample:

Incumbent or other CR user(except microphone user)

TV incumbent user Microphone userFractional useof TV channel

Other CR user or non-microphone incumbent (regulations permitting)

Example:

6 MHz Unused(6 MHz)6 MHz

f

GuardBand

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Fractional Bandwidth UsageFractional Bandwidth UsageTo minimize the interference to adjacent narrowband i b t (IU )incumbent users (IUs)

When the narrowband IU is appeared on the adjacent TV channelBy using the guard band, we can decrease the interference to y g g ,narrowband IUIt can be also advantageous to narrowband IUs appearing in the same TV channel

Narrowbandincumbent userTV channel

Fractional use ofTV channel

6 MHz 6 MHz6 MHz

f

Guardband

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Fractional Bandwidth UsageFractional Bandwidth UsageTo increase the throughput

We can increase the throughput by using the fractional BW additionallyAnd, we can make a larger pool of bandwidth available to each userAvailable BW pool: 5,6,7,8 MHzp , , ,If we use more than 5 MHz fractional BW, we can satisfy the minimum peak throughput (1.5 Mbps for DL, 384 kbps for UL)Like the whole BW usage mode it is also suitable to PMP applicationLike the whole BW usage mode, it is also suitable to PMP application

Fractional use ofNarrowband

incumbent usersTV channel

TV channel TV channel

incumbent users(except wireless

microphone)

f

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Unused(6 MHz)2 MHz6 MHz 6 MHz 6 MHz 6 MHz

Superframe StructureSuperframe Structure

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Superframe Element DefinitionsSuperframe Element DefinitionsPreamble – synchronization, channel estimation

Two symbols long with 5 short and 2 long training sequences

SCH – superframe control header – Info onSCH – superframe control header – Info on System typeChannelChannel bondingQuiet periods (time to, duration of)

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Frame StructureFrame Structureframe n-1 frame n frame n+1 ...

Time...

MAC Slot Number

FCH Ranging

k k+1 k+3 k+5 k+7 k+9 k+11 k+13 k+15 k+17 k+20 k+23 k+26 k+29s FCH

Sel

f-is

tenc

e

g g

UCS Notification

Burst CPE #2

Burst CPE #1

Burst CPE #3

Burst CPE #1TV Channel N

s+1

s+2BW Request

mbl

e DS

-MA

P

Sco

ex

Burst CPE #4 Burst CPE #5

Burst CPE #2

Burst CPE #4

Burst CPE #3

anne

l Num

ber

Pre

am

Burst CPE #7

Burst CPE #5

nceLo

gica

l MA

C C

ha

US

-MA

P

Burst CPE #6

Burst CPE #8

Burst CPE #9

Sel

f-co

exis

ten

Burst CPE #6

Burst CPE #7

TV Channel N+1

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Burst CPE #8

TTGDS US

s+L

RTG

Frame Element DefinitionsFrame Element DefinitionsPreamble – synchronization, channel estimation

Long training sequence and optional short training sequenceThere’s also an upstream burst preamble

FCH – frame control header, info on size of DS- and US- MAPFCH frame control header, info on size of DS and US MAP and channel descriptors (PHY characteristics)MAPs – resource scheduling info for user burstsRanging – timing offset, power adjustmentUCS – urgent coexistence situation, incumbent detection reportreportBW Request – self-explanatorySSS - sliding self-coexistence slots – used by coexistence beacon to improve coexistence with neighbors BCH – burst control header for upstream – ID information

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SensingSensingProposed methods still remain to be evaluated and compared (Ti T )(Tiger Team)Several techniques were introduced at previous meetings and have been included in the PHY spec p

Energy detection (full bandwidth or pilot)Multi-resolution spectrum sensing and Analog auto correlationPN511 or PN63 sequence detectionPN511 or PN63 sequence detectionSegment sync detectorCyclostationary feature detectionSpectral correlationOptimal radiometer

Primary waveforms are DTV and analog FM for wirelessPrimary waveforms are DTV and analog FM for wireless microphones

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SensingSensingFast sensing Fine sensing

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ConclusionConclusionSpectrum-agile cognitive radios: a new paradigm in wireless communicationscommunications

Currently, much of the spectrum allocated but unusedSpectrum allocation reform underwayAd d ( iti / il ) di b i il blAdvanced (e.g., cognitive/agile) radios becoming available

Cognitive radios enable new applicationsg ppIEEE 802.22 and Cellular applications discussed here

• Cognitive radios techniques are being standardized faster than anticipatedp

“Spectrum is like disk-space, the more you have it, the more you will use it”

Open research topics on coexistence Spectrum sensing, interference avoidance…

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