1 1040 Henry Nsma May 2008 V3

© 2008 AT&T Knowledge Ventures. All rights reserved. AT&T and the AT&T logo are trademarks of AT&T Knowledge Ventures.

UHF TV White Space--A New Challenge for Spectrum Managers

Annual Meeting, National Spectrum Managers AssociationArlington, VA

May 20-21, 2008

Paul HenryAT&T Labs – Research

Middletown, [email protected]

© 2008 AT&T Knowledge Ventures. All rights reserved.

Underutilized Spectrum

Can ‘white space’ spectrum be successfully managed ?


UHF TV Whitespace

Channel 54 in the Eastern US(graphic courtesy of Shared Spectrum Co. from a contribution to IEEE 802.18 SG1)

May 2004: FCC proposes to allow unlicensed use of TV whitespace• Primarily UHF ~500-700 MHz (chan 21-51) --

Desirable propagation characteristics• Must protect TV and wireless microphone• Smart (cognitive) radio may be needed

Unlicensed operationAllowed

Not allowed

Nov 2004: IEEE802.22 formed to explore WRAN (~33 km nominal range)

Oct 2006: FCC allows low-power fixed use; regulations TBD• Continues inquiry re portable use; regulations 1H08 3Q08

Dec 2007: OFCOM (UK) Report• 112 MHz to be allocated for unlicensed use after Digital Switchover (2012)

Feb 2009: US DTV transition (2012 in UK)


Available Spectrum(after Digital TV transition in Feb 2009)

*6 MHz/channel


Wireless Residential Multimedia Networking

Broadband Access

Media &Communications

Server

White space (cog radio) modem

PDA Remote

• Capability• 19Mbps per 6 MHz TV channel• Multimedia with QoS (incl HDTV), Internet, VoIP• Portability

• Modest power: ~10mW • Technical challenge: protect incumbent users

Typ path loss ~75dB


Keep white space devices outside of TV service area.

Geolocation -- GPS • Authoritative database – central control• Unreliable indoors• Increased device cost

Spectrum sensing• White space users scan for vacant channels• Hidden-node problem

What is ‘radius of destruction’ for white space device?

Protecting TV Users

TV Service Area

Residential white space

network


Radius of Destruction

To avoid interference to DTV:•Air path loss > Pt – DTV tolerance – penetration loss + TV antenna gain

= +10dBm + 104 – 10 + 8 = 112 dB

•Propagation loss (Longley-Rice model): 112 dB implies Rd ~ 2 km – Faster decay than inverse-square

•Note: Outdoor WRAN (802.22): 4 watt transmitter implies Rd ~ 15 km!•Must inhibit transmission whenever within ~2 km of ‘viewable’ DTV signal

– Can white space device ‘sniff’ for TV signal and then make reliable decision?

TV transmitterWhite space

device

DTV receiver sensitivity: -84 dBm

DTV Interference tolerance: -104 dBm

Rd


Spectrum Sensing--The Hidden Node Problem

TV transmitter

DTV sensitivity -84dBm

White space device

Shadow

Device sensitivity margin = shadow fading + penetration loss + antenna gain difference•Shadow fading in 90% of locations < 15dB*•Typical penetration loss ~10dB**•Antenna gain difference ~ 8dB*

Required device margin ~ 15 + 10 + 8 = 33 dB (~ 90% successful detection)

Device sensitivity = -84 dBm -33 dB = -117 dBm

Demonstrated device sensitivity: -115 to -120 dBm

*R.A.O’Connor, IEEE Trans Broadcasting, Sept 2001

**M.A.Sturza, Working Paper #16, New America Foundation, Jan. 2007

DTV spectrum


Wireless Microphone

•Low power (working range < 100m)•No standard signature like DTV; therefore very hard to detect•Solution – Easily recognized beacon; protective bubble•Problems

– Abuse of protection– Unlicensed users (e.g. schools, churches); squatters’ rights

WSD MicRcvr

ProtectiveBubble

Beacon


Field of Battle

OpposedCox communications

Nat Assn BroadcastersNFL

NASCAR●●●

In FavorDell

GoogleMicrosoftPhilips

●●●

FCC Docket ET 04-186

MobilityUVerse

• Radio science lost in political shouting match

• FCC labs conducting independent evaluation


FCC Field Tests

Initial tests summer 2007•DTV detection: Philips -115dBm; Microsoft device failed•Wireless mic detection (no beacon): Many false positives•Technology not good enough for definitive field tests

Recent activity•Google laboratory: -120dBm sensitivity•Ongoing tests: Philips, Microsoft, Motorola, Adaptrum•No abatement of political posturing


Breaking the Logjam --Motorola and Google Proposals

Goal: Get past the squabbles over spectrum sensing

Dec. ’07: In FCC filing Motorola proposes 2 classes of white space devices

– <10mW (e.g. WLAN): spectrum sensing only– >10mW (e.g. 802.22 WRAN): Geolocation with spectrum sensing

backup– Minimal public reaction

March ’08: Google proposes geolocation for all white space operation

– Calls press conference• “WiFi on steroids”• “Gigabit rates”

– Lots of headlines – Mission Accomplished– Probably consistent with Google’s aspirations,

but unacceptable to proponents of bluetooth-like applications

Intense lobbying continues


Takeaways

• UHF TV white space• Opportunity to use sparsely occupied, attractive spectrum

• Must protect digital TV and wireless microphone• Technologies: Spectrum sensing, geolocation, beacon• Protection achievable in lab setting; field tests to come

• Intense political posturing; logjam at FCC

• DTV transition Feb 2009 less than a year away; stay tuned…..


Thank you!