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© 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, NJpsh@research.att.com
© 2008 AT&T Knowledge Ventures. All rights reserved.
Underutilized Spectrum
Can ‘white space’ spectrum be successfully managed ?
© 2008 AT&T Knowledge Ventures. All rights reserved.
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)
© 2008 AT&T Knowledge Ventures. All rights reserved.
Available Spectrum(after Digital TV transition in Feb 2009)
*6 MHz/channel
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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
© 2008 AT&T Knowledge Ventures. All rights reserved.
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…..
© 2008 AT&T Knowledge Ventures. All rights reserved.
Thank you!
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