The document discusses using unused TV spectrum, known as TV white spaces, for unlicensed wireless devices. It notes that while spectrum sensing technology has shown promise in the lab for identifying vacant TV channels, field tests so far indicate the technology is not reliable enough. Two proposals aim to break the political logjam around this issue - one separates devices into low-power ones using spectrum sensing and higher-power ones using geolocation databases, while another calls for all devices to use geolocation databases. The transition to digital TV in early 2009 adds urgency to resolving these issues.

1. UHF TV White Space --A New Challenge for Spectrum Managers Annual Meeting, National Spectrum Managers Association Arlington, VA May 20-21, 2008 Paul Henry AT&T Labs – Research Middletown, NJ [email_address]

2. Underutilized Spectrum Can ‘white space’ spectrum be successfully managed ?

3. UHF TV Whitespace 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 Channel 54 in the Eastern US (graphic courtesy of Shared Spectrum Co. from a contribution to IEEE 802.18 SG1) Unlicensed operation Allowed 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)

4. Available Spectrum (after Digital TV transition in Feb 2009) *6 MHz/channel

5. 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

6. Protecting TV Users 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? TV Service Area Residential white space network

7. 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 R d ~ 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 transmitter White space device DTV receiver sensitivity: -84 dBm DTV Interference tolerance: -104 dBm R d

8. 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

9. 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 Mic Rcvr Protective Bubble Beacon

10. Field of Battle Opposed Cox communications Nat Assn Broadcasters NFL NASCAR ● ● ● In Favor Dell Google Microsoft Philips ● ● ● FCC Docket ET 04-186 Radio science lost in political shouting match FCC labs conducting independent evaluation Mobility UVerse

11. 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

12. 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

13. 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…..

14. Thank you!