1 CADENCE DESIGN SYSTEMS, INC.

The Evolution of Spectrum Sharing in the IEEE 802.22 WRAN Standards Process

John Notor

February 21, 2006

Rev 2

2

Background

• The IEEE 802.22 Wireless Regional Area Network (WRAN) Working Group is developing a point to multipoint fixed wireless access network standard intended to operate world wide in the unused segments of the terrestrial TV broadcast bands.

• To date, only the US Federal Communications Commission (FCC) has created an initiative to allow this to take place – the so-called TV Band NPRM 1.

• Other regulatory agencies world wide have expressed interest in similar initiatives.

• This presentation is a snapshot of the present activity based mostly on publicly available material (see Bibliography).

1. Notice of Proposed Rulemaking (NPRM).

3

802.22 Network Overview [ref 1]

• DSL rates to the edge of coverage.• Lightly licensed base station (BS).• Unlicensed CPE’s• Base station power: > +36 dBm• CPE Tx Power: +36 dBm EIRP

2. Customer Premise Equipment (CPE)

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802.22 Network Overview [ref 8]

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WRANRepeater

TV TransmitterWRAN

Base Station

WirelessMIC

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WRANBase Station

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: CPE집

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: WRAN Base Station

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Typical ~33kmMax. 100km

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Deployment Scenario

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Spectrum Sensing to Protect Incumbents

• Licensed Incumbents:

– TV Broadcasters:

– NTSC (US/Canada/Japan analog TV), ATSC (US, Canada DTV), PAL (Europe analog TV), SECAM (France analog TV), DVB-T (Europe/worldwide DTV).

– Land Mobile Radio Networks:

– Public Safety (police, fire, etc.), Commercial (cabs, towing services, etc.)

– Wireless Microphones and other TV broadcast related devices (in the US, FCC rules, Part 74 Low Power Auxiliary Station devices).

• 802.22 Approach:

– Avoid operating on Land Mobile Radio channels.

– Use planning, GPS, databases for Base Station planning, licensing.

– Use Base Station authorization/control and distributed sensing, in BS and CPE’s, to avoid unintentional operation on TV channels.

– Use sensing to mitigate interference to Part 74 devices.

6

TV Broadcast - Analog TV

Analog TV (NTSC) Spectrum [ref 14]

• Power primarily confined to Video and Audio carriers.

• Distinctive double peaked spectrum makes identification by spectrum profiling relatively easy.

• Relatively high narrowband power levels compared to DTV.

7

TV Broadcast – US DTV

Digital TV (ATSC) Spectrum [ref 14]

• Power spread over center 5.38 MHz within a TV channnel.

• Pilot tone is a distinctive feature when observed in a narrowband receiver.

• Pilot tone power is 11.3 dB below average power measured in a 6 MHz bandwidth.

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TV Broadcast – Europe, worldwide DTV

Digital TV (DVB-T) Spectrum [ref 13]

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Part 74 Devices, Including Wireless Microphones [ref 7]

• Wireless microphones are devices covered under Part 74 of the FCC rules:

– They are classified by the FCC as “Low Power Auxiliary Stations”.

– May be operated in the TV band by TV broadcast license holders under the aegis of their broadcast license.

– Wireless microphones are licensed secondary users of the TV spectrum.

– Most wireless microphones use analog FM transmission, although there are some digital units.

– Occupied bandwidth is limited to 200 kHz by FCC rules.

– Power output is limited to < 50 mW in VHF, < 250 mW in UHF, 85% of units operate at < 50 mW.

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Typical Wireless Mic Link Performance [ref 7]

Handheld and BodypackWireless Microphone Transmitter

Power Levels

-90

-80

-70

-60

-50

-40

-30

1

11 21 31 41 51 62 72 82 92

102

112

122

132

142

152

162

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183

193

203

213

223

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243

253

263

273

284

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Distance (feet)

Po

we

r at

Rec

eiv

er (

-dB

m)

• UHF, 10mW• Indoor measurement

Handheld (dark trace)

Bodypack (light trace)

Signal levels vary more than 50dB over a 40 foot distance due to multi-path and body absorption.

11

Typical Wireless Microphone Spectra

• The following show some typical spectra for wireless microphones:

– Low frequency voice content spectrum.

– High frequency voice content spectrum.

– An unmodulated spectrum.

• Most of the signal energy is contain in about a 40 kHz bandwidth.

• The no modulation case is the worst case in terms of spectrum width because of short term carrier drift.

• The character of the spectral shape is somewhat amorphous, so a relatively high CNR is required to assure good probability of detection.

12

Low Voice Spectrum: Resolution BW = 10 kHz Courtesy of Ahren Hartman, Shure, Inc.

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High Voice Spectrum: Resolution BW = 10 kHz Courtesy of Ahren Hartman, Shure, Inc.

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Unmodulated Spectrum: Resolution BW = 10 kHz Courtesy of Ahren Hartman, Shure, Inc.

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Sensing Parameters: Estimates and Analysis courtesy of Gerald Chouinard, CRC, Canada [ref 12]

802.22 WRAN Incumbent Sensing

Frequency (MHz) 617 UHF TV Channel: 38

Sensing thresholds DTV NTSC Part 74 Beacon

Reference sensing thresholds (dBm) -116 -94 -107 -120

Channel bandwidth (MHz) 6 6 0.2 0.01

Reference sensing antenna gain (dBi) 0 0 0 0

Omni antenna aperture (m^2) 0.02 0.02 0.02 0.02

Reference power-flux-density (dB(W/m^2)) -128.7 -106.7 -119.7 -132.7

Reference field strength (dB(uV/m)) 17.1 39.1 26.1 13.1

Maximum field strength for service protection 41 64 -30.0 13.1 dB(uV/m)

Proposed reference field strength for sensing 17.1 39.1 26.1 13.1 dB(uV/m)

Margin for the sensing threshold 23.9 24.9 -56.1 0.0 dB

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Sensing Parameters: Estimates and Analysis courtesy of Gerald Chouinard, CRC, Canada [ref 12]

Sensing Receiver DTV NTSC Part 74 Beacon

Sensing antenna gain (dBi) 0

Omni antenna aperture (m^2) 0.02

Antenna noise temperature (K) 290

Noise field strength generated by nearby LE equipment (dB(uV/m))

-99If local RF noise is generated by other LE

systems in the neighborhood, this noise will need to be added to this equation and will result in lower C/N at the output of the sensor RF front-end.

RF noise temperature resulting from nearby LE equipment (K)

0

Antenna height, HAAT (m) 10

Coupling loss (dB) 0.5

Downlead loss (dB) 4

Pre-selection filter loss (dB) 2

LNA Noise Figure (dB) 6

RF front-end Figure of Merit: G/T (dBK^1) -37.12 Sensing Carrier-to-Noise ratio (C/N) [6 MHz BW] -22.305 -0.3 1.5 1.5

dB

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Sensing Parameters: Estimates and Analysis courtesy of Gerald Chouinard, CRC, Canada [ref 12]

Required detection performance

Probability of detection (true-positive) 90% 90% 90% 90%

Note:values with orange background are placeholders, not reliable numbers.

Probability of false alarm (false positive) 10% 10% 10% 10%

C/N requirements for the specified detection performance for "BW*Time=1"

DTV NTSC Part 74 Beacon

DTV energy detection 13.5       dB

DTV pilot tone energy detection -3.1     dB

DTV horizontal sync detection -13.0     dB

DTV PN511 cyclostationary detection -18.0     dB

DTV PN63 cyclostationary detection -15.0       dB

NTSC carrier detection   5.0     dB

NTSC colour sub-carrier detection   25.0     dB

Part 74 Wireless micro energy detection     20.0   dB

Part 74 Beacon energy detection     -3.0 dB

Part 74 Beacon decoding       5.0 dB

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Sensing Parameters: Estimates and Analysis courtesy of Gerald Chouinard, CRC, Canada [ref 12]

Sensing time requirement to meet the C/N at the sensing threshold

DTV NTSC Part 74 Beacon Total time period over which sensing has to

take place

DTV energy detection 634.45       us 10.762 MHz

DTV pilot tone energy detection 8,364     us  

DTV horizontal sync detection 3.35     us 0.77 ms

DTV PN511 cyclostationary detection 142.45     us 96.79 ms

DTV PN63 cyclostationary detection 35.12       us 72.58 ms

NTSC carrier detection   0.57     us

NTSC colour sub-carrier detection   56.55     us

Part 74 Wireless micro energy detection     356.78   us

Part 74 Beacon energy detection     35.59 us

Part 74 Beacon decoding       225.11 us

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Notor’s Calculation of Wireless Mic DFS Threshold

• Assume the following:

– Use an energy detection approach, 40 kHz bandwidth.

– Required CNR in a 40 kHz bandwidth for high probability of detection: ~16 dB.

– High CNR requirement needed to overcome the noise like properties of voice/music modulation.

– Assume a 5 dB receiver noise figure.

• Calculation

– kTB: -174 dBm/Hz

– Noise gain, 40 kHz BW: + 46 dB

– Receiver noise figure: + 5 dB

– Required CNR: + 16 dB

– DFS Threshold: -107 dBm

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DTV Co-Channel Sensing

DTV Service Area

Edge ofServiceContour

Limit of DFS Sensing Capability

DFS Margin:48–116 km

Cognitive Radio Range to 23 dB D/U Limit

17.1 < R < 32.4 km(+36 dBm EIRP)

R

D/U Range Margin:15.6–93.3 km

Pilot Tone Sensing in Fixed Systems [ref 14]

•30 m base station antenna height • 9 m TV receiving antenna height

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Beacon vs Wireless Mic Sensing [ref 7]

Microphone Signal (D)

Beacon TX and Wireless

Microphone TX

Microphone RX

Radius of Protection = R (feet)

Unlicensed Device TX

Interference Signal (U)

Beacon Distance = R + B (feet)

D/U > +20 dB for no interference to microphone

R+B = 15 times R for D/U > +20 dB

(Example: R=50 feet, B=750 feet)

Microphone Power (D) = +10 dBm

U.D. Power (U) = +26 dBm

D/U = (10-26)+12 (spreading factor over 6MHz*) = -4 dB when R=B

(*Assumes unlicensed device spreads power over at least 6 MHz channel)

Theoretical propagation model

Beacon signal needs to transmit beyond the radius of protection.

22

802.22 Key Proposals in Play for March

• ETRI-FT-Philips-Samsung Proposal: PHY [ref 3,4,5,8]

– OFDMA both in uplink and downlink

– QPSK, 16-QAM, and 64-QAM, spreaded-QPSK

– OQAM is also being considered, but it has been submitted as a separate contribution

– More than 30 sub channels per TV channel

– Contiguous channel bonding up to 3 TV channels (and beyond in a stack manner)

– Data rate range from 5Mbps to 70Mbps

– TDD, FDD

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802.22 Key Proposals in Play for March

• ETRI-FT-Philips-Samsung Proposal: Sensing [ref 3,4,5,8]

– Dual Sensing Strategy: Energy detection and Fine/Feature detection

– Energy Detection: To meet the speed and power requirement

– Power spectrum distribution in the entire band is obtained

– On request basis, detect the power level of selected channel in very short time

– Examples are MRSS, RSSI

– Fine/Feature Detection: To meet the minimum sensitivity requirement

– Fine sensing is applied for the selected channel

– Feature Detection: detecting digital modulated signals

– Examples include CSFD, field-sync detection

– FFT based spectral analysis: detecting narrowband analog modulated signals, most of part 74 devices

– Distributed Sensing Strategy : Frequency usage information is collected and managed at Base-station

– Either the BS makes the detection decision based on the collective measurement results or CPE’s can make the decision

– Can be implemented as a stand alone sensing block with an omni-directional antenna

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802.22 Key Proposals in Play for March

• ST-Runcom Proposal: PHY [ref 9]

– Duplexing Technique: TDD

– Multiple Access Method: TDMA/OFDMA

– OFDM Symbols allocated by TDMA

– Sub-Carriers within an OFDM Symbol allocated by OFDMA

– Diversity: Frequency, Time, Code, Space

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802.22 Key Proposals in Play for March

• ST-Runcom Proposal: Sensing [ref 9]

– RF Sensing simultaneously with transmission using Dynamic Frequency Hopping (DFH).

• During a DFH operation cycle

– BS schedules the system to switch (hop) to channel (set) A

– BS and CPEs perform data transmissions on channel (set) A

– BS performs, and schedules CPEs to perform spectrum sensing on channel [0, A-n] and [A+n, N]

– CPEs report sensing measurement results

– BS performs report processing

– BS performs channel selection and acquisition

– BS announces DFS decision for the next operation cycle

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802.22 Key Proposals in Play for March

• ST-Runcom Proposal: Sensing [ref 9]

Initial Sensing

Validation time of CH A

Transmitting on CH ASensing on CH ([0, A-n],

[A+n, N])

Less than Grace Period

Validation time of CH B

Less than Grace Period

Transmitting on CH BSensing on CH ([0, B-n],

[B+n, N])

Time

• Validation time – The latest time a channel is validated to be vacant

• Grace period – The maximum period of time a incumbent can tolerate interference for

LE operations, from the beginning of the incumbent’s operations

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802.22 Spectrum Sensing Tiger Team

• Meets via telecon and email (802.22 reflector).

• Purpose: to pursue closure on the Spectrum Sensing Simulation Model [ref 10].

• Process (Notor’s view):

– Propose and evaluate proposals for determining sensing efficacy.

– Develop agreed-upon sensing scenarios.

• This is a stepping stone on the way to “defining what done looks like”.

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Sensing Tiger Team: Working Toward Clarity [ref 13]

DTV Protection Contour

WRAN

DTVTransmitter

d

DTV receiver

interference region

for each DTV receiverkeep-out region

sensing region

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Final Thoughts

• Within the IEEE 802.22 Working Group process, sensing technology at the conceptual, strategic and practical level are still in the early stages of definition/implementation.

• In addition to the issues pointed to in this presentation, there is a need to extend sensing beyond just co-channel sensing, to account for the TV receiver’s limitations and the proposed change of regulatory paradigm:

– Imperfect reception of a weak signal in the presence of one or more strong signals in the band.

– The lack of taboo channel planning in a geographic region, which, in the past, avoided assigning TV channels to certain frequencies to minimize the negative impact on reception of other channels due to poor receiver characteristics.

– The need to set transmit power levels in a friendly way given near far issues, and planning issues.

• Finally, there continues to be a lack of coherent and common understanding about the strengths and weaknesses of a sensing approach to co-existence in the radio, regulatory, and broadcast communities.

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Bibliography

The following documents are referenced in this presentation, and are available on the IEEE 802.22 web site: http://www.ieee802.org/22/.

September 2005:

1. 22-05-0007-46-0000_RAN_Requirements.doc

November 2005:

2. 22-05-0096-00-0000_Thomson_Proposal_Presentation.ppt.

3. 22-05-0100-01-0000_Samsung_Proposal_Presentation.ppt.

4. 22-05-0105-01-0000_Philips-FT_PHY-MAC_Proposal_Presentation.ppt.

5. 22-05-0109-01-0000_ETRI-SEM-GATech_Proposal_Presentation.ppt

January 2006:

6. 22-06-0006-00-0000_UHF_TV_ Band_White_Spaces.ppt

7. 22-06-0007-01-0000_Primary-User-Protection-in-802.22-Proposals.ppt

8. 22-06-0005-01-0000_ETRI-FT-Philips-Samsung_Proposal.ppt

9. 22-05-0097-02-0000_STM-Runcom_PHY-MAC_Proposal_Presentation.ppt

10. 22-06-0028-01-0000-Spectrum-Sensing-Simulation-Model-GC.doc

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Bibliography

The following documents are not available publicly:

11. Shure_IEEE_BTS_Presentation_101105.ppt.

12. Sensing Thresholds-r4.xls, Gerald Chouinard, Communications Research Center, Canada, gerald.chouinard@crc.ca

13. Geometry for Scenario 2.ppt, Soo-Young Chang, Huawei Technologies

The following are available on the web:

14. DVB-T Transmission Systems, Glenn Doelhttp://www.itu.int/ITU-R/conferences/rrc/rrc-04/intersession/workshops/damaskus/docs/Presentations/ntl_1_DVB-T_systems.pdf

15. 18-04-0030-04-0000-proposal-part-15-244-cognitive-radio-operation-in-tv-band.ppt, John Notorhttp://grouper.ieee.org/groups/802/18/Meeting_documents/2004_July/18-04-0030-01-0000-proposal-part-15-244-cognitive-radio-operation-in-tv-band.ppt