Download The Evolution of Spectrum Sharing in IEEE 802.22 Wireless

The Evolution of Spectrum Sharing in the IEEE 802.22
WRAN Standards Process
John Notor
February 21, 2006
Rev 2
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CADENCE DESIGN SYSTEMS, INC.
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).
2
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)
3
802.22 Network Overview
[ref 8]
Deployment Scenario
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WRAN
Base Station
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Wireless
MIC
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TV Transmitter
WRAN
Base Station
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WRAN
Repeater
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Wireless
MIC
: WRAN Base Station
Typical ~33km
Max. 100km
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: CPE
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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.
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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.
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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 Bodypack
Wireless Microphone Transmitter
• UHF, 10mW
Power Levels
• Indoor measurement
Power at Receiver (-dBm)
-30
Handheld (dark trace)
-40
-50
-60
-70
-80
Distance (feet)
294
284
273
263
253
243
233
223
213
203
193
183
173
162
152
142
132
122
112
102
92
82
72
62
51
41
31
21
11
1
-90
Bodypack (light trace)
Signal levels vary more than 50dB over a 40 foot distance due to
multi-path and body absorption.
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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.
11
Low Voice Spectrum: Resolution BW = 10 kHz
Courtesy of Ahren Hartman, Shure, Inc.
12
High Voice Spectrum: Resolution BW = 10 kHz
Courtesy of Ahren Hartman, Shure, Inc.
13
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
Sensing thresholds
UHF TV Channel:
38
DTV
NTSC
Part 74
Beacon
-116
-94
-107
-120
Channel bandwidth (MHz)
6
6
0.2
0.01
Reference sensing antenna gain (dBi)
0
0
0
0
0.02
0.02
0.02
0.02
-128.7
-106.7
-119.7
-132.7
17.1
39.1
26.1
13.1
Maximum field strength for service protection
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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
Reference sensing thresholds (dBm)
Omni antenna aperture (m^2)
Reference power-flux-density (dB(W/m^2))
Reference field strength (dB(uV/m))
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Sensing Parameters: Estimates and Analysis
courtesy of Gerald Chouinard, CRC, Canada [ref 12]
Sensing Receiver
DTV
NTSC
Sensing antenna gain (dBi)
Part 74
0
Omni antenna aperture (m^2)
0.02
Antenna noise temperature (K)
290
Noise field strength generated by nearby LE
equipment (dB(uV/m))
-99
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)
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RF front-end Figure of Merit: G/T (dBK^1)
Sensing Carrier-to-Noise ratio (C/N) [6 MHz BW]
Beacon
If 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.
-37.12
-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
Note:values with orange
background are
placeholders, not reliable
numbers.
Probability of detection (true-positive)
90%
90%
90%
90%
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:
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-174 dBm/Hz
– Noise gain, 40 kHz BW:
+ 46 dB
– Receiver noise figure:
+ 5 dB
– Required CNR:
+ 16 dB
– DFS Threshold:
-107 dBm
DTV Co-Channel Sensing
Pilot Tone Sensing in Fixed Systems
DTV Service Area
Edge of
Service
Contour
[ref 14]
Limit of DFS
Sensing Capability
DFS Margin:
48–116 km
D/U Range Margin:
15.6–93.3 km
Cognitive Radio Range to
23 dB D/U Limit
R
17.1 < R < 32.4 km
(+36 dBm EIRP)
•30 m base station antenna height
• 9 m TV receiving antenna height
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Beacon vs Wireless Mic Sensing
[ref 7]
Theoretical
propagation model
Beacon Distance =
R + B (feet)
Beacon signal needs to
transmit beyond the radius of
protection.
Microphone Power (D) = +10 dBm
U.D. Power (U) = +26 dBm
Radius of Protection
= R (feet)
D/U = (10-26)+12 (spreading factor over
6MHz*) = -4 dB when R=B
D/U > +20 dB for no interference
to microphone
Beacon TX and
Wireless
Microphone TX
R+B = 15 times R for D/U > +20 dB
Microphone
Signal (D)
(Example: R=50 feet, B=750 feet)
Microphone
RX
Interference
Signal (U)
(*Assumes unlicensed device spreads
power over at least 6 MHz channel)
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Unlicensed
Device TX
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]
Less than Grace Period
Validation time of CH A
Validation time of CH B
Less than Grace Period
Initial Sensing
Transmitting on CH A
Sensing on CH ([0, A-n],
[A+n, N])
Transmitting on CH B
Sensing on CH ([0, B-n],
[B+n, N])
• 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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Time
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
d
DTV
Transmitter
sensing region
interference region
for each DTV receiver
keep-out region
DTV receiver
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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, [email protected]
13. Geometry for Scenario 2.ppt, Soo-Young Chang, Huawei Technologies
The following are available on the web:
14. DVB-T Transmission Systems, Glenn Doel
http://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 Notor
http://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
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