IEEE 802.11af: PHY Specification

IEEE 802.11af:
TV White Space based WLAN
Hyoil Kim
Wireless and Mobile Networking Lab. (WMNL)
School of ECE
Ulsan National Institute of Science and Technology (UNIST)
Ulsan, Republic of Korea
Presentation Outline
 Introduction to TV White Space
 IEEE 802.11af: Architectural Framework
 IEEE 802.11af: MAC Specification
 IEEE 802.11af: PHY Specification
 IEEE 802.11af: Regulations
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Spectrum White Spaces
 Under-utilized legacy spectrum
– sub-GHz: average spectrum utilization: 13-17% (2007)
– white space (WS): temporarily vacant licensed spectrum
 opportunistic reuse of WS
– dynamic spectrum access (DSA), cognitive radio (CR)
– IEEE 802.22 WRAN, ECMA 392 (ECMA TC48-TC1), IEEE 802.11af
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TV White Space (TVWS)
 TVWS: white space in TV bands (VHF/UHF)
– 54–698 MHz (TV channels 2–51)
– standardization:
• IEEE 802.11af-2013 (a.k.a. Super Wi-Fi)
• IEEE 802.22 WRAN
• ECMA 392 (equivalently, ECMA TC48-TC1)
 Benefits (compared to ISM/UNII)
– smaller path loss & better wall-penetrability
– larger coverage
– more evenly-distributed
data rates
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TVWS in Korea [3]
Use Cases of TVWS
Rural Broadband
Home Network
http://www2.nict.go.jp/wireless/smartlab/project/astra_wlan.html
Smart Grid
Cellular Offload
http://www2.nict.go.jp/wireless/
smartlab/project/astra_ran.html
http://www2.nict.go.jp/wireless/smartlab/project/astra_sun.html
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http://www.ict-qosmos.eu/project/ technicalhighlights/scenarios-and-business-models.html
TVWS Identification
 Spectrum sensing (via signal detection)
– field test by FCC (2008) showed limitations of sensing
• Adaptrum, I2R, Microsoft, Motorola, Philips
– an optional feature (FCC ruling 10-174 on WS, 2010)
 Geo-location database (GDB)
OET Report,
FCC/OET
08-TR-1005,
2008
– possesses location-specific spectrum availability
– e.g., Spectrum Bridge, Google Spectrum Database
http://showmywhitespace.com/
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http://www.google.com/get/spectrumdatabase/
Worldwide Activities on TVWS
 The AIR.U Initiative (2012)
– a consortium of educational
associations, public interest
groups and high-tech companies
(e.g., Google, MS)
– (2013/07) first on-campus Super Wi-Fi @ WVU
– (2013/11) Declaration Networks plan for
Super Wi-Fi at 500+ university campuses
 Super Wi-Fi at Africa
– (2013/03) Google, wireless Internet via TVWS
@ South Africa
 Super Wi-Fi at Asia
– (2013/11) Gardens by the Bay @ Singapore
– (2014/01) Ministry of Science, ICT, and
Future Planning, TVWS 시범사업 @ Korea
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http://www.fiercewireless.com/tech/story/goo
gle-unveils-tv-white-space-test-bed-southafrica/2013-03-26
Presentation Outline
 Introduction to TV White Space
 IEEE 802.11af: Architectural Framework
 IEEE 802.11af: MAC Specification
 IEEE 802.11af: PHY Specification
 IEEE 802.11af: Regulations
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IEEE 802.11af: An Overview
 Finalized in Feb. 2014 as IEEE 802.11af-2013
 802.11af: enhanced coverage, moderate rate
– channel BW
6, 7, 8 MHz (region-specific)
– peak rate
384.0 Mbps (6 or 7 MHz), 568.9 Mbps (8 MHz)
– coverage
< 1km
– TVHT (TV High Throughput) PHY
• based on VHT (Very High Throughput) PHY
• use parameters for 40 MHz channel (sampling freq. scaled accordingly)
– channelization:
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TVHT_W,
TVHT_W+W, TVHT_2W,
TVHT_2W+2W, TVHT_4W
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IEEE 802.11af: Terminology
 White Space Device (WSD)
 Geolocation Database (GDB)
– a DB that stores geographic-location-specific information, e.g., permissible
frequencies and operating parameters for WSDs
– a DB whose operation is mandated or authorized by a regulatory authority
 White Space Map (WSM)
– representation of the information on identified available frequencies
obtained from a GDB
 Registered Location Secure Server (RLSS)
– a local DB that organizes geographic location and operating parameters of its
related BSSs
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IEEE 802.11af: Terminology
 Geolocation-Database-Dependent Entities (GDD)
– entities whose operation is dependent on information received from a GDB
 GDD enabling Station
– equivalent to the AP STA
– authorized to control the operation of GDD dependent STAs and securely
access the GDB
 GDD dependent Station
– equivalent to the STA
– a STA that is under the control of a GDD enabling STA
 Registered Location Query Protocol (RLQP)
– a query protocol for registered location information that is received and
transported by generic advertisement service (GAS) Public Action frames
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IEEE 802.11af Architecture
 APs (GDD enabling STAs) are required to
– securely communicate with GDBs
– maintain the WSMs and other information received from GDBs
– transmit a contact verification signal (CVS) to inform GDD dependent STAs
that the map they received is still valid
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IEEE 802.11af Mechanisms
 Channel Availability Query (CAQ)
– to obtain one or more WSMs of available channels
for an area or a geolocation
 Channel Schedule Management (CSM)
Public Action frames
- CAQ, CSM, CVS, NCC,
GDD Enablement Req.,
GDD Enablement Rsp.,
WSM Announcement
– to obtain start and ending times for each available channel
- Public Action frames:
for inter/intra-BSS and
 Contact Verification Signal (CVS)
AP to unassociatedSTA communications,
– sent by AP (a GDD enabling STA), for GDD dependent STAs
and GAS
to verify if they are still receiving frames from their AP
 GDD Enablement
– the procedure where a GDD enabling STA forms a network and
maintains the network under the control of a GDB
 Network Channel Control (NCC)
– to inform a local channel controller that has a view of nearby transmitters and
their emissions footprints
 WSM Announcement
– sent by a GDD enabling STA to provide a WSM to GDD dependent STAs
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Presentation Outline
 Introduction to TV White Space
 IEEE 802.11af: Architectural Framework
 IEEE 802.11af: MAC Specification
 IEEE 802.11af: PHY Specification
 IEEE 802.11af: Regulations
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White Space Map (WSM)
 WSM procedure
– WSM includes a list of available WS channels
and power limitations as directed by the GDB
GDD enabling
STA
GDD dependent
STA
• the WSM may be updated by the GDB
– a GDD enabling STA should transmit the WSM
to its GDD dependent STAs, via
• GDD Enablement response,
• CAQ response, or
• WSM Announcement
– GDD dependent STAs can transmit only in the channels specified by the WSM
 WSM Announcement frame format
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White Space Map (WSM)
 WSM element
– WSM Type = 1
• TV band WSM
– WSM Information
•
•
•
•
channel index
max. power
valid duration
max. channel
bandwidth
• map version
– increased by 1
whenever the
WSM is updated
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GDD Enablement
 GDD Enablement procedure
GDD dependent
STA
GDD enabling
STA
– allows a GDD enabling STA to form a network
satisfying regulatory requirements
– availability of GDD enablement service is
notified by GDD enabling beacon signals
transmitted by a GDD enabling STA
• Upon receiving a GDD enabling beacon signal,
the GDD dependent STA can initiate the GDD Enablement procedure
by sending out a GDD Enablement request
 GDD Enablement Request / Response frame format
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GDD-Dependent STA State Transition Diagram
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Channel Availability Query (CAQ)
 CAQ procedure
– to obtain the list of available channels
for the operation of a GDD STA
CAQ requesting
STA
– CAQ requesting STA: GDD dependent STA
or GDD enabling STA
– CAQ responding STA: GDD enabling STA
• CAQ response contains WSM
 CAQ frame format
– Reason Result Code field: 1 for request, 2-6 for response
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CAQ responding
STA
Channel Schedule Management (CSM)
 CSM procedure
CSM requesting STA
CSM responding STA
– to obtain the channel schedule information
for the operation of a GDD STA
– CSM requesting STA: GDD enabling STA
• shall not be a GDD dependent STA
– CSM responding STA: RLSS or another GDD enabling STA
• CSM response contains channel schedule
 CSM frame format
– Reason Result Code field: 0-1 for request, 2-12 for response
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Channel Schedule Management (CSM)
 Channel Schedule Descriptor
– channel index
– availability starting time in UTC
and timestamp
– availability duration in minutes
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Network Channel Control (NCC)
 NCC procedure
– used to control frequency usage in TVWS
NCC requesting
STA
NCC responding
STA
• NCC requesting STA requests usage of
selected frequencies from its WSM while
providing its spectrum mask
• NCC responding STA provides the allowed channels
and max. transmit power constraints
– may be performed whenever WSM changes
– NCC requesting STA: GDD dependent STA
or GDD enabling STA
– NCC responding STA: GDD enabling STA or RLSS
 NCC frame format
– Reason Result Code: 0 for request, 1-4 for response
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(repeated)
Contact Verification Signal (CVS)
 CVS procedure
– transmitted by a GDD enabling STA
GDD enabling
STA
GDD dependent
STA
• to establish which GDD dependent STAs
are within the range of the GDD enabling STA
• to notify whether the available channel
information from the GDB has been updated
– a GDD dependent STA verifies its WSM via the Map ID field in CVS
• if their MAP ID match, the STA resets its dot11GDDEnablementValidTimer
to 60 seconds
• if they do not match, the STA initiates CAQ procedure
 CVS frame format
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Presentation Outline
 Introduction to TV White Space
 IEEE 802.11af: Architectural Framework
 IEEE 802.11af: MAC Specification
 IEEE 802.11af: PHY Specification
 IEEE 802.11af: Regulations
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TVHT Channelization
 Basic Channel Unit (BCU): W = 6, 7, or 8 MHz
– TVHT_MODE_1: W
– TVHT_MODE_2C: 2W
– TVHT_MODE_2N: W+W
– TVHT_MODE_4C: 4W
– TVHT_MODE_4N: 2W+2W
 mandatory:
– TVHT_MODE_1 (W)
– a single spatial stream (SS)
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TVHT PHY channelization [2]
TVHT vs. VHT: Bandwidth & OFDM
 TVHT PHY is based on 40 MHz VHT OFDM PHY of 11ac
– CBW40: 128 subcarriers (SCs) in 40 MHz, # occupied SCs (NST) = 114
– 144 SCs per BCU (not 128), for 55 dB ACLR (Adjacent Channel Leakage Ratio)
guard bands
for roll-off
6 MHz
7 MHz
8 MHz
5.33 MHz
5.33 MHz
7.11 MHz
BCU (MHz)
6
7
8
# SCs per BCU
144
168 (= 144 * 7/6)
144
# SCs used
128
128
128
BW used (MHz)
5.33 (= 6 * 128/144)
5.33 (= 7 * 128/168)
7.11 (= 8 * 128/144)
scaling factor
for sampling freq.
7.5 (= 40/5.33)
7.5 (= 40/5.33)
5.625 (= 40/7.11)
# occupied SCs (NST)
114
114
114
# pilot tones (NSP)
6
6
6
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(per
BCU)
TVHT vs. VHT: PPDU Format
 VHT PPDU
 TVHT PPDU
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CCA and MCS
 CCA BUSY Conditions (for a primary channel)
– 6/7 MHz: VHT PPDU at or above -88 dBm
– 8 MHz: VHT PPDU at or above -87 dBm
 MCS and minimum sensitivity
TVHT_MODE_1, NSS=1
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TVHT PHY Characteristics
Characteristics
TVHT
aSlotTime
24 us (6/7 MHz)
20 us (8 MHz)
9 us
aSifsTime
120 us (6/7 MHz)
90 us (8 MHz)
16 us
aCCATime
< 15 us (6/7 MHz) < 4 us
< 11.25 us (8 MHz)
aPPDUMaxTime
20 ms
aPSDUMaxLength 1,065,600 octets
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VHT
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5.484 ms
4,692,480 octets
Presentation Outline
 Introduction to TV White Space
 IEEE 802.11af: Architectural Framework
 IEEE 802.11af: MAC Specification
 IEEE 802.11af: PHY Specification
 IEEE 802.11af: Regulations
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Spectrum Regulations by Regions
FCC [4]
ETSI, Ofcom [5,6]
TVWS
54-698 MHz
470-790 MHz
Channel
bandwidth
6 MHz
8 MHz
Maximum
EIRP
Portable WSDs – 100 mW
Flexible (according to frequency
(40 mW if adjacent to an occupied chan.) and location)
Fixed WSDs – 4 W
TVWS
allocation
Static (daily, up to 48 hours)
Dynamic (e.g., typically 2 hours)
TVWS
vacation DL
N/A
AP – 60 seconds
STA – 1 second
RLSS
relays WSM from GDB to
GDD enabling STAs
calculates WSM for its BSSs
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FCC Regulation [7]
 Fixed device
– allowed to communicate with fixed & personal/portable devices
– required to
• determine its geographic location
• access GDB
• operate with antennas mounted outdoors
– max power: 1 W at transmitter output, 4 W EIRP with antenna gain
 Personal/portable device
– allowed to communicate with fixed & personal/portable devices
– Mode I: controlled by a fixed or a personal/portable Mode II device
• Mode I and II interaction: Mode II is master and Mode I is client
– Mode II: independent device; needs to access GDB
– max power: 100 mW EIRP with no antenna gain
• 40 mW when operating in an adjacent channel to an occupied channel
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Ofcom Regulation [5]
 Master TV WS device (WSD)
– for operation in UHF TV bands, it is required to
• discover approved TV WS databases (WSDBs)
• communicate information to the WSDBs
– WSD unique device identifier, antenna characteristics, etc.
• receive information from the WSDBs and follow the instructions
– lower/upper frequency boundaries, max. permitted EIRP spectral densities, max.
bandwidth, time validity parameters, etc.
 Slave WSD
– for operation in UHF TV bands, it is required to
• receive information from its master WSD and follow the instructions
 power requirement
– power: POOB (dBm/(100 kHz)) ≤ max{ PIB (dBm/(8 MHz)) - AFLR (dB), -84 }
• POOB: out-of-block EIRP spectral density
• PIB: in-block EIRP spectral density
• AFLR: adjacent frequency leakage ratio (54 ~ 84 dB)
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References
[1] IEEE Std 802.11af-2013, “Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications, Amendment 5: Television
White Spaces (TVWS) Operation,” IEEE, February 2014.
[2] A.B. Flores, R.E. Guerra, and E.W. Knightly, “IEEE 802.11af: A Standard for
TV White Space Spectrum Sharing,” IEEE Commun. Mag., October 2013.
[3] S.W. Choi et al., “Technology Standard Trends for Utilization in TV White
Space,” ETRI, August 2011.
[4] Electronic Code of Federal Regs., Title 47, part 15, subpart H, Television Band
Devices.
[5] Ofcom, “Regulatory Requirements for White Space Devices in the UHF TV
band,” July 2012.
[6] ETSI, “EN 301 598 White Space Devices (WSD); Wireless Access Systems
Operating in the 470 MHz to 790 MHz Frequency Band,” October 2012.
[7] FCC, “Second Report and Order and Memorandum Opinion and Order,”
ET Docket No. 08-260, November 2008.
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