IEEE 802.11af, also referred to as White-Fi and Super Wi-Fi,
is a wireless
computer network
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
ing standard in the
802.11
IEEE 802.11 is part of the IEEE 802 set of local area network (LAN) technical standards, and specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) computer com ...
family, that allows
wireless local area network
A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office buildi ...
(WLAN) operation in TV
white space spectrum in the
VHF and
UHF bands between 54 and 790 MHz.
The standard was approved in February 2014.
Cognitive radio
A cognitive radio (CR) is a radio that can be programmed and configured dynamically to use the best wireless channels in its vicinity to avoid user interference and congestion. Such a radio automatically detects available channels in wireless spec ...
technology is used to transmit on unused portions of TV channel band allocations, with the standard taking measures to limit interference for primary users, such as analog TV, digital TV, and wireless microphones.
Physical layer
The physical (PHY) layer in 802.11af is based on the
orthogonal frequency-division multiplexing (OFDM) scheme specified in
802.11ac.
[Broadcast TV&Radio( DVB-T, Digital Radio Mondiale) also uses OFDM in this band.] The propagation path loss as well as the attenuation by materials such as brick and concrete is lower in the UHF and VHF bands than in the 2.4 and 5 GHz bands, which increases the possible range compared to 802.11 a/b/g/n/ac.
The frequency channels are 6 to 8 MHz wide, depending on the regulatory domain.
Up to four channels may be bonded in either one or two contiguous blocks.
MIMO operation is possible with up to four streams used for either
space–time block code
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why differen ...
(STBC) or
multi-user
Multi-user software is computer software that allows access by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processing systems for mainframe computers may also be considered "multi-user", to avoid leaving t ...
(MU-MIMO) operation.
Data rates
The achievable data rate per spatial stream is 26.7 Mbit/s for 6 and 7 MHz channels and 35.6 Mbit/s for 8 MHz channels.
With four spatial streams and four bonded channels, the maximum data rate is 426.7 Mbit/s in 6 and 7 MHz channels and 568.9 Mbit/s for 8 MHz channels.
GI (Guard Interval) : Timing between symbols
Spectrum regulation
Access points and stations determine their position using a satellite positioning system such as
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
and use the Internet to query a
geolocation database
TV White Space database, also commonly referred to as (TV) geolocation database, is an entity that controls the TV spectrum utilization by unlicensed white spaces devices within a determined geographical area. Its sole objective is to enable unlic ...
(GDB) provided by a regional regulatory agency to discover which frequency channels are available for use at a given time and position.
In the United States, the
Federal Communications Commission
The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdicti ...
(FCC) permits TV white space operation in 6 MHz channels between 54 and 698 MHz in
TV channels
Television, sometimes shortened to TV, is a telecommunication Media (communication), medium for transmitting moving images and sound. The term can refer to a television set, or the medium of Transmission (telecommunications), television tra ...
2, 5, 6, 14–35, and 38–51, with the
geolocation database
TV White Space database, also commonly referred to as (TV) geolocation database, is an entity that controls the TV spectrum utilization by unlicensed white spaces devices within a determined geographical area. Its sole objective is to enable unlic ...
granting use for up to 48 hours.
For mobile stations, allowed transmit power is fixed to 100 mW per 6 MHz channel, or 40 mW if an adjacent channel is in use by a primary user.
In the European Union, the
European Telecommunications Standards Institute
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...
(ETSI) and
Ofcom permit TV white space operation in 8 MHz channels between 490 and 790 MHz, with the GDB granting use for up to 2 hours.
The allowed transmit power is dynamically set on a per-station basis, based on factors including the geographical distance to the next primary user in the given frequency.
This closed-loop scheme requires each station to report its position after a timer has expired or it has moved 50 m or more, and to stop transmitting within 5 s when instructed to do so.
Compared to the open-loop scheme used by the FCC, the closed-loop scheme used by the ETSI and Ofcom is more granular and allows for a more efficient spectrum utilization.
Comparison with 802.11ah
IEEE 802.11ah is another WLAN standard for sub 1 GHz operation being developed by the IEEE.
Unlike 802.11af, it operates in unlicensed bands.
Its main application is expected to be in sensor networks.
Comparison with 802.22
In addition to 802.11af, the IEEE has standardized another white space cognitive radio standard,
802.22.
While 802.11af is a wireless LAN standard designed for ranges up to 1 km, 802.22 is a
wireless regional area network (WRAN) standard, for ranges up to 100 km.
Coexistence between 802.22 and 802.11af standards can be implemented either in centralized or distributed manners and based on various coexistence techniques.
See also
*
Super Wi-Fi
*
Geolocation Database
TV White Space database, also commonly referred to as (TV) geolocation database, is an entity that controls the TV spectrum utilization by unlicensed white spaces devices within a determined geographical area. Its sole objective is to enable unlic ...
Notes
References
{{IEEE standards
af