HOME

TheInfoList



OR:

IEEE 802.11af, also referred to as White-Fi and Super Wi-Fi, is a wireless
computer network A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...
ing standard in the 802.11 family, that allows wireless local area network (WLAN) operation in TV white space spectrum in the VHF and
UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...
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 channels in its vicinity to avoid user interference and congestion. Such a radio automatically detects available channels, then accordingly change ...
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 In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission used in digital modulation for encoding digital (binary) data on multiple carrier frequencies. OFDM has developed into a popular scheme for ...
(OFDM) scheme specified in 802.11ac.Broadcast TV&Radio(
DVB-T DVB-T, short for Digital Video Broadcasting – Terrestrial, is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 and first broadcast in Singapore in Fe ...
,
Digital Radio Mondiale Digital Radio Mondiale (DRM; ''mondiale'' being Italian and French for "worldwide") is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting—p ...
) 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 Space–time block coding is a technique used in wireless, wireless communications to transmit multiple copies of a data stream across a number of Antenna (radio), antennas and to exploit the various received versions of the data to improve the r ...
(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 leavi ...
(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 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 unli ...
(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 government that regulates communications by radio, television, wire, internet, wi-fi, satellite, and cable across the United States. The FCC maintains j ...
(FCC) permits TV white space operation in 6 MHz channels between 54 and 698 MHz in TV channels 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 unli ...
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 operating in the field of information and communications. ETSI supports the development and testing of global technical ...
(ETSI) and
Ofcom The Office of Communications, commonly known as Ofcom, is the government-approved regulatory and competition authority for the broadcasting, internet, telecommunications and mail, postal industries of the United Kingdom. Ofcom has wide-rang ...
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 unli ...


Notes


References

{{IEEE standards af