144 Software Networks
The only bands which are heavily used are those employed by
telecom operators which, owing to the TDMA and CDMA techniques,
exhibit excellent degrees of utilization. The bands reserved for TV
channels, which are below 1 GHz, are particularly attractive to
operators. These TV channels could be used by access points to
achieve ranges of hundreds of meters. Such ranges demonstrate that
Wi-Fi technology is capable of serving the needs of WiMAX and 4G
clients.
The WiFi standard IEEE 802.11af – which must not be confused
with IEEE 802.3af, or PoE (Power over Ethernet) – is called TVWS
(TV White Space). The expression “white space” refers specifically to
those frequencies which are not used by wireless television channels.
The operational bandwidth for cognitive radio covers dozens of digital
television channels. The data rates achieved by this method may be
very high indeed. The name of the product is “White-Fi”, also
sometimes called “Super Wi-Fi”.
One important question relates to the way in which cognitive radio
is used. It is for each state to regulate this usage. The main solutions
pertain to the way in which unoccupied frequencies are used. A
number of solutions suggest themselves, depending on the coverage of
the cognitive access point. If the band is not occupied at the access
point’s location, it can be assumed that it is not occupied within a
radius of a few meters of that point. This category includes Wi-Fi
access points inside buildings with limited power, only covering the
inside of the building. A second solution is to refer to a bandwidth
management server, which knows where the bands are available.
Thus, a common discipline needs to be used between the primary and
secondary users. With this in mind, though, will TV operators manage
to reach an agreement with Wi-Fi 802.11af users? Standardization
work is being carried out in different working groups, such as IEEE
P1900, with a view to proposing solutions acceptable for both parties.
A third, more remote, solution could stem from the ability for each
device to measure the interference and indicate to the secondary users
whether or not they can exploit the frequency.
At the physical level, the method used in IEEE 802.11af is FSS
(Fixed Subcarrier Spacing) with OFDM. The channels used in OFDM
www.it-ebooks.info
The only bands which are heavily used are those employed by
telecom operators which, owing to the TDMA and CDMA techniques,
exhibit excellent degrees of utilization. The bands reserved for TV
channels, which are below 1 GHz, are particularly attractive to
operators. These TV channels could be used by access points to
achieve ranges of hundreds of meters. Such ranges demonstrate that
Wi-Fi technology is capable of serving the needs of WiMAX and 4G
clients.
The WiFi standard IEEE 802.11af – which must not be confused
with IEEE 802.3af, or PoE (Power over Ethernet) – is called TVWS
(TV White Space). The expression “white space” refers specifically to
those frequencies which are not used by wireless television channels.
The operational bandwidth for cognitive radio covers dozens of digital
television channels. The data rates achieved by this method may be
very high indeed. The name of the product is “White-Fi”, also
sometimes called “Super Wi-Fi”.
One important question relates to the way in which cognitive radio
is used. It is for each state to regulate this usage. The main solutions
pertain to the way in which unoccupied frequencies are used. A
number of solutions suggest themselves, depending on the coverage of
the cognitive access point. If the band is not occupied at the access
point’s location, it can be assumed that it is not occupied within a
radius of a few meters of that point. This category includes Wi-Fi
access points inside buildings with limited power, only covering the
inside of the building. A second solution is to refer to a bandwidth
management server, which knows where the bands are available.
Thus, a common discipline needs to be used between the primary and
secondary users. With this in mind, though, will TV operators manage
to reach an agreement with Wi-Fi 802.11af users? Standardization
work is being carried out in different working groups, such as IEEE
P1900, with a view to proposing solutions acceptable for both parties.
A third, more remote, solution could stem from the ability for each
device to measure the interference and indicate to the secondary users
whether or not they can exploit the frequency.
At the physical level, the method used in IEEE 802.11af is FSS
(Fixed Subcarrier Spacing) with OFDM. The channels used in OFDM
www.it-ebooks.info