140 Software Networks
there is a proprietor (also known as a primary) who is not using them
at a given time. For this to work, we must either drastically limit the
range so as to remain in an environment without conflict with the
primary, or have a server which records the use of frequencies and
enables the cognitive access points to discover the usage sites and use
the frequencies with no danger of interference. The IEEE 802.11af
standard uses television bands, and is known as TVWS (TV White
Space) or sometimes Super Wi-Fi.
There are still numerous developments under way in the field of
new-generation Wi-Fi, such as IEEE 802.11ah, which pertains to
long-range Wi-Fi of around a kilometer, but with much lower data
rates. Its uses are mainly in the domain of the connection of “things”,
such as intelligent electricity meters or healthcare equipment.
Numerous other standards are in the reflection phase; one of these is
IEEE 802.11ax, which is an improvement of IEEE 802.11ac, with four
times the capacity.
6.3. IEEE 802.11ac
IEEE 802.11ac is a version of Wi-Fi designed to surpass 1 Gbps,
using multiple antennas, which can run simultaneously but in separate
sectors. Two mutually complementary solutions have been put in
place to obtain the target data rates. The first, which is fairly simple,
consists simply of increasing the capacity of the transmission channel
using the 5 GHz band, which is much freer than the 2.4 GHz band.
The range of this higher-frequency band is a little less. In addition,
obstacles hamper the signals somewhat. However, the available
bandwidth is 200 MHz, which is much greater than the 83.5 MHz
assigned to the 2.4 GHz band, which enables us to have Wi-Fi
channels whose band is 80 MHz, and optionally, 160 MHz.
The second solution pertains to the directionality of the signals
emitted, using a set of specific antennas. This technique involves
allowing the transmission of several communications on the same
frequency, but in different directions. There is spatial multiplexing,
hence the name of this technique: SDMA (Space Division Multiple
Access). Figure 6.3 illustrates this technology.
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there is a proprietor (also known as a primary) who is not using them
at a given time. For this to work, we must either drastically limit the
range so as to remain in an environment without conflict with the
primary, or have a server which records the use of frequencies and
enables the cognitive access points to discover the usage sites and use
the frequencies with no danger of interference. The IEEE 802.11af
standard uses television bands, and is known as TVWS (TV White
Space) or sometimes Super Wi-Fi.
There are still numerous developments under way in the field of
new-generation Wi-Fi, such as IEEE 802.11ah, which pertains to
long-range Wi-Fi of around a kilometer, but with much lower data
rates. Its uses are mainly in the domain of the connection of “things”,
such as intelligent electricity meters or healthcare equipment.
Numerous other standards are in the reflection phase; one of these is
IEEE 802.11ax, which is an improvement of IEEE 802.11ac, with four
times the capacity.
6.3. IEEE 802.11ac
IEEE 802.11ac is a version of Wi-Fi designed to surpass 1 Gbps,
using multiple antennas, which can run simultaneously but in separate
sectors. Two mutually complementary solutions have been put in
place to obtain the target data rates. The first, which is fairly simple,
consists simply of increasing the capacity of the transmission channel
using the 5 GHz band, which is much freer than the 2.4 GHz band.
The range of this higher-frequency band is a little less. In addition,
obstacles hamper the signals somewhat. However, the available
bandwidth is 200 MHz, which is much greater than the 83.5 MHz
assigned to the 2.4 GHz band, which enables us to have Wi-Fi
channels whose band is 80 MHz, and optionally, 160 MHz.
The second solution pertains to the directionality of the signals
emitted, using a set of specific antennas. This technique involves
allowing the transmission of several communications on the same
frequency, but in different directions. There is spatial multiplexing,
hence the name of this technique: SDMA (Space Division Multiple
Access). Figure 6.3 illustrates this technology.
www.it-ebooks.info