Page 408 - From GMS to LTE

394 From GSM to LTE-Advanced Pro and 5G

5–7 Application dependent
4 TCP/UDP

3 IP
2 802.2 Logical Link Control (LLC)

1 802.3 802.11b 802.11g 802.11a 802.11n
(Ethernet)
Figure 6.1 The WLAN protocol stack.

Table 6.1 Different PHY standards.

Standard Frequency band Theoretical top speeds

802.11b [3] 2.4 GHz (2.401–2.483 GHz) 1–11 Mbit/s
802.11g [4] 2.4 GHz (2.401–2.483 GHz) 6–54 Mbit/s
802.11a [5] 5 GHz (5.150–5.350 GHz and 5.470–5.725 GHz) 6–54 Mbit/s
802.11n 2.4 GHz (as above) 6–600 Mbit/s
5 GHz (as above)
802.11ac 5 GHz (as above) Up to 6.93 Gbit/s
802.11ad 60 GHz Up to 6.76 Gbit/s

environment mainly depended on the distance between the sender and the receiver as
well as on the number and kind of obstacles between them, such as walls or ceilings – in
practice, around 5 Mbit/s could be achieved with this standard but only over short
distances of a few meters.
To ensure connectivity over a larger distance, the number of bits used for redundancy
was automatically adapted. This reduced the speed down to a few hundred kilobits per
second under very bad signal conditions.
The 802.11b standard used the 2.4 GHz ISM (Industrial, Scientific and Medical) band,
which can be used in most countries without a license. One of the most important condi-
tions for the license‐free use of this frequency band is the limitation of the maximum transmis-
sion power to 100 mW. It is also important to know that the ISM band is not
technology‐restricted. Other wireless systems such as Bluetooth also use this frequency range.
The 802.11g standard specified a much more complicated PHY as compared to the
802.11b standard to achieve datarates of up to 54 Mbit/s. In practice, around 25 Mbit/s
is reached on the application layer under good signal conditions. This variant of the
standard also uses the 2.4 GHz ISM band and has been designed in such a way as to be
backward compatible with older 802.11b systems. This ensures that 802.11b devices
can communicate in newer 802.11g networks and vice versa. More about the different
PHYs can be found in Section 6.6.
In addition to the 2.4 GHz ISM band, another frequency range was opened for
WLANs in the 5 GHz band. As with the 802.11g standard, datarates between 6 and 54