Page 409 - From GMS to LTE

Wireless Local Area Network (WLAN) 395

Mbit/s were specified. In practice, however, 802.11a devices never became very popular,
as they had to be backward compatible with 802.11b and g, and the support of several
frequency bands increased the overall hardware costs.
Owing to rising datarates in local networks and Internet connections via cable and
ADSL, it was necessary to further increase the speed of WLAN networks. After several
years of standardization work, the companies involved finally agreed on a new air inter-
face, which was then specified in IEEE 802.11n. By doubling the channel bandwidth to
40 MHz and using numerous other improvements that are described in more detail
later in this chapter, PHY data transfer speeds of up to 600 Mbit/s can be achieved. In
practice, typical data transfer rates under favorable radio conditions are in the region of
70–150 Mbit/s. In addition, the specification supports both the 2.4 GHz and the 5 GHz
bands. This has become necessary as 2.4 GHz is widely used today, and in cities it is not
uncommon to find many networks per channel. The 5 MHz band is still much less used
today and hence allows higher datarates in favorable transmission conditions.
While 802.11n has broad device support today, the industry has already moved for-
ward again with the 802.11ac standard, which is typically supported by mid‐tier and
high‐end WLAN devices coming to the market today. By using channel bandwidths
of 80 and 160 MHz in the 5 GHz band, improved modulation and other methods to
increase datarates (which will be described later), a theoretical peak datarate of 6.9
Gbit/s has been specified. However, in practice, achievable datarates are much lower,
but still go significantly beyond what is possible with 802.11n devices. A further step
in the evolution of WLAN is 802.11ad, which uses the 60 GHz band to achieve even
higher datarates in practice than 802.11ac but only over short line‐of‐sight distances.
Additional 802.11 standards, which are shown in the Table 6.2, specify a number of
additional optional WLAN capabilities.

Table 6.2 Additional 802.11 standard documents that describe optional functionality.

Standard Content
802.11e [6] The most important new functionalities of this standard are methods to ensure a
certain Quality of Service (QoS) for a device. Therefore, it is possible to ensure a
minimum bandwidth and fast media access for real‐time applications like Voice over
Internet Protocol (VoIP) even during network congestion periods. Furthermore, this
standard also specifies the direct link protocol (DLP), which enables two WLAN
devices to exchange data directly with each other instead of communicating via an
access point. DLP can effectively double the maximum data transfer speed between
two devices.
802.11f [7] This standard specifies the exchange of information between access points to allow
seamless client roaming between cooperating access points. It is used in practice to extend
the range of a WLAN network. More about this topic can be found in Section 6.3.1.
802.11 h [8] This extension adds power control and dynamic frequency selection for WLAN
systems in the 5 GHz band. In Europe, only 802.11a devices that comply with the
802.11h extensions can be sold.
802.11i [9] This standard describes new authentication and encryption methods for WLAN. The most
important part of 802.11i is 802.1x. More about this topic can be found in Section 6.7.
802.11w Introduces protection of management frames to protect against attacks such as
network de‐authentication/disassociation. New Wi‐Fi‐certified devices supporting
802.11ac must support this functionality today.