Industrial Communication
WiFi in the 5 GHz Band
Whitepaper
Contents
Introduction ...................................................................................................................................... 3
IEEE Standards........................................................................................................................... 3
ETSI Standards ........................................................................................................................... 4
European Harmonization ............................................................................................................ 4
Dynamic Frequency Selection .................................................................................................... 4
Transmission Power Control – TPC............................................................................................ 5
Differences between USA and Asia ............................................................................................ 5
Radio Channels ............................................................................................................................... 6
2.4 GHz Band.............................................................................................................................. 6
5 GHz Band................................................................................................................................. 6
The Advantages of the 5 GHz Range.............................................................................................. 7
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Introduction
The historical development of wireless LAN technology is closely connected to the standards that
have been introduced by organizations throughout the years. The two most important of these
organizations are the Institute of Electrical and Electronics Engineers (IEEE) and the European
Telecommunications Standards Institute (ETSI).
IEEE Standards
In 1997, the IEEE adopted the initial version of the 802.11 standard for wireless networks. The
original version used the license-free ISM band (Industrial, Scientific, Medical 2.4 to 2.483 GHz) for
transmission, making data transfer rates of max. 2 Mbps (gross) possible. In the following years,
the 802.11 standard expanded with a variety of enhancements. One of the enhancements
introduced in 1999 was the 5 GHz band in which provided for gross data rate of 54 Mbps.
However, the standard, which was termed 802.11a, was of little interest to some countries as this
band was not authorized for private use due to interference with military radio networks and radar
applications. The wider use of 5 GHz WLANs was also restricted by its exclusive use in closed
spaces and the relatively low transmission power.
The 802.11b standard was also adopted in 1999 as an extension to the 2.4 GHz band. With gross
data transfer rates of 11 Mbps, this marked the first time in history that speeds could be reached in
wireless networks that were truly useful in productive implementations - as compared to the
widespread use of 10 Mbps Ethernet networks. Since this frequency range could be used privately
in many countries without a license, the 802.11b technology rapidly spread. Devices developed
under the 802.11b standard could be certified by the WiFi Alliance which drove interoperability
between products developed by different manufacturers. Due to the proliferation of WiFi products,
the WiFi seal was often erroneously regarded as a standard in and of itself.
Shortly thereafter, in 2003, the IEEE introduced the new 802.11g standard. While it continued to
use the ISM frequency band, it was able to achieve a gross data rate of 54 Mbps with the same
modulation methods as 802.11a (OFDM). Sharing the same 2.4 GHz frequency band made the
802.11g standard backwards compatible with devices manufactured in accordance with the
802.11b version, which had gained a great deal of popularity by then. This compatibility and
competitive performance helped the 802.11g standard achieve such great success. With the
802.11h enhancement in September 2003, the private use of the 5 GHz band was finally possible
even outside of closed spaces. To protect military applications in the 5 GHz band, the DFS and
TPC procedures were prescribed. However, the use of DFS and TPC allowed significantly higher
transmission power (maximum 1000 mW) than in any of the other standards that were valid until
then. The next level of the 802.11 hierarchy, the 802.11n variation, has been released in
September 2009. This version promises gross data rates of up to 600 Mbps over extremely long
distances. In order to protect current technology investments, 802.11n devices are compatible with
the 802.11a/b/g components currently in use.
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ETSI Standards
ETSI adopted the first standard for controlling remote data transfers as early as 1996 under the
name of Hiperlan (High Performance Radio Local Area Networks). The first version (Hiperlan Type
1) was intended for use in the frequency range of 5.15 to 5.30 GHz with a transmission rate of 20
Mbps. As no manufacturers took up this standard, Hiperlan initially had no practical significance.
With the new version in 2000, Hiperlan Type 2, ETSI introduced a WLAN solution that operates in
the 5 GHz band similar to IEEE 802.11a, and also provides a gross data rate of 54 Mbps.
However, as the frequencies and the OFMD modulation method that was also used for 802.11a
overlapped, it was necessary to adapt the standards between IEEE and ETSI to avoid disruptions
to the systems.
European Harmonization
To standardize the use of the 5 GHz band in Europe, the European Commission issued the ETSI
301 893 standard on July 11, 2005. The member states of the EU were obliged to implement this
by October 31, 2005. Instead of the three sub-bands described in the 802.11a/h standards (5150 5350 MHz, 5470 - 5725 MHz and 5725 - 5875 MHz for the UK), the ETSI 301 893 standard
regulates three frequency bands with different specifications:

5150 MHz - 5250 MHz

5250 MHz - 5350 MHz

5470 MHz - 5725 MHz
The guidelines focus on preventive measures for avoiding disruptions to other systems that use the
same frequency band. This includes radar equipment that counts as "primary applications". The
"secondary applications" such as WLAN have to change the frequency as soon as a conflict is
detected.
Dynamic Frequency Selection
Dynamic Frequency Selection (DFS) was stipulated to prioritize primary applications. DFS initially
assumes that no channel is available in the corresponding frequency band. The WLAN device
selects an arbitrary channel at the start and performs what is known as a Channel Availability
Check (CAC). Before sending to a channel for 60 seconds (Channel Observation Time, COT), a
check is run to see if a different device is already working on this channel and the channel is
therefore occupied. If this is the case, then a different channel is checked by the CAC. If not, then
the WLAN device can perform the transmission operation. Even during operation, a check is run to
see if a primary application such as a radar device is using this channel. This exploits the fact that
radars frequently work according to the rotation method, whereby a tightly bundled directional
transmission signal is transmitted by a rotating antenna. A remote receiver perceives the radar
signal as a short pulse (radar peak). If a device receives such a radar peak, it pauses the
transmission operation and monitors the channel for further pulses. If additional radar peaks occur
during the COT, then a new channel is selected automatically. A check of this type is required to
be carried out every 24 hours. This is why interrupting the data transmission for 60 seconds is
unavoidable. DFS is stipulated for the frequency ranges of 5250 - 5350 MHz and from 5470 - 5725
MHz. It is optional for the frequency range of 5150 - 5250 MHz.
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Transmission Power Control – TPC
Dynamic adjustment of the transmission power is intended to reduce radio interference.
Dynamically adjusting the transmission power facilitates the shared use of the 5250-5350 MHz and
5470 - 5725 MHz frequency bands with satellite services. TPC should cause an average reduction
in the transmission power by at least 3 dB compared with the maximum permitted transmission
power. TPC determines the minimum transmission power necessary to maintain the connection
with the partner (such as an access point). If TPC is not used within these frequency bands, then
the highest permissible average EIRP and the corresponding maximum EIRP density are reduced
by 3 dB. This restriction does not apply to the frequency range of 5150 - 5350 MHz. Without DFS
and TPC, a maximum of only 30 mW EIRP is permitted. When DFS and TPC are used, a
maximum 1000 mW EIRP is permitted as the transmission power (compared with 100 mW with
802.11 b/g, 2.4 GHz, DFS and TPC are not possible here). The higher maximum transmission
power not only compensates for the higher attenuation of 5 GHz radio waves in air, it also makes
noticeably longer ranges possible than in the 2.4 GHz range.
Differences between USA and Asia
The USA and Asia use different frequency bands and maximum signal strengths that are different
than the European standard. In the USA, three sub-bands, each 100 MHz wide, are used for
wireless networks in the 5 GHz band. The "lower band" ranges from 5150 - 5250 MHz, the "middle
band" ranges from 5250 - 5350 MHz and the "upper band" ranges from 5725 - 5825 MHz. In the
lower band, a maximum average EIRP of 50 mW is permitted; in the middle band this is 250 mW
and 1 W in the upper band. In Japan, the use of the 5 GHz band is possible to a limited extent:
only the lower band of 5150 - 5250 MHz is released for private use.
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Radio Channels
2.4 GHz Band
In the EU, up to 13 DSSS channels are available within the usable frequency range of 2400 to
2483 MHz. In the rest of the world, only the first 11 of these are available. Due to the fact that the
frequency ranges used on the channels partially overlap, no more than three channels can be
operated in parallel without interference between the frequencies.
5 GHz Band
In the usable frequency space of 5.13 to 5.805 GHz, up to 19 channels are available in Europe,
divided into frequency ranges to which different conditions of use can apply:

5150 - 5250 MHz (channels 36, 40, 44 and 48)

5250 - 5350 MHz (channels 52, 56, 60 and 64)

5470 - 5725 MHz (channels 100, 104, 108, 112, 116, 120, 124, 128, 132, 136 and 140)

Band 3: 5725 - 5875 MHz (channels 147, 151, 155 and 167)
Note: The frequency ranges and radio channels in band 3 may only be used in Great Britain.
The following table shows which channels may be used in the different regions.
Table 1: Channels to be used in different regions
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Frequency Ranges for Indoor and Outdoor Use
The use of the methods described in ETSI 301 893 for reducing mutual interference in the 5 GHz
band (TPC and DFS) is not stipulated for all fields of application. The following table provides
information about the permitted use and corresponding transmission powers within the EU:
Table 2: Permitted Transmission Powers within the EU
Note: Other regulations may apply to use in other countries. Please refer to the current wireless
network regulations for the country in which you want to operate a wireless LAN device, and make
sure you set the country of operation in the WLAN settings.
The Advantages of the 5 GHz Range
When evaluating the various standards in the 802.11 group, the obvious question arises as to why
the 802.11a standard should be further enhanced by 802.11h despite gross data rates that are
identical to the 802.11g standard and a lack of compatibility with older equipment. The question
regarding compatibility lost momentum when dual-band components entered the market. These
devices can selectively transmit according to the a/b/g standards rendering them capable of
adapting ideally to the possibilities provided in the respective environment. Since the compatibility
mode between the standards in the 2.4 GHz band is paid for by significantly reduced transfer rates,
b/g compatibility does not play a major role in professional applications. The 802.11a/h standard's
main advantages are clearly derived from the frequency band used:

Free channels: In the 2.4 GHz band, only 13 channels are available. Moreover, these
channels overlap excessively with one another. Due to this overlapping, the maximum possible
number of parallel independent connections is limited to 3 channels.

Low level of interference: Since the ISM band has been released for use for a number of years,
a great number of radio applications have been established for the 2.4 GHz band. As such,
802.11b/g standard WLANs are often forced to compete with interference from these
applications.  In contrast, the relatively recent release of the 5 GHz band for private use gives
WLAN usage a very prominent position in this frequency range. Other than military
applications, which are isolated from 802.11a/h by special mechanisms, there are virtually no
sources of interference.

Higher performance: The 5 GHz band allows for significantly higher performance than the 2.4
GHz band. This makes 5 GHz band WLANs much better suited for outdoor applications and
directional radio connections (point-to-point) than wireless connections in the 2.4 GHz band.
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Due to possible changes in standards and equipment, the features described in this document
in the form of text and images are subject to confirmation by Schneider Electric.
Design: Schneider Electric
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