Standard Ieee 802.11B/G And Ieee 802.11A/H - Phoenix Contact FL WLAN 24 AP 802-11 User Manual

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1.2.4.3 Fresnel zone
For an optimum radio link, a zeppelin-shaped free zone, known as the Fresnel zone, is also
required. The usual formula can only be used to calculate the free space attenuation
(see "Free space attenuation" on page 1-4) if the Fresnel zone is completely clear.
Usually the Fresnel zone is only taken into account for outdoor applications, but it also
applies for indoor installations. However, it is rarely used indoors because the distances are
short and other factors largely determine the range.
PWR POE HOST 1 2 3 4
PWR HOST 1 2 3 4
Figure 1-5 The Fresnel zone
Table 1-4 Diameter of Fresnel zone depending on the distance
Distance in m Fresnel zone in m
2.4 GHz
5 0.8
10 1.1
20 1.6
30 1.9
50 2.5
1.3

Standard IEEE 802.11b/g and IEEE 802.11a/h

Standard IEEE 802.11b was the first standard to introduce a competitive and reasonably-
priced technology to the market, which could be used to implement wireless networks.
Devices that meet this standard are now considered mature and immune to interference,
and are therefore ideal for professional use in industrial applications.
Basic specifications for IEEE 802.11b/g:
– Frequency band: ISM band in range from 2400 MHz to 2485 MHz
– Use of wireless range is free of charge and does not require a license
– Gross data transmission rate for 802.11b: 1 Mbps, 2 Mbps, 5.5 Mbps, and 11 Mbps
– Gross data transmission rate for 802.11g: 6 Mbps, 9 Mbps, 12 Mbps, 18 Mbps,
36 Mbps, 48 Mbps, and 54 Mbps
– Net data transmission rate: 1 ~ 25 Mbps
– Band spread method: DSSS (Direct Sequence Spread Spectrum)
Functions and wireless technology
Half
diameter
Fresnel zone
Curvature of the earth
Distance in m
5 GHz
0.5 100
0.7 200
1.0 300
1.3 500
1.6 1000
PWR POE HOST 1 2 3 4
PWR HOST 1 2 3 4
719000011
Fresnel zone in m
2.4 GHz 5 GHz
3.5 2.3
5 3.3
6.1 4.0
7.9 5.2
11.2 7.4
1-7
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