Chapter 5 WLAN Planning
5.1 Site Survey
The following operating and environmental conditions must be considered when performing a site
survey:
Data rates –
The sensitivity and the radio range are inversely proportional to data rates. Therefore, the
maximum radio range is achieved at the lowest workable data rate, and a decrease in receiver threshold
sensitivity occurs as the radio data rate increases.
Antenna type and placement –
Proper antenna configuration is a critical factor in maximizing radio
range. As a general rule, the radio range increases in proportion to antenna gain and height.
Physical environment –
Clear or open areas provide better radio range than closed or filled areas.
Clear line of sight (LOS) is required to establish a good and reliable wireless link.
Obstructions –
Metal shelving or a steel pillar can hinder devices. To avoid placing these devices in
locations where those obstructions are between the sending and receiving antennas.
5.2 Data Rate
The table below is the referenced data about over what range the WAP-7000 with what kind of antenna
could operate under what data rate. You might also know the relationship between the data rate and the
maximum radio range; for example, the bridge with 17dBi antenna could operate well under 6 Mbps data
rate within 17 KM. The actual performance is still depending on your environment.
Maximum Distance
(17dBi Antenna)
Maximum Distance
(23dBi Antenna)
6 Mbps
17.72 KM
30.79KM
9 Mbps
16.82KM
29.36 KM
12 Mbps
16.07KM
28.07 KM
18 Mbps
14.64KM
25.60 KM
24 Mbps
11.66 KM
20.26 KM
36 Mbps
8.21 KM
16.85 KM
48 Mbps
3.72KM
12.23 KM
54 Mbps
1.84 KM
7.32 KM
5.3 RF LOS (Line-of-Sight)
For the wireless communication, the Line-of-Sight (LOS) will be the major issue over building up the
wireless link. This evaluated procedure is to reduce the obstructions and to avoid the multiple-path signal
degrading the communication quality.
The first requirement is the Line-of-Sight (LOS) between the both sides’ Antennas. The radio line-of-sight
concept is the area along the radio linking path through which is the bulk of the radio signal power travels.
The area is known as the first Fresnel Zone of the radio link. For the radio link, it should avoid to be
affected by obstacles in this path, including the ground within 60% of the first Fresnel Zone.
The following figure illustrates the concept of a good radio line-of-sight.
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