The coverage range of an omnidirectional antenna is measured by the coverage radius, while that of a directional antenna is measured by the coverage distance. To calculate the coverage radius or coverage distance, you need to determine the maximum transmission distance of signals in advance. The following describes how to calculate the maximum transmission distance.
The RSSI is calculated as follows (regardless of factors such as the interference and line loss):
RSSI = Radio transmit power + TX antenna gain – Path loss – Signal attenuation caused by obstacles + RX antenna gain
Indoor semi-open scenario
2.4 GHz: L = 46 + 25lg(d)
5 GHz: L = 53 + 30lg(d)
Table 1 lists the typical values of the relationship between the path loss and signal transmission distance.
Outdoor coverage scenario
2.4 GHz and 5 GHz: L = 42.6 + 26lg(d) + 20lg(f)
Table 2 lists the typical values of the relationship between the path loss and signal transmission distance.
Backhaul scenario
5 GHz: L = 32.4 + 26lg(d) + 20lg(f)
Table 3 lists the typical values of the relationship between the path loss and signal transmission distance.
The following table lists the attenuation values of typical obstacles summarized from historical empirical data. The actual attenuation values are subject to the site survey results.
Obstacle
Thickness (mm)
2.4 GHz Signal Attenuation (dB)
5 GHz Signal Attenuation (dB)
Synthetic material
20
2
3
Asbestos
8
3
4
Wooden door
40
3
4
Glass window
50
4
7
Heavy colored glass
80
8
10
Brick wall
120
10
20
Brick wall
240
15
25
Armored glass
120
25
35
Concrete
240
25
30
Metal
80
30
35
Assume that the maximum transmission distance of 5 GHz signals in an indoor semi-open scenario is calculated. The edge field strength is –65 dBm; the transmit power of the AP radio is 20 dBm; the antenna gain at 5 GHz is 6 dBi; the signal attenuation caused by obstacles is 8 dB; and the receiver is a mobile phone (the antenna gain is usually 0). The corresponding formula is as follows (the value of the RSSI is the edge field strength):
RSSI = Radio transmit power + TX antenna gain – Path loss – Signal attenuation caused by obstacles + RX antenna gain
–65 = 20 + 6 - [53 + 30lg(d)] - 8 + 0
d = 10
The maximum transmission distance of 5 GHz signals is 10 m.
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