Aerohive HiveAP 20, Руководство по развертыванию

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Deployment Guide 19
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The goal of this section is to provide some background on Wi-Fi propagation and how to lay out a wireless network.
While RF (radio frequency) engineering is a rather complicated science, this section provides a simple overview on
the basics of Wi-Fi propagation and channel layout that you need to be able to install an enterprise WLAN.
The first thing to know is that Wi-Fi is forgiving. Wi-Fi tends to transmit a bit farther than you expect, and even in
cases of interference, it tends to just work. This can be both a blessing and a curse. It is a blessing because people
will likely have access to the network, and it is a curse because your overall performance might be suboptimal
without obvious symptoms, like lack of connectivity. Understanding the basics presented in this section will help
ensure a high performance layout.
The first concept to understand is signal strength and how it relates to throughput. Radio power is measured in dBm
(decibels relative to one milliwatt) where 0 dBm = 1 milliwatt, but decibels increase using a log10 math function.
Rather than dusting off your old math books and pulling out your calculator, look at the dBm-to-milliwatt converter
that appears below. Often in Wi-Fi, dBm and milliwatts (mW)
— and microwatts ( W) — are used interchangeably. The
following table converts between the two units of measurement.
In RF, there is also a relative measurement that you can use to compare two numbers. This measurement is simply
dB (without the "m"). To see how this concept is applied, consider how radio signal propagation changes over a
distance and how it can be affected.
Figure 3 on page 20 shows signal strength over distance as a curve that has the
best signal strength closer to the access point. It also shows noise. In general, noise is considered to be low-level
background RF signals that can interfere with a WLAN. This noise tends to be the garbled background RF that comes
from everything from the sun and stars to man-made interfering devices like Bluetooth headsets. It is impossible to
block out noise and it should not be attempted. This low level of background noise is called the "noise floor".
dBm-to-milliwatt
20 dBm = 100 mW 2 dBm = 1.6 mW
15 dBm = 32 mW 1 dBm = 1.3 mW
10 dBm = 10 mW 0 dBm = 1.0 mW
5 dBm = 3.2 mW -1 dBm = 794 µ W
4 dBm = 2.5 mW -5 dBm = 316 µ W
3 dBm = 2.0 mW -10 dBm = 100 µ W