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Designing WLANs is a complex task that
requires a thorough understanding of the underlying technology and
design principles. If you are new to WLAN design and deployment, we
strongly recommend that you read a good book on this topic, such
as
The Certified Wireless Design
Professional Official Study Guide. Additionally, consider the following tips
and tricks.
·Just because your AP's
maximum output power can be set to 17 or 20 dBm does not mean that
it should be set to this value. You should consider the fact that
most Wi-Fi client devices, such as laptops, tablets, or desktops
with Wi-Fi adapters, have a lower output power, typically 13 or 15
dBm. As a result, a client might “hear” a 20 dBm AP from a very
long distance, but the AP might not “hear” the client.
Additionally, APs with high output power create unnecessary
interference with other APs in dense WLAN environments. If you
design your WLAN for performance rather than coverage, you will
probably want to have a rather dense placement of APs. Here,
stronger does not necessarily mean better. You might consider
lowering the power level so that it matches the power level of
client devices.
·If you design your WLAN
for coverage rather than performance, using high AP output power
might be acceptable. However, be sure to read the AP specifications
to find out the actual power level it can provide. Remember that
the maximum allowed power level might be different for different
channels!
·Signal level does not
tell you the whole story. Consider an 802.11n AP operating in the
2.4 GHz band with the standard omnidirectional antenna and the
default 17 dBm output power placed on a map with no obstructions.
If you select the Signal Level
visualization, TamoGraph will
draw a very large (a few hundred meters) circle around your AP.
Does this mean that the whole area can be considered to be covered
by the AP? Of course not, because, for example, at the distance of
approximately 300 meters the signal level would be about -90 dBm.
Yes, the signal is there; your client device might even detect the
AP and display it on the list of available networks; but there
would be no connectivity. First, because the AP might not “hear”
the client, as explained before. Second, even marginal connectivity
requires the signal-to-noise ratio of at least 4 dBm. Considering
that the typical noise level in the 2.4 GHz band in urban areas is
about -90 dBm, the signal level must be at least -86 dBm. At that
level, the client might be able to connect, but the throughput
would be extremely poor. That said, the Expected PHY Rate
or AP Coverage Areas
visualizations might be much
more informative than the Signal Level
visualization. TamoGraph does
not draw the signal level if the difference between it and the
noise level is below 4 dBm.
·It is a common practice
nowadays to use the 2.4 GHz band for legacy, low throughput devices
and the 5 GHz band for newer, high throughput 802.11n devices. When
you put a dual-band AP on the floor plan, both the 2.4 GHz and 5
GHz radios are enabled by default and both are selected on the AP
list on the left panel of the main application window. This means
that the Signal Level
or Expected PHY Rate
visualizations will show you
cumulative pictures; if more than one radio is included in the
visualization, they will show the values for the strongest AP.
However, you will probably want to estimate coverage and expected
PHY rates for each band individually, because the range of 5 GHz
radios is shorter and because the attenuation level for 5 GHz
signals is higher. To do that, press the Select APs
button on the toolbar and use
the checkboxes next to the APs to select and deselect them
individually. You can also group APs by band and then select or
deselect all 5 GHz or 2 GHz APs with a single click. You might
notice that while good coverage is available in the 2.4 GHz band in
the entire area, 5 GHz coverage is not available
everywhere.
·Selecting the right
antennas for your AP might considerably increase signal level,
decrease interference, and, therefore, improve performance. If the
antennas of your APs are replaceable, this adds another degree of
freedom to your WLAN design. Using TamoGraph, you can select an
antenna from a large collection of generic and vendor-specific
antennas. You can also view antenna patterns in 3D.
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