weaker WiFi transmit power may not
be able to talk back to the access point.
This causes connection attempts to fail.
Coverage problems are normally resolved by adding more access points,
using antennas with a higher gain, or
increasing the transmit power of the access points. Still, notice that increasing
the power will also increase the noise
levels. Thus, it is normally recommended
to go with better antennas or more
Signal to noise ratio
The quality and rate of a connection depends on the signal-to-noise ratio (SNR)
that a receiving device detects. As described previously, attenuation or loss
of signal strength happens easily. So, as
the signal level goes down, the SNR goes
down, and so does the transmission
rate. A device that is “too far” from an
access point may be able to see the network to which it wants to connect, but if
the SNR is too low it will not be able to.
Another factor that affects the SNR is
the noise floor, which can be defined as
the ambient or background level of radio energy on a specific channel. This
background energy can include modulated or encoded bits from nearby 802.11
transmitting radios or unmodulated energy coming from non-802.11 devices
such as microwave ovens, Bluetooth devices, cordless phones, and so on. The
higher the noise levels are, the lower the
SNR will be.
The worst-case scenario is when you
have a weak signal and high noise levels, this fatal combination will greatly
lower your SNR. This, in turn, will cause
performance and connectivity problems. Still, identifying SNR problems is
very simple, you just need a tool that can
measure both signal strength and noise.
One thing to notice though, is that even
though in the past most WiFi adapt-
ers could measure noise levels, there are
not many of those anymore. Thus, you
may need to acquire a dedicated trou-
bleshooting tool that will provide this
information. There are many WiFi trou-
bleshooting or even surveying tools that
can do this.
Here are two options for how to resolve connectivity problems cause
by a low SNR.
1. Improve the coverage of your Wi Fi
network and make sure you have
a signal strength that is at least 20
dBm higher than the noise floor. (For
voice over WiFi deployments you
want your signal strength to be 30
2. Lower the noise floor on your environment by using channels with a
low amount of WiFi traffic, and by
removing non-WiFi devices that increase the noise floor on the WiFi
channels you are using. On cases
where the non-WiFi device generating the noise can’t be removed or disabled, you will need to reconfigure
your access points so they won’t use
the channels with a high noise floor.
Legacy 802.11 devices
Older WiFi devices are still around.
But they do not support today’s higher
data rates. So when they connect to a
WiFi network, they will transmit only
at lower data rates. Not only that—a
user may be using a legacy device that
does not support higher data rates without realizing it. This can be a problem
Identifying problems with signal-to-noise ratio is very simple.
You just need a tool that can
measure both signal strength
and noise. There are many WiFi