In this lesson,
we're going to discuss coverage in wireless networks.
Coverage is a measure of how large
of an area around a wireless transmitter
there is sufficient signal strength
for a wireless device to utilize.
Basically, it comes down to how much physical area
you can use with your wireless devices
before you get outside the coverage area
and you lose signal.
To determine your coverage area,
you're going to conduct a wireless site survey.
This will generate a heat map showing the areas
with the highest level signals in green.
Then as they get weaker,
it goes to yellow, orange, and red with the weakest signals.
Now, the signal is always going to be measured
from your client using the RSSI,
and this is measured in decibels.
If you're going to measure it from your access point,
you're going to measure it in EIRP,
and you're going to do that in dBi.
Now, one of the most common issues experienced
by wifi users is insufficient wireless coverage.
For example, let's say you have a three-story townhouse
and you only have a single wireless access point
on the main floor of that home.
Well, it's going to be unlikely to provide you
with sufficient coverage all the way up
on the third story of your townhouse.
In this case,
if you're using your laptop on the first floor,
everything's going to work just fine
because you have really high RSSI value.
But when you go up to the second floor,
that RSSI value is going to lower
because the signal got weaker as you got further away,
and the signal has to now go
through the ceiling of the first floor
to get into that second floor you're sitting at.
Now, if you go up another level to the third floor,
that signal may be too weak
to even register by your wireless client,
or it can drop you completely.
Now, if this happens,
you're going to need to find a way to boost up that signal
and make it stronger so you can increase your coverage area.
To do this, you can use a signal booster to raise the power,
you can use an antenna with a stronger dB rating,
you can use a wireless repeater,
or you can add a second wireless access point
that can operate in an extended server set
or ESS configuration with your initial access point.
Remember, the coverage area
for a single wireless access point
is affected by two main factors,
the amount of power that the transmitter is sending out,
and the size of your antenna.
If you replace a five-decibel antenna
with a nine-decibel antenna,
you're going to effectively double your range
under the right conditions.
As for the power being sent out, unfortunately,
you're normally going to be limited
in your ability to control that,
because there's a maximum amount of power
that the FCC and regulators allow us to use
inside of the wireless frequency range.
But you could use a wireless repeater.
Now, a wireless repeater is simply a layer one device
that has two radios built into it.
You plug this device into a power outlet
and you configure it to connect to your wireless network.
Now, one of the radios grabs the signal
from your wireless network.
Then it's going to boost up the signal
and send it out again off its other radio.
This way, when the signal comes in
on one side of the device,
it's going to be repeated out
at full strength on the other radio too.
This will extend that wireless network
into an additional area of space
because you have this new signal
going out from this repeater.
For example, let's say if this repeater
receives a signal at negative 70 RSSI.
It can retransmit again
on the other side at negative 30 RSSI,
effectively making it a brand new signal.
So in the example of the three-story townhouse,
I might want to have my first wireless access point
on the first floor.
Then I could have a repeater on the second floor.
Now, at this point,
we'll probably have some signal on the third floor,
or we could put another repeater
on the third floor to boost that signal even more
when it reaches it from the second floor.
Finally, we could use an extended server set
to cover the entire building properly.
In one of my old houses,
I actually ran ethernet twisted-pair cable
from the basement to the second floor of my house,
and then I connected a second wireless access point there.
These two wireless access points worked together
to provide coverage over the entire home,
one from the top down from the second floor,
and one from the bottom up going from the basement.
And this gave me adequate coverage for the whole house.
Now, each wireless access point operated
on a different channel,
and I could roam from upstairs to downstairs
and my devices would automatically switch
from one access point to the other
as they needed to to maintain coverage.
These days, we also have wireless mesh systems available,
and they rely on a combination of repeaters
and access points that are put into a single device,
provide full coverage for larger homes and offices.
Instead of having to run ethernet cables to each device,
they instead rely on internal wireless radios
to send the data from one device to the other
and create a whole house mesh network
for the wireless network with sufficient coverage.