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In this lesson,

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we're going to discuss coverage in wireless networks.

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Coverage is a measure of how large

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of an area around a wireless transmitter

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there is sufficient signal strength

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for a wireless device to utilize.

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Basically, it comes down to how much physical area

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you can use with your wireless devices

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before you get outside the coverage area

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and you lose signal.

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To determine your coverage area,

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you're going to conduct a wireless site survey.

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This will generate a heat map showing the areas

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with the highest level signals in green.

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Then as they get weaker,

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it goes to yellow, orange, and red with the weakest signals.

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Now, the signal is always going to be measured

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from your client using the RSSI,

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and this is measured in decibels.

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If you're going to measure it from your access point,

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you're going to measure it in EIRP,

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and you're going to do that in dBi.

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Now, one of the most common issues experienced

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by wifi users is insufficient wireless coverage.

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For example, let's say you have a three-story townhouse

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and you only have a single wireless access point

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on the main floor of that home.

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Well, it's going to be unlikely to provide you

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with sufficient coverage all the way up

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on the third story of your townhouse.

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In this case,

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if you're using your laptop on the first floor,

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everything's going to work just fine

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because you have really high RSSI value.

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But when you go up to the second floor,

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that RSSI value is going to lower

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because the signal got weaker as you got further away,

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and the signal has to now go

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through the ceiling of the first floor

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to get into that second floor you're sitting at.

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Now, if you go up another level to the third floor,

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that signal may be too weak

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to even register by your wireless client,

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or it can drop you completely.

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Now, if this happens,

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you're going to need to find a way to boost up that signal

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and make it stronger so you can increase your coverage area.

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To do this, you can use a signal booster to raise the power,

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you can use an antenna with a stronger dB rating,

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you can use a wireless repeater,

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or you can add a second wireless access point

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that can operate in an extended server set

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or ESS configuration with your initial access point.

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Remember, the coverage area

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for a single wireless access point

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is affected by two main factors,

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the amount of power that the transmitter is sending out,

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and the size of your antenna.

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If you replace a five-decibel antenna

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with a nine-decibel antenna,

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you're going to effectively double your range

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under the right conditions.

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As for the power being sent out, unfortunately,

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you're normally going to be limited

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in your ability to control that,

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because there's a maximum amount of power

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that the FCC and regulators allow us to use

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inside of the wireless frequency range.

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But you could use a wireless repeater.

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Now, a wireless repeater is simply a layer one device

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that has two radios built into it.

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You plug this device into a power outlet

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and you configure it to connect to your wireless network.

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Now, one of the radios grabs the signal

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from your wireless network.

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Then it's going to boost up the signal

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and send it out again off its other radio.

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This way, when the signal comes in

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on one side of the device,

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it's going to be repeated out

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at full strength on the other radio too.

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This will extend that wireless network

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into an additional area of space

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because you have this new signal

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going out from this repeater.

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For example, let's say if this repeater

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receives a signal at negative 70 RSSI.

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It can retransmit again

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on the other side at negative 30 RSSI,

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effectively making it a brand new signal.

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So in the example of the three-story townhouse,

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I might want to have my first wireless access point

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on the first floor.

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Then I could have a repeater on the second floor.

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Now, at this point,

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we'll probably have some signal on the third floor,

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or we could put another repeater

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on the third floor to boost that signal even more

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when it reaches it from the second floor.

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Finally, we could use an extended server set

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to cover the entire building properly.

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In one of my old houses,

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I actually ran ethernet twisted-pair cable

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from the basement to the second floor of my house,

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and then I connected a second wireless access point there.

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These two wireless access points worked together

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to provide coverage over the entire home,

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one from the top down from the second floor,

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and one from the bottom up going from the basement.

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And this gave me adequate coverage for the whole house.

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Now, each wireless access point operated

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on a different channel,

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and I could roam from upstairs to downstairs

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and my devices would automatically switch

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from one access point to the other

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as they needed to to maintain coverage.

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These days, we also have wireless mesh systems available,

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and they rely on a combination of repeaters

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and access points that are put into a single device,

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provide full coverage for larger homes and offices.

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Instead of having to run ethernet cables to each device,

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they instead rely on internal wireless radios

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to send the data from one device to the other

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and create a whole house mesh network

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for the wireless network with sufficient coverage.