Wi-Fi Site Survey: What It Checks Before You Add Access Points

The Wi-Fi drops in the meeting room, it crawls in the warehouse, and the first reflex is to buy one more access point.
Sometimes that is the right answer. Often, the new access point ends up on the same channel as its neighbour, and the
problem gets worse. Before buying, a site survey measures what the wireless network really does, room by room. Cisco
Meraki strongly recommends doing one before the access points are deployed, and another one after
(Meraki, Conducting Site Surveys).

What is a site survey?

Someone walks the premises with a laptop and survey software. At each spot, they record signal strength, noise, the
channels in use and interference. Meraki notes that survey software already knows the coverage patterns of its access
points, which makes a predictive survey, done on a floor plan, possible. It still recommends an onsite survey for the
best coverage and performance
(Meraki, Conducting Site Surveys).
A floor plan shows neither the metal filing cabinet, nor the kitchen microwave, nor the neighbour’s network.

1. Signal strength and noise

Two measurements come first. For a network that has to carry calls, Meraki aims for a signal of about -67 dBm at the
edge of the covered area, with a signal to noise ratio of at least 25 dB
(Meraki, Conducting Site Surveys).
Below that, the connection often holds, but calls break up and files drag. The survey shows where the threshold is met
and where it is not.

2. Channels

In 2.4 GHz, the standard defines fourteen channels, but only three do not overlap, channels 1, 6 and 11
(Meraki, Channel Planning).
Neighbouring access points should overlap a little, so devices move from one to the next without dropping, but on
different channels. Otherwise they form a single domain where everyone waits their turn, like an old Ethernet hub (same
source). In 5 GHz, some channels require dynamic frequency selection (DFS): an access point that detects radar has to
leave the channel at once (same source). That is why an access point added without a channel plan can slow the
network down instead of helping it.

3. Walls and materials

Meraki recommends not mounting an access point near metal or concrete walls, which weaken the signal sharply
(Meraki, Conducting Site Surveys).
Its high density guide says to take building materials into account when placing access points
(Meraki, High Density).
No official source gives a fixed loss per type of wall. Only a measurement in your premises gives it for your walls.

4. The number of devices

Coverage is not enough. An access point shares its spectrum among every device connected to it, and each one gets less
when there are many. Meraki calls it high density beyond 30 devices on one access point, and aims for about 25 devices
per radio, or 50 per access point
(Meraki, High Density).
A full training room is not designed like a hallway.

5. The 5 and 6 GHz bands

Meraki recommends full coverage in both 2.4 and 5 GHz, steering devices toward 5 GHz
(Meraki, High Density).
The 6 GHz band of Wi-Fi 6E adds many channels, but Meraki expects less range than in 5 GHz, and only devices that
support WPA3 can connect to it. Many devices do not have a 6E card yet
(Meraki, Wi-Fi 6E FAQ).
The survey tells you whether 6 GHz is worth it in your premises today.

What the report should contain

• a map of signal and signal to noise ratio, room by room;
• the channels in use and the interference found, including the neighbours’;
• the proposed location of each access point, with the reason;
• the security settings found. The Canadian Centre for Cyber Security calls for WPA3 in all new deployments, a guest
  network separated on a restricted VLAN, and changed default passwords. It also advises limiting signal strength, so
  someone parked nearby cannot attack it
  (ITSP.80.002).

After installation, measure again

Meraki recommends a second survey after deployment, then adjustments based on its results
(Meraki, Conducting Site Surveys).
That survey confirms the installed access points deliver the coverage planned on paper. The Canadian Centre also says
to update access point firmware regularly
(ITSAP.80.009).

Frequently asked questions

How do you do a Wi-Fi site survey?

Someone walks the premises with survey software and records, at each spot, signal strength, noise, channels and interference. Cisco Meraki recommends an onsite survey before the access points are deployed, and another one after.

Is a survey on a floor plan enough?

It helps to prepare, because the software knows the access points’ coverage patterns. Cisco Meraki still recommends an onsite survey, which sees the real walls, metal and interference.

Where should a business install its Wi-Fi access points?

Where the survey shows the need, away from metal or concrete walls, with a slight overlap between neighbouring access points set on different channels, counting the devices, about 25 per radio according to Cisco Meraki.

To go further

Our article on Wi-Fi for a growing office explains why a flat
network slows down, and the one on guest Wi-Fi how to keep
visitors apart from your workstations. Wireless design is at the heart of our
Business networking, Aruba Wi-Fi
and Cisco Meraki pages.

What now?

Your Wi-Fi keeps dropping and you are not sure about adding access points? MPJM’s
free network analysis looks at Wi-Fi and switches, coverage, cabling,
and who can connect to what. It is offered to businesses with 10 or more workstations.

P.S. Sixteen questions, eight domains, a clear picture of your strengths and blind spots: start the assessment.