Wireless Surveys · Topic 1 of 2
Site Surveys
Learn why and how to run a wireless site survey, the difference between predictive, passive and active surveys, and what to measure and record on site.
- 5 min
- A site survey measures real radio conditions to plan or check a network.
- A predictive survey uses software, a passive survey listens, and an active survey is joined to the network.
- Use a test device like the real clients and measure at the height clients work.
What it is
A site survey is the work of measuring the radio conditions in a place, to plan or check a wireless network.
A plan on paper cannot know what the real walls, furniture and neighbouring networks do to the signal. A survey replaces guesses with measurements.
Surveys are done before the network is built, to choose the layout, and after it is built, to prove that it works.
How it works
A survey follows a clear sequence and uses one of three main types.
Types of survey
| Type | What it does | When to use it |
|---|---|---|
| Predictive | Uses software and a floor plan to estimate coverage | Early planning, before any hardware is on site |
| Passive | Walks the site and listens, measuring signal, noise and networks | To check coverage and the radio environment |
| Active | The test device is joined to the network and measures real performance | To check throughput, roaming and delay |
The next page covers predictive tools in more detail. A common approach is to predict first, then run a passive survey on site, and finish with an active check after installation.
Before you start
Prepare the survey with the customer.
- Agree the coverage areas and the minimum quality.
- Agree the number and type of clients and the applications.
- Obtain floor plans or draw a sketch.
- Find out the building materials and any restricted areas.
- Note where cables, power and mounting positions are possible.
The minimum quality depends on the use. Voice and video need a stronger and cleaner signal than basic web access.
On site
Walk the site with a test device and record measurements at many points.
- Use a test device that is similar to the real clients. A different radio can give very different readings.
- Measure at the height where clients really work, such as desk height.
- Record the signal strength, the noise, the channel use and the networks that you can hear.
- Mark each reading on the floor plan.
- Take extra readings near corners, lifts and metal obstacles.
If you place a temporary access point to test a location, put it at the planned height and power. Then measure around it.
A survey is only as good as the test device. Use the same type of client that the users will have, and the same band.
Using RouterOS during a survey
A MikroTik device can measure the environment too.
/interface wireless scan wlan1
/interface wireless registration-table print statsscanlists the networks, channels and signal levels that the radio can hear.- The registration table shows the signal and rates of the clients that are connected to a test access point.
Scanning interrupts normal service on that radio, so use a spare radio or a quiet period.
Outdoor and link surveys
An outdoor link survey checks the path between two points.
- Is there a clear line of sight, and is the Fresnel zone free?
- How high must the antennas be to clear the obstacles?
- Is there interference from other links on the band?
- Can the mast and the cables be installed safely?
Check the path at the time of year when trees have leaves. Look for other radio users near the site.
What to record
Write a report so the work can be repeated or checked.
- The floor plan or map with the readings marked.
- The signal strength and the noise at each point.
- The channels in use by neighbours.
- The planned access point positions, channels and power.
- The problems found and the actions to fix them.
After installation
Run a validation survey when the network is built. It confirms that the coverage meets the agreed targets and that roaming works as people move.
Adjust the power or the channels if the readings do not match the plan.
A survey made during a quiet weekend may not show the interference of a busy weekday. Repeat a check when the site is in normal use.
What to remember for the exam
Seven facts cover this topic.
- A site survey measures real radio conditions to plan or check a network.
- A predictive survey uses software, a passive survey listens, and an active survey is joined to the network.
- Use a test device like the real clients and measure at the height clients work.
- Record signal strength, noise and channel use at many points on the floor plan.
- Scan on a live radio interrupts service.
- Outdoor surveys check line of sight and the Fresnel zone.
- A validation survey after installation confirms that the design works.
Common mistakes
These four errors are common.
Trusting the plan alone. Real walls and neighbours change the result.
Using a different test device. Its radio may report very different values.
Surveying at the wrong time. Interference changes during the day and across the week.
Skipping the report. Without notes, you cannot repeat or check the work.
Check yourself
Work through these three questions.
What is the difference between a passive and an active survey?
A passive survey listens and measures signal, noise and networks. An active survey joins the network and measures real performance.
Why should the test device be similar to the real clients?
Different radios report different values. A similar device gives results that match what users will see.
What does a validation survey do?
It runs after installation to confirm that the coverage meets the agreed targets and that roaming works.
Topic 1 of 2 in Wireless Surveys
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