Wireless Troubleshooting · Topic 2 of 3
Signal Quality Metrics
Understand signal strength, noise floor, SNR, CCQ and data rates, and how to read them in RouterOS to judge the quality of a wireless link well.
- 4 min
- Signal strength is in dBm, and a value closer to zero is stronger.
- The noise floor is the background energy, and a lower value is better.
- SNR is signal minus noise floor, in dB.
What it is
Signal quality metrics are the numbers that tell you how good a wireless link really is.
A strong signal alone is not enough. The link also needs low noise, a high data rate and efficient use of the air.
RouterOS shows these numbers in the registration table and in the monitor command, and you can compare them to find the cause of a problem.
How it works
Each metric describes a different part of the link.
Signal strength
Signal strength is the power the receiver sees, measured in dBm. The values are negative. A value closer to zero is stronger, so minus 55 dBm is better than minus 75 dBm.
Many devices have more than one chain, and the table can show a value for each chain. A big difference between the chains can point to a faulty antenna or cable.
Noise floor
The noise floor is the background radio energy on the channel, also in dBm. A lower value is better, so minus 95 dBm is quieter than minus 80 dBm.
Interference, other networks and other devices raise the noise floor.
Signal to noise ratio
SNR is the difference between the signal and the noise floor, in dB.
SNR (dB) = signal (dBm) - noise floor (dBm)A signal of minus 60 dBm with a noise floor of minus 95 dBm gives an SNR of 35 dB. If the noise rises to minus 80 dBm, the SNR falls to 20 dB although the signal is the same.
SNR matters more than raw signal. A strong signal in a very noisy channel can still give a poor link.
Data rate
The data rate is the speed the two devices use on the link right now. A higher SNR allows a higher modulation and a higher rate, and a lower SNR forces a lower rate.
The registration table shows the transmit rate and the receive rate separately. They can differ because each direction has its own conditions.
CCQ
CCQ (client connection quality) is a percentage on the legacy wireless package. It compares the best possible time needed to send the data with the time that was really needed.
A high CCQ means the air is used efficiently. A low CCQ means many retries, often because of interference, a hidden node or a weak signal.
Reading the numbers together
| Signal | Noise floor | CCQ | Likely meaning |
|---|---|---|---|
| Strong | Low | High | Healthy link |
| Weak | Low | Medium or low | Distance or an obstruction |
| Strong | High | Low | Interference on the channel |
| Strong | Low | Low | Hidden node, a busy channel or a hardware fault |
Always look at several numbers before you decide on the cause.
Where to see them
/interface wireless registration-table print stats
/interface wireless monitor wlan1- The registration table shows the signal, the rates and the CCQ for each client.
monitorshows the current channel and the noise floor for the interface, and values for the whole radio.
On the wifi driver the registration table shows the signal and the rates. The set of values can differ from the legacy package, so check which columns your version shows.
Using the numbers
Measure at the place where the client works, not next to the access point. Measure again at different times, because noise changes during the day.
Use the numbers to decide the fix:
- Weak signal: move the device, change the antenna or add an access point.
- High noise: change the channel or find the interference source.
- Low CCQ with good signal: look for hidden nodes and busy channels.
Do not raise the transmit power to fix a noisy channel. It does not lower the noise, and the client still cannot answer.
What to remember for the exam
Seven facts cover this topic.
- Signal strength is in dBm, and a value closer to zero is stronger.
- The noise floor is the background energy, and a lower value is better.
- SNR is signal minus noise floor, in dB.
- A higher SNR allows a higher data rate.
- CCQ shows how efficiently the air is used, and it is a percentage on the legacy package.
- The transmit rate and the receive rate can differ.
- A strong signal with a high noise floor still gives a poor link.
Common mistakes
These four errors are common.
Judging by signal alone. The noise floor decides how usable the signal is.
Misreading negative numbers. Minus 90 is weaker than minus 60.
Measuring beside the access point. The numbers do not match the client location.
Adding power to fix noise. The noise stays and the uplink does not improve.
Check yourself
Work through these three questions.
How is SNR calculated?
SNR is the signal in dBm minus the noise floor in dBm. The result is in dB.
A signal of minus 60 dBm and a noise floor of minus 80 dBm give what SNR?
The SNR is 20 dB. A lower noise floor would raise it.
What does a low CCQ with a good signal suggest?
The air is being used inefficiently, for example because of interference or hidden nodes, so there are many retries.
Topic 2 of 3 in Wireless Troubleshooting
Test yourself on Wireless Troubleshooting
The full MikroTik MTCEWE question bank has 476 questions, with timed practice exams and an explanation for every answer.
This study guide is independent and is not affiliated with, endorsed by, or sponsored by MikroTik. Vendor names, certification names and exam codes are trademarks of their respective owners and are used for identification only.