Over the course of several years designing, installing, supporting and troubleshooting WLAN’s I have run across some repeat offenders in the wireless interferer’s area. So, I thought it would be a good idea toblog about this issue for a quick explanation.
Here are two repeat offendors causing poor wireless network performance:
1) Microwave Ovens
The spectrogram below is a 5 minute recording of the 2.4Ghz RF spectrum in our office. We utilize dual radio access points and most all of the client devices are on 5Ghz so the activity in the 2.4GHz spectrum is pretty minimal. In other words this is a clean spectrum recording, relatively.
In contrast below is a recording I made while I ran our office microwave for two cycles. One cycle was for a minute and a half which is represented by the first interference event. The second cycle was for a minute only and is represented by the second interference event. You can see in the spectrogram that the majority of the interference is within the bandwidth positioned where channel 11 resides. However there is also some bleed over into channels all the way down to channel 1 and up to channel 14. Also important to note is that the strength of the microwave signal is -28dBm which is a full 72dB above the noise floor. This interference on the wireless network system is almost as strong as if I were measuring the strength of an AP that was 6 feet from my laptop.
2)Blue Tooth (BT)
Blue Tooth is the other repeat offender that I run into quite often. Mostly, I see it in the educational space where students have BT turned on with their phones, or teachers have purchased their own BT keyboard and mouse or the school has implemented Promethean white boards and/or Sympodium Smart tablets. All these devices use BT for communication and when used individually most often do little harm to the Wi-Fi signal. However, I have gone into some classrooms to troubleshoot issues and just using my Android phone to search for BT devices I pick up anywhere from one to two dozen BT devices all broadcasting within a 300 foot radius. This many BT devices all at once will bring the RF in the area to its knees and render it unusable. This is a primary reason we suggest dual radio/dual band AP’s in the classroom environment. BT does not interfere with the 5Ghz spectrum and with the dual radio/band AP’s having a 5GHz radio available the devices that are 5GHz interoperable can utilize it instead of the noisy 2.4GHz spectrum.
The spectrogram recording below was also done over a 5 minute period and shows an interference event about one and half minutes in length. The interference event was a BT headset for my Android phone. I used the headset to listen to music from an app on the phone. During this interference event we can see that the headset disturbs the entire channel range as show in the spectrogram and noted in the Active Devices Table from the Spectrum Analysis application.
Controlling these devices in most environments is difficult or next to impossible. You could shield the break room with metal mesh or manually sweep classrooms looking for BT devices but realistically that would not be possible. What is realistic and achievable is to make sure when you are planning a Wireless LAN deployment that you design with dual radio access points.
If you do need some help designing your secure wireless network to avoid these issues, you can contact us here to talk to one of our consultants at no charge. We’ve also got some great free resources that you can download to get you going in the right direction, one in particular you might find useful is our Free Wireless Design kit! Best of luck!