There are a lot of new devices that uses Zig-Bee. These could be door locks, thermostat temp sensors , light switches for home automation. If you go here you can see some certified ones.
Generally these work fine in a residential situation but I have been attending more and more installations where they have been installed in commercial installations without regard to the existing environment and the Wifi Stopping the Zig-Bee working at all some times.
Zig-Bee and WiFi both exist in the 2.4Ghz Band and unfortunately they share the same frequencies as well
There MUST be careful planning to make sure they can both exist a the same time. As you would for a Wifi Design.
In Zig-Bee there are 16 Channels so different devices can communicate at the same time in the same area.
Unfortunately the16 Channels overlap with the 13 Wifi Channels in Australia
You know the rule: ONLY USE 1,6,11 in 2.4Ghz in Commercial WIFI designs
In Zig-Bee the channels are 11 to 26
If the Wifi 2.4Ghz usage of Spectrum is low, things work OK, the Zig-Bee has enough dead air time to communicate. NOTE: Zig-Bee and Wifi can not detect each other. Each is seen as interference to the other.
I have noticed most manufactures set their devices to default to channels 26,25,20,15 as they assume WiFi will be on 1,6,11 to try and avoid interference but the side lobes of the Wifi go here and tend to swamp the Zig-Bee.
I have seen lights that take 10 seconds to turn on or Door locks that take 10 seconds to open because the Zig-Bee has to re transmits so many times to overcome the WiFi interference.
A lot of Zig-Bee devices are battery powered and these transmitters just waste battery power. I have seen devices with a rated battery life of 6 months only last 1 month in high utilization WiFi environments.
In a battle between Zig-Bee and WiFi Zig-Bee normally looses.
Moving Wifi to 5Ghz is a great idea but a lot of devices ONLY work on 2.4Ghz
Generally if you want Zig-Bee to work you need to stop using WiFi channel 11
Then you can use Zig-Bee Channel 24 25 26 without any worries.
But this only works if you have complete control of the spectrum.
in the below example only 1,6,11 are used in WiFi and side lobes at this location for Zig-Bee is OK for Channels 15,20,25,26
In a commercial situation you generally cannot control the neighbors or the employee devices.
and I can bet is a WiFi device on auto channel sees 11 free it will take it !
You need to keep the Zig-Bee Device as far as possible from the AP and the Client so the side lobes have fallen off so much to not interfere
Channelizer from Meta Geek is great as it have a view option to show Zig-Bee channels
At one site the channel 6 Wifi Channel was so busy and AP too close. You can see how big the side lobes were when measured at the Zig-Bee Device (it was configured to use channel 15 and 20)
It was never going to work
At a better designed site the AP is away from Zig-Bee Device It was using channel 26 and 11
Channel 26 is away enough not to be too effected by side lob but if channel 1 or channel 6 was busy Zigbee Channel 11 would be effected.
Imagine Zig-Bee Locks at a private high density student accommodation tower. With all the students running their own Wifi hot-spots on 2.4Ghz on channels 1-13 (The 1,6,11 rules is not being obeyed).
Xbox, Nintendo, Cheap WiFi cameras Wifi connected TVs and phones streaming Netflix.
You could never control the spectrum. The locks will not work very well and the battery life will be very poor.
Wifi and Zig-Bee NEEDS TO BE DESIGNED with will NOT just work together!
Thank you to my daughter for her drawing skills in sketch-it for the pictures.
No comments:
Post a Comment