GPS Synchronisation

GPS Synchronisation

What is GPS Synchronisation?

GPS Synchronisation is a feature available on select airMAX products from Ubiquiti. When used, GPS synchronisation drastically reduces interference on co-located devices by syncing the devices' TX transmissions which would typically be 'heard' by half-duplex radios in co-located environments.

How is interference reduced with GPS Synchronisation?

Imagine two speakers trying to give a presentation to a crowd at the same time within close proximity to one another. When the first speaker starts broadcasting, the second speaker's crowd erupts in applause... The first speaker's crowd will more than likely not be able to hear that broadcast clearly. However if both speakers transmit simultaneously albeit with a slight overlap, the chances of both crowds hearing their speaker are greater.

GPS Synchronisation works in the same manner, making all the AP's transmit to the clients simultaneously which substantially reduces interference while improving the quality and performance to the clients.

Frequency reuse:

The larger your deployment, the more channels you require, so it is recommended to reuse channels for back-to-back devices on the same tower in order to utilise the spectrum efficiently. This is based on the idea that hardware will 'hear' very little interference when mounted on opposite sides.

In a x4 AP tower configuration, where generally 4 channels would be required to limit interference, only two channels are utilized using frequency reuse. Placing the AP's on the same channel back-to-back ensures limited interference and increased scalability as the amount of interference is significantly lower out the back lobes. When using the PS-5AC and a Horn antenna of your choice there are no back lobes and interference is reduced even further.

Is GPS Synchronisation always necessary?

There are a few situations where you would not get any benefit from this technology and possibly even significantly degrade your network. Non co-located environments would be the most obvious but it is also not practical for low interference environments. Any situation where client devices can 'hear' the transmission from multiple AP's on your synchronised tower is not suited for GPS Synchronisation.

Blog post by Abby Carelse

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