Tips for optimizing GNSS (GPS) in MOTOTRBO

For some time now, GPS is being referred to as GNSS in MOTOTRBO (though the term is used interchangeably). This change is to accommodate other systems like GLONASS and BDS in the radio hardware. I had this questions via my FAQ page the other day and thought this might be useful for everyone else.

So, here are some ideas on how to improve your GNSS throughput and performance:

The right expectations

Before installing the system, it's important to explain to the customer (and understand for your self) that:

  1. The radio system can only pass a certain number of updates per channel
  2. That the number of updates will decrease if more radio users are added to the system
  3. Car Navigation systems use a feature known as snap-to-road that makes them seem highly accurate - this is not the case. GPS (or GNSS) accuracy is dependent on a number of factors - this includes things like the way in which the radio is held; the weather; obstructions etc.
When most people think GPS, they think of something from the movies: a dot moving in real-time across a map. In my experience this is often part of the problem.

Speak less.

Yes, this sounds dumb but it's one way of alleviating the problem. Encouraging users to avoid using the radio as a boredom-cure-cum-social-tool will make some improvement since radios that are in a call will not send a location update.

Smaller groups.

Arrange users into smaller talkgroups so that not everyone is party to a call. The fewer radios that are in a call, the more opportunity they have to send updates.

Time to first fix.

If possible, switch on portable radios outdoors and way from the users body to get a cold fix quicker.

GPS Revert

To free up voice channels, GPS can be offloaded onto a seperate data-only (otherwise known as a Data Revert) channel.

Enhanced GPS Revert

On a MOTOTRBO system, GPS updates can optionally be offloaded onto a separate channel. This frees up voice channels and provides a free channel for radio-to-dispatch data only messages. Additionally, the GPS updates can be coordinated thus preventing collisions and retries by using Enhanced GPS.

There is a lot of information on this in the MOTOTRBO System Planners. In Capacity Max, there is a similar feature known as high efficiency GPS.


Single CSBK data will allow you to send more GPS updates by stripping unnecessary data from update packets. Find out more here.


  1. Hi Wayne,

    According to the system planner document, if header compression is enabled then Enhanced GNSS must be enabled for the home (voice) channel but not enabled for the revert channel.

    Which channel should have header compression enabled?
    If the home (voice) channel is slot 1 and the revert channel is slot 2,
    how should the repeater be configured (which repeater slot gets Enhanced
    GNSS enabled?)

    Rather confusing.

    1. Enhanced GNSS should be enabled on the slot which is used by the radio to send location updates to the Control Station/MNIS.


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