The use of two satellite systems is now the standard for many current outdoor handhelds, bicycle devices and wearables from Garmin. GPS & GLONASS is usually already activated in the device settings. Alternatively, you can switch to GPS & GALILEO or GPS only.
Many current Garmin devices allow these GNSS* combinations:
- GPS + GLONASS (currently the Garmin standard)
- GPS + GALILEO
Positioning with the help of two GNSS has its advantages. The availability of two systems means that more satellites are available. This can have an impact on the time to first positioning (TTFF = time to first fix) and the positioning accuracy.
*GNSS = Global Navigation Satellite System
How many GPS, GLONASS & GALILEO satellites are available?
(status: November 2021)
- GPS: 30 operational satellites
- GLONASS: 23 operational satellites
- GALILEO: 22 operational satellites
Information on the current statuses can be found here:
Check the live positions: in-the-sky.org
What are the advantages of using two satellite systems simultaneously?
A good example is shown in the figure. Due to the availability of only four GPS satellites and an unfavourable satellite geometry in a mountain valley (three out of four GPS satellites are in a row), the position determination is relatively inaccurate. The accuracy is shown as "25 m".
The same applies to large cities. High buildings ("urban canyons") can also cause shadows effects, there are fewer satellites in the direct field of view of the GPS receiver.
In addition, "multipathing" effects often occur in mountains and cities, caused by walls, snow, facades of buildings & road surface. Reflected satellite signals also result in poorer accuracy.
What positive effect has a second GNSS?
More satellites distributed over the sky can lead to a more favourable distribution ("geometry") and thus to a better accuracy and a faster positioning (TTFF).
Garmin defines GPS accuracy as follows:
Accuracy of the position in m (CEP, Circular Error Probable: 50% of all measurements are within the specified radius (e.g. 25 m), 50% of all measurements are outside of this radius).
Another note: At least three satellites are required to determine the position, and at least four satellites must be in use to determine the GPS altitude.
What are the disadvantages of using GPS, GLONASS and GALILEO simultaneously?
The disadvantage is the slightly increased power consumption of the GPS receivers, in my experience it is about 10% (GPS handhelds like Garmin Oregon or eTrex). The situation is likely to be similar for bike computers and wearables.
Garmin – GPS only, GPS & GLONASS or GPS & GALILEO – What do you recommend?
This is a generally difficult topic, as many factors play a role: chip manufacturer, firmware, algorithms, GPS antenna type, antenna placement, energy consumption of the GPS receiver and antenna, available energy, mounting of the device, environment, …
My recommendation is to deactivate GLONASS or GALILEO if possible and to use GPS only, especially when you want to increase the battery life. Switch a second GNSS on when necessary (mountains, cities, forests with a high tree density). GPS + GLONASS should be preferred over GPS + GALILEO as this is the Garmin standard … and the devices could be optimized in this respect.
Figures (screenshots Garmin eTrex 32x):
Excellent satellite reception; GPS + GLONASS (left) does not lead to a better accuracy compared to GPS only. The accuracy is always 3 m. GPS: 02 – 30, GLONASS: 68 – 84.
Edge cycling devices
Since the devices are attached to the handlebars, signal shadows can occur through the rider’s body. So I would recommend to use GPS + GLONASS, except you want to save battery.
The situation is different for wearables.
For example, when you run, the wearable is attached to a second dynamic system: your moving arm. The GPS antenna usually points somehow to the side and not skywards, your body causes shadowing when receiving satellite signals. All these factors can lead to GPS inaccuracies.
Therefore, it is better to get the maximum out of it by using GPS + GLONASS – this setting is also the Garmin standard for wearables and is continuosly optimized.
However, runners report that the pace can be more consistent when using only GPS. Try it out!
Must read: Garmin fenix GPS accuracy
What GNSS technology trends can be expected in 2022 and beyond?
There are now handheld devices with chips that support not only simultaneous reception of multiple GNSS ("multi-GNSS"), but also of multiple frequencies ("multi-band"). Examples are the GPSMAP 65s and the GPSMAP 66sr (review), launched in 2020. These devices can provide a faster TTFF and a better accuracy. However, my experience shows that no miracles should be expected – standard GPSMAP devices are already very good in terms of accuracy (in my opinion the helix antenna plays a big role).
An example of such a chip is the Broadcom BCM47755, which can use GPS, GLONASS, BeiDou (the Chinese GNSS), QZSS (the Japanese GNSS), and GALILEO, as well as two frequencies (L1 + L5). Similar chips come from Sony and Airoha.
A similar development can be seen in wearables. In 2021, Coros and Huawei launched wearables with multi-GNSS and multi-band (Coros Vertix 2, Huawei Watch GT 3, Huawei Watch GT Runner). For Garmin, I expect this in 2022; for example, with a possible fenix 7 series.
Garmin might have initiated another development with the new GPSMAP 79s handheld (launched late 2021). The GPSMAP 79s does not provide multi-band. But it is equipped with multi-GNSS for simultaneous reception of GPS, GLONASS, Galileo, QZSS and BeiDou satellites. In my opinion, this will become the standard for future Garmin handhelds and Edge devices.