Heard of GLONASS? It’s a Russian radio-based satellite navigation system that both complements and provides an alternative to GPS. GLONASS is fully supported in several Xperia™ smartphones having a Qualcomm Snapdragon S2 or S3 processor and the latest software! In this article, Magnus Persson from Sony Mobile explains more about how GLONASS improves positioning and how you can incorporate this feature into your own apps.
Hi, I’m Magnus Persson, Positioning Specialist at Sony Mobile. Have you ever noticed how your navigation application suddenly slows and starts lagging when driving in downtown cities, just when you need precise instructions the most? This is mostly likely caused by the surrounding buildings blocking the view towards the GPS satellites. In order for a phone to calculate a good position, a clear line of access to four or more satellites is needed. If the signals have bounced off a wall before reaching the receiver, it will reduce the accuracy of the position. This is where GLONASS, another version of satellite based positioning system, can help.
What are GPS and GLONASS?
GPS stands for Global Positioning System and is a satellite based positioning system owned and maintained by the US Air Force. The GPS system currently contains 31 active satellites transmitting signals. GPS is used by millions of civil devices to calculate the position.
GLONASS stands for Globalnaya Navigatsionnaya Sputnikovaya Sistema and is also a satellite based positioning system but is owned and maintained by the Russian Space Forces. GLONASS development started in 1976 but it was not until October 2011 that full global coverage with modern satellites was achieved with 24 active satellites. Hence the number of GLONASS-only devices is very limited.
How GLONASS improves positioning
It’s simple math – by supporting both systems in a receiver, the number of available global satellites increases from 31 to 55. Therefore, more geographic locations are able to receive four or more signals from satellites, which in turn means more successful position calculations and also better accuracy of the calculated positions in challenging environments.
Field tests in downtown San Francisco found that the positioning accuracy of adding GLONASS improved as much as 50%. The test were executed with the help of Qualcomm using two Sony Ericsson Live with Walkman™ smartphones, and 600 measurements were recorded and analyzed per device.
|Configuration||Number of satellites used*||CEP 68% (m)**|
|GPS + GLONASS||
* The number of satellites in average that were used to calculate the position. More satellites usually mean a more reliable and accurate location.
**CEP 68% means that 68% of the 600 measurements are within this distance, in meters, from the reference location. Hence lower values mean better accuracy.
How your app can benefit from GLONASS
Now that you understand the benefits of using GLONASS, the next step is ensuring that your app utilises it. If you’ve already developed an Android™ app using the GPS provider, mostly likely it’s already using GLONASS satellites to improve the positioning accuracy and navigation experience for the phones and software supporting GLONASS.
The GLONASS enhancement is transparent and backwards compatible with the existing applications but there are ways to see the benefit of the GLONASS satellites. One way is to download and install the free GPS Test application by Chartcross Ltd. from Android Market. The satellites numbered 65 to 88 are GLONASS satellites that are being tracked.
If you would like to indicate in any way in your application if GLONASS satellites are used to calculate the position you can do so by checking the GpsSatellite objects returned by the getSatellites method. If the PRN value returned by getPrn is between 65 and 88 and the usedInFix method returns true the last position was calculated using a GLONASS satellite.
To save power, the GLONASS receiver is only activated in problematic locations, such as in an urban environment with high rise buildings. Therefore, if you are in an open sky environment where there are enough GPS satellites available to calculate a good accuracy position, GLONASS will automatically be switched off temporarily to enhance the battery lifetime.
So the next time you’re having problems getting a fix on your location, use an Xperia™ smartphone supporting GLONASS to get faster and more accurate location information.