What is GLP Mode ?

“GLP” is an abbreviation for ‘GNSS Low Power’. This is one of the latest features developed by MediaTek to further reduce (the already very low) power consumption of their GNSS chips in tracking mode.

You may have heard the term “FLP” first. FLP and GLP are one and the same thing. FLP was the first name given to this mode during its beta stage, but due to a trademark concern, it was later officially changed to GLP.

This new mode has been made by MediaTek specifically for the rapidly growing number of wearable devices, as well as the new compact battery-driven IoT products where power consumption can sometimes be a deciding factor in the overall success of the product.

In this article, I will teach you how to enable and use the new GLP mode, as well its benefits and drawbacks. Please note that this guide can be used not only for GTOP’s GNSS modules, but should be more or less applicable to other MediaTek based positioning modules as well. However, wherever needed, I will only reference data from tests done with our own modules.

Please make sure that you request GLP-enabled firmware from your supplier, as this is not a standard feature, and will not work on existing MediaTek GNSS modules unless they have been upgraded to the latest core firmware.

Before explaining the steps, it’s important to recognize that this mode is not for everyone, and it’s certainly not suitable nor recommended for lifesaving or emergency equipment where positioning accuracy is vital. I would only recommend the use of this mode in positioning devices where the GPS role is not a critical one. For example in devices where power consumption is a more serious concern than high-positioning accuracy.

You may not hear this from others promoting this feature, but there is no doubt a slight impact on the positioning accuracy of the module in this mode. In our tests we saw the normal positioning accuracy of the module go from an average of 2.0 CEP to around 5.0 CEP with the GLP enabled. Do not be alarmed if this happens, this is normal. Also, please understand there are many applications, where GLP is ideal as it will get the job done (from positioning and navigation perspective), while tremendously extending your battery life.

To Enable GNSS Low Power (GLP) Mode

To enable or disable GLP mode, please use the PMTK commands below :

• Enable: $PMTK262,3
• Disable: $PMTK262,0

How GLP operates ?

GLP mode works on a duty cycle of 1 second to achieve the overall power saving.

The MediaTek chipset is automatically able to switch between GLP and normal cycles depending on the latest conditions. For instance : a module in GLP mode will only switch back to normal mode :

• when it is in a difficult environment, and it needs to keep higher accuracy
• when decoding of a navigation message is required

Below figure gives a visual representation of how GLP mode operates :

How to test GLP mode yourself ?

Please use the following steps to test the GLP Mode on your evaluation board or device :

FW Settings :

1. Choose 115200 UART Baud Rate, and output NMEA only.
2. Disable SBAS

The above two steps are recommended if you want to get the lowest possible power consumption, but they are not mandatory.

Testing Steps :

1. Test under Open Sky Conditions.
2. Enable GLP mode using PMTK262,3 command.
3. Wait until the module gets a valid fix.
4. Wait at least 60 seconds for the mode to enter GLP mode.
5. Allow the module to collect all almanac and all visible satellite ephemeris and EPO data.
6. Wait until the modules finishes EASY generation

Now you can start measuring the current !

When it comes to power consumption we refrain from using a single value without clarifying whether it’s the minimum, average or the peak value. It’s often the case that some vendors will choose to show only a single value which in some cases is the lowest they achieved. To avoid confusion later on, it’s best that you clarify with your vendor what their values mean.

For example: GLP mode cannot give you a constant 5mA power consumption (as some have reported), since it’s not a continuous mode. Also, 5mA perhaps is lowest possible value. On average you should be looking at power consumption of between 10 to 14 mA. This value also depends on the design of the module. For instance, GNSS modules without additional LNA can get slightly lower power consumption overall (e.g 1 to 2 mA), but not having an LNA may affect the RF performance, mainly if you plan to use the module with passive antennas. There are other considerations as well, such as the power supply management design of the module. So, please do take in to consideration the power consumption of the LNA that you’ll be adding to you board, especially if you plan to use passive antennas with such modules.

The above power consumption data currently only represents GPS modules. We are still in process of verifying the effects of GLP mode on GPS/Glonass modules. We are expecting to see an average reduction of 5mA at least.

We will keep you posted once we have the test results.

If you have any questions, please feel free to contact us anytime.