GNSS with eDRX and 2G fallback

I would like to use the GNSS functionality on HL7802. I am connected to a MQTT broker via TLS where I can set the ping period to a couple of minutes. I figured that it may be possible to use eDRX and keep GNSS receiver active so that it uses the internal RF resources every time the module is in eDRX sleep.

  1. Will the GNSS automatically resume every time the module enters eDRX sleep?

  2. Does this only work when connected to an LTE cell? I have the module configured to use CAT-M1 and 2G fallback (no NB-IoT) and it does sometime connect to GSM cells but I need the GNSS location also in those cases. I would like to get rid of having to switch the modem to airplane mode before accessing GNSS receiver.

Hi @jakub.polonsky,

For these questions, you can refer to this topic: GNSS stop to work


Hi and thank you for the link.
I think it does not address my questions completely.

  1. There is no mention in that post whether the GNSS resumes automatically when module enters eDRX sleep. I can only assume that it does.
  2. The post says that GNSS can be enabled in PSM sleep mode and Idle-DRX/eDRXmode. Without mentioning the distinction between 2G and LTE mode. I have tried successfully eDRX in LTE mode but when I am connected to a GSM cell, I have found that PSM is not enough to start the GNSS receiver. It always returns +GNSSEV: 1,0 to AT+GNSSSTART=0. For example, I set PSM to AT+CPSMS=1,10000111,00001010.

Can the GNSS really run under PSM in 2G? If so, can you give me an example of the AT command to set said PSM?

HI @jakub.polonsky,

Power Saving Mode (PSM) is a 3GPP feature that allows the HL78xx to minimize power consumption by registering on a PSM-supporting LTE network. It is not available on 2G networks.

You can refer to Section 3.3 3GPP Power Saving Features on page 25 of the HL78xx Product Technical Specification and
Section 5.3 GNSS/LTE Co-Existence on page 2 of AirPrime - HL78xx - GNSS Behavior.
The following links are attached:

Thank you. So if I get it correctly, there is no way to use some sort of a power-saving scheme where the modem would keep network registration and TLS connection open under 2G and at the same time operate its internal GNSS receiver. This is only supported in LTE.