Best possible LTE configuration for GPS fix

[Ramani]

I have a thingy91 device and want to implement the following requirements.

Expectation:

NRF9160 should remain in deep sleep mode and on the button click event do the following activities and again go to deep sleep mode:

1) Register LTE-M/NB-OIT and connect to MN(Mobile Network)(IBasis simcard),

2) Acquire GPS(I am using AGPS)

3) Send this GPS fix to Azure Cloud.

NOTE: The duration of this button can be 1day to 4/5days. 

I am referring AGNSS example and configuration and applying it.

Can you please help me identify the best possible configurations to quickly use the GNSS to get a fix and put the LTE in Ideal mode: 

1) CONFIG_LTE_EDRX_REQ=y,  does this required for my requirement?

# PSM requested periodic TAU 8 hours

CONFIG_LTE_PSM_REQ_RPTAU="00101000"

# PSM requested active time 6 seconds

#CONFIG_LTE_PSM_REQ_RAT="00000011", is it possible to reduce to a minimum level of 2 seconds?

Please also explain which method is best for my scenario out of eDRX/PSM or both

Let me know if you need more details.

[runsiv]

Hi 

I would use PSM and set keep alive for 6 days as it is the maximum amount of time the device is allowed to sleep. I would not use eDRX. 

Keep in mind PSM will only work if your network support it, so I would enable it and if it is supported. 

Just in case you are not aware we also have a course on devacademy for Cellular IoT

Regards

Runar

[Ramani]

runsiv , Thanks for yor reply.

Just want to inform that when I have button even then device will do the following activities:

1)Connect to MN,

2)Get GPS fix(AGNSS)

3)Send data to cloud

4)Trun off GNSS, LTE(Complete modem)

5)Go to deep sleep mode to save the battery,

So, my modem is completely remain turned off between gap of(could be 1day, 2days, 3days, 4days or 5days).

In this case any use of keep alive?

Keep alive means are you taking aboue this config:CONFIG_LTE_PSM_REQ_RAT or something else, can you let me know.

Thanks

Ramani

[Ramani]

runsiv , In the above comments, I mean to say "CONFIG_LTE_PSM_REQ_RPTAU" config, not the mentioned one.

[runsiv]

Hi 

There is a few things here make me a bit uncertain of what the best solution would be. 

For there to be any gain to turn the modem completely of instead of using PSM it should be of more than around 60 hours. If else you will spent more power doing all the connection with the central. However if you use Azure there is an known issue CIA-351 

"If a device-bound message is sent to the device while it is in the LTE Power Saving Mode (PSM), the TCP connection will most likely be terminated by the server. Known symptoms of this are frequent reconnections to cloud, messages sent to Azure IoT Hub never arriving, and FOTA images being downloaded twice.

Affected platforms: nRF9160

Workaround: Avoid using LTE Power Saving Mode (PSM) and extended DRX intervals longer than approximately 30 seconds. This will reduce the risk of the issue occurring, at the cost of increased power consumption." 

As I presume you don't want to wake up every 30 second it makes little sense to use PSM which again means you will use more power to do the handshaking with the central. 

A way around this would be to for example use nRF Cloud or AWS. You could for example have a look at this lesson from our Cellular course  where we use nRF Cloud and send the data over to Azure to get around the Azure termination issue

Regards

Runar

[Ramani]

runsiv , your answer looks more suitable when I don't turn off the device, but my requirement is straightforward, 
-> Come out from deep sleep mode(power off),

->Connect to LTE,

->Get GNSS fix

-> Turn off LTE/GNSS/All other enabled modules and Go to deep sleep mode

So, what LTE setting here will help me get the GNSS fix very quickly after LTE is connected to the Network?

[runsiv]

That is correct, it all depends on how often you wake up. I will check regarding doing nothing else then just turning of everything,  however since you will need to reestablish the connection I'm not sure how much can be done to improve it. 

Regards

Runar