LTE-M consuming way to much power to transmit 100 bytes UDP every 15 seconds, please help me understand why.

[EDLT]

I'm using the UDP sample from SDK 1.8.0 with the following modifications:

• No PSM
• No eDRX
• Send 100 bytes every 15 seconds

This is on the nrf9160-DK board.

I suspect I can improve power consumption by disabling RRC idle mode, but I cannot find any documentation on how to do this.

I am unsure of the actual cDRX timing parameters as what seems like DRX events are sporadic.

Here are some power profile images and a modem trace if that's helpful.

The above image shows large period of almost continuous activity after the TX event for ~5 seconds and then iDRX activity until the next TX event.

This is the activity while RRC connected. 

I am seeing an average of 10mA, with 22mA during the connection period. I was expecting the average current consumption to be 2.5 - 4mA.

7723.trace-2022-02-14T21-46-37.030Z.bin

[JONATHAN LL]

Hi,


What version of NCS are you on?

Regards,
Jonathan

[EDLT]

Hi Jonathan,

Version is 1.6.1.

Since posting this I was able to make significant improvement using RAI and socket options to get an early RRC release to idle. I guess I'm surprised most by the 2nd power profile image where the signaling is almost constant and there is no discernable/regular cDRX duration and inactivity period.

[EDLT]

Jonathan,

There are times when the RRC connected period looks much cleaner and one can determine a consistent cDRX active/inactive period. The current consumption is more than halved around 11mA. What would cause this outcome over the other where it looks like the radio is constantly on and current consumption is much higher?

Thanks,

Eric

[JONATHAN LL]

The network is mostly in control of the timing so cDRX is not something that the device has control over. I dont have a good answer i am consulting our internal experts and i will update. 

Regards,
Jonathan

[EDLT]

Jonathan,

While awaiting an answer about what determines the cDRX duty cycle, I'm wondering if there is a way to know when the modem has finished sending all its data.

When using the RAI feature, if we send more than 600 bytes or so, I notice there are two outgoing transmissions. I imagine this is because the modem was not able to send out all data before we indicated there was not more data with the RAI_NO_DATA socket option.

If we can know when all the data has been transmitted, then I can better time the use of the RAI_NO_DATA option to conserve power.