eDRX enabled but no observable reduction in power consumption

[Bhumi]

Hello Nordic team,

We are using an nRF5340 as the host processor, and an nRF9160 module is mounted on top of it.
All LTE modem AT commands are sent from nRF5340 to nRF9160.

We have enabled eDRX mode on the nRF9160, and the device is entering reduced power mode successfully.

eDRX Configuration:

The following AT command is sent to enable eDRX:

AT+CEDRXS=1,4,"0001"

The network negotiates and responds with:

+CEDRXS: 4,"0001","001","0001"

OK

From this response, we understand that:

• LTE‑M eDRX is accepted by the network
• The requested eDRX value is successfully negotiated

Observed Behavior

• After enabling eDRX, we can see a clear difference in the current waveform pattern
• The RF spike frequency is reduced, and the device is clearly entering reduced power mode
• So functionally, eDRX appears to be working

However:

• The average current consumption remains almost the same
• Measured current is approximately ~110 µA
  • Before enabling eDRX
  • After enabling eDRX
• No noticeable reduction in average power consumption is observed

Measurement Setup

• Power is measured at the supply side
• Energy harvesting circuit is enabled
• Battery is also connected

Questions

1. Is it expected that eDRX mainly changes the current pattern (paging cycle) but does not significantly reduce the average current, especially when PSM is not enabled?  

Power consumption Measurement:

 

[Simon D-M]

Hi,

Bhumi said:

• What is the typical default iDRX paging interval used by the nRF9160 when the modem is in Idle and eDRX is not enabled?
• Is this iDRX interval fully network‑controlled, or does the modem have a typical/default range it operates in (for example, a few seconds)?

The iDRX is fully network-controlled, so I can't give you a precise value. But I had to give you a range, it should range from ~100ms to ~10sec by default.

Bhumi said:

Is there any recommended way (AT command, trace, or observable behavior) to infer or verify the effective iDRX cycle duration on a running device?

You should be able to see it in the modem traces. You should also be able to see the paging on the power measurement. It should do a spike when the paging is happening.

Bhumi said:

Are there any specific prj.conf options that should be enabled or disabled when evaluating power consumption reduction using eDRX?

When measuring the current, you should not have the modem traces enabled. They are drawing power, so while having them activated you won't get a relevant value for power consumption.

To learn more about power management with cellular, you can check these blogs. They are a bit old, but they are mostly still relevant.

LTE-M vs NB-IoT Field Test: How Distance Affects Power Consumption

Maximizing battery lifetime in cellular IoT: An analysis of eDRX, PSM, and AS-RAI

Best regards,

Simon D-M