How to select/buy an eDRX low-power capable SIM Card for the nrf9160?

[Wisen]

Hello,

I'm doing some initial investigation with the nrf9160 DK and after some reading and testing, it's clear that significant part of the low-power capabilities is determined by the SIM Card itself and not nrf9160 alone.

For example, the iBasis SIM card shipped together with the DK doesn't seem to like PSM mode when in roaming (Australia, Telstra Network in my case).

But the real issue seems to be the missing capability of a SIM Card to be turned OFF during the eDRX "quiet" periods. For example, in my case, the floor power consumption for PSM mode is around 6uA while the floor consumption in eDRX is above 50uA.

By measuring the SIM_1V8 line (TP20 in my DK 0.8.3 board) voltage it's easy to note that the eDRX mode is not powering the SIM Card off, even when setting it to very long intervals (1100b or 1310.72 seconds).

Moving forward I would like to know how I can identify if a SIM Card supports being powered OFF during eDRX apart from running a connection test? Is there any command I can use to read the SIM Card capabilities?

I can see some comments on this topic: https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/hardware-design/posts/measuring-psm-idle-current-on-the-nrf91-dk, where Timo Vayrynen mention this is specified at 3gpp 31.102 Chapter 4.2.18, but I'm not sure how to request such feature for my SIM Card provider/Mobile Telecom?

In a realistic scenario, how likely is to find SIM Cards that support being powered OFF in an eDRX cycle under 81.92 seconds?

Any help/guidance is appreciated.

Regards,
Mike M.

[Heidi-Irene Harvey Sollie]

Hi!

          The iBasis SIM card shipped together with the DK doesn't seem to like PSM mode when in roaming (Australia, Telstra Network in my case)

Yes, it looks like iBasis blocks PSM and eDRX for roaming users.

          The eDRX mode is not powering the SIM Card off, even when setting it to very long intervals (1100b or 1310.72 seconds)

UICC deactivation during the eDRX idle mode cycle is an optional part of the spec, so it's not a given that SIM Cards that support eDRX support UICC deactivation as well. 

From what I've heard, SIM cards with this feature enabled are not commercially available. This is probably because a card with 100-200k write times costs much less than one with 2 million writes. This will naturally contradict the idea of "low-cost IoT devices" if one needs to use an expensive SIM card.

You will have to request this kind of SIM card from the network operator.

          Moving forward I would like to know how I can identify if a SIM Card supports being powered OFF during eDRX apart from running a connection test? Is there any command I can use to read the SIM Card capabilities?

Yes, the file EFad in the SIM card controls UICC deactivation during eDRX. The content of that file is possible to read using AT+CRSM. 

This command reads the EFed:

AT+CRSM=176,28589,0,0,0

Here is one example of a response: 

+CRSM: 144,0,"00000102"

where the response is "00000102".

Byte 1 should be

‑    '01' normal operation + specific facilities.

‑    '81' type approval operations + specific facilities.

 

Bit 4 in byte 3 (i.e 00000010) indicates the UICC deactivation in eDRX

b4 is used to indicate whether the UICC polling interval to retrieve proactive commands can be modified (as described in TS 31.101 [11]) or whether the UICC interface can be deactivated (as described in clause 5.1.11) during eDRX cycle.

b4 = 0: the ME is not authorized to modify the polling interval and/or disable the UICC interface during eDRX cycle.

b4 = 1: the ME is authorized to modify the polling interval and/or disable the UICC interface during eDRX cycle.

 

          In a realistic scenario, how likely is it to find SIM Cards that support being powered OFF in an eDRX cycle under 81.92 seconds?

It doesn't look like enabling UICC deactivation with an interval of 81.92 seconds contradicts the eDRX spec, but again, you will need an operator who is willing to enable this feature for you. 

Please let me know if there's anything more I can do for you.

Best regards,

Heidi

[Wisen]

Thank you!

About the Bit 4, I understand it allows to change (or not) the pooling interval as we as disable the UICC. Now, where can I read the "pooling interval"?

Meanwhile, I'll get a few different SIM cards and read the file contents to try to understand the differences.

[Heidi-Irene Harvey Sollie]

Hi!

There is no interface to read the UICC polling interval at the moment.

The default used for UICC polling is 30 seconds, which can be changed by the UICC itself. The modem uses the eDRX cycle for UICC polling if that is allowed by the UICC.

Best regards,

Heidi