Parameter meanings in 2022-05-04 LPWAN Coverage doc, PSM and eDRX columns?

[tedhavelka]

Hello Devzone,

My name is Ted, and I recently came across a 2022 May 4 LPWAN Coverage document on one of Nordic Semi's technical guides.  The specific guide is titled iBases ESIM International Coverage Update.  But I am confused by the meaning of the value pairs in the right most four columns.  Looks like these are in units of seconds, which makes sense for at least the two columns number 9 and 10 from left, where "PSM T3412 and T3324" appears above these columns.

What do these values represent?  Are these maximum supported timer periods, and shorter periods are possible?  In what way do these values define which periodic Tracking Area Update (periodic-TAU), Active Time and eDRX values we can expect to be granted in our given geographies?

Some background to these questions:

I've posted some related tickets to this question recently:  87176, 87451, 87734, but I am still having trouble obtaining any non-zero T3412 and T3324 timer values.  I'm working in a large metropolitan area with population of roughly two million, between Seattle and the Bay Area on United States west coast.  At least one of the major Mobile Network Operators listed in the United States rows of the LPWAN coverage document operates in our city.  Given this I surmise that at least for LTE-M type network registration I should be able to see my nRF9160 based device be granted some valid periodic-TAU and Active Time values.

Per ticket 87451 I am performing the AT command sequence to first turn off modem, then request a PSM, then turn modem on:

AT+CFUN=0

AT+CPSMS=1,,,"00010010","00001111"   . . . periodic-TAU of 180 minutes, active time ( 2 sec * 15 ) = 30 seconds

AT+CFUN=1

Entering these commands by hand there is plenty of delay, so I am confident the modem is off by the time I enter my PSM values to request from the MNO.  I check modem status and granted values as per the above linked Devzone tickets, namely by issuuing AT+CFUN?, AT+CEREG=5 followed by AT+CEREG?, AT%XMONITOR.  Command AT+CGDCONT? tells me whether my device registered with any network or not.  I almost never see either full name or short name of the MNO, two parameters which AT%XMONITOR returns.

I have tried multiple different values for periodic-TAU and Active Time.  I'm searching for ones which local MNO will grant.

Command AT+CEREG? consistently returns "11100000", "11100000" as its last two fields.  This looks like bad news to me.  Until I can learn correct AT command sequence, and confirm or disconfirm local network provider support I cannot enjoy the battery-enabling low power support touted as one of the nRF9160's greatest design features.  All clarifying help to these questions appreciated!

- Ted

[Albrecht Markus Schellenberger]

Hello Ted,

tedhavelka said:

Given this, would you please confer with others on your team to see whether anyone knows with certainty what these values mean?

Referring to #288379. You have already been in touch with our expert in this area. I’m afraid I will not be able to contribute with that much more around this topic.

tedhavelka said:

I asked what the number pairs mean in the last four columns of this document.  You replied that these might be the minimum values.  I am testing this now, making sure I program my nRF9160, ncs v1.6.1 based device to ask for nearest equal or greater periodic-TAU and active time values for USA, Los Angeles region, and carrier AT&T, per the values in second to final row, column nine.

As I also mentioned in my last replies: I’m not quite sure what the above mentioned values are. It could be the values iBasis has tested with as well. That being said, it doesn’t matter in my opinion. It is the carrier that decides the PSM values. And they can change frequently, so I do not really see a point to focus to much on them.

Tracking Area Update and Active Time are up to the carrier / mobile virtual network operator and not Nordic Semiconductors responsibility. If you would like to receive details, I recommend you to get in touch with them.

tedhavelka said:

That is, I must also issue AT%XMONITOR to see whether the older period-TAU was granted, correct?

Yes.

Regards,

Markus

[tedhavelka]

Hello Albrecht,

Thank you for your help.  I hope you will forgive my persistent, sometimes repeat questions.  Nordic Semi Team has been consistently responsive and knowledgeable.  My questions are an effort to do my homework before posting new tickets on Devzone, and likewise before asking for help from other technical support teams such as iBasis.  Given that iBasis coverage document is prominently featured in Nordic's celular and PSM coverage guide, I figured it was important to be sure the meaning of those unclear columns of data.

On my end I understand my team will likely meet remotely with iBasis later this week.  It has taken a little longer to connect with them on our specific questions.  I'll bring the same document and columns to their attention when we meet.

"It is the carrier that decides the PSM values. And they can change frequently, so I do not really see a point to focus to much on them."

So I can neglect PSM values, but the on-line power profiler pushes me in the opposite direction:  the only way I can achieve an estimated battery-supporting low power use is to have PSM enabled.  This is why I have been so focused on learning how to most reliably request PSM, how to tell whether we've been granted PSM, and respond in hardware and firmware accordingly.

To be clear, my team and I have understood for a while that not all network operators support PSM.  This power savings feature may be more well supported in Europe today than in the United States.  We also understand that not all possible PSM settings will be supported even where PSM and Active Time are supported.  We understand, or surmise that there is logic in the 9160 modem firmware to accept alternate PSM values when those are available, but not the originally requested ones.

Let's suppose my network operator doesn't offer PSM.  My device will need to search for and register with a network operator each time it wakes.  Let's say also I have a battery which could sustain device operation for three years so long as average daily current draw is in the range of 7uA or less.  If I must operate without PSM, could I still achieve a daily average current draw less than 10 uA?

Nordic's Online Power Profiler estimates that without PSM the nRF9160 will draw about 655uA.  I know from physical testing however that I can put our custom board into deep sleep, draw less than 10uA, and wake from that.  When the nRF9160 modem wakes I see it draw varying currents, upwards of 25mA with some peaks.  This however lasts only about 20 to 30 seconds in most cases.

Carrying out some simple scratch math on paper, I find that I could reach a daily average current in the few tens of uA, if I am willing to put device into deep sleep and wake only one time a day.  Here I assume also that the modem would need to average 25uA for only about half a minute at longest.  If the modem draws an average of 25 milliamps while network searching, then each minute of search raises my daily average current by about 17uA.

The Online power profiler and estimator does not seem to have a feature for lower power estimates in the absence of PSM.  This would be useful.  While no PSM is not ideal, some products might still be useful even if they needed to achieve a low power while registering with networks on each wake event.

Best I open another Devzone ticket to ask about this fallback strategy, when PSM is not available?

- Ted

[Albrecht Markus Schellenberger]

Hello Ted,

tedhavelka said:

If I must operate without PSM, could I still achieve a daily average current draw less than 10 uA?

I unfortunately will not be able to give you a universal answer here, as this depends on a lot of factors, starting with the environment the nRF9160 is surrounded with and how well functionality of the application is adapted to the respective use case.

PSM and thus, optimising power consumption is a challenging topic. It can not be fully investigated on paper in advance, so testing and verification along the way is required. As already mentioned, a good starting point could be to talk to the carrier to receive concrete details about if and how PSM is allowed for connecting devices in different tracking areas.

Since iBasis is a MVNO, meaning UE’s with their SIM card will connect to a carrier based on a roaming contract, talking to the carriers itself should be considered as well. Possibly, they can offer you a subscription that suits better to your specific use case.

tedhavelka said:

Best I open another Devzone ticket to ask about this fallback strategy, when PSM is not available?

Yes, you are welcome to do so.

Regards,

Markus

[lucusdam]

thanks for share

1v1 lol