What is best way to use AT%MDMEV command after long PSM time and possible re-locationing

[Arttu]

Hello.

What is correct way to use AT%MDMEV commands(searh status) to establish connection after long PSM/sleep time (168h). Our devices are used to track wild animals so devices can move long distances during PSM and locate outside of old basestation coverage area. We are using modemFW 1.3.5.  Currently  our  connection task by default uses search status 1 and if we are unable to establish connection we use search status 2. We have detected some connection problems on live devices which travel long distances during PSM and try to re-establish connection for weekly check up. So for our use case should we use search status 2 everytime as default?

[Michal]

Hello,

I have asked the experts for their input.

Best regards,

Michal

[Michal]

Hello again,

This is the answer they came up with:

So the background of the %MDMEV: SEARCH STATUS is that in power up and PSM wake-up scenarios modem indicates when the light search part has been completed and when the search has been fully completed. During the light search modem scans channels stored in cell history and channels on which a cell most likely could be deployed. In some use cases it might be reasonable to stop the scan after the light search has been completed. The stop can be done by deactivating modem, in which case naturally the registration, IP addresses etc. are lost due to which a new registration needs to be done before it is possible to send user data again. If the stop is not triggered, modem automatically continues the scan until it is fully completed.

So for our use case should we use search status 2 everytime as default?

I’m afraid there is no straight answer to this, but here are couple of aspects to consider:

• Do we need to send the data right now? If not, how long can we wait? Stopping the search means a new registration, i.e. extra signalling which will consume energy. If the user data transfer can wait long enough, the extra signalling may not be a problem but actually a better choice. Note, there is no extra signalling in case the application anyway always deactivates modem after sending user data.

• Would it be reasonable to do a light search several times before the next full scan? For example, application could activate modem once a day and stop the scan after the light search has been completed, and only once per week let the modem do a full scan.

• How many full scans can the battery manage?

• Is the device typically on area where there is a good coverage? If it is, then it is more likely that the light search is enough. In other words, if cell is not found during the light search, it is likely just a temporary issue and it might be good to try another light search before allowing a full scan.

• Would the modem wake-up from PSM anyway due to periodic TAU (see %XT3412)? Even without user data to be sent, modem will do periodic scans after it wakes up from PSM. If the use case is not time critical, then it is likely better to deactivate modem at this point. Also, the longer it takes to perform the periodic TAU, the more likely it is that a new registration is needed anyway.

Best regards,

Michal

[Arttu]

Thank you for detailed response.
Our TAU(%XT3412) is set to 170h so that wont wake the modem in our case atleast.

Michal said:

For example, application could activate modem once a day and stop the scan after the light search has been completed, and only once per week let the modem do a full scan.

This is worth testing if we can fix some network communication problems with this.