When does the nrf9160 modem decide to perform an LTE network search?

[EDLT]

Hello,

I'd like some clarification on the nrf9160 modem behavior. What is the criteria for the modem to perform a network search?

I've used the default search pattern for ultra-low power profile and subscribe to modem events. When I put the device into a shielded enclosure and it disconnects, I don't see any subsequent search events. However, when I remove the device from the enclosure, I am connected again to the network quickly.

What is the modem doing when it is disconnected? I would expect to get a number of search events within the first few minutes of not being connected. 

Apologies in advance if I'm missing something clearly stated in the 3GPP spec that the describes what is actually going on there.

Thanks!

P.S. Using MF 1.3.1 with NRF Connect 1.9.1

[gjoasen]

Hi

When setting the search pattern using PERIODICSEARCHCONF it is possible to set the band_optimization parameter to specify how often a full search should be carried out. However, I want to have the first searches of my search pattern to be light searches, but as the period between searches becomes longer I want every search to be a full search. I don't see how I can do that with the PERIODICSEARCHCONF command. 

However, if one could get the LIGHT_SEARCH_DONE event when a the light search has completed, I could set every search to be a full search, and then stop the first searches once the light search has completed, but let the full search complete once the interval between searches is longer. 

Looking at the lte_lc.h header file, it is commented under the lte_lc_modem_evt enum:
"Indicates that a light search has been performed. This event gives the application the chance to stop using more power when searching networks in possibly weaker radio conditions."

This does not give any indication that only the first light search will generate a light search event, and should probably be updated? 

[Michal]

Hello,

Would a following procedure be suitable?

1. Activate modem and let modem start searching.

2. When modem notifies that light searches has been completed, deactivate modem with +CFUN=4.

3. Wait a short period, e.g. 10s or what ever was the idea to be in idle between the first searches.

4. Repeat steps 1-3 as many times wanted.

5. Configure %PERIODICSEARCHCONF for longer idle periods (shorter periods were already passed above).

6. Activate modem and wait until modem finds a cell by searching according to the configuration in step 5.

This approach possibly (depending on use case) requires also configuring the %PERIODICSEARCHCONF again after suitable cell has been found and modem has successfully registered to network. This is because if later the cell is lost, the periodic searches are started again. If the configuration still is such that the idle periods are very long, it could take very long time before a suitable cell is found again. Therefore, it should be considered whether a regular periodic search configuration (that contains also the shorter periods) should be taken again into use after successful registration.

Best regards,

Michal

[EDLT]

I've recently noticed that when manually setting the periodic search, the band optimization is ignored. The pattern of light and deep searches does not represent the band optimization value I've chose. Whether the value is 1 or 20, there's no discernible difference in behavior. See attached picture. Here I've set the search pattern band optimization to 5, so I expect every 5th search to be all the bands I've locked in (2,4,5,12).

Is this the correct behavior? Have I missed something?

I do have the data profile set to ultra low power...this value also seem inconsequential.

[Michal]

Hello,

I have some insight from our experts.

<band_optimization> parameter in the %PERIODICSEARCHCONF configuration refers to “all band search” in the AT command document. It is not possible to affect on whether modem does light search or full search. The “all band search” means that every supported band will be fully searched. The other searches in between these “all band searches” are something less, i.e. it does not specifically mean the light search. If there were more bands locked or no band lock at all, the difference could be seen.

Best regards,

Michal

[Achim Kraus]

In the case of 1 => "depending on %XDATAPRFL", is there any documentation, what the values 0-4 there means? Except, that the power consumption is considered to be higher and lower?