LTE connection timeout & retry policy

Question

Hello, 
 in our application, we use nb-iot and PSM with wake-up period of 60 minutes. 
 CONFIG_LTE_NETWORK_TIMEOUT is set to default value (600 seconds). 
 In case bad link quality is present, or no network at all, what behavior should we expect? 
 Let's say the modem goes to sleep and link quality goes very bad. 
 Will the modem: 
 
 wake up 
 try to scan for 10 minutes 
 fail to connect 
 go to sleep 
 wakeup the following hour? 
 
 Is that correct? We have to understand what will be our current consumption when link quality is very bad, and how to limit this to a reasonable value. 
 Thanks 
 Marco

Øyvind · Accepted Answer

Sorry for the slow response to this ticket. The solution to this issue could be the use of Periodic cell search configuration %PERIODICSEARCHCONF , this is found in LTE Link Controller library under lte_lc_periodic_search . 
 For your application it may also be good to use Modem domain event notification %MDMEV and Search Status 1 which allows your application " a chance to stop the modem from using more power on searching networks from possibly weaker radio condition ". The modem team also suggests the following: 
 
 Limit the used bands with band lock as much as possible, i.e. inform modem which bands can be skipped. 
 Resolve suitable relation between light searches and full searches for the use case. Let's say for example that application tries to send data once per hour. The relation of light and full search could be that only light search is done by default (modem deactivated after light search done), but if sending of data has failed 4 times in a row, then full search is allowed for the fifth attempt to send data. This way we make sure that all bands are fully scanned at least at some point (every fifth attempt). 
 
 Let me know how this works for you! Kind regards, Øyvind

LTE connection timeout & retry policy

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