SARA-R42 - Application note
UBX-20050829 - R02 Network registration Page 21 of 58
C1-Public
The described behavior has to be considered especially in roaming conditions.
7.1.1.1 OOS scan timings
The scan algorithm is implemented when attempting to gain service at power-up and when the
out-of-service (OOS) condition is detected. A full system scan is interspersed with sleep intervals to
reduce power consumption. The algorithm starts with a sleep time of 30 s which is applied 10 times,
then the sleep time is incremented to 45 s, which again is applied for other 10 times, finally the sleep
time is set to 60 s.
Each full system scan starts with the search of recently used cells, if available, which are coming from
an internal database updated every time the device can find full service on a cell. Then the full system
scan continues triggering a band scan for all enabled bands. At each step, the full scan considers all
the enabled RATs ordered according to the configured relative priority. RAT and band settings can be
configured with the +URAT and +UBANDMASK AT commands if not locked.
This algorithm is maintained until a suitable cell providing full or limited service is found and the device
can camp on it.
To keep power consumption even lower, the recommendation is to implement an algorithm on the
application processor to switch the device off if not able to gain service for a long period of time and
then switch it back on after a while to try to get full service again. The duty cycle can be selected by
the host application based on the tradeoff between power consumption and maximum tolerable delay
before regaining cellular coverage.
7.2 First time registration setup
It is important to set the operator profile first because this operation will configure the default RAT
and band mask for that corresponding profile. If the +UMNOPROF set command is issued after the
+URAT or +UBANDMASK AT commands, then it will override any past configuration the host application
has made. The module is programmed with auto-cops, so no AT command is required to trigger the
network registration.
☞ AT+CFUN=0/1 can be used to trigger a registration cycle with switch-off detach (which does not
need the DETACH_ACCEPT message from the network). A detach of type normal can be obtained
with the AT+CGATT=0 command.
☞ The AT+COPS=2/0 cycle shall be used when looking for a more suitable PLMN, as per SIM settings
related to the preferred operator list available through the +CPOL AT command.
☞ The AT+COPS=2/0 cycle triggers a high priority PLMN scan, so this cycle shall be avoided in
roaming conditions.
7.2.1 PAP/CHAP
If PAP or CHAP authentication is to be configured, the +UAUTHREQ AT command shall be entered.
If the authentication is required on the initial default bearer, the setting shall be entered in
de-registered state.
7.2.2 Change of PDN settings (APN name and PDP type)
To change the PDN settings for the initial default EPS bearer established during LTE attach, edit the
<cid>=1 PDN by means of the +CGDCONT AT command, as shown in Table 9.
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