Howto "AT^SXRAT" (Cinterion specific)

[Norbert van Bolhuis]

Hi Giancinto,

Thanks for your response (again)!

I hope we can continue discussing the below.


 > It can, but I consider it a workaround for strange situations.  The
 > normal mode should be enough.
 > You mentioned about that this is for the 5%, which can qualify as
 > "strange situation".
 > When the applications start playing with the RAT and the operator
 > selection, however, they become quickly complicated due to all rules
 > and exceptions to them that they have to introduce.
 >
 >> Not even when the signal really is too weak or when we're near the
 >> 2G<->3G or 3G<->4G RAT-switch-over threshold?
 >
 > The standard has an hysteresis for switching, which should guarantee
 > some stability (the acceptable values are not fixed but instead
 > broadcast by each cell, so that it is possible to design smaller and
 > more dense cells and bigger cells).
 > If you are at the border of 2 or 3 cells, all equally weak, then it is
 > possible that you switch often.  This should be visible in the
 > AT^SMONI response.
 >


We were advised to switch to manual selection
(AT+COPS=2,<format>,<opName>,<AcT>) to make this ~ 5% of systems connect
properly.
We can learn about all what's available in the area with
"AT^SNMON="INS",2" and then use AT+COPS=2 to select the "best" one
and basically stick to this.
ModemManager doesn't support this, so it'll be quite some work.

The reason seems to be the hysteresis doesn't work well in certain
cases. The hysteresis doesn't work between operators (since operators do
not align their thresholds/hysteresis) and the hysteresis
doesn't seem to work well in poor coverage areas.
I do like to stress we see many, many RAT switches but hardly any
operator/cell switches. Also, we cannot (easily) know the (cell)
thresholds that are broadcasted.

This makes it hard to judge whether or not to switch over to manual
selection and to know what it'll gain.

Do you happen to have more info on the precise problem with the
broadcasted thresholds/hysteresis and more importantly, what to do or
info to gather to better judge what manual selection will bring us?

Thanks!

Regards,
Norbert