- This topic has 10 replies, 1 voice, and was last updated 7 years, 10 months ago by fede.
4th March 2013 at 16:51 #68891RajGuest
Need some information regarding SACCH position for VAMOS :
Shifted SACCH is only for DTX cases?
If above is true then what will be SACCH mapping for User1 if both the
calls are full rate (VAMOS)4th March 2013 at 18:08 #68892pixGuest
shifted sacch is applied to any kind of VAMOS, for the user on the 2nd subchannel.
DTX has nothing to do with it.
As far as i remember, the SACCH is shifting by one frame (+1) compared to the user in subch 1. I’m not 100% sure about this anymore…5th March 2013 at 16:21 #68893RajGuest
So for subchannel 0 it will be 12th number frame and for subchannel 1 it will be 13th number frame?
if both calls are full rate.
I have seen few things here but got confused
3GPP 45.001, section 13.4
3GPP 45.002, Figure 7c, 7d6th March 2013 at 10:44 #68894fedeGuest
you can refer to the table at paragraph 188.8.131.52 in the spec 45.002.
For FullRate the sacch is always on position 12th (alias Table 1), except when the mobile is VamosII and tsc assigned belongs to TscSet2.
In this last case the position is the 13th (alias Table 1a).7th March 2013 at 20:09 #68895pixGuest
oh yes, that’s right, the MS that can use the 13th frame must be VAMOS-II.
(i reckon the tsc set 2 will always be used if there is at least one VAMOS II MS in the pair, so that’s not really a constraint)
Thanks for the clarification,
pix8th March 2013 at 14:51 #68896fedeGuest
3GPP added also some new codes of “channel mode”:
1 1 0 0 0 0 0 1 speech full rate or half rate version 1 in VAMOS mode (Note 3)
1 1 0 0 0 0 1 0 speech full rate or half rate version 2 in VAMOS mode (Note 3)
1 1 0 0 0 0 1 1 speech full rate or half rate version 3 in VAMOS mode (Note 3)
1 1 0 0 0 1 0 1 speech full rate or half rate version 5 in VAMOS mode (Note 3)
Note 3: This code point is only used for a mobile station that indicates support for VAMOS-II (see
3GPP TS 24.008).
I guess that these new codes will be used together with VAMOS-I and TscSet2.
But what about a VAMOS-II mobile receives an assignment with TscSet2 and an old channel mode code ?
Probably it should not apply the shift, but it is not clear to me.
Anyone can clarify it ?8th March 2013 at 14:53 #68897fedeGuest
> I guess that these new codes will be used together with VAMOS-I and TscSet2.
I wanted to say VAMOS-II8th March 2013 at 22:04 #68898pixGuest
I’ve been studying this one year ago, so I’m very rusty, but as far as i remember the new channel codes are used exclusively with TSC set 2.
There cannot be TSC2 with any other codes.
If there is, it means the BSC is going bananas 🙂11th March 2013 at 10:30 #68899fedeGuest
if you mean that new codes have to be used exclusively with VAMOS-II+TscSet2, then I agree with you.
The new codes seem to me the only info, that BTS can check to know about the presence of the shift (at least if no other proprietary infos are added in Abis RSL).
But from mobile point of view for the application of the shift seems to enough VAMOS-II+TscSet2 (see 45.002).
In any spec they refer to the new codes for the application of the shift.
So everything works. But they did this stuff very complicated without reason.12th March 2013 at 20:33 #68900pixGuest
VAMOS itself is very complex, and they had to make it work within the current constraints of GSM design, which was done 25yrs ago !!!
I wasn’t surprised by the complexity as much as the fully transparent integreation of VAMOS. It’s a nice piece of work IMO. And it gives us something to talk about. Can’t put a price on that 🙂
cheers13th March 2013 at 08:36 #68901fedeGuest
yes, stuff interesting anyway