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SACCH FOR VAMOS

Viewing 11 posts - 1 through 11 (of 11 total)
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  • #68891 Reply
    Raj
    Guest

    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)

    #68892 Reply
    pix
    Guest

    hi,

    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…

    #68893 Reply
    Raj
    Guest

    Hi,

    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, 7d

    #68894 Reply
    fede
    Guest

    Hi Raj,

    you can refer to the table at paragraph 6.3.1.1 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).

    #68895 Reply
    pix
    Guest

    fede,

    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,

    pix

    #68896 Reply
    fede
    Guest

    hi pix,

    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 ?

    #68897 Reply
    fede
    Guest

    Errata corrige:

    > I guess that these new codes will be used together with VAMOS-I and TscSet2.

    I wanted to say VAMOS-II

    #68898 Reply
    pix
    Guest

    fede,

    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 ๐Ÿ™‚

    #68899 Reply
    fede
    Guest

    pix,
    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.

    #68900 Reply
    pix
    Guest

    fede,

    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 ๐Ÿ™‚

    cheers

    #68901 Reply
    fede
    Guest

    yes, stuff interesting anyway
    cheers ๐Ÿ™‚

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