Frame Structure and Multiframe questions

Sylvain Munaut 246tnt at
Sat Apr 26 09:26:10 UTC 2014


> FTT2 and channel multiplexing is SDCCH/8 + SACCH/8.
> Now how does the phone know the multiframe structure of FTT2 ?
> In other words how does the phone know how long it has to wait, so that it
> can transmit in the right time-slot ?

The multiframe structure is entirely defined by the channel time. For
SDCCH/8 channel, it will be a 51 multiframe and GSM 05.02 has the
detail of which frame maps to which subchannel.

The GSM time (i.e. frame number and frame alignement) is the same for
all the ARFCN in a cell. So the phone can just use the current (FN %
51) and see if this is a frame that maps to the subchannel that was
assigned to it.

It's pretty well documented in GSM 05.01 and GSM 05.02.  The GSM05.01
has a quick explanation with a couple of well made graphics and GSM
05.02 has the actual reference tables with all the details.



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