Hi,
I am trying to understand the Multiframe structure in GSM. Here is my question:
Lets say that in a particular cell, only two GSM frequencies are available to cater to all the traffic.
FB is the frequency of the beacon channel and FT is the frequency of the traffic channel.
FBT0 is having the following configuration FCCH + SCH + BCCH + CCCH.
Now a phone which is in this cell, gets paged for an incoming SMS.
The phone responds to the paging request and gets an immediate assignment. The immediate assignment assigns it a channel
with the following configuration:
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 same question applies to the BTS if we are talking about down-link ?
Is there a relation between the multiframe structure of FBT0 and FTT2 ?
Thanks and Regards, R M
Hi,
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.
Cheers,
Sylvain
baseband-devel@lists.osmocom.org
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R M -
Sylvain Munaut