[Tetra] TETRA Demodulation

Harald Welte laforge at gnumonks.org
Tue Jan 4 19:58:45 UTC 2011


(we have a mailinglist and we should use it... and write in english for
sylvain's benefit)

On Tue, Jan 04, 2011 at 08:16:12PM +0000, Dieter Spaar wrote:
> Kleine Korrektur:
> 
> Das Muster im vorherigen Bild ist natuerlich drei Bursts mit
> "Frequency Correction Field" und dann einer ohne, das koennte
> eventuell etwas mit dem Frame bestehend aus vier Slots zu
> tun haben.

The tdma multiplex of TETRA is unfortunately much more complicated than in GSM.
I only really understood it earlier today while reading a textbook, from the
specs it is very difficult to understand.

The Frequency Correction Field is only present in the sync bursts (SB), which
in turn are only (required to be) sent in Frame number 18 , but not on every
multiframe.  Interestingly, the SB is also present in _every_ timeslot, but not
in every Frame 18 of every TS.

The formula for the Timeslot Number is "4-(MN+1)mod4", it is indicated in Table
9.25 in Chapter 9.5.1



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