(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
Hi all,
based on the output that Dieters' demodulator from the OP25 project, I have now written some (simplistic) code to detect the Synchronization and normal burst training sequences and to split the received bitstream into bursts.
Based on the samples that I took here in Berlin some time ago, we get 724 bursts, all of them seem to have excellent training sequences - despite still using hard bits.
The received bursts are split into their BLK1/BLK2/BBK components. However, as we don't yet have a viterbi decoder for the RCPC convolutional code, we cannot recover the actual Layer2 PDUs yet.
The code is now in git, the README has been extended a bit to reflect the current state.
-
Harald Welte