Hi all,
in TETRA, the only part of the signal that is transmitted with a well-known scrambling code is the BSCH in the SB1 (first half of the downlink SYNC block). We can finally decode that since yesterday and get proper MCC/MNC and TDMA time information.
The colour code + MNC + MCC is used as the scrambling sequence for all other messages of the cell, specifically also the BNCH containing the SYSINFO messages.
I've recently added code to indicate when a BNCH block is to follow, but the de-scrambled type-2 bits do not look plausible at all.
So there's most likely still some problem with the de-scrambling. The de-interleaving, de-puncturing and viterbi decoder are the same code (even with different parameters), so I don't think that there are likely problems caused by them.
Regards, Harald
I've recently added code to indicate when a BNCH block is to follow, but the de-scrambled type-2 bits do not look plausible at all.
I've fixed the scrambling sequence computation now. And as zecke has found out how they really use the CRC, we now get correct CRC on most of our frames. Those that don't are probably speech frames that of course don't have a CRC...
So we now get the BNCH / SYSINFO PDU as well as some MAC-RESOURCE PDUs from SB2 and NDB bursts.
On 01/07/2011 01:06 PM, Harald Welte wrote:
I've fixed the scrambling sequence computation now. And as zecke has found out how they really use the CRC, we now get correct CRC on most of our frames. Those that don't are probably speech frames that of course don't have a CRC...
Yeah, pretty embarassing how hard it is to fill the gap from the math class I had to really using it... :}
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Harald Welte -
Holger Hans Peter Freyther