GR-GSM TRX

Vadim Yanitskiy axilirator at gmail.com
Thu Jun 22 13:11:37 UTC 2017


Hi Piotr,

I just wrote a simple (more or less working) GNURadio block for
connection with OsmocomBB. It is named "TRX Interface" and currently
only capable to transform (in Osmocom bursts are followed by a bit
different header) and send received bursts through the UDP link.

If you remember, I had a problem with UDP source port. So, I spent
some time and finally solved this challenge. My first idea was to
inherit the existing 'Socket PDU' implementation and I started to
look for a way I could do that. After a few minutes of searching,
I have found your mails with the same question, and a brief answer
from Sylvain, that it is impossible :(

So, I have copied actual implementation, stripped out everything
related to TCP and implemented a feature to set UDP source port.
Now I am able to receive all DL bursts, coming from GR-GSM to my
trxcon application.

At the moment I am working on TDMA scheduler, which is almost
finished. It's time to start writing GR-GSM blocks for burst
transmission. The following thoughts / questions are in my mind:

  - TX should be simpler than RX, because we don't need to detect
    bursts and correct any errors.

  - Both receiver and transmitter should be time synchronized.
    I think, the SCH clock from the 'GSM Receiver' block may be
    easily shared. Moreover, actual clock indications could be
    forwarded to my block.

  - If I am correct, to transmit a burst, one should be converted
    to symbols. How can we do that?

  - We cannot simply use the existing 'GMSK Mod' block, because
    GSM uses TDMA. Right? If so, point me to the right direction.

P.S. This message is posted at the baseband-devel mailing list.

With best regards,
Vadim Yanitskiy.
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