Reception problem with gsm-tvoid and gsmdecode

GNU Radio
1

Hi all,

I would like to ask you a basic question.
I receive the BCCH and CCCH (PCH and AGCH) GSM channels with gsm-tvoid
and
gsmdecode. I use USRP. For instance, to do that, I type something like:

./gsm_scan.py -p d -r e -c 104 | …/…/…/gsmdecode/src/gsmdecode -i >
myfile.txt

The problem is that a lot of messages are missed. While I am receiving I
can
see warning messages like the followings:

sch.c:254 ERR: conv_decode 7
gsmstack.c:162 cannot decode fnr=0x002921c8 ts=0
gsmstack.c:162 cannot decode fnr=0x002921ce ts=0
gsmstack.c:162 cannot decode fnr=0x002921e2 ts=0
gsmstack.c:162 cannot decode fnr=0x002921ed ts=0
gsmstack.c:162 cannot decode fnr=0x002921f1 ts=0
…
…
sch.c:254 ERR: conv_decode 7
gsmstack.c:162 cannot decode fnr=0x00292229 ts=0
sch.c:254 ERR: conv_decode 1
…

The BTS (Base Station) from I am receiving is really near my USRP.
What Could I do to solve this? Any Suggestion?

Thanks in advance for your time.
Cheers

Jose

2

On Wed, May 13, 2009 at 12:31:23PM +0200, José Carlos R. wrote:

see warning messages like the followings:
gsmstack.c:162 cannot decode fnr=0x00292229 ts=0
sch.c:254 ERR: conv_decode 1
…

The BTS (Base Station) from I am receiving is really near my USRP.
What Could I do to solve this? Any Suggestion?

Thanks in advance for your time.
Cheers

Jose

Jose,

The airprobe list is most likely a better place to ask this question.
AFAIK the people who wrote gsm_scan.py are not on this list, or if
they are they have been very quiet.

Eric

3

Thank you for your reply Eric.
I asked this question in gnu radio mailing list because may be the
problem
is the hardware.

I could see there was a problem with the synchronization. Sometimes,
some
gsm messages are missed due to a synchronization lost. Besides, i think
it
can be enhanced by software. Do you think the hardware (USRP) is not the
problem?

Thanks. Cheers,

Jose

2009/5/13 Eric B. [email protected]