Packet Decoder block malfunction after demodulation!

Dear list,
I’m using a typical UHD USRP source (USRP2) --> Low-Pass filter --> GMSK
Demod --> Packet Decoder --> File Sink receiver flow-graph in GnuRadio
to
receive the signal I’m transmitting with a mirrored transmitting flow.
The problem is that the Packet Decoder (Output type - “byte”; Access
Code -
field left blank; Threshold -" -1") doesn’t really do anything, the
signal
streams blocks there, and the file that the File Sink should create with
the
data from Packet Decoder is always empty.
The rest of the flow-graph seems to be working properly, I can visualize
the
received signal, that seems to be the same as the transmitted one.
If I take out the Packet Decoder, the file that results form the File
Sink
has a size larger than 0 bytes, which leads me to believe that the
problem
is with this block.
Any ideas or similar problems?
Thanks,

Vlad.


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On Wed, Jun 15, 2011 at 9:53 AM, Vlad Stoianovici <
[email protected]> wrote:

The rest of the flow-graph seems to be working properly, I can visualize
the
received signal, that seems to be the same as the transmitted one.

Are you sure its not doing what its supposed to do? Look at the work()
function
in your packet decoder. If the input doesn’t fit the requirement of the
algorithm to
produce the output then it won’t produce anything at its output. Think
of it
this way.
Suppose the packet decoder block produces output items only when the
input
is greater
than the threshold = T. If the input is constantly under T then there is
nothing produced.

If I take out the Packet Decoder, the file that results form the File
Sink

John,
I did the simulation of the receive - transmit flow, bypassing the Usrp
sink
and source and putting in their place a Channel Model block and it
works,
meaning that you were right.
This probably means that there is a problem with my USRP sink and source
parameters, probably the sample rate, which I am currently
investigating.

Vlad.

John A.-5 wrote:

Are you sure its not doing what its supposed to do? Look at the work()


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