Modulation packet loss

GNU Radio
1

Hi,

When doing any type of modulation, I’m losing the last packet or two.
I’m
wondering if it’s possible to either get rid of packetization all
together
or to output the piece of the last packet received even though it
doesn’t
get filled completely. Inside of packet.py, it seems to be stuck in
here:
msg = self._msgq.delete_head()

and doesn’t get to call

ok, payload = packet_utils.unmake_packet(msg.to_string(),
int(msg.arg1()))

Another issue I’ve been having that’s less important is whenever I’m
using
it with USRP’s from one computer to another, the beginning chunk of data
gets lost. This may have to do with some sort of synchronization but I
would have no clue where to start with that.

Thanks, Patrick

2

On Mon, Mar 11, 2013 at 11:46 AM, Patrick C. [email protected]
wrote:

ok, payload = packet_utils.unmake_packet(msg.to_string(), int(msg.arg1()))

Another issue I’ve been having that’s less important is whenever I’m using
it with USRP’s from one computer to another, the beginning chunk of data
gets lost. This may have to do with some sort of synchronization but I would
have no clue where to start with that.

Thanks, Patrick

The packetization adds a number of features. You get the access code
and header to help acquire your data at the receiver, a CRC check to
see if the packet was received without errors, and other features like
whitening of the data for better transmit and receive properties.

You could do without the packetizing, though, and just continuously
transmit a stream of samples if that’s all you need to do. But its
likely that you’ll need some kind of header to determine starts of
packets or frames or something like that.

Also, be aware that there is no channel coding in a lot of the digital
examples. That means that if any bit is incorrect at the receiver, the
CRC check will fail and the packet will be marked as bad. You would
want to add some kind of channel coding into your system to help with
this.

Tom

3

I am actually trying to work with the OFDM block and it seems like
packetization is kind of integrated into the OFDM module. Can you
confirm
this? And do you know where I could find channel coding/FEC examples?

Thanks,
Pat

4

On Tue, Mar 19, 2013 at 7:07 PM, Patrick C. [email protected]
wrote:

I am actually trying to work with the OFDM block and it seems like
packetization is kind of integrated into the OFDM module. Can you confirm
this? And do you know where I could find channel coding/FEC examples?

Thanks,
Pat

They are fairly closely tied together, but you should be able to
separate them.

What version of GNU Radio are you using? If you track the master
branch on git, we recently updated the OFDM transmitter
implementation. Martin B. and Ben R. have done a lot of work
to restructure the code, which might help with what you are
attempting.

Tom