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Re: [Discuss-gnuradio] modulation packet loss

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] modulation packet loss
Date: Mon, 18 Mar 2013 09:29:48 -0400

On Mon, Mar 11, 2013 at 11:46 AM, Patrick Cunniff <address@hidden> wrote:
> 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

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


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