SDR-Based BERT

I often have to test hardware RXs and though I have a hardware BER test
fixture, it’s kind of ancient and difficult to work with. I have
fantasized about using a USRP to transmit a PRB (pseudo-random
bit-sequence) to a RX modem. The data would then be brought back into
GnuRadio and compared with the originally transmitted PRB to determine
the
actual BER.

To align the data, I figured I could correlate the sent code against the
received data to determine any offset and align the data for comparison.
The correlation should be pretty forgiving to bit errors if the right
PRB
is chosen, I think.

My question is: does anyone have additional thoughts about this? I
don’t
think that this sort of tool exists yet in GnuRadio. I have seen BER
tools
and even a nice BER block from Balint, but I think they all assume the
data
is already aligned. I imagine that Balint’s block could still be used
if
the alignment was done first. Am I missing any other tools out there?

As for getting the received data back into the flowgraph, I imagine that
this might require a new source, like a synchronous serial port. I have
used libmpsse to work with some of the MPSSE-enabled FTDI chips before.
Maybe that could be implemented as a source block. My other thought
was
to use a LFTX board and bring in the clock and data as separate RX
channels
then proceed from there.

Thanks!

On Tue, Jun 25, 2013 at 11:50 PM, Dan CaJacob [email protected]
wrote:

use a LFTX board and bring in the clock and data as separate RX channels
then proceed from there.

Thanks!

Hey Dan,

That’s a good problem. My only recommendation at this point is the
correlate_and_sync block that I’m working on for burst modems. Started
it at our last hackfest. You can find the code on my github repo
(https://github.com/trondeau/gnuradio.git) in the ‘grhack13’ branch.
It’s working in a very specific case but is close to working
generically. It sounds close to what you want.

Tom