Re: [Discuss-gnuradio] USRP Receiver config problem

[Eric Blossom]

On Thu, Mar 26, 2009 at 01:24:37PM -0400, address@hidden wrote:
> Hi,
> 
> I am trying to run ALOHA MAC on gnu radio. The modulation scheme used is
> GMSK. The Tx and Rx chains are as follows:
> 
> Tx Chain:
> 
> src -> framer -> crc enoder -> fec encoder -> preamble -> nrz ->
> interpolator -> Gauus filter -> FM modulator -> gain -> usrp_tx
> 
> Rx Chain
> 
> usrp_rx -> filter -> demod -> integrator filter -> correlator -> fec
> decoder -> crc decoder -> extract frame
> 
> For some reason, I am unable to receive the frame when I run my python
> scripts. I tested USRP boards by passing a simple sine-wave and it is
> received correctly. I checked the output of usrp_tx on oscilloscope and it
> does display the frame going through. To test, whether there was any
> problem in the signalblocks I replaced usrp_tx by a filesink and dumped
> the output of Tx chain in a file. I replaced the usrp_rx by this file and
> the frame was correctly received. I think this means that there is problem
> of configuration with usrp_tx and usrp_rx. Following are the configuration
> scripts:


How are you doing symbol timing recovery on the receiver?

Generating logging data using gr.file_sink's at varous points in the graph is
often helpful in seeing what's going on.

Eric