Re: [Discuss-gnuradio] USRP Receiver config problem

[satarkar]

Hi,

Thanks for the reply, Eric!

I plotted the output of usrp_rx and it did show frame coming out. I am
attaching the output with this email (the tx keeps sending the frame if it
doesn't receive the ack hence more than one bursts in the image). Also,
when I use replace the usrp_rx with the tx_output file it gives
segmentation fault sometimes and runs correctly at other times. For the
segmentation fault I tried using debug as per the instructions in the wiki
page, but when I attach the process, and press enter, the script doesn't
run until I quit the gdb in the otehr window. Can you help me with this?

Also I am using the linux 2.6.18. Is this the problem with version? I
found some posts online saying that.

-Sumit

> 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:
>
> usrp_tx:
>
> cordic_freq =29.32e6
> sw_interp = 8
> usrp_interp = int (128e6 / sw_interp / data_rate)  #160
> fs = 128e6 / usrp_interp  #128e6/160 = 800e3
>
> u = usrp.sink_c (0, usrp_interp)
> u.set_tx_freq (0, cordic_freq)
>
> usrp_rx:
>
> r_cordic_freq = 29.32e6               # IF frequency
> r_data_rate = 40e3
> r_samples_per_symbol = 8
>
> r_usrp_decim = int (64e6 / r_samples_per_symbol / r_data_rate)        # 80
>
> r_fs = r_data_rate * r_samples_per_symbol                     # 800 e3
>
> #  initialize USRP
> r_u = usrp.source_c (0, r_usrp_decim)
> r_u.set_rx_freq (0, -r_cordic_freq)
>
> Can someone help me with this?
>
> thanks and regards,
>
> -Sumit
>
>
>
>
>
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e_usrp_output.txt.jpeg
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