[Discuss-gnuradio] IEEE 802.15.4 on USRP N210

[Sebastian Bader]

Hello everyone,

I am very fresh in the field of SDRs and encounter some problems in
the implementation. But some basic information first.

I am trying to communicate between gnuradio (USRP) and 802.15.4 sensor
nodes, as it has been done before (see Thomas Schmid @ UCLA). Because
the hardware has evolved since then, I am using USRP N210s as the
interface to the computer. The N210s are equipped with XCVR2450
daugtherboards. I am using basically the ucla_zigbee_phy
implementation and found an existing adaptation to the UHD driver
online (Master Thesis by Kresimir Dabcevic).

Now to the problem. After some minor changes in the test codes (see
attachments), I can communicate between two N210s at 2.475 GHz.
Problem 1: When changing the center frequency on both Tx and Rx,
communication does not work any longer. Even a 5 MHz shift does the
deal.
Problem 2: Packets send from a sensor node are not received. The
packets are sent from TinyOS. At the N210 receiver I check whether I
find a SFD in the stream, but this does not happen (sending 1/sec).
When increasing the transmission rate to 1/10msec, I occasionally
detect a SFD. I have tried both with CC2420 and RF230 transceivers
communicating at channel 25 (2.475 GHz).

I checked the received spectrum for both USRP tx and node tx with a
simple FFT application. The result is attached as well. For this test
I let the transmitter send every 10msec. Also here I have the feeling
that
the node signal is only processed occasionally.

I played a bit around with sample rates. When increasing the sample
rate (before 1M) to 10M I seem to find the SFD more often, though it
is hard to tell, as the SFD then is also found relatively often in the
noise. I tried to filter the noise with the power squelch in the code,
but the threshold has to be very low to get something from the node,
which in itself is quite weird.

I hope someone might have an idea or a tip what else I could check out.

Thanks in advance, Sebastian

uhd_cc2420_rxtest.py
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uhd_cc2420_txtest.py
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nodeFFT.png
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usrpFFT.png
Description: PNG image