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Re: [Discuss-gnuradio] IEEE 802.15.4 on USRP N210

From: Marius
Subject: Re: [Discuss-gnuradio] IEEE 802.15.4 on USRP N210
Date: Wed, 27 Jul 2011 22:27:29 +0200

Hi Sebastian!

I don't really understand what you're trying to archive, but here's a
stack for 802.15.4:

> 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

Works fine here. The XCVR is a much better choice than the RFX,
because it has TX gain.

> 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.

How did you change the frequencies? If you change the center-frequency
on a FFT your USRP2 <-> PC communication breaks down? What is the

> Problem 2: Packets send from a sensor node are not received.

Do you send a full 802.15.4 MAC sublayer? The stack you mentioned uses
a Packet Sink that drops packets on certain conditions. I changed that
recently for my efforts.

> I have the feeling
> that
> the node signal is only processed occasionally.

In that case try attaching the GDB and log (verbose define statement
at the C code). Actually if GNU Radio drops vectors it outputs an "S"
indicating an overflow.

> I played a bit around with sample rates.

To demodulate you need at least 2 * the frequency of the channel. So
in case of 802.15.4 something like 5 MS/s should be sufficient.

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

I actually finished a project on 802.15.4 and used USRP2s with the
WIESEL stack to analyze a real-time sensor network. I'll commit some
stuff quite soon (this week). E. g. a complete demod and mod path in
GRC. Most stuff is in German though. :)


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