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I am currently working on Z-Wave protocol. With my HackRF One and scapy-radio I try to sniff the communications between two devices.

However devices can transmit at different speeds :

  • 9,6 kbps
  • 40 kbps
  • 100 kbps

As I can only decode communications at 40 kbps, I imagine my graph is unable to manage other speeds.

Some informations about Z-Wave communications :

  • Frequency (EU) : 868.4 MHz
  • Modulation : GFSK

And my GRC graph :

GRC flow graph

So my question is : How to modify the graph to decode and sniff 9,6 and 100 kbps signal too ?

Antoine Foucault
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    Have you managed to decode all three bands? – PoltoS Aug 25 '15 at 10:51
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    I'm sorry to answer so late. I decoded 100 kbps with Manos's solution because signal encoding is the same for 40kbps and 9,6 kbps so you just have to adjust sample rates. For 9,6 kbps you have to write a new block to decode Manchester signal encoding and you resample too. – Antoine Foucault Oct 12 '15 at 07:03

1 Answers1

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As an easy workaround, I would suggest to take the input stream from the HackRF and connect it into 3 different decoders, each one with the desired parameters. Then each Packet sink block will publish messages at the same Socket PDU block.

I am not familiar with the Z-Wave, but if the 3 different data rates share the same spectrum bandwidth, then there is no more job for you and you are done. But if they do, which I believe that is true for your case, you need some extra steps.

First of all you have to sample the time domain signal with the maximum sampling rate required by the Z-Wave. For example, if for the 3 different data rates the spectrum bandwidth is 4, 2 and 1 MHz you have to sample with 4e6 samples/s. Then you perform SRC (Source Rate Conversion), also known as re-sampling, for each of the different streams. So for the second rate you may want to re-sample your input stream of 4e6 samples/s to 2e6 samples/s. Then you connect re-sampled streams at the corresponding decoding procedures

                                              +---------------+
                                              |Rest blocks 0  |
              +--------------------------------->             |
              |                               |               |
              |                               +---------------+
              |                                                
 +------------+        +--------------+           +---------------+
 |            |        |              |           |Rest blocks 1  |
 | Source     +----------> Resampler 1+------------->             |
 |            |        |              |           |               |
 +------------+        +--------------+           +---------------+
              |                                                
              |    +--------------+           +---------------+
              |    |              |           |Rest blocks 2  |
              +-----> Resampler 2+-------------->             |
                   |              |           |               |
                   +--------------+           +---------------+

GNU Radio already ships with some resamplers, you can start using the Rational Resampler block.

Manos
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  • Ok so if I understand I just need to manage sample rate to decode efficiently Z-Wave ? The decoding procedure stay the same (in my case from "Frequency XFlating Filter" to "Packet sink" blocks) for each re-sampled signal. [Here](http://z-wavealliance.org/wp-content/uploads/2015/02/ZAD12837-1.pdf) I found a document which describe what you are talking about (bandwith & co.) for the different data rates. I will try to decode 100 kbps as it looks similar to 40 kbps signal regarding center-frequency and bandwith (page 3). Thanks for your help ! – Antoine Foucault Aug 06 '15 at 12:08