Re: [Discuss-gnuradio] Overview of packet decoding?

[Martin Braun]

Hey Connor,

don't worry,  you'll get there! It's a big question, though, and you
should go step-by-step or it can be frustrating. You also may need to do
frequency synchronization since you're not at baseband.

First, can you see your signal in the time sink when you're
transmitting? If so, that's a good first step. Once that's working,
adding the header would be the next step. Take a look at the examples in
gr-digital/examples/packet.

Cheers,
Martin


On 01/23/2017 11:55 PM, Connor Wolf wrote:
> Hi there!
> 
> I'm experimenting with a USRP, trying to transmit and receive a simple
> manchester-coded bfsk signal, and I'm stuck on how to properly build a
> message packet, and actually extract the data from the received waveform.
> 
> Basically, I have the receive chain all functional, and I can see the
> data in a time-sink window, but I've been unable to figure out where to
> go from there.
> 
> Right now, I'm using a random PDU generator, with a custom block that
> does the manchester encoding. Here is my current flow-graph:
> Inline image 1
> http://imgur.com/a/tBqyw
> 
> (Note that the repeats are primarily to make the data easier to see in
> the time window)
> 
> I'm pretty clearly missing a few things - There's no header or
> synchronization, and I'm not sure how to add them. 
> 
> As I understand it, I need to do a few things to make this a "real" system:
> 
>   * Prepend synchronization and header to the data (do I do this in PDU
>     form, or as bytes? 
>     If this is done in the bytes stage, I'd need to also modify the
>     stream length tag, I guess.
>   * Synchronization and header and detection
>   * clock recovery (easy since it's manchester)
>   * data unslicing (Is that the right term?)
> 
> I'm relatively clear on how I'd do this manually (I've done this kind of
> thing with simple OOK-ed radios on a microprocessor before), I have no
> idea how to implement the system within gnuradio. The only example that
> seems relevant is the `uhd_packet_tx.py` and `uhd_packet_rx.py` files,
> but for some reason when I try to run them, the `uhd_packet_rx.py`
> example disables the USRP rx as soon as a single message is received,
> and I've been unable to determine why.
> 
> Any help would be wonderful, I'm currently more or less flailing
> randomly and realizing how little I know about RF anything.
> 
> I'm using GNURadio 3.7.10.1, with a USRP B205mini-i on windows, if it's
> relevant.
> 
> -- 
> Connor Wolf
> Sr. Technician / Code Monkey
> Akela Inc
> 
> 
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>