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Re: [Discuss-gnuradio] unexpected underruns

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] unexpected underruns
Date: Tue, 1 Aug 2017 18:04:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

Ah, cool, but then I wouldn't start by packetizing data.

Simply send your file GMSK-Modulated; drop the packet encoding; think about it: the MIMO coding (usually) happens *after* the data has been formed to logical data units.

A few notes on your flowgraphs: Don't use the WX GUI elements in new flowgraphs. We have deprecated them, since no-one can maintain them, and the Qt GUI sinks have shown to be both more stable and efficient. As far as I can foresee your application's needs, Qt has replacements for all the WX visualizations you'd need.

For the receiver, I'd guess you'd first simply start by just recording from to channels, and then experimenting with things like cross-correlation, and estimating the channel matrix based on your known transmit signal. I wouldn't be surprised if the channel is rather boring in your setup – I blindly assume you're doing this indoors, and that limits the path difference and the amount of change (and hence, the delay spread and the doppler spread) your signals are subject to, especially since your bandwidth is so low. Of course, having a flat channel is nice :) but it also means that it might be quite hard to get any actual MIMO gain, because the two RX antennas might be very correlated. If in doubt, increase bandwidth. Be agressive with roll-off / Bandwidth factors of your GMSK.


On 08/01/2017 05:51 PM, Rui ZOU wrote:
Hi Marcus,

My goal is to first build a 2-by-2 space multiplexing MIMO using two X310s and GNU Radio. As I'm new to all this stuff, I'm starting from building 2 parallel SISOs. If there are some good kick-start materials or any resources, they will be very valuable. Thanks.


On Tue, Aug 1, 2017 at 11:37 AM, Marcus Müller <address@hidden> wrote:

Hi Rui,

sorry, I might simply have missed those, and didn't find your first email when I saw your recent one! I apologize.

So, hm, interestingly, we have a severe bug in the packet_encoder block (its design is pretty bad, and that triggers an unexpected behaviour underneath). That might mean the packet_encoder is just consuming items as fast as it can, without actually producing packets. In other words, packet_encoder is broken; you can't use it right now.

The more appropriate way of dealing with data might be in the example flowgraphs that you'd find under /usr/[local/]share/doc/gnuradio/examples/digital/packet_loopback_hier.grc ; it's a lot more complicated, though, and you'd have to write a message / PDU source that gives you the data you want to transmit, rather than the Random PDU block!

I don't really know if that is the way to go. What is it, that you want to build? Maybe the mailing list can advise?

Best regards,


On 08/01/2017 05:26 PM, Rui ZOU wrote:
Here are the two flowgraphs I have used. I have tried to attach the two files in my first email. Probably failed in doing that. If still not seen, please let me know so I will try again. Thanks for your help.

Running the first flow graph will cause GRC stop responding instantly, while the second one can run for a little while and produce lots of 'L' before going not responsive.


On Tue, Aug 1, 2017 at 11:09 AM, Marcus Müller <address@hidden> wrote:

Hi Rui,

don't know, to me, it looks like replying didn't work out great, since my mail client showed your mail in a new thread. Really, replying to a mailing list mail should be nothing more than hitting the "reply" or "reply all" button.

Anyway, even the slowest PC/laptop/Raspberry Pi/… I could think of would be able to deal with these rates, so there's very, very likely something wrong with the GNU Radio flowgraph you're using. Maybe you'd want to share that!

Best regards,


On 08/01/2017 04:59 PM, Rui ZOU wrote:
Hi Marcus,

Sorry for leaving the title empty, that's the first time to post to a mailing list. This is also the first time to reply, no sure if I replied correctly.

I use 390.625k as the sampling rate because this is the lowest I can get using the Ettus X310 without giving me a warning saying that the sampling rate cannot be provided by the hardware. The application is just transmitting a file using GMSK modulation on the two daughter boards of X310.


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