Re: [Discuss-gnuradio] Constant carrier digital transmission

[Marcus Müller]

Hi Frank,

really, with the advances of the drivers and hardware capability and the changes in GNU Radio architecture, your problem isn't that comparable to the problem in 2009; again, please don't rely on Nabble posts; Nabble is just a mirror of the GNU mailing list archives (and adds some kind of forum infrastructure), and it has been down lately for quite some time. I don't trust it, personally, and usually urge people to directly sign up to the mailing list and use the official archives; so here's the link to the official mailing list archive's thread:

http://lists.gnu.org/archive/html/discuss-gnuradio/2009-03/msg00552.html

Anyway, let us really discard the idea of describing your problem in terms of a problem from 2009; that just makes things more complicated, because then I'd have to explain what happened to GNU Radio in the last seven years, and why Ettus N210 & B210 driven via gr-uhd isn't like a USRP1 driven via libusrp. What you're really asking is analogous to "my 2012 Ferrari won't start; I found this 1920 Ford Model T hand crank start discussion, but I can't find the hand crank in my Ferrari's trunk". Things simply don't work like that anymore.

So, this has really become much easier: The USRP sink reads stream tags, which can contain a start-of-burst, and a end-of-burst info; the N210 and B210 USRPs (unlike what was available in 2009) keep an internal device time, so that they can even be used to transmit samples at a specified time, without having to continuously send before that time.

It's important to understand the concept of stream tags to work with this (that concept wasn't around in 2009 in the shape that it's built into GNU Radio since roughly 2011), so I'm referring you to the official GNU Radio tutorials [1].

Chapter 5 should explain Tags and Message Passing, but the tutorial chapters built atop of the previous ones, so I'd recommend starting with the first and working to the fifth; you will be rewarded with being able to fully understand Chapter 6, which is about interfacing what you've built in chapters 1-4 with real USRP hardware, and with an instant understanding of [2], the documentation of how to send "bursty" samples to the USRP via stream tags!

For a demo of how to use stream tags to tune at a specific time and annotate, see [3]; if you run that as

./freq_hopping.py -r 2.5e5 -N 10000 -t 500 -f 2.4e9 -c 100 -d 2.5e6  -v  

with your B210 attached, you should see its TX LED blink exactly twice per second.

Best regards,

Marcus

[1] http://tutorials.gnuradio.org
[2] http://gnuradio.org/doc/doxygen/classgr_1_1uhd_1_1usrp__sink.html
[3] https://github.com/gnuradio/gnuradio/blob/v3.7.10.1/gr-uhd/examples/python/freq_hopping.py

On 15.08.2016 13:07, Inspire Me wrote:

Hi Marcus

My apologies if I posted incorrectly, I am new to this. Thank you for responding.

The posts I was referring to are http://gnuradio.4.n7.nabble.com/Constant-carrier-digital-transmission-td27764.html

I do understand that things have moved on since 2009. I was hoping to have a look at the code mentioned in the post for the GMSKSpacecraftGroundstation. https://moo.cmcl.cs.cmu.edu/trac/cgran/wiki/GMSKSpacecraftGroundstation I have not been able to find it. I was wanting to see how it was done.

I have the almost the identical situation described in the post. I was thinking I need a Flag Source feeding some sort of switch logic that checks if no message is present on the data stream input and then selects the flag input, sends one flag; repeats check and send until a data arrives on the data stream input. 

We are currently using Ettus N210 & B210 hardware. I have a Tx chain working except for the flag stuff. For testing I have Mux'd in a vector of flags (0x7E) and can successfully talk to the receive end.

Any help would be greatly appreciated. 

Kind Regards

Frank

On 15 August 2016 at 20:29, Marcus Müller <address@hidden> wrote:

Hi Frank,

**which** post from March 2009? Would you happen to have a mailing list
archive [1] link (please don't use Nabble).

At any rate, what applied 7 years ago regarding messages will probably
not apply now, anymore.

I think it would be very worthwhile if we didn't discuss this based on
something from 2009; what program/flowgraph/python script are you
specifically looking at?

Best regards,
Marcus


[1] http://lists.gnu.org/archive/html/discuss-gnuradio/2009-03/index.html

On 15.08.2016 10:41, Inspire wrote:
> Hello
>
> I am relatively new to gnuradio, I have only been working with it for 6
> weeks.
>
> I came across your posts from march 2009 relating to continuously
> transmitting 0x7E's when no messages are present in the queue. I am facing
> the exact issue with our implementation in GNURadio. I need to send out
> continuous flags when no messages are in the queue but immediately (within a
> few flags) switch to sending data when a message arrives. I have gone
> looking for the HDLC Source code spoken about but have not found it.
>
> Q1. How was this solved ?
>
> I am struggling with getting my head around how to ensure the continuous
> stream of Flags given that gnuradio buffers up and schedules transmission
> based on buffers. I am also struggling with how to do the switching between
> streams.
>
> I know 2009 was a long time ago, but any help would be greatly appreciated.
> The mentioned source code example or any other example code would be of
> great benefit as GNURadio documentation is confusing and some times
> non-existent.
>
> Kind Regards
> Frank
>
>
>
> --
> View this message in context: http://gnuradio.4.n7.nabble.com/Constant-carrier-digital-transmission-tp27764p61217.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
>
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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