Re: [Discuss-gnuradio] chat app with OFDM -- Asynchronous TX

[Martin Braun]

On 02/11/2016 02:08 PM, Nicolas Cuervo Benavides wrote:
> Hi Martin,
> 
> Thank you for answering me. At the Rx I am not able to see any data
> after the first message (which is correctly decoded and printed) is
> received. However I may start thinking that the messages are getting
> stuck in the tx, which is rather confusing. I checked three things after
> I start both Tx and Rx, and in both I am watching at the spectrum in
> frequency/waterfall sinks:
> 
> 1. The message is ready to send, so I hit 'enter'. I get an 'U' at Tx
> (which I expect, as I am no longer sending data) and I correctly receive
> the message in the Rx. However, I do not see the message still in my
> loopback in the Tx part.

The U shouldn't happen because we're in bursty mode, and are setting eob
bits appropriately. Still, I remember seeing this and I think it was a
transient issue.

> 2. I hit "enter" again, the receiver is getting nothing, but now I see
> the message in my loopback. However, I can't see my OFDM waveform at the
> transmitter:
> https://drive.google.com/file/d/0B10fLbRQIxbdOXdzTGI3SGNDNTA/view?usp=sharing
> 
> 3. I hit "enter" one more time. Again, Rx is not getting anything, but
> now my waveform is there, which confuses me as the frequency sink is
> connected at the same point where the USRP sink is, meaning that the
> signal has been there but is not yet shown. So the flowgraph is stuck:
> https://drive.google.com/file/d/0B10fLbRQIxbdR1NNdDBsV2xsNkE/view?usp=sharing
> 
> Then the behavior is not much different afterwards. I keep hitting enter
> to see that, at the receiver, I am getting power over the air, but no
> data is being processed. This waterfall sink is the result of having the
> "enter" pressed at the Tx part:
> https://drive.google.com/file/d/0B10fLbRQIxbdSy1iM0FMRHRyT0E/view?usp=sharing
> 
> So the Rx is running continuously, and the Tx is sometimes putting
> something in the air, but that something does not come with each 'enter'
> press, and is not being decoded as a message. Is this behavior
> comparable with what you were having years ago?

Of course not, my demos are always perfect and flawless :) Just kidding,
but this in particular did work. However, I remember having to send
messages twice or something like that.

Sorry I don't have any better solution from the top of my head.

Cheers,
M