Re: [Discuss-gnuradio] Simultaneous transmissions, UHD, metadata

[ragh]

Thanks for the response Josh. Unfortunately I am still clueless on how
to accomplish my task. So let me explain what I am trying to do.

There are two nodes (a node has a N210+WBX and a powerful enough CPU)
and I want both of them to transmit a carrier signal at the same time.
This is the sequence of steps I am thinking of:

Step1: Node1 transmits a reference (trigger) sequence
Step2: Node2 correlates on the reference and finds the time at peak correlation
Step3: At a certain time T from the peak-time, both Node1 and Node2
transmit a carrier signal (const_wave) reasonably simultaneously

--
Having described the task, let me take a stab at how I would go about it.

1. Note t1 = timestamp of last sample of reference sequence. t2 =
timestamp of peak correlation sample. Set time reference according to
t1, t2.
2. Assume there is a gr_signal_source that accepts time offsets from
time reference and populates metadata accordingly.
3. Assume gr-uhd recognizes the metadata and transmits the buffer at
the right time.

I understand that metadata does not get through in gr-uhd (at least
currently)... but I am not sure how else the task can be done. Any
comments/suggestions will be greatly appreciated.

Thanks,
Ragh

>> Hi All,
>>
>> I have used gnuradio-companion and the N210 without too much problems.
>> What I would like to do, however, is to send data at particular time
>> instant, something like tx_timed_samples.cpp. But I would prefer to do
>> this in python for various reasons. I am new enough to this stuff that
>> I can't tell if this can be done with the current code (gnuradio +
>> uhd) or if this requires some effort to do and if so, what is the best
>> path to follow?
>>
>
> The thing about gnuradio is that something has to be written in C++ at
> some level. So, we have this tagging interface in gnuradio which can be
> used to decorate samples (example: timestamps, end of burst, ...).
> Currently, the gnuradio-uhd blocks dont do anything with the tags, which
> could easily change, but... tags are pretty new and we havent yet
> invented the block that would take some kind of input and generate a
> tagged/decorated output stream that the uhd sink block would use. So
> maybe you can invent that motivating example. I should note that this
> may be a better discussion for the gnuradio mailing list.
>
> -Josh
>
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