Re: [Discuss-gnuradio] Questions regarding packet_tx and uhd_packet_tx

[Martin Braun]

The burst shaper actually has a manual page:

https://gnuradio.org/doc/doxygen/classgr_1_1digital_1_1burst__shaper__cc.html

The resampler will give you some rolloff, so you have a more usable
digital signal going to the USRP. Check out uhd_packet_?x for details on
how the USRP is configured. Its sampling rate is the rate at which it'll
consume data from the resampler.

-- M

On 08/17/2017 09:31 AM, Rui ZOU wrote:
> Hi,
> 
> I'm studying the example packet_tx and uhd_packet_tx in
> /usr/local/share/gnuradio/examples/digital/packet. I have some questions
> regarding the process of packet transmission and the flow graph.
> 
> Why burst shaper block is needed? How do its parameters affect tx/rx?
> 
> Why polyphase arbitrary resampler block is needed? How do its parameters
> affect tx/rx?
> 
> Packets are generated at the host at fixed intervals with variable
> length in a range. What parameters are passed to the USRP to control the
> actual rate of transmission? Or this is not controlled explicitly by the
> flowgraph, so the USRP just transmits at whatever rate it sees suitable.
> Is it the sample rate of USRP sink?
> 
> From the flow graph, the process to generate baseband symbols is clear.
> How the modulating pulse is generated and how it is multiplied with the
> baseband symbols are not clear to me. Is it achieved by the polyphase
> arbitrary resampler block? In digital communication textbooks, the
> baseband modulating pulse is a continuous waveform. If generated in
> digital system, like using GNU Radio in a computer, how to do it then?
> 
> Regards,
> 
> Rui
> 
> 
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