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Re: [Discuss-gnuradio] Using USRP to transmit and receive samples

From: West, Nathan
Subject: Re: [Discuss-gnuradio] Using USRP to transmit and receive samples
Date: Thu, 17 Oct 2013 23:53:32 -0500

On Thu, Oct 17, 2013 at 11:14 PM, JPL <address@hidden> wrote:

We have used Matlab to generate *.mat file, a file around 1966240 complex number OFDM samples.
Thinking to (I) transmit between two USRPs, (II) let the receiver side saving data into file, and later (III) putting the file on Matlab for demodulation.

1. What is the best way to do it? like create GRC blocks? or UHD example?
2. How can I make sure that the TX part will stop when those 1966240 samples are sent. and RX part will stop when completely receiving those 1966240 samples?
3. Should the file type be the *.dat?



I'll attempt to respond to both questions since they are really the same thing.

First, this is kind of a weird way to use GNU Radio. GNU Radio provides you an environment to do all of the signal processing you want to do in c++ or (if you want) python. The flowgraph of file -> transmit antenna --> over the air --> receive antenna -> file followed by signal processing in Matlab is sort of not the point of GNU Radio. There's nothing saying you cannot do this, but you might look in to  implementing whatever signal processing you are doing in GNU Radio. This will reduce the round trip time of testing and make the whole experience a little better. ( you're basically doing an even slower version of what we call flying blind: http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#Flying-Blind )

Re: your other email and question about GR file sink/source:
About the file sinks... http://gnuradio.org/redmine/projects/gnuradio/wiki/FAQ#What-is-the-file-format-of-a-gr_file_sink
Basically it's a binary file just like you would expect if you open a file with 'b' flag in most languages I'm familiar with. If you're dumping complex floats in there then you'll need to read two float values.

2. There is a block called head. It takes a number of samples to pass through and then quits. But again, you might consider your approach here.

3. I've never actually looked in to the format of a .mat file, but connecting that (regardless of data inside the file) to a UHD source would be spewing garbage out. The .dat extension you might see in GR literature is just a convention we use to denote it's data; it's not really a special format.


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