Re: [Discuss-gnuradio] Analog and Digital Transmission in parallel

[Marcus Müller]

Hi Przemek,

yes, generating multiple different waveforms at once should be possible – after all, the USRP really doesn't care about what it's transmitting.

To me this sounds like you're taking the 2.5MHz bandwidth that the USRP has at 2.5MS/s, and divide it into channels – one for each of different modulations. Is that understanding correct?

A note: a wav source doesn't really have a sampling rate. It really just gives you the samples from the wav file, as sequence of numbers. The fact that some header in the wav file says "this has a sampling rate of 16kS/s" doesn't change anything about that sequence of numbers. Your DSP application's job is to generate a digital signal that makes sense out of that – which means you'll need operations that have an interpolating characteristic – i.e. for one sample going into that operation, >1 come out.  GNU Radio, however, really doesn't care or even know about the sampling rates – all operations are done on the sequence of numbers that your sample stream is, and frequencies are only meaningful as fraction of the sampling rate.

Best regards,

Marcus

On 12.06.2016 16:11, Przemek Lewandowski wrote:

Hello everybody 

Im creating multi mudulation transmitter - project at my university. I have a conceptual problem. 

I have analog modulations: AM, SSB, FM - narrow and wide

and digital modulations: qam, qpsk, gfsk

and I want to have largest bandwith as possible :) to transmit all modulations simultanously.

Scheme of my transmitter is: 

/ AM \

wav source (16 KHz) - Matrix multiply    - SSB -   Matrix Multiply -> USRP Dev

- FM N -

   - FM W -

 

   - QAM -

   - QPSK -

   \ gfsk -

 

 

And now is my question :)

I have now Sample Rate for whole project and Device - 2Mega Samples

When I want to transmit all analog modulations with rate o 2 MS it is good 

But when I want to add one of digital modulation to analog modulation, I get Underrun after 3 minutes.

But best is that when I run all digital modulation (no analog modulation) it behave properly.

I have put sample sate probes on all modulations and after WAV file and here can be interesting thing:

1) when analog is transmitted only output Sample Rate of WAV Source is 16 KHz, but when digital is send Sample Rate is 2.5 Mega samples

Is it proper to send analog and digital modulation in parallel ?? I I see this, there are two different sample rate here ?!

All The Best 

Przemek

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