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[Discuss-gnuradio] Multiple channel Tx burst

From: redsalsifi
Subject: [Discuss-gnuradio] Multiple channel Tx burst
Date: Wed, 18 May 2016 14:32:43 +0200
User-agent: Roundcube Webmail/1.0.6

Hi Everyone,

My flowgraph (http://i.imgur.com/Deo8jbq.png) is used to convert a formated packet from UDP to a 2-FSK modulated signal sent on a specific radio channel. Each of the the modulation branch has a different baud rate (Variable BR_X) and center frequencies.

The "preamble_v2" block handle the selection of the channel based on a specific header on the PDU, which is stripped before it gets out of the block in order to give only the raw data to the rest of the modulation chain.

My concern is actually the end of each channel chain .. how can i perfectly multiplex my different asynchronous channels into one sink (USRP in this case) ?

Here is some options I came up with (parameters on blocks are not important here):

 - Adder : (http://i.imgur.com/1V7nroZ.png)
Of course, it's not working because the adder waits for one sample on each input to produce one sample, so I may code a custom block to output null samples when there is no input sample .. which is dirty because it would not be burst tx anymore.

 - Multiple USRP sink : (http://i.imgur.com/Hr8EiyG.png)
Simply put one USRP sink for each channel, but there may be collisions.

 - Complex to Message to Complex : (http://i.imgur.com/40lxtWR.png)
Seems like it will solve the collision problem, but the packet_len tag is altered during the modulation chain and I can't figure out how to recalculate it.

I think this "problem" can be resolved by many ways due to the options offered with tags, custom blocks and uhd command interface but i haven't figured out a correct one yet !

Have anybody been stuck on a multiple channel asynchronous transmission ?

Thanks in advance :)


Gnuradio v3.7.5
libuhd   v3.7.5

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