[Discuss-gnuradio] Multiple channel Tx burst

[redsalsifi]

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 :)

-JM


Gnuradio v3.7.5
libuhd   v3.7.5