[Discuss-gnuradio] time tags for transition time using USRPs

[Henning Bredenberg]

Hi all,

In the attached picture a flow graph is shown where i use the "random"  
pdu generator for a fixed sized pdu (1200 bytes here). The  
pdu_to_tagged_stream block makes it accessible for a simple BPSK  
modulation to send it over a coax cable to another USRP B200. A time  
sink shows what the transmitter transmits and what the receiver should  
receive ideally.
By inserting some different delays, e.g. a uniformly distributed (0 to  
80 ms in the disabled block here), i want to emulate a communication  
system. My questions are:

1. How can a realize a burst transition that transmit the fixed sized  
burst, i.d. the pdu, in a 20 ms slot whereas the last 60ms no  
transition occurs before a new pdu is generated by the message_strobe  
block? By now it is a continuous transition no matter what i change.

2. I want to store the time from generating the pdu till my second  
USRP receives it. Tagging the time should be an option to realize  
that. Since a have no clue: How can i realize that using time tags?  
The simplest case is - without any delays - that the pdu is generated  
and transmitted in a 20ms slot plus the processing time which should  
be small compared to the 20 ms.

I am thankful for any kind of help. Thanks and have a nice weekend,
Henning

Flow Graph.png
Description: PNG image