[Discuss-gnuradio] Problem:Discontinuous Transmission of random packets exhibiting a two state markov model (using benchmark_tx.py example)

[Venkat Vinod]

Hello All,
          
            I'm trying for discontinuous transmission of random packets to exhibit two state markov model(ON and  OFF cycles).The states for  markov model are generated by predefined transition matrix. I utilized the benchmark_tx.py example in digital section ,which has discontinuous transmission for every 5 packets.

Currently, I made little modifications to the code so that for ON state random packets are transmitted and for the OFF state, time.sleep function is performed. The program runs fine for small burst of packets (1,2 or 4 packets for ON cycle) but, if I transmit big burst of packets(10,15 or 20 packets for ON cycle) then OFF cycle is completely dead which causes in continuous transmission.

Questions: 

       1.  I assume  the flow-graph is still active even during the OFF cycle(data is still processing through the GNU blocks)??

        2. Is time.sleep() function is an appropriate way to use for OFF cycles in my model ?? If not can anyone suggest me better way to break the transmission using GNU blocks ??

        3. Is there anyway to control the transmission at python level by using single or multiple flowgraph model or suggestion to implement any new block ???   

    Multiple flowgraph Approach : 

         I tried to provide a two flowgraph model for ON and OFF cycles;I switch between the two depending on the markov state. 

ON cycle flow -graph:

  packet modulator --------> modulator ----------> ampl -----------> usrp sink

OFF cycle flow-graph 

  packet modulator --------> modulator ----------> ampl ----------->null sink

  

        4. Does my problem has anything to do with in band timestamp of packets ???    

              

 It would be great if someone guide if I'm wrong in understanding GNU Radio architecture.Thanks in advance.

Model : USRP 1 + RFX 2400 

OS :  Ubuntu 9.0.4

                                                                             

 Regards 
Venkat Vinod Patcha

Research Assistant

Electrical Engineering

Louisiana State University