Problem:Discontinuous Transmission of random packets exhibiting a two state markov model (using benc

GNU Radio
1

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*
      1. 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 V. Patcha
Research Assistant
Electrical Engineering
Louisiana State University

2

On Mon, Feb 14, 2011 at 3:09 AM, Venkat V. [email protected]
wrote:

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)??

Kind of. Technically, yes, the flowgraph is still active, but it’s not
doing anything because there is no data coming from the message source
of the packet_modulator. When we issue the send_pkt command, that
inserts data into a message source that then feeds the rest of the
flowgraph with the packet.

  1. 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 ??

That should be fine. You are sleeping the main thread, but the flow
graph is running in a separate thread, so it will continue doing its
thing while you sleep.

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

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

Shouldn’t.

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

Are you using UHD or the legacy interface?

Regards
Venkat V. Patcha
Research Assistant
Electrical Engineering
Louisiana State University

Tom