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

[Tom Rondeau]

On Mon, Feb 14, 2011 at 3:09 AM, Venkat Vinod <address@hidden> wrote:
>
> 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)??

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.


>         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 ??

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.


>         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 ???

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 Vinod Patcha
> Research Assistant
> Electrical Engineering
> Louisiana State University


Tom