Transmit time synchronization

Hello all,

I am trying to implement a multi-relay cooperative network using
gnuradio
and USRP B200. I cannot figure out how to synchronize the relay
transmissions using GNU-Radio (without editing FPGA code or using
external
clock source).

I created an out of tree module derived from the tags_demo example of
uhd
but i encounter a problem with the packet encoder.

my flow graph is something like

USRP source —> tagging_block —> DBPSK demod -->packet decoder -->
encoder --> mod --> USRP sink.

sorry disregard previous mail

I am trying to implement a multi-relay cooperative network using
gnuradio
and USRP B200. I cannot figure out how to synchronize the relay
transmissions using GNU-Radio (without editing FPGA code or using
external
clock source).

I created an out of tree module derived from the tags_demo example of
uhd
but i encounter a problem with the packet encoder.

my flow graph is something like

USRP source —> tagging_block —> DBPSK demod -->packet decoder -->
encoder --> mod --> USRP sink.

when i attach tag debug block, i see that the packet decoder is not
propogating my tags. Are their any substitutes to the encoder or is
there
any problem with my code which is attached. Any help would be very
welcome.
Thanks!

On Mon, Oct 13, 2014 at 5:53 AM, Muhammad Shahmeer Omar <

On 10/13/2014 08:57 AM, Muhammad Shahmeer Omar wrote:

my flow graph is something like

USRP source —> tagging_block —> DBPSK demod -->packet decoder -->
encoder --> mod --> USRP sink.

when i attach tag debug block, i see that the packet decoder is not
propogating my tags. Are their any substitutes to the encoder or is

The packet_decoder block has a message queue in the middle of its
implementation, so tags are not propagated. Not sure how to get around
this.

thanks for the input Jeff. I am fairly new to GNURadio so any
suggestions
on how i can create the said network. My main goal is to implement the
multiple relay network and demonstrate its advantages. As i understand
it,
a differential modulation scheme is my only option if i want to achieve
diversity gain on rx without having to estimate the channel. Any
suggestions on how i go about doing this?