How to implement TDM on USRP1 and GNU Radio

Hello everyone,

I’m working on implementation of two-way relaying model using GNU Radio
(with GNU Radio Companion as interface) and 3 USRP1s (each has one
daughterboard and one VERT2450 antena). The relay node (R) decodes
from two end nodes (A and B) separately and performs a bitwise XOR on
messages before transmitting the XORed data to end nodes. This model
well with short message.

However, at the moment, nodes A and node B are running on their own and
user can just start/stop transmitting/receiving by hand. It’s needed to
have timing synchronization. This can be done by adding a beacon in node
This beacon is a pulse, transmitted each time before node R is able to
receive signal. Node A and node B transmit their message once the end of
the beacon is received. This process requires system to perform TDM. The
flow chart for each node can be found here:

My problem is that I don’t know how to design a TDM to manage the
transmit/receive phase. In particular, in end nodes, we need to notice
transmitter when the beacon is received and tell it to transmit; in
node, we need to tell it when to transmit the beacon, when to receive

Does anyone have experience with TDM on USRP and GNU Radio? Please give
some clue for that. Should I write some new blocks or modify the python
script generated by GNU Radio Companion?

Any help would be greatly appreciated.

Hoang from Vietnam.

Ngo K. Hoang
Faculty of Electronics and Telecommunications -
University of Engineering and Technology (UET) - Vietnam National
University, Hanoi (VNU)
Vice-president of Student Association of UET
Alternative email: [email protected]
Mobilephone: +84.163.682.7874