Re: Re: [Discuss-gnuradio] reducing the latency in tunnel.py

[Michael Buettner]

> > Hi all,
> >
> > I would like to send a MAC layer control packet every 4 ms from computer A
> > to computer B to tell B when to send data using USRP and GNU Radio.  It is
> > like TDMA and a frame is 4 ms. I am trying to do this work by modifying
> > tunnel.py in the gnuradio-example folder. I removed the carry sensing part
> > and added the control packet in the tunnel.py.
> >

> Hi Jane,

>I published a paper on this issue:
>http://www.andrew.cmu.edu/user/gnychis/nychis_nsdi09.pdf


>If you read it, you will understand all of the latencies involved and why
>your turnaround time is so high.  We propose mechanisms to overcome these
>challenges in the GNU Radio / USRP architecture, and built code to support
>it, but it was decided that the new blocks that our code uses are no longer
>going to be supported by GNU Radio.  So, our code in summary does not work
>with GNU Radio now.  But, maybe you can apply some of the techniques we
>mention to achieve what you want.

>- George

Another study you could look at is ftp://ftp.cs.washington.edu/tr/2009/10/UW-CSE-09-10-02.PDF

It gives another overview of where latency comes from, and shows how you can get around some of it. 

We were able to get turnaround times for our application below 300 us by making a few simple modifications to the GNU Radio C++ code.  

It would still eat up a chunk of your 4 ms slot, but might be low enough overhead for your application. 

-michael