Simple ARQ MAC over TDMA; using GNU Radio and USRPs in GRC

GNU Radio
1

Hey list,

For those who were not at the GR Conference 2012: I presented some work
demonstrating a simple ARQ MAC over TDMA; using GNU Radio and USRPs in
GRC. Its very cool work, I encourage anyone to take a peek at the
slides, and checkout the repo and run the examples.

The MAC layer work is actually the work of John M. (I’m just the
messenger). He will be continually polishing and debugging the code over
the next week or so. There should be a wiki page soon…

So, I promised at the presentation that I would email the slides and the
relevant information to checkout the repository.

– Here is the presentation (pdf format):

https://github.com/guruofquality/grextras/blob/pre_cog/pre_cog_pres.pdf?raw=true

– Here are some teaser screenshots from the slides:

http://i.imgur.com/HYgeb.png
http://i.imgur.com/EvDof.png

– The code is available on the pre_cog branch of grextras:

GRExtras main wiki page:
Home · guruofquality/grextras Wiki · GitHub
GitHub URL
$ git clone GitHub - guruofquality/grextras: Advanced GNU Radio Blocks
Check out this branch:
$ git checkout pre_cog
GRC flowgraphs are here:
/examples/*.grc
Contact
[email protected]
[email protected]

Note: Users will have to generate the tdma hier block first, and then
reload GRC to use the top level simple MAC block.

2

Hi Josh,

A quick question, what is the time reference you are using for the TDMA
engine? Is it GPS or something else? How accurate about the time
synchronization?

On Wed, Sep 26, 2012 at 1:31 PM, Josh B. [email protected] wrote:

– Here are some teaser screenshots from the slides:
$ git clone GitHub - guruofquality/grextras: Advanced GNU Radio Blocks

Feedback is always welcome!
-Josh

Discuss-gnuradio mailing list
[email protected]
Discuss-gnuradio Info Page

–

Alex,
Dreams can come true just believe.

3

On 09/26/2012 03:20 PM, Alex Z. wrote:

Hi Josh,

A quick question, what is the time reference you are using for the TDMA
engine? Is it GPS or something else? How accurate about the time
synchronization?

In this case we tested in the LAB with shared reference and PPS. GPSDO
per USRP should be great too. Both of these options will be highly
accurate.

Now, it should be possible for a more advanced TDMA engine to try and
determine the transmit windows without explicit synchronization. I hope
we get this into the example as well.

The guard interval parameter could be modified depending upon the
accuracy.

-josh

4

This system used a 1PPS to sync the radios - for the sake of getting it
up
and running quickly. A GPSDO would work just as well, with ~50 ns of
accuracy, which is pretty good.

Alternatively, as Josh said, you could synchronize the radios with other
methods, like over-the air broadcast of a “system time”. The beauty of
this solution is that you could potentially implement this functionality
on
high protocol layers(i.e. link management) and use the ctrl ports of the
blocks to make adjustments to the USRPs time.

I should have better documentation up next week so you can mold this to
your application.

-John