Re: [Discuss-gnuradio] DSRC demodulation with gr-ieee802_11

[Jean-Baptiste Truffault]

OK, I try to record a new signal and I tell you if I get something new.

2014-09-24 17:51 GMT+02:00 Bastian Bloessl <address@hidden>:

On 09/24/2014 04:14 PM, Jean-Baptiste Truffault wrote:

Sorry for the time, I had some trouble with the 3.7.3 install, finally I
installed the 3.7.5 thanks to the script
http://www.sbrac.org/files/build-gnuradio.

First, I recorded a DSRC signal thanks to Gnu Radio and my USRP N210
(with a CBX daughter card): 5Msps, 5.127 GHz. I now use this file as
source. It contends some DSRC exchanges that I would like to decode (I
am quite sure that the record is good thanks to the shape of it, cf
attached picture [3_fft.png]).

I don't think so. This does not look like a 10MHz OFDM signal...

My grc scheme [1_grc1.png & 2_grc2.png] is very similar of yours, I just
attached it to be sure.

This looks OK.

My first idea is that it comes from the OFDM frame detection because of
the strange shape of it (cf [5_autocorrelation.png]), it acts like there
were always something to decode when the messages come with a burst on
the FFT [3_fft.png].

The autocorrelation is always high so frame detection is triggered all the time. This might happen when you start the USRP source. Try to drop samples at startup (skip head block).

Another thing that is different from your result is the constellation
scope that may have 4 clusters (instead of one on the 4_constellation.png)

Since you are not synced on a real frame you just see noise.

Best,
Bastian