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

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]).

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

The problem is when I read the debug from the OFDM Decode Mac,

at the first time I launch the script, I get something like: 

80 be 44 b5 e1 71 e5 57 31 ac 58 4e 0b db b8 1f 

03 63 c7 b4 1b e5 2c 8c 76 da 20 f5 c2 e0 8e bc 

62 ad 12 37 d5 07 1a 5f e6 d4 03 a4 e7 db 1c 9c 

eb 99 1c 52 e8 83 13 06 ac 08 70 4b bf 71 0c ab 

74 52 2c fc f9 ca 05 4a 29 55 c9 c6 cb 7c f8 51 

22 60 6f 5f 64 d7 55 f9 32 f6 79 7c 61 ea 89 86 

f3 33 ea 85 43 52 12 6e b2 92 e7 3c 81 5c 49 f2 

b6 30 03 dc c4 15 f4 cd f0 a1 5a 1b c9 88 a8 94 ...

the second time I launch the script, I get something completly different that looks like:

00 ee 2b f8 e9 7c d4 5e 93 22 e9 fc d4 1a 9e 1a 

d5 3e 03 0b 93 da 15 fe 3a 2f 53 fd c0 9c 98 a6 

9e 8f 8c 0f 30 cc f6 a6 16 46 81 54 b7 95 3a 1e 

20 36 20 b6 91 3c 20 55 ab 02 ea a4 9f e8 69 88 

97 77 c8 de 92 25 0e 18 6b e1 29 4f e6 3c 86 65 

b0 7a 61 0b 47 d6 22 38 19 4c 0b b9 fb 1b 53 83 

aa 4b d7 fe 9f 4d de 0f 8b 99 a7 de a4 09 0d d5 

1c d5 6c dc 66 bf 5f 7c dc b7 a3 fa 88 b3 c8 7b 

11 1b 04 41 1a 41 5d 51 74 ea 48 11 33 d2 d1 82 ...

Those results should be the same because they come from the same record file... 

The debug indicates that the  checksum is wrong so the frame is dropped and I do not receive anything on the OFDM Parse MAC Block.

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]. 

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)

I would be very kind if you had some idea where I did something wrong ! 

Thanks in advance for your time and your help !

2014-09-23 4:16 GMT+02:00 Bastian Bloessl <bloessl@ccs-labs.org>:

Hi,

On 09/22/2014 03:51 PM, Jean-Baptiste Truffault wrote:

I installed the module as described here:
https://github.com/bastibl/gr-ieee802-11 and tried to use the
examples/wifi_rx.grc file to start. Here begin my problem: using the
same record_source_file, I have several results printed on my console.
It's seems that the module cannot detect OFDM frames.

I'm afraid you have to be a bit more verbose... What did you do? And what exactly went wrong?

Did you follow the steps in the readme?

I'm using Gnu Radio 3.7.2 with USRP N210, my record_source_file is
sampled with 5Msps at 5.127 GHz.

IIRC, you need at least 3.7.3 (will add that to the readme).

Best,
Bastian