Gr-ieee802-11: connecting two usrp devices

Dear All,

I need your help. May be someone did it before:

I use ‘IEEE 802.11 a/g/p OFDM Transceiver’ project, Ubuntu 13.04,
GNURADIO 3.7.

I start the transmission using the first laptop and USRP N200 device by
running the ./ofdm_tx.py.
It is transmitting;

Meanwhile I use the second laptop and USRP N200 device as the receiver
by running the ./ofdm_rx.py.
I activated the ofdm_decode_mac debuging function to see the messages.

The problem is that all frames are dropped. The copy paste of the
terminal is below:
SHORT Frame!
SHORT copied 1039
Decode MAC: input 7
Decode MAC: frame start – len 153 symbols 7 encoding 6
received complete frame - decoding
coding rate 0.666667
2016
80 1f 3a c7 6f b6 fb 4e 7a 24 e8 6d 23 bb 44 a2
60 24 21 26 93 3e d8 98 e0 df 0f 0f 8a ba 3c d2
a5 a4 68 13 71 e8 56 bd ec 4c 79 ea 5a 9b 7d e0
1a ae 3b 3d 8c 68 93 7c b6 ca 3b 08 33 70 73 78
6c 23 47 a2 9d 01 e4 e0 3e 73 6a 84 8f fb 23 a8
01 fa 13 40 6e 62 96 3d 53 76 f6 09 2d fe 4e bd
3e cc 79 97 71 e3 22 1c c7 54 5c 36 5f 50 24 fb
2f f3 41 0f 1e a7 30 c2 9d 71 cc 66 b5 8f 9f 97
94 ba f4 b9 48 27 28 f6 c8 d9 b4 81 75 56 f3 43
f8 98 9d 5d a8 aa 1a 49 85 1a 22 fc 70 e2 20 d1
48 6d 6a 8c 26 c3 ae
…:.o…Nz$.m#.D.`$!&.>…<…h.q.V…Ly.Z.}…;=.h.|…;.3psxl#G…>sj…#…@nb.=Sv…-.N.>.y.q."…T\6_P$./.A…0…q.f…H’(…uV.C…]…I…".p.
.Hmj.&…
Checksum wrong – dropping
Do you know what can cause this?

Thanks in advance!

On 2013-12-02 13:25, Nasi wrote:

The problem is that all frames are dropped. The copy paste of the
terminal is below:

Did you play around with the gain and see if that helps?

Is frame detection working or are you just streaming samples into the
flow graph that make absolutely no sense?

Decode MAC: input 7
Decode MAC: frame start – len 153 symbols 7 encoding 6

What are you sending? Is it correct until this point?
This is a QAM64 2/3 modulated 153 byte frame. Did you send this?

Did you try other modulation and coding schemes?

Bastian

Hi,

Thanks for reply!

Did you play around with the gain and see if that helps?
That did not help. The problem is that in the file ‘’ the code always
checks for the value:

if(result.checksum() != 558161692) {
dout << “checksum wrong – dropping” << std::endl;
return;
}

I am not familiar with CRC. Why does it check always for 558161692?
Another important and strange thing is that in the transmitted frames
CRC is always different than the receiver side CRC value (I print them
to see that).

Is frame detection working or are you just streaming samples into the
flow graph that make absolutely no sense?
I did not change anything in the flow graph: the message strobe is
connected with -> OFDM MAC block.
How can I activate frame detection? I thought that is by default. I run
ofdm_rx file usually. May that is the reason…

Decode MAC: input 7
Decode MAC: frame start – len 153 symbols 7 encoding 6

What are you sending? Is it correct until this point?
This is a QAM64 2/3 modulated 153 byte frame. Did you send this?
Not actually. I send BPSK 1/2 always. How can it be like this?

Did you try other modulation and coding schemes?
I will try. I go mad because of this does not work.

It seems like I receive everything wrongly in the device. That looks
like a device problem.

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