Re: [Discuss-gnuradio] IEEE 802.11 a/g/p transceiver - Data not being received at any frequency other than 5.89G

[Bastian Bloessl]

Hi,

On 01/24/2017 12:17 AM, Qurat-Ul-Ann Akbar wrote:
> I did the following things that you suggested:
>
> 1) The gain is normalized and in the example file wifi_rx and tx it was
> set to 0.75. I changed the gain to a bunch of values but nothing is
> really changing. Also the scope plot in the receiver just shows noise
> and even when I get some decoded message on the console I don't see
> anything changing in the scope plot and the constellation plot is random
> as well during the transmission. At 5.89 GHz (which is default in the
> script when I downloaded it), it shows some packets on the console with
> random sequence numbers but doesn't work at all at any other frequency
> which I set by the frequency in the GUI.

I don't understand what exactly you are doing. The module is 
creating/decoding a baseband signal. It just instructs the hardware to 
tune to a certain frequency. So if your device works only on one 
particular frequency, it might be an issue of the device, the 
interference on the other channels, the antenna, etc ...

However, I think that it is much more likely that you changed something 
in the flow graph and forgot to put the "freq" parameter properly in the 
HW source/sink. Maybe one device is not retuning when you click the GUI.


> 2) I followed the instructions for testing wifi_rx with a wifi card on
> your page. The beacon frames are not being detected by wifi_rx and
> nothing gets printed on the console. I dont know whats wrong exactly. I
> have tested my setup with a simple script sending a single and double
> tone message at a frequency of 2.5 GHz and its successful so I dont
> think its a hardware problem.

Make sure that these are 11a or 11g beacons (OFDM). Not 11b or some 
compatibility mode. You will have to set the sample rate to 20MHz.

> Can you kindly tell me what could be going on ?


Sorry, but I have no idea. Make sure that there are no 
overruns/underruns ('O's and 'U's printed on the console).

Best,
Bastian



> Thanks a lot,
> Annie
>
> On Wed, Jan 18, 2017 at 12:24 AM, Bastian Bloessl <address@hidden
> <mailto:address@hidden>> wrote:
>
>     Hi,
>
>     On 01/17/2017 11:57 PM, Qurat-Ul-Ann Akbar wrote:
>
>         1) The sequence numbers are not in accordance with the data.
>         Sometimes
>         the first packet I get has sequence number 0 but at other times
>         I get
>         sequence numbers like 5 or 41. The mac frame length is 524. An
>         example
>         sequence numbers pattern was 5,36,452,753,961. I do not
>         understand why
>         are the sequence numbers random? The antennas are very close to each
>         other so shouldn't the packet loss rate be very low? And are packets
>         corrupted and GNU Radio can not decode them properly?
>
>
>     The unreliability can have multiple reasons, like
>     - too high gain
>     - too low gain
>     - overruns/underrruns
>     - DC offset (try different LO offsets)
>
>     The constellation plot is usually a good indicator how good it works.
>     Placing the USRPs side by side doesn't always make things better.
>
>
>         2) My transmission does not work for any frequency other than
>         5.89G. I
>         can't understand what could be the reason for this. Not even
>         5.88G. My
>         daughter board supports 1.2G to 6GHz.
>
>
>
>     Can you describe a bit more verbose what you did and what happened?
>     Actually, that should work by just changing the frequency in the GUI.
>
>     To debug, it might also be helpful to test your setup with a WiFi
>     card. This is helpful to understand if the problem is in the sender
>     or the receiver.
>
>     Best,
>     Bastian

--
Dipl.-Inform. Bastian Bloessl
Distributed Embedded Systems Group
University of Paderborn, Germany
http://www.ccs-labs.org/~bloessl/