D means that your network card dropped packets. That usually only happens if your computer is CPU-overloaded, so that the Operating system can't keep up with getting data from the network card. Of course, dropped packets mean that your received signal is irreparably damaged.
You'll need to find a way to reduce CPU usage (hard) or get a faster PC. Best regards, Marcus On 01/26/2017 05:06 PM, Qurat-Ul-Ann Akbar wrote: > Hi, > > I changed the sample rate to 20 MHz and changed the beacon frames to > be 11g and now the receiver receives some WiFi packets. But it shows a > parse error which says : > > new mac frame (length 10) > ========================================= > frame too short to parse (<20) > WIRESHARK: received new message > message length 10 > WIRESHARK: d_msg_offset: 0 to_copy: 43 d_msg_len 43 > WIRESHARK: output size: 32768 produced items: 43 > > And there are some "Ds" printed on the console as well. I read through > the previous threads about the frame not being able to parse but > didn't find anything useful. I checked Wireshark and the packets make > sense over there and I can see the different beacon frames and RTS/CTS > transmissions as well. I also saw your wifi receiver video on Youtube > and my constellation plot looks nothing like yours. Its very random. > Can you kindly tell me what you think could be going on ? > > Best, > Annie > > On Tue, Jan 24, 2017 at 1:25 AM, Bastian Bloessl <[email protected] > <mailto:[email protected]>> wrote: > > 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 > <[email protected] <mailto:[email protected]> > <mailto:[email protected] <mailto:[email protected]>>> > 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/ > <http://www.ccs-labs.org/%7Ebloessl/> > > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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