Bastian Bloessl-2 wrote > Hi, > > I only have some tips that you might want to try. > > - set the lo_offset to 11M > - use the LMS equaliser (the other one is total non-sense :-) > - change the gain > - use the 5GHz band or assert that it’s really purge-G (non-compatible > mode) > > The last one is important. In the 5GHz-band you usually have 11a, which is > perfectly fine. > In the 2.4GHz band 11g is often in a mode that is backwards compatible > with 11b. This mode uses a different preamble that is currently not > supported. > > Some APs (or a MacBook) can be configured to use 11g-only mode. These > frames should work. > > Best, > Bastian > > >> On 09 Dec 2015, at 17:50, Ke Xu <
> kexukezhao@ > > wrote: >> >> Hi everyone! >> I am a beginner of GNU Radio and i'm studying 802.11 recently.I >> found >> a very nice work in https://github.com/bastibl/gr-ieee802-11/tree/master >> and >> it does me a great favor. I connected two USRP B210,one run wifi_tx.grc, >> the >> other run wifi_rx.grc, it worked and i can see the decoded "hello world" >> in >> my terminal.But when i use the wifi_rx.grc to receive existing WIFI >> signal(such as wifi in home) to get the AP' SSID,it failed,i got nothing >> but >> disorder code(i enabled the debug in OFDM Decode MAC block).It seems that >> the flow breaks in the checking checksum step because the checksum is not >> equal to 558161692,the OFDM Parse MAC block has never been excuted. >> What shall i do? Chould the wifi_rx.grc receive existing WIFI signal >> correctly? I notice that the receiver is limited to BPSK and QOSK, does >> this >> caused the problem? I'm not familiar with CRC, can anyone explain why the >> checksum is a constant? >> Thanks in advance! Any advice will be welcome! >> > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@ > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio Hi,Bastian Thanks for your advice and time. I have tried what you have said. I use a wireless router as the AP, as it does not support 11a, I cannot use the 5G band, but it support '11g-only', so i set it to this mode. And in my testbed, there are many other APs, i have no idea which mode they operate on. I also annotate the checksum operation in 'OFDM Ddcode MAC' block because if don't, I will get nothing output in my terminal. I set the sample rate of my USRP N210 to 20M. Sometimes I can get some meaningful string output but it is not sent by my AP. I also get some beacon frames rarely, however its decoded SSID is messy code. What confused me is that I can see a lot of decoded mac address which belong to other APs in my testbed and none for my own AP. Best regards, Ke Xu -- View this message in context: http://gnuradio.4.n7.nabble.com/How-to-receive-existing-AP-s-signal-using-gr-ieee802-11-tp57253p57272.html Sent from the GnuRadio mailing list archive at Nabble.com. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
