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Re: [Discuss-gnuradio] How to receive existing AP's signal using gr-ieee

From: Bastian Bloessl
Subject: Re: [Discuss-gnuradio] How to receive existing AP's signal using gr-ieee802-11?
Date: Thu, 10 Dec 2015 09:46:34 -0800


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.


> On 09 Dec 2015, at 17:50, Ke Xu <address@hidden> 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! 

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