Re: [Discuss-gnuradio] Successful transmission in gr-ieee802-11 with adding extra samples (before OFDM preamble)

[Bastian Bloessl]

On 2014-11-29 12:34, Isen I-Chun Chao wrote:
> Okay, I got it.
>
> One more quick question.
> I have been pretty confused about what the sync long and sync short are,
> respectively, responsible for?

Sync short is for frame detection and searches for the cyclic pattern of 
the short preamble (autocorrelation). Once a (potential) frame is 
detected, sync long correlates sync_length samples with the long 
preamble and searches for peaks to align OFDM symbols.


> Thanks.
>
> /Best Regards,
> Isen I-Chun Chao/
>
> On Sat, Nov 29, 2014 at 6:29 AM, Bastian Bloessl <address@hidden
> <mailto:address@hidden>> wrote:
>
>
>
>     On 2014-11-29 12:28, Isen I-Chun Chao wrote:
>
>         Hi Bastian,
>         Thanks for your reply.
>         The peaks you mentioned is like the correlation result?
>
>
>     Yes, exactly
>
>
>         /Best Regards,
>         Isen I-Chun Chao/
>
>         On Sat, Nov 29, 2014 at 6:21 AM, Bastian Bloessl
>         <address@hidden <mailto:address@hidden>
>         <mailto:address@hidden <mailto:address@hidden>>> wrote:
>
>              Hi Isen,
>
>
>              On 2014-11-29 07:01, Isen I-Chun Chao wrote:
>
>                  Hi,
>                  I am using gr-ieee-802-11 and putting a custom block,
>         which is
>                  responsible for adding a 90-sample preamble at the head
>         of incoming
>                  sample stream, right after the output of WiFi PHY Hier,
>         as attached
>                  figure, generator.png. So the sample stream is changed
>         as attached
>                  figure, adding_preamble.png.
>
>                  However, in the case of use of transceiver.grc, I can still
>                  successfully
>                  decode received data, which is keep printing out "Hello
>         World!".
>
>                  Does anyone know why adding extra samples at the head of
>                  transmission
>                  samples does not affect the receiving results? Does it
>         because
>                  somewhere
>                  in Rx side detect the OFDM preamble so the payload can
>         be normally
>                  processed without being affecting by the extra samples
>         placed before
>                  OFDM preamble?
>
>
>
>              The sync long block does matched filtering with the long
>         preamble
>              and searches for peaks in a configurable window (sync length
>              parameter). Looks like even if you add 90 symbols the peak
>         that the
>              block is looking for is still in the window.
>
>              Best,
>              Bastian
>
>
>
>     --
>     Dipl.-Inform. Bastian Bloessl
>     Distributed Embedded Systems
>     University of Paderborn, Germany
>     http://www.ccs-labs.org/~__bloessl/ <http://www.ccs-labs.org/~bloessl/>

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