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

[Bastian Bloessl]

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