Re: [Discuss-gnuradio] Pilot Subcarrier in new OFDM PHY

[Tom Rondeau]

On Sat, Jul 6, 2013 at 9:31 AM, YAXIONG XIE <address@hidden> wrote:
> Hi all,
>      I am using the new OFDM PHY to get data from USRP. The new OFDM PHY is
> using pilot subcarrier. I think that it using the pilot because it want
> using pilot to help decode the data subcarrier. But when I checking the
> source code in the channel equalizer, I didn't find any code that using
> pilot to help decoding.
>    According my opinion, the equalizer just updating the channel state and
> didn't do anything except that. We should do interpolation using the pilot
> subcarrier channel state to help decoding the data, right? But the source
> code didn't do that.
>    So I am wondering why the new ofdm PHY code using the pilot.
>    Thanks
>    Yaxiong
>
> --
>
> Yaxiong Xie


Correct, currently the pilots are not being used. This is future work
for the OFDM project.

You still need to declare which subcarriers are pilots at the
receiver, though, so that you know not to try and use them for data.

The current implementation uses a 1-tap equalizer that is calculated
based off the preamble. For slowly changing channels, this is ok and
you can still receive the entire packet. Obviously, using the pilots
throughout will be more robust and handle other channel conditions,
and we really look forward to seeing this implemented :)

Tom