Re: [Discuss-gnuradio] What are coase freq. estimation and fine freq. estimation in OFDM? Did the implementation in gnuradio follow the 802.11 standard?

[Yingjie Chen]

Thanks for you reply, Tom.

 So what you mean is that gnuradio only use one symbol to do the time & frequency (including coarse and fine)synchronization, as well as CSI estimation, is that right?

 You also said the coarse freq. offset estimation is slight different. Can you show me some references only related to coarse freq. offset estimation in gnuradio. Thanks in advance.

Best,

Kay

2013/4/15 Martin Braun (CEL) <address@hidden>

On Sun, Apr 14, 2013 at 03:57:31PM +0800, Yingjie Chen wrote:
> Hi guys,
>
> I have check the 802.11 standard before. It said the coase freq. estimation is
> done in short preamble, and the fine freq. estimation is done in long premable.
> However, to my best knowledge, gnuradio only uses one preamble for
> synchronization. So how are these two freq. estimation works done in one
> preamble. BTW, can anyone tell me the exact different between coase one and
> fine one? Are they both related to the FFT bin aligning?

The OFDM stuff in GNU Radio has *nothing* to do with 802.11x. It's just
a more-or-less generic OFDM implementation.

I very much so recommend reading the Schmidl & Cox OFDM sync paper [1];
their algorithm is pretty much what is used GNU Radio. It also explains
the difference between coarse and fine frequency offset (short: coarse =
integer multiples of sub-carrier offset, fine=smaller than that).

In the original paper, they suggest 2 symbols for synchronisation (of
time & frequency) as well as initial CSI estimation. This can also be
done with 1 symbol, which is done in the current OFDM stack.

The OFDM work that was recently added can handle both 1 or 2
sync-symbols; the estimation of the coarse freq. offset is slightly
different for these cases.

However, this type of sync needs modification if you want to adapt it to
802.11.

MB

[1] Schmidl, T.M.; Cox, D.C., "Robust frequency and timing
synchronization for OFDM," Communications, IEEE Transactions on ,
vol.45, no.12, pp.1613,1621, Dec 1997




--
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

_______________________________________________
Discuss-gnuradio mailing list
address@hidden
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio