# Re: How many preambles uesd in ofdm example for frame synchronization, 10 short preambles?

Thanks for your reply. I still have one question. I try to plot the peak
detection data to observe the the shape of the peak, which seems like
a plateau(square wave).I have done a simulation before in matlab. If
only
one preamble exist, when the 1st half of the preamble correlate with 2nd
half, the shape of peak should be much sharper(like a triangle), because
the repeated pattern is not enough.
My question is :
If gunradio only use one preamble with 2 repeated pattern, the shape of
the
peak should look like a triangle rather than a plateau, is that right?

2013/4/6 Tom R. [email protected]

On Sun, Apr 07, 2013 at 11:49:14AM +0800, Yingjie C. wrote:

Thanks for your reply. I still have one question. I try to plot the peak
detection data to observe the the shape of the peak, which seems like
a plateau(square wave).I have done a simulation before in matlab. If only
one preamble exist, when the 1st half of the preamble correlate with 2nd
half, the shape of peak should be much sharper(like a triangle), because
the repeated pattern is not enough.
My question is :
If gunradio only use one preamble with 2 repeated pattern, the shape of the
peak should look like a triangle rather than a plateau, is that right?

No, the plateau is correct. Since your correlation window is 2x half of
1 symbol, the cyclic prefix will increase your peak (in AWGN channels to
the length of the cyclic prefix).

MB

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

Dipl.-Ing. Martin B.
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

Thanks for your reply, Martin. I still have one question. I have done
the
simulation for PN peak normalization process in matlab. I try to plot
the
P(refer to correlation result between 1st half and 2nd half) and R(refer
to
the power of 2nd half symbol) . However, when I plot the P and R in the
same picture using gr_plot_float in gnuradio, the curve seems different
my
simulation result. The R curve seems to be up-side-down against P curve.
Please check the attached file for reference. Thank you again.

2013/4/8 Martin B. (CEL) [email protected]