Re: [Discuss-gnuradio] OFDM TX/RX

[CEL]

Oooh, that's a nice plot!
This is way better than I would have anticipated. Can I attribute that
to awesome whitening properties of the code itself and following
scramblers/interleavers?

Marcus
On Tue, 2018-03-27 at 02:31 -0700, Ron Economos wrote:
> CCDF (Complementary Cumulative Distribution Function) is often used to show 
> PAPR probability. Here's what the GNU Radio DVB-T2 transmitter looks like at 
> 32K (27841 active) carriers with an without tone reservation PAPR reduction.
> 
> Ron
> On 03/27/2018 02:09 AM, Müller, Marcus (CEL) wrote:
> > On Fri, 2018-03-23 at 14:21 -0700, Martin Braun wrote:
> > > If you've
> > > increased the number of carriers, PAPR also goes up (a bit).
> > 
> > Yep, by the same factor as you increase the number of carriers (proof
> > idea: time-symbol with worst PAPR is the discrete dirac over the vector
> > of FFT length N. That has a PAPR of N/1 = N if freq domain samples were
> > amplitude-limited to 1.)
> > 
> > The probability to hit a PAPR that bad is, however, limited.
> > Considering an M-PSK modulation on the N subcarriers. Then there's a
> > total of M^N possible time-domain OFDM symbols, but only M·N of these
> > are worst-PAPR, so
> > P(worst PAPR for N carriers) = M·N/M^N = N / M^(N-1)
> > assuming equally likely symbols. Since M^N pretty certainly grows
> > faster than N, your likelihood of ending up in the "worst PAPR"
> > scenario actually drops with N.
> > 
> > The story looks a bit different if you're not interested in the worst-
> > PAPR-symbol, but in all symbols that have a PAPR worse than some
> > threshold, e.g. 20dB. Especially for LTE, there's a lot of
> > simulative/monte carlo PAPR>threshold curves, as things like trading
> > clipping for amplifier efficiency plays a very commercially relevant
> > role there.
> > 
> > Best regards,
> > 
> > Marcus
> 
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