How do you reduce the PAPR with existing block in GRC ?
I've tried with Scrambler->Encoder CCSDS->Interleaver but it doesn't
seems to work. I'm still not having any signal at the output of the OFDM
receiver.
Guillaume
Le 27/03/2018 à 11:58, Ron Economos a écrit :
Yes, I think the whitener does the trick. If you plot the PAPR of band
limited white noise, it's pretty much the same curve.
Ron
On 03/27/2018 02:36 AM, Müller, Marcus (CEL) wrote:
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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