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From: | guillaume.tochou |
Subject: | Re: [Discuss-gnuradio] OFDM TX/RX PAPR |
Date: | Thu, 29 Mar 2018 14:42:18 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 |
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 (proofidea: 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 wereamplitude-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_______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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tx_ofdm.grc
Description: application/gnuradio-grc
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