What is PAPR? and its relationship to OFDM

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Iain Explains Signals, Systems, and Digital Comms

3 жыл бұрын

Explains the Peak to Average Power Ratio (PAPR) and shows why it is important for OFDM digital communications. Sometimes this is also called Peak to Average Ratio (PAR).
Related videos: (see iaincollings.com)
• OFDM Waveforms • OFDM Waveforms
• OFDM and the DFT • OFDM and the DFT
• What is a Cyclic Prefix in OFDM? • What is a Cyclic Prefi...
• How does OFDM Overcome ISI? • How does OFDM Overcome...
• How are OFDM and xDSL (DMT) Related? • How are OFDM and xDSL ...
• What are Channel Capacity and Code Rate? • What are Channel Capac...
• What is Water Filling for Communications Channels? • What is Water Filling ...
Full categorised list of videos with PDF Summary Sheets: iaincollings.com
Note that when discussing the OFDM case (top right hand drawing showing the five waveforms), I wanted to keep the diagram simple, so that I could explain the "phase alignment" problem, so I didn't draw waveforms for all the carriers. I probably should have mentioned it, but I only drew waveforms for the following multiples of the base frequency: 1, 2, 4, 8, 16. It was too complicated to draw all the other multiples (3, 5, 6, 7, 9, 10 ...). Also note that the diagrams I showed are "baseband". In other words, I didn't show them after they are up-converted to the carrier frequency
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Пікірлер: 46

@AbuSous2000PR Жыл бұрын

you make what is difficult... very easy and fun to learn

@iain_explains Жыл бұрын

That's so great to hear. I'm really glad you like the videos.

@ankitsinha4124 3 жыл бұрын

Your videos are pure delight to watch. Thanks a lot

@iain_explains 3 жыл бұрын

Glad you like them!

@raedal-moussawy4737 3 жыл бұрын

Excellent Explanation

@user-oo7lv7bj7x 3 жыл бұрын

Thanks for your sharing! But I have a problem. How does the PAPR affect the digital beamforming process? Looking forward to your detailed answer.

@rushabhpatel573 3 жыл бұрын

Thanks iain. J have never liked signals nd systems in my college. But your videos have made me fall in love with it.❤️

@iain_explains 3 жыл бұрын

Glad you like them!

@mohamedahmedellban6312 3 жыл бұрын

thank you so much

@danikay321 3 жыл бұрын

Very nice and clear video! Thanks!

@iain_explains 3 жыл бұрын

Glad it was helpful!

@ananthakrishnank3208 2 ай бұрын

I'm glad that I found your channel ;)

@iain_explains 2 ай бұрын

Welcome aboard!

@saa7913 5 ай бұрын

عشت ❤❤

@saa7913 5 ай бұрын

مشكور ❤❤🎉

@RajasubramaniamBalakrishnan 3 жыл бұрын

Very helpful, Thank you.

@iain_explains 3 жыл бұрын

Glad it was helpful!

@mehmetfatihayten8269 Жыл бұрын

Good tutorial, thanks Iain !

@iain_explains Жыл бұрын

Glad it was helpful!

@YGurin-gw7su Жыл бұрын

Thanks! So how to deal with that? Is CFR will be enought? How artifical reduction of the peak affect the signal?

@whyargon 2 ай бұрын

legendary explanation

@iain_explains 2 ай бұрын

Thanks.

@yasserothman4023 3 жыл бұрын

Thanks for sharing may I know how did single carrier fdma solved this problem by adding n point dft block before the m point ifft where n

@iain_explains 3 жыл бұрын

Thanks for the suggestion. I've added it to my "to do" list.

@linn8007 3 жыл бұрын

Thank you so much

@iain_explains 3 жыл бұрын

You're most welcome

@zeeshanahmad2786 5 ай бұрын

I think PAPR mostly impact TX PA efficiency, that was a must aspect to explain

@bacnguyenkhac154 2 жыл бұрын

Very useful !! Thank you, sir !

@iain_explains 2 жыл бұрын

Glad it was helpful!

@bacnguyenkhac154 2 жыл бұрын

@@iain_explains beside PAPR factor, as i know that sensitive to carrier offset and drift also has influence on Ofdm signal, i hope in the future you will have a lecture like this to explain about that. It will be very helpful and i really appreciate what you've contributed, sir

@iain_explains 2 жыл бұрын

Thanks for the suggestion, I've added it to my "to do" list.

@werdasize 2 жыл бұрын

So just to clarify, when you say perform IDFT you mean that we first add all the carrier signals in the frequency domain and then take it back to time domain to see the combination (something like that peak you draw). The diagram with carriers is in the time domain, that’s why I got confused.

@iain_explains 2 жыл бұрын

Yes, the "carriers" are in the time domain. They are time domain waveforms at their given frequency. All real signals (ie. signals that exist in the real world) are time domain signals. I think you are confusing things when you say "add all the carrier signals in the frequency domain". If you are adding things in the frequency domain, then only things with the same frequency will add together (at each frequency). Signals at different frequencies don't "add together in the frequency domain". But two time domain signals at different frequencies can add together in the time domain. Hope this helps.

@ebeb9156 Жыл бұрын

But didnt we use fixed point FFT and choose "power window" relative to noise floor? (FFT shifts) In that case we at risk of saturation inject "colour noise" to whole symbol, instead of compression problem

@dahlia2631 3 жыл бұрын

Thanks for the post... One query..in ofdma the subcarrier division is equal ryt...like say LTE each subcarrier will be 15KHz so this c1,C2,c3 waveforms u mentioned will not be applicable ..so how PAPR explains for ofdma? For this reason Uplink uses SC -Fdma ryt

@iain_explains 3 жыл бұрын

Yes you're right - for the waveforms that I drew. I wanted to keep the diagram simple, so that I could explain the "phase alignment" problem, so I didn't draw waveforms for all the carriers. I probably should have mentioned it, but I only drew waveforms for the following multiples of the base frequency (ie. the 15 kHz frequency in the example you mention): 1, 2, 4, 8, 16. It was too complicated to draw all the other multiples (3, 5, 6, 7, 9, 10 ...). Also note that the diagrams I showed are "baseband". In other words, I didn't show them after they are up-converted to the carrier frequency (I'm pretty sure you realise that already). Thanks for your comment.

@tasheido 3 жыл бұрын

How would variable gain affect the OFDM system? I mean using compression enhancing the signal near the average and compressing the peaks. And doing the opposite at the receiver side.. ?

@iain_explains 3 жыл бұрын

Good idea. And these sort of things are done in some systems. The problem is to design and implement the non-linear amplifier that would be needed. An alternate is to use non-uniform sampling levels, with more levels at the lower voltages. Other schemes are also used, which check for peaks in each symbol before transmission, and then rotate some subcarriers to reduce the peaks. For these schemes, it is necessary to set aside some data bits in the symbol in order to let the receiver know which subcarriers were rotated.

@tasheido 3 жыл бұрын

By “rotating carriers” you mean rotanting the phase to another constellation point on some carriers? Or to move a specific datapoint on the data stream to a different carrier according to some rule? (Like a scrambler) or is it something else? Seems like a good idea. And BTW Iain thank you for the video series, its a great primer on these topics Good work!

@iain_explains 3 жыл бұрын

"Yes", to your first question. "No", to your second question. And thanks, I'm glad the videos are helpful.