What is Water Filling for Communications Channels?

[@anb9840]

Ahmad Bazzi has a very nice video explaining water filling from a convex optimization perspective.

[@rushabhpatel573]

such lucid explaination. Thanks Iain!

[@iain_explains]

Glad you liked it!

[@minoh1543]

Thank so much sir! it is very helpful for intuitive understanding.

[@iain_explains]

Glad it was helpful.

[@tuongnguyen9391]

Wow water filling with concrete numerical example ! I really appreciate this !

[@iain_explains]

Glad it was helpful!

[@gamingandmusic9217]

Please make videos on OFDM time and frequency synchronisation.
explain schmidl cox algorithm for frequency and timing correction.

[@iain_explains]

Thanks for the suggestion. I'll see what I can do.

[@truptiwagh1941]

Thank you..Very nice conceptual explanation

[@iain_explains]

Glad you liked it

[@alimuqaibel7619]

Thanks for the excellent explanation

[@iain_explains]

I'm glad you liked it.

[@tamaldatta9311]

Thanks,, Your explanation is very precise and easy understandable.. Can you please upload video on SCFDMA.

[@iain_explains]

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

[@sporech9374]

Thank you for explaining clearly! One question, where do the coefficients of 0.8 and 0.7 in front of the power come from?

[@iain_explains]

I just chose those values as examples. As I explain later in the video, at the 10:50 mark, DSL channels have this general functional relationship with frequency (where the gain of the channel drops off with frequency).

[@martagavilan5948]

Thanks your explanation really helps a lot

[@iain_explains]

Glad to hear that!

[@behnazm430]

Thanks! You explained the concept very clear and understandable! I wish you had videos on reverse water filling in information theory!

[@iain_explains]

Thanks for the suggestion. I'm not really familiar with that topic, but I'll look into it.

[@dimitrisv.1729]

Sorry if i am wrong. This video assumes 1 transmit antenna, right?
Also, in your example we try to estimate the number of subchannels(N) given Pt.
In OFDM systems, N is determined by the length of IFFT and all of them have to be utilized in order to transmit an OFDM symbol. So we have to find the K, which satisfies N subchannels and then we decide the required Pt. Is it right?

[@iain_explains]

Note that water filling is not limited to wireless communications. However, yes, in the wireless case, the video shows the situation for a single antenna scenario. In the case where OFDM (wireless) or DMT (wireline, DSL etc.) are being used, yes, the length of the vector is fixed in the respective standard. However it is not necessary to put energy into each subcarrier in the OFDM/DMT symbol. And likewise it is not necessary to put equal energy into each subcarrier. This can be done by using different constellations in each subcarrier, with different powers. Of course, as I mentioned, water filling requires knowledge of the channel, so it is generally not used in wireless communications with rapidly fading channels.

[@karamany9870]

could you recommend books that cover these information theory topics?

[@iain_explains]

This is a good introduction to Information Theory: T.M. Cover and J.A.Thomas, “Elements of Information Theory”

[@朱时捷]

Thanks! Could you teach us more knowledge about Network Information Theory?

[@iain_explains]

Good suggestion, thanks. I'll add it to my "to do" list.

[@leslierusch1705]

Thanks!

[@AllYourMemeAreBelongToUs]

13:38 Water filling