What is MIMO OFDM?

Explains some of the different versions of MIMO OFDM from a block diagram perspective.
Related videos: (see iaincollings.com)
• 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...
• Why is the OFDM Symbol Prefix Shorter in 5G Mobile and 802.11ac WiFi? • Why is the OFDM Symbol...
• How are OFDM Sub Carrier Spacing and Time Samples Related? • How are OFDM Sub Carri...
• Why is Subcarrier Spacing Bigger in 5G Mobile Communications? • Why is Subcarrier Spac...
• MIMO Communications • MIMO Communications
• Why doesn't MIMO work in Line-of-Sight (LoS) Channel Conditions? • Why doesn't MIMO work ...
• Quick Introduction to MIMO Channel Estimation • Quick Introduction to ...
• What is Beamforming? • What is Beamforming? (...
• What is Hybrid Beamforming? • What is Hybrid Beamfor...
• What are Spatial Diversity and Spatial Multiplexing in MIMO? • What are Spatial Diver...
• What is Massive MIMO? • What is Massive MIMO?
• What is Multi-User MIMO Communications (MU MIMO)? • What is Multi-User MIM...
• What is Multi Channel Beamforming? • What is Multi Channel ...
For a full list of Videos and Summary Sheets, goto: www.iaincollings.com
.

[@johncgibson4720]

OMG, You are going to really take on this challenge. I was right to sub all along when I first saw your episode with frequency shift.

[@iain_explains]

Glad you're finding the videos useful.

[@AM-tu1rc]

A very complex topic, glad to see yet another great explanation from you

[@iain_explains]

Thanks. Glad you liked it.

[@aplnx]

That is the best explanation that I have ever seen! Congratulations!

[@iain_explains]

Thanks for your nice comment. I'm so glad you liked the video.

[@othmans1]

It will be really great to have transmission Mode session, especially from TM6 to TM9

[@royakhanzade2393]

Very good explanation of a pretty complex topic! Many thanks, Professor!

[@iain_explains]

Glad you liked it!

[@MrAlnaja]

Thank you for a great job. Your explanation is extraordinary

[@iain_explains]

Glad it was helpful!

[@mustaphasadok3172]

Thank you professor. Best Channel for Wireless Communications

[@iain_explains]

Glad you think so!

[@DsBoyan]

Great video! Thanks!

[@iain_explains]

Glad you liked it!

[@aksaichin]

Nice

[@scottshi2909]

Thank you professor! I like the video! May I understand this way for pic2 and pic3? Pic 2 is actually time domain analog BF using phase shifter in RF domain. However, due to OFDM is multi-carrier waveform, phase shifter cannot cover all the subcarriers if channel coherence is small. So a per subcarrier granulity is needed. Pic 3 is actually freq domain digital BF using precoding in baseband. This is still similar to analog BF but it is PER subcarrier phase control instead of using uniform phase for all data per chain. A few questions: For mmWave, the BW will be large, but it seems phase shifter is commonly used for mmWave beamforming (802.11ad/5G). You mention Pic2 may still work in some degree, but would Pic2 still be helpful for mmWave case? since mmWave is usual really large bandwidth (~GHz). WIth Pic3, to make it work well it needs per carrier and per ant channel est. The amount of channel estimates and feedback could be huge, for example for 8 chains and 1024 subcarriers, it would be 8*1024 channel estimates. And also channel can be out dated, would Pic3 be still practical than Pic2 which is more simpler but less efficient? Thank you!

[@iain_explains]

Great comment. Yes, everything you mention is correct. There's still lots to do in research in these areas.

[@pitmaler4439]

Thank You. In pic 3: What does that beamformer exactly do? It gets one stream -does it gives a phaseshift according to the different antennas so that the amplitudes add coherently? That must then happen in the frequency domein, I suggest.

[@iain_explains]

Yes, that's correct. And yes, it's happening in the frequency domain. That's what I point out when I say that BF1 is beamforming the first subcarrier of each antenna. And BF2 is beamforming the second subcarrier of each antenna. And so on. The subcarriers are each at different frequencies. Perhaps this video may help: "OFDM and the DFT" kzbin.info/www/bejne/kGWvepqEnLN0oqs

[@jasminnadic2103]

Thank you, I have a more general question concerning the in- and output of the IDFT. The input must be in frequency domain. How can you imagine that? Is it a function depending on f (e.g. s(f))? Or what data does that block get? There are many lines, does it gets functions with different frequencies (s(f1), s(f2),....)? The output is surely a normal function depending on t e.g. s(t). Thank you.

[@iain_explains]

Perhaps this video will help: "OFDM and the DFT" kzbin.info/www/bejne/kGWvepqEnLN0oqs

[@mustaphasadok3172]

Hi professor, I have some trouble to get more insight in Cyclic Delay Diversity technique used in many MIMO based standards. I can't find a complete reference on the subject. Thank you

[@iain_explains]

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

[@lucidasser7153]

Hallo, I have a short question. With regard to both pics on the left side. In the lower pic, we can adjust phase and amplitude with these BFs. That is clear. But in the upper picture (OFDM Spacial Multiplexing), how do we adjust phase and phase and amplitude there? I assume we must give something like the channel matrix and then we calculate the precoding matrix to multiply it with the symbol vector - but there seems not to be anything like that in the pic. Thanks a lot.

[@iain_explains]

This video should help: "What is MIMO OFDM?" kzbin.info/www/bejne/oZKzfGhujNF6Y6M

[@nelebauer7864]

To allocate the cases into digital and analog beamforming, is it right that only the 2. image shows analog beamforming? Only there you have the phase-shifters at the end.

[@iain_explains]

Yes, that's true. Although even that case could be done with digital beamforming. I didn't discuss where the ADC fits into the design. I've got a video coming up in a couple of weeks, on the topic of Hybrid Beamforming, so keep a look out for that.

[@knutlohmann8205]

Thank you. I know that you can express amplitude, frequency and phase in this notation : Asin(2pif+phi) - I believe that is the polar notation. Can you also express the frequency in the EULER notation? I know the expression Aexp(j*phi). But there you haven't the frequency. Is there anything like Aexp(f+phi)? Thank you.

[@iain_explains]

I think these videos will help to explain it: "How do Complex Numbers relate to Real Signals?" kzbin.info/www/bejne/in26dmZuba-KfdU and "Visualising Complex Numbers with an Example" kzbin.info/www/bejne/nonPZqiOa76mnpI

[@Julia-hu4xe]

Thanks, I refer to the OFDM Multicarrier Beamforming on the lower left side: how do I have to think about that BF1 operation? We are in the frequency domain, that's clear. So for each subcarrier, we get a point in the IQ plane - that is what I know how we "feed" the IDFT. But how does BF1 now beamforms that point in the frequency domain? Does BF1 moves the point a bit within the IQ plane? I hope you understand my question. Thank you.

[@iain_explains]

Great question. Yes, that's right. Transmit beamforming adjusts the phase of the transmitted signal (on each subcarrier) (... and in some cases the amplitude as well) for each antenna, in such a way that each signal adds up constructively in the direction of the intended receiver.

[@agtech4837]

is nice

[@mehmetfatihayten8269]

Hi, thanks for the video, I have a question. In 4G or NR standards, is each subchannel reserved for a user or we are occupying more than 1 subchannel in our mobile phones? If we are using only one subchannel, is it the motivation to use MIMO-OFDM systems?

[@iain_explains]

Short answer: Each resource block allocates users to sub channels per symbol (ie. different OFDM symbols can have different users allocated to different sub channels).

[@agtech4837]

thank you sir.it is interesting topic. i want to ask here is, is there any book which work on peformance analysis of MIMO-OFDMA parameters? like channel capacity of MIMO BER SNR beamforming and any other performance parameters using matlab codes? i hope you read and respond to my question.Thank you!

[@iain_explains]

Sorry, I'm not aware of any books that cover MIMO-OFDMA and have Matlab code.

[@seokchanbaek2951]

Thank you professor. Your videos are really helpful. I have one question: in the pictures above, the output of IDFT block is a baseband signal with frequency ranging e.g., 0 - 20 MHz? And these signals must be upconverted to a carrier frequency, e.g., 3GHz for transmission? Is the beamforming operation in the pictures applied to a carrier wave (or a base band signal)? It is really confusing to me, especially when we consider digital beamforming.

[@iain_explains]

Yes, that's right, the output of the IDFT needs to be unconverted. For digital beamforming the phase-shifts and amplitude scaling is done at the baseband.

[@natanijelvasic]

@@iain_explains Do we ever try to apply beam-forming to the carriers as well as the sub-carriers?

[@franzMTB]

So this meams that multicarriers waveforms like OFDM can not apply to beamforming?

[@iain_explains]

No. It means you need to do beamforming separately on each subcarrier.

[@missingno.8798]

​@@iain_explains​ Hello professor, i wonder does each subcarrier beamform simultaneously throgh the same beamformer in fig.3 ? It seems in fig.2 they go into a same beamformer simultaneously.

[@abdelbarifalloun7362]

hello sir, i sent you a message in researchgate, i enjoy your videos and I want to give me sir any idea about NOMA MIMO especially NOMA, i appreciate any time you can give me. thanks very much

[@iain_explains]

I'm glad you're interested in my videos. Have you seen my videos on NOMA? "What is NOMA in 5G Mobile Communications?" kzbin.info/www/bejne/jnSxq2ZoiZiNmKM and "How does 5G NOMA compare to 4G OFDMA and 3G CDMA?" kzbin.info/www/bejne/Z4GWhJxoaLSmeZo

[@user-im5nj8js5s]

謝謝你，因為你的解釋，讓我聽懂什麼是MIMO OFDM，希望我們能保持聯繫

[@iain_explains]

I'm glad the video helped you.