How are Beamforming and Precoding Related?
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- เผยแพร่เมื่อ 23 ต.ค. 2021
- Explains the relationship between Beamforming and Precoding in multi-antenna communication systems. Also discusses the relationship to Diversity.
Related videos: (see iaincollings.com/)
• What is Beamforming? • What is Beamforming? (...
• What is Hybrid Beamforming? • What is Hybrid Beamfor...
• How does Antenna Spacing affect Beamforming? • How does Antenna Spaci...
• What is Multi Channel Beamforming? • What is Multi Channel ...
• MIMO Communications • MIMO Communications
• What is Multi-User MIMO Communications (MU MIMO)? • What is Multi-User MIM...
• What is Massive MIMO? • What is Massive MIMO?
• How is Data Sent? An Overview of Digital Communications • How is Data Sent? An O...
• How are Data Rate and Bandwidth Related? • How are Data Rate and ...
• What is a Matched Filter? • What is a Matched Filter?
• How are Matched Filter (MF), Zero Forcing (ZF), and MMSE Related? • How are Matched Filter...
• How are Correlation and Convolution Related in Digital Communications? • How are Correlation an...
For a full list of Videos and accompanying Summary Sheets, see the associated website: www.iaincollings.com
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Hi, I am a PhD student from Germany. The explanations are crystal-clear, Thank you so much for your effort, much appreciated.
You are welcome! I'm glad the videos have been helpful.
You make these topics crystal clear to everyone. Thank you very much.
That's great to hear. I'm glad the videos are helpful.
Professor Ian, thank you so much for this video and the video breaking down beamforming in general. I am an undergraduate writing a survey paper on satellite communications and I have struggled for weeks reading through papers about beamforming before discovering your videos. You taught me in two videos what I needed to know to understand what all of these papers are on about. I think you just helped me pass my class!
That's so great to hear! I'm glad you found my video, and that it was helpful.
As a M.S in signal and information processing, I must say Iain you did great presentation here with ease understanding and master of the beam forming methodology. Thank you for the sharing
Thanks for your nice comment. I’m glad you liked the video.
To put it simply, beamforming is a precoding technique where weights are evaluated so as to maximize the SNR.
Thank you so much for the great explanation. I asked this question several months ago in the comments and just now I saw that you posted this video. It was great and I appreciate it.
Glad it was helpful!
I have been looking for this for long time. Thank you alot
Glad you found my video - and that it helped. Have you seen that I've got other videos on related topics too? iaincollings.com
Thank you for these awesome videos. You speak very clearly and take your time to go into great detail. I really enjoyed them.
Thanks for your nice comment. I'm so glad you like the videos!
I did MIMO course not long ago. I wanted to dive into topic about that precoding and beamforming, cuz didn't get difference between both. But i forget to do that, and it was nice surprise from you to remember me.
Time after time, you always nail to choose confusing topics and simply explain them.
I'm glad the video helped. And I'm very pleased to hear that you like the other videos too.
Too many presentations on these technical subject provide either no or ambiguous illustrations.....Ian illustrations perfectly complement his dialogue. Thanks again
I'm glad you like the presentation approach.
Thank you Dear Iain for this clear explanation. I m so glad espacially to see step by step telling progress about beamforming and its types.
Glad it was helpful!
This explanation is really clear~Thank you very much!!!
Glad you liked it.
Great video as always!
Thanks, I'm glad you liked it.
Thanks a lot Sir for the simplicity in explanation
I'm glad you found it useful.
Perfect explanation! Thank you very much !
Glad it was helpful!
谢谢！ You explained it very clearly.
Thanks. Glad you think so!
Thank you so much for the video.
Glad you found it useful.
Super!
Great video! Wish I had seen this video during my PhD period which would save me much time. All the materials use the main/side lobes to explain beamforming/beamsteering but no one uses it for digital beamforming/precoding which made me not clear on the real world effect of precoding. Actually they should be illustrated in a similar way as in this video.
Glad it was helpful! It's great to hear that it's given new intuition.
@@iain_explains Please make a video on Hybrid precoding and why there is a need to optimize the weights.
Superb explanation. Thank you very much sir! 🙂👍👍
My pleasure!
Very informative and helpful video for students! Thanks for sharing
Thanks for watching!
So thanks dear. So useful
Glad it was helpful!
Thank you so much, Professor! ❤
You're very welcome!
Thank you so much.
You're welcome!
Great video and explanations. Is it possible to explain different beam-forming types: Grid of beams, eigen beamforming, MRT, zero forcing etc. ?
Good suggestion, thanks. I've added "types of beamforming" to my "to do" list. Some info can be found in these videos: "What is Multi Channel Beamforming?" th-cam.com/video/e6scR0C4RAc/w-d-xo.html and "MIMO Communications" th-cam.com/video/TC19gMQ6azE/w-d-xo.html
Too good ! Thanks Iain
Glad you liked it!
Hi professor Iian, big big thanks from a new follower. Very helpful explains for wireless engineers and students. Looking forward to more state-of-art topics (5G etc.). If you do not mind, could you please tell about what is the design goal of the coodbook defined in the 3GPP specifications? Is it for minimizing the interference of the system? Thanks a lot.
Welcome to the channel. Glad you like the videos. For 5G topics, have you seen my videos on NOMA in 5G? th-cam.com/video/XCNz32T3ZbA/w-d-xo.html and th-cam.com/video/1P3Si23OsC8/w-d-xo.html . In terms of your 3GPP codebook question, can you be more specific? There are a number of codebooks defined in that standard.
Thank you Professor. You saved us a lot of time to get insight to this topics. Best regards.
Just for other viewers the mixer for frequency trasposition in diagrams with only \theta can be misleading....an exp j \theta is more clear.
Glad it was helpful!
great lecture. thanks
Glad it was helpful!
@@iain_explains why the number of beams formed by a ULA is equal to the number of antennas?
If you have L antennas, then you could send a different data stream off each antenna, and have L data streams - but they would all interfere with each other and you would need L receive antennas in order to be able to "untangle" them (that's what standard MIMO does, by inverting the channel LxL matrix at the receiver). Or, you could pre-invert the channel at the transmitter, which effectively forms L beams, each one carrying its own data stream towards its own single receiver (and there will be L receivers). This is what Multi-user MIMO does. You don't need to pre-invert L streams, you can do less than that if you want. But you can't do more than L, because you only have L degrees of freedom.
Thanks for the video and the explanation, very interesting. So each spatial directions, happens in the same time but in different frequencies? It's difficult to visualize how, let say in your example, an antenna can form different beams in the same time and in the same frequency
Same time, same frequency. This video might help: "What is Multi-User MIMO Communications (MU MIMO)?" th-cam.com/video/0ncIWlhsu1A/w-d-xo.html
Your explanation is always fantastic. Thank you. If we assume SU-MIMO situation, can we understand that we send different streams via different beams through each multipath between BS and one ue??
In SU-MIMO you could do what you describe (that would be called "multi-channel beamforming"). But you could also simply pick the strongest path, and put all the transmit power into just a single beam in that direction (that would be called "beamforming"). For multi-channel BF you need to know all the channel gains, but for plain BF you only need to know the direction of the strongest path. It really comes down to how good your channel estimation is.
Thank you so much! could you tell us if the codingbook approach that is used in this work [Deep Reinforcement Learning for Distributed Dynamic MISO Downlink-Beamforming Coordination] considered digitial or analog?
Very Nicely explained Ian. Can you please follow it up by explaining how the precoding weights/beamforming weights can be derived from the channel esimates. How the channel estimates will be derived from each UE? E.g for beamforming one of the signals used is the SRS signal which each UE transmits in certain freq bands. So does enodeB does a interpolation of the signal across entire frequency to get a complete channel estimate for that particular UE? Thanks once again Ian...
Thanks for the suggestion - it's a good one. This topic has been on my "to do" list for some time. I really need to get onto it. I've just raised it up the priority order.
@@iain_explains Thanks a lot Iain. Really appreciate the way you simply things ... looking forward to your explanation ..
Could you do a video on Carrier Frequency Offset estimation using preambles? (Auto/cross correlation magic)
Thanks for the suggestion. I've added it to my "to do" list.
There's a thumbs up from me, and hello from Mullumbimby - they would love you down here ;)
I've never been to Mullumbimby unfortunately. I'll have to put it on my "to do" list 😁
thanks for the video Iain. Great info! Wondering how beamforming (sending the same data over multiple antennas) work at the same time as Spatial Multiplexing (where different data sent over the same antennas) ??
This video will hopefully help: "What are Spatial Diversity and Spatial Multiplexing in MIMO?" th-cam.com/video/MNA0xn7EeyY/w-d-xo.html
@@iain_explains thanks Iain, really helpful indeed!
thanks for the very clear explanation! in precoding, can happen that the signals have different frequencies? do we still use matrix notation?
The signals that are being precoded are digital baseband. They don't have "frequencies". This video might give more insights to the multi-carrier case: "What is MIMO OFDM?" th-cam.com/video/kaPK58WlG-A/w-d-xo.html
Thank you :)
You're welcome!
Do you have a book? Perhaps a DVD set with all your videos compiled?
I think you are an impressive educational resource that shouldn't depend on TH-cam to outlive yourself.
Thanks for the suggestion. I've been thinking along these lines, but haven't taken any action yet. I need to think about the best delivery model. For now, TH-cam seems to be working pretty well.
At 7:56, if you're talking about beamformers being defined in columns, I don't think that is correct. I think the correct description is that each row defines a beamformer that produces a superposition of all the input data streams, thus giving the desired emission distribution. This would then be multiplied by the inverse CSI matrix to produce the required data stream seen at the UE. Is this an appropriate description in your view?
It all depends on whether you're talking about transmit beamforming or receive beamforming, and whether you write the input/output as a column-vector multiplying on the right hand side, or a row-vector multiplying on the left hand side. In this case, you seem to be talking about receiver beamforming ("that produces a superposition of all the input data streams"), whereas I was talking about transmit beamforming (that puts each data stream onto all of the antennas). For example, you can see from the equation that I wrote, that the data signal c_{1,k} will contribute to the signal that is sent on each of the the antennas (ie. x_{1,k}, x_{2,k}, x_{3,k}), because when the matrix multiplication is done, c_{1,k} will be multiplied by the elements in the first column of the matrix. Therefore the first _column_ is doing the transmit beamforming for the first data stream c_{1,k}.
@@iain_explains I was referring to the transmit side, I was just looking at it in terms of the sum of all signals sent to each antenna, not as each signal being sent to all antennas. As long as all members of the precoding matrix are non-zero and complex, then all signals are sent to all antennas, but with mixed amplitude/phase combinations for each input stream, and that would give the required beamforming for different input data streams.
Yes, that's right.
It seems that in analogue beamforming we can have only one constellation symbol as input (one stream) or in general digital beamforming case many constellation symbols could be used, right ? It's what we called rank indicator ?
Thank you in advance
Yes, that's right.
To do beam forming, you need to send the same symbols on the antennas from the array then precode it.
So how could you serve 3 users (transmitting differents data) with a 3-antennas array simultaneously using beam forming to null the interference between the channels. Or do you need 3 clock cycles?
I think this video will help to answer your question: "What is Multi-User MIMO Communications (MU MIMO)?" th-cam.com/video/0ncIWlhsu1A/w-d-xo.html
So firstly we calculate the channel matrix, than on top of that we adds up some ZF coefficients in to the same matrix ? Is it the same ZF that we have in the uplink ? Could we use ZF interchangeably in DL and UL ?
I'm not sure what you mean by "adds us some ZF coefficients", sorry. Perhaps this video will help to explain ZF more: "How are Matched Filter (MF), Zero Forcing (ZF), and MMSE Related?" th-cam.com/video/U3qjVgX2poM/w-d-xo.html
Great explanation!
Could you please refer me to a good book about precoding and beamforming?
Here are a couple of suggestions. They are both very detailed, and may be more mathematical than you are looking for though - I don't know. D. Tse and P. Viswanath, “Fundamentals of Wireless Communication” and B. Clerckx and C. Oestges, "MIMO Wireless Networks: Channels, Techniques and Standards for Multi-Antenna, Multi-User and Multi-Cell Systems"
@@iain_explains Thank you Professor for your kind and informative reply.
In digital beamforming if i want to transmit 2 independent data streams from a transmitter ULA having 4 elements towards 2 receivers that are placed at different locations, does each data stream is transmitted from half elements of ULA with their corresponding steering vector/ weights? if the data streams are to be transmitted simultaneously
Good question, but no. Both streams will use all the antennas. It's referred to as Multi-User MIMO. See this video for more details: "What is Multi-User MIMO Communications (MU MIMO)?" th-cam.com/video/0ncIWlhsu1A/w-d-xo.html
In the last picture, precoding section,
we have like C_1,k complex symbol intended for user 1, C_2,k complex symbol intended for user 2, C_3,k complex symbol intended for user 3,. For C_1,k to reach user 1 (under high snr or zero forcing case), we adjust the phases and amplitudes across all the antennas such that a beam is generated for user 1 direction. Similarly we adjust the phases and amplitudes to form a beam for user 2, while sending C_2,k. Similarly for C3_k.
But, how do we achieve simultaneous transmission to all three users in the same frequency and time? Doesn't beamforming provide simultaneous transmission possibility ?
The matrix (shown as a 3x3 square of dots) adds all the user's signals together (with appropriate beam forming coefficients - which are the column of the matrix) to give the signals that need to be sent from each antenna, so that all users are sent at the same time and at the same carrier frequency (... each with their appropriate beam former).
Can you please explain MRC, MRT, ZF and MMSE based beamforming design in your futher videos? Moreover, can you explain analog and digital beamforming schemes ?
Perhaps you haven't discovered my webpage yet. I've got videos available on all of those topics. You can find the categorised list here: iaincollings.com
@@iain_explains Thank you for quick response.
Thank you. Haven't you mentioned in another video that in analog beamforming you can only change the phase and in digital beamforming you can change both, amplitude and phase?
Here in analog beamforming you can change both too.
Ah yes, you're right. It's often said that analog beamforming is "phase only" beamforming - but this is generally within the context of hybrid beamforming where the antennas don't have their own seperate amplifiers (due to practical restrictions that relate to the size and number of the antenna elements - typically for mm-wave communications). In general though (at lower transmission frequencies) it is possible to implement a seperate adaptive amplifier for each antenna element, and then you have the case I describe in the bottom left hand picture.
@@iain_explains can it also be that you say that because here the amplifiers are fixed installed and cannot be adapted?
If the amplifiers are not adaptive, then yes, that's right.
@@iain_explains
Dear can u please make a video on open loop codeook based precoding( How UE Knows which index to use?)
BTW your Explanation of the things is the best on the internet.
Thanks.Sir can you please make video for how to draw constellation diagram for 4FSK, 8FSK,.., MFSK.
There's not a "constellation" diagram, as such, for frequency shift keying, since each symbol waveform is at a different frequency. There's really only one degree of freedom (frequency), compared with two degrees of freedom for QAM (amplitude and phase). The equivalent thing would be a single line, to represent the frequency parameter, with dots along it, at the frequencies of the various symbol waveforms.
@@iain_explains Thanks sir.
Hi sir, is precoding still per subcarrier? In 5G/LTE, the DMRS ref signal is not on every subcarrier, how does that precoding operate on subcarriers that has no DMRS on it?
Interpolation is used to estimate the channels in between. You might find this video helpful: "Channel Estimation for Mobile Communications" th-cam.com/video/ZsLh01nlRzY/w-d-xo.html
Please can someone confirm if I understand this well: If beamforming is performed in an analog manner, then the phase shifters are usually time delay lines. BUT, if beamforming is performed digitally, then we can create sinusoids with different phase but without delaying symbols among them, so symbols exactly start and end at the exact same time just having different phases. This would not happen with analog beamforming which would have the exact same sinusoids but with sligth delays between them. I understand that such time delays are negligible when working with high frequencies and symbols that may have tens of thousands of cycles/symbol. But I would like to be sure that this is like I say and I wonder the implications on the receiver side... Thank you.
Yes, that's right.
For digital precoding do antenna spacing play an important role ? When I read some paper, it seems that some author completely ignore this spacing issue and focus on the mathematical formulation stuff instead.
There's an assumption that it's a plane wave. Other than that, it's just the amplitude and phase of the channel gain at each antenna that matters. ... and also an assumption that each element acts as an isotropic antenna (ie. they are not so close together that energy is coupled between the elements.)
Thanks. In Digital Beamforming: you give the same Signal to the single paths (after the base band unit). Is that right?
Sorry, I'm not too sure what you mean.
@@iain_explains
In the upper right picture there you have the white box. I assume that is the Baseband Unit where the digital processing for the digital beamforming take place.
As from there what signal do we have? You give it to three cables which connect to the three antennas. Are that three different signal or is it one signal what you give to every antenna?
Thank You.
Yes, the box you refer to is where the digital beamforming is implemented in baseband. This allows for both amplitude and phase changes to the data symbol coming in from the left of the box (compared to analog beamforming, which only has phase changes). The output from that box shows the three signals (one for each antenna) that each have their own amplitude and phase (determined from the digital beamforming precoding vector), which are then each up-converted using a carrier signal (with the same phase for all antennas). This video might help (it covers the more general Multi-Channel beamforming case): "What is Multi Channel Beamforming?" th-cam.com/video/e6scR0C4RAc/w-d-xo.html
@@iain_explains Thank You, and in Digital Beamforming there is an own RF chain to every antenna as is generally known. So theoretically you can also vary the frequency of every antenna. Is that right?
I guess, it is a bit senseless because one want be economical with the frequency and don't need to take different frequency because of the beamforming.
I was wondering what kind of book can we get this information from ?
You might like to try this one: B. Clerckx and C. Oestges, "MIMO Wireless Networks: Channels, Techniques and Standards for Multi-Antenna, Multi-User and Multi-Cell Systems"
In Digital why do you have to multiply the signal with the phase two times?
one was in the digital Box and then again with the same phase as per your figure.
The "same phase" analog phase change that's on each antenna in the Digital case, comes from the carrier oscillator signal. It doesn't change the direction of the beam, since it's only the relative phase offsets that affect that.
@@iain_explains Just to clarify you mean it's a carrier frequency to transform the signal to passband?
Yes.
Very clear explanation, wish more videos about channel modelling and channel estimation.
Thanks for the topic suggestion. I've got it on my "to do" list. I assume you're already seen the videos I already have on the topic? See iaincollings.com
@@iain_explains Yes professor, I have watched your two estimation video, while I hoping there could be more videos of this topic