Statistical Modelling of MIMO Communication Channels

[@davebordenkircher8131]

This is of great help to me in my research project. Thank you for the excellent video. I have been an avid watcher since I was a second year.

[@iain_explains]

I'm so glad you're finding the videos useful. It's great to hear.

[@someguy1507]

Hello professor, First, thank you for all the help you give us with your videos! I have a small question though: You mentioned at the start of the video that the elements of the H vector can be modeled as i.i.d. samples of a normal distribution with a mean of 0. My understanding of H is that each value is a gain value, where the magnitude is how much the signal is amplified/attenuated, and the phase is how much the signal is delayed/out-of-phase. With this assumption, then: why is the mean of this sample zero? Isn't perfect reception, where an antenna receives the waveform with no gain or phase offset, the value "1"? This makes me feel that this should be the "average" value, as a mean of 0 implies that the "average" antenna does not get a signal at all, or gets a very highly suppressed signal, which doesn't sound right. If we assume that even a slight change in the environment can completely change the phase of the signal, then shouldn't the random number be formed with a normally distributed magnitude of mean 1, and a uniformly distributed phase? Am I just overthinking this?

[@iain_explains]

Hopefully this video helps: "What is Rayleigh Fading?" kzbin.info/www/bejne/Y3eyn4x4j5yNnLM

[@someguy1507]

@@iain_explains That explained literally everything I had on my mind. Thank you so much!

[@mopol4400]

hello Mr first thank you for all these information. what is spatially correlation channel in a short answer please ?

[@iain_explains]

Spatial correlation at a receiver is when transmission paths (that are random and depend on the location of the user, the base station and the scatterers) are more likely to come in (for receivers), or go out (for transmitters), from certain directions, compared to other directions. In other words, the communication paths are random, but there is correlation in the angle parameter between different paths. An example is explained at the 4min mark of the video.

[@amitbora6336]

Hi professor, I have a doubt. We know that due to the diversity, a 4x4 MIMO system has better BER performance than a 2x2 MIMO system. But how about in a spatially correlated channel? Will the BER of a 4x4 spatially correlated MIMO system be worse than a similarly spatially correlated 2x2 MIMO system? Thanks a lot, and wish you merry Christmas and a very happy new year!

[@iain_explains]

It all depends on the spatial correlation. However, in general, having more antennas is better.

[@tianyuez]

Dear Professor, thanks for your great lectures! I've been watching your videos for 5 hours and they taught much more than my professors taught me in 4 years! And by the way, is it possible for you to give some lectures on OTFS, which is a very hot topic today? And do you think it is good research idea to integrate radar with communication? Many thanks!

[@iain_explains]

Thanks for your comments. I'm so glad you have found the videos useful. And yes, thanks for the suggestion, OTFS is up near the top of my "to do" list. Hopefully I'll have a video on it in the next few weeks.

[@tianyuez]

@@iain_explains Thanks you very much professor. Looking forward to your videos on OTFS.

[@mohamedessam4704]

Hello sir, I found out that the spatial correlation matrix for 2 transmitting antennas and 2 receiving antennas (2x2 case), is a 4x4 Matrix I thought for the (2x2) case, I would have a spatial matrix of size (2x2) I need to know how to get the H matrix(impulse response) given the spatial correlation matrix and say for example H11 only how to calculate the rest H12 and H22 etc.. if you have an explanation for that I would be very thankful

[@iain_explains]

The spatial correlation matrix is shown in the video (bottom centre of the page). It is the Kronecker product of R and S. So yes, in the 2x2 antenna case, the spatial correlation matrix is 4x4. To generate channel values, use the formula in the middle of the page. Generate H_w by filling it with zero mean unit variance Gaussian values, and then multiply by R^(1/2) and S^(1/2), as shown.

[@saitejabhushanam4232]

sir, while watching your video on cosine with some phase I got a doubt In the magnitude spectrum of cos(wot), how can it have magnitudes at 2 frequencies as Sinusoidal signals should have only one frequency right?

[@iain_explains]

I think you must be referring to the delta at w_o and the other one at -w_o. It would be a good idea to watch my video "What is Negative Frequency?" kzbin.info/www/bejne/nauZcn6NYrdpb9U