Thank you professor. A simple question: how do we know the number of paths, L? Is it something that needs to be estimated a priori? Also, in directional channels, do we need to estimate the direction (e.g. DOA) of each of the L paths? I think estimating the number of paths and their directions is very common in radar, but not sure about wireless communications. Also, it would be appreciated if you can make a lecture about the common types of channel models for sub-6 GHz and mmWave band.
We generally don't know how many paths there will be, but we can estimate it. Do we need to estimate it? Not necessarily in communications, since we are not interested in obtaining the location of the user (as in radar) but the content of the signal that the user is transmitting. But if the number of paths is small, then one can utilize this property to simplify the channel estimation. Different channel models will be covered in later lectures in the 2021 edition, but generally speaking the answer is: LOS channels are modeled by spatially correlated Rician fading and NLOS channels are modeled by spatially correlated Rayleigh fading. The correlation structure depends on the propagation environment as well as carrier frequency.
Hi Emil, thanks for the nice video. I have a query to clarify my understanding to distinguish between diversity and beamforming gain. My understanding of diversity and beamforming gain is as follows: Diversity gain is the gain due to improvement in the instantaneous SNR while beamforming gain is the improvement in the average SNR. Am I right?
Hello Professor! Thank u so much for these amazing videos. Just a quick Question, at 27:07 in the video particularly, you kindly mentioned that the beam-forming gain gets the curves of the outage probability to the left, does it mean that SNR gets smaller?! As i know beam-forming gain gets Number of radiating elements * power
That the beamforming gain moves the curve to the left leads to the following: If you compare two curves for a given SNR, then the left curve will have a smaller outage probability at that SNR. If you compare two curves for a given outage probability, the left curve will achieve it at a lower SNR. So a beamforming gain is beneficial.
Communication Systems, Linköping University, LIU I was confusing about the role of diversity gain and beamforming gain. So here is what i understood: The role of beam-forming gain becomes more significant or “dominant” in LOS AWGN channel as it facilitates higher power at the point of reception and minimizes radiation in undesired directions, While the effect of the diversity gain is more beneficial or more significant in rich scattering environment (NLOS channels) As a results, fading channels-which naturally exist in our real channels- necessitate using multiple antennas which ensures regardless of how high the scattering level is, channel becomes more hardened against multi-path fading and channel capacity tends to be closer to non-fading AWGN channels with the use of multiple antennas.
Excellent work professor. I have never understood beamforming and diversity gains like this before.
It makes a lot of sense to watch this video
Nice work professor, hope to see more
Thank you professor. A simple question: how do we know the number of paths, L? Is it something that needs to be estimated a priori? Also, in directional channels, do we need to estimate the direction (e.g. DOA) of each of the L paths? I think estimating the number of paths and their directions is very common in radar, but not sure about wireless communications.
Also, it would be appreciated if you can make a lecture about the common types of channel models for sub-6 GHz and mmWave band.
We generally don't know how many paths there will be, but we can estimate it. Do we need to estimate it? Not necessarily in communications, since we are not interested in obtaining the location of the user (as in radar) but the content of the signal that the user is transmitting. But if the number of paths is small, then one can utilize this property to simplify the channel estimation. Different channel models will be covered in later lectures in the 2021 edition, but generally speaking the answer is: LOS channels are modeled by spatially correlated Rician fading and NLOS channels are modeled by spatially correlated Rayleigh fading. The correlation structure depends on the propagation environment as well as carrier frequency.
Nice videos keep uploading
Hi Emil, thanks for the nice video. I have a query to clarify my understanding to distinguish between diversity and beamforming gain. My understanding of diversity and beamforming gain is as follows:
Diversity gain is the gain due to improvement in the instantaneous SNR while beamforming gain is the improvement in the average SNR.
Am I right?
Yes, this is a good explanation. Beamforming gain gives a higher average SNR and diversity gain gives smaller variations around the average SNR.
Can you help me by giving me the name of the book from which my doctor explains I am really in big trouble
You can read about all these things in Fundamentals of Wireless Communications by Tse/Viswanath. web.stanford.edu/~dntse/wireless_book.html
Hello Professor. Can we have the slides for the lectures?
Hello Professor! Thank u so much for these amazing videos. Just a quick Question, at 27:07 in the video particularly, you kindly mentioned that the beam-forming gain gets the curves of the outage probability to the left, does it mean that SNR gets smaller?! As i know beam-forming gain gets Number of radiating elements * power
That the beamforming gain moves the curve to the left leads to the following: If you compare two curves for a given SNR, then the left curve will have a smaller outage probability at that SNR. If you compare two curves for a given outage probability, the left curve will achieve it at a lower SNR. So a beamforming gain is beneficial.
Communication Systems, Linköping University, LIU I was confusing about the role of diversity gain and beamforming gain. So here is what i understood:
The role of beam-forming gain becomes more significant or “dominant” in LOS AWGN channel as it facilitates higher power at the point of reception and minimizes radiation in undesired directions, While the effect of the diversity gain is more beneficial or more significant in rich scattering environment (NLOS channels)
As a results, fading channels-which naturally exist in our real channels- necessitate using multiple antennas which ensures regardless of how high the scattering level is, channel becomes more hardened against multi-path fading and channel capacity tends to be closer to non-fading AWGN channels with the use of multiple antennas.
Yes, this is a good summary.