As there is no RF chain in the smart reflecting surface, how reflecting elements can change the angle of reflected signal? What are the limitations of IRS based wireless communication? What are difficulties that may occur during it's practical implementation? What is the possibility of its consideration beyond 5G?
Hi!
I'm explaining this in two videos on the topic:
https://youtu.be/CDt0JNrOKxk
https://youtu.be/ysSf1K2NUu0
Here are some short answers. Each "reflecting element" is not changing the angle of the reflected signal, but it is creates a time delay. This is the same thing as a phase-shift if we consider a narrowband channel. It is the combination of different phase-shifts among the elements that creates reflected beams in particularly directions.
The main limitation is how to estimate which phase-shifts that are needed to reflect the signals in the right direction and how to tell the IRS to reconfigure itself.
It is still uncertain what role an IRS might play in future networks. There are some suggested use cases, but no convincing evidence that IRS is so much better than alternative methods that it will be worth turning it into products.
You can get detail on how to achieve this on Youtube and more importantly from colleagues in a forum like this.
Dear Prof Emil, we are think of intelligent reflecting surfaces based cognitive radio networks and want to perform secrecy analysis on that. Is this the right way to proceed?
Dear Prof Emil Björnson , Both videos are very informative. Thanks for such nice explanation. I request you take the channel/angle estimation in some of your future talks.
Thanks Anand Jee for the question.
IRS contain metamaterials, they are periodic repetition of metal dielectric composite as you might be knowing, and together they are engineered to scatter a part of the signal received at such an angle that it re orients the reflected beam towards the desired receiver
Following paper describes how reflecting elements can create time delays (phase shifts) as well as more about the relationship between the phase shift and reflection amplitude of each IRS reflecting elements.
https://arxiv.org/pdf/2002.10112.pdf
Is there difference between IRS and Backscatter communication? The Backscatter transmitter can also change the phase of the incident signals and do not modulate its own message on the incident signal.
Physical angle-of-departure can be manipulated through introducing a certain phase-shift (or time-delay) at each element of IRS. With some basic assumptions (well recognized), a simple geometrical relationship between physical angle and the required phase-sihft to achieve that angle can be formed. This is similar to conventional beamforming or AoA estimation methods used for antenna arrays.
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