We have now released the ninth episode of the podcast Wireless Future, with the following abstract:
In this episode, Emil Björnson and Erik G. Larsson answer questions from the listeners on the topic of reconfigurable intelligent surfaces. Some examples are: What kind of materials are used? When can the technology beat traditional relays? How quickly can one change the surface’s configuration? Are there any real-time experiments? How can the research community avoid misconceptions spreading around new technologies?
You can watch the video podcast on YouTube:
You can listen to the audio-only podcast at the following places:
6 thoughts on “Episode 9: Q/A on Reconfigurable Intelligent Surfaces”
Emil, Erik, thanks for a very nice and informative episode. You have touched upon possible regulatory issues. Could you discuss in some details, e.g., how does a RIS depend on carrier frequency? How does a RIS affect other service providers using different frequencies in the same service area?
Hi Hong, thank you for listening!
Figure 3 in the following paper show the frequency response of an RIS element, for a particular implementation:
I think that similar behaviors will appear also for other implementations. The RIS might have a stable frequency response for a few hundred MHz. Since there is no bandpass filtering, the RIS will also affect the channels of other service providers in the same area.
Dear Professor, Thank you for this educational episode! I’m not sure what the role of the RIS is. According to reports, RIS can modify the propagation environment and act as a mirror or scatter. But, regardless of the incoming signal’s AoA, can the RIS simply reflect it at a specific angle? If yes, how can we accomplish this?
Yes, the RIS can change the angle of the reflected signal. You can think of it like rotating the mirror to control the reflection angle, but it is done electrically by changing the properties of the surface: One adds different amounts of phase shifts to different parts of the surface to mimic the effect of a mechanical rotation. We discuss it further in this paper: https://arxiv.org/pdf/1911.03359.pdf
Thanks for your kind reply! I have read this paper, and it says the phase shift of the RIS is designed according to the AoA of the incoming signal $theta_i$ and the AoD of the reflected signal $theta_r$. However, for a mirror, no matter what the AoA of incoming signal is, the AoD of the reflected signal is always equal to the AoA. Can IRS just acts like a “magic mirror” to reflect the signal with a certain angle shift $c$ when the phase shift of the IRS is irrelated with the AoA of the incoming signal but only related with the certain angle shift $c$ ?
Yes, it can act as a magic mirror in that way. The phase shifts are moving the reflection angle from what you would expect from Snell’s law. Equation (13) says how much it needs to be shifted. It depends both on the incident angle and the desired reflection angle.