Reconfigurable Intelligent Surfaces Through the Lens of Array Signal Processing

Recording of the keynote speech that Prof. Emil Björnson delivered at the IEEE CAMSAP 2023 (https://camsap23.ig.umons.ac.be) and IEEE SITB 2024 (https://sites.google.com/view/sitb2024/).

Abstract:
Wireless communication systems have traditionally been designed to operate under the channel conditions provided by nature, with the Shannon capacity being the ultimate limit. The advent of reconfigurable intelligent surfaces (RIS) changes the status quo by adding the ability to control wave propagation, thereby modifying the capacity. A RIS is an array of reflecting elements with properties that can be tuned to synthesize the reflection behavior of a differently shaped object. The larger the surface is, the greater performance improvements are possible. The gains are achieved by adapting the RIS configuration to the channel coefficients from the transmitter to the receiver via the RIS, which must be estimated in practice. The estimation challenge grows with the number of reflecting elements, in terms of the signal resources required for pilot signaling. The problem differs from the classical estimation problems in multi-antenna communications because the RIS is blind and substantially larger. Hence, the estimation dimensionality might be the showstopper for practical RIS deployments. In this talk, we will look at how array signal processing theory provides suitable tools to describe and analyze RIS-aided communication systems. We will explore how these tools enable us to model the physical channels and discover how to simplify the channel estimation problem by exploiting fundamental properties, such as the array geometry, array responses, and channel geometry. It turns out that, under the right circumstances, array processing methodology can solve the estimation challenge. The talk will end with an outlook on unsolved showstoppers for RIS technology.

The slides can be downloaded here:
https://github.com/emilbjornson/prese...