How to Train Intelligent Reflecting Surfaces?

Abstract

This letter discusses the rationale of Intelligent Reflecting Surface (IRS) based transmission, state-of-the-art methods available for IRS training, and their challenges. Though IRS is known for its ability to constructively combine several multipath components by using their phase information, extracting the phase information for a large number of IRS elements requires extensive training overhead. This work proposes a multi-mode grouping method for low overhead IRS training and moderate combining benefit. Moreover, the letter includes directions to adaptively utilize user’s mobility and(or) quality of service requirement for the appropriate mode selection.