Fast Channel Estimation for IRS-Assisted OFDM

In this letter, we study efficient channel estimation for an intelligent reflecting surface (IRS)-assisted orthogonal frequency division multiplexing (OFDM) system to achieve minimum training time. First, a fast scheme with reduced OFDM symbol duration is proposed arbitrary frequency-selective fading channels. Next, under the typical condition that IRS-user line-of-sight (LoS) dominant, another based on novel concept of sampling-wise IRS reflection variation proposed. Moreover, pilot signal and pattern are jointly optimized both schemes. Finally, schemes compared in terms time performance via simulations, as well against benchmark