Channel Estimation for Double Intelligent Reflecting Surface Assisted MISO System in Sub-6G

In contrast to the single intelligent reflecting surface (S-IRS) systems, improved performance is attainable by employing double-IRS (D-IRS) in a wireless-communication system. Nevertheless, precise channel estimation is crucial in D-IRS assisted wireless communication systems for achieving significant performance enhancements. In some specialized communication scenarios, obstacles may block the communication links between IRS<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> and IRS<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>, thereby diminishing the potential gains of the D-IRS system. To tackle these challenges, this article introduces a novel D-IRS method with maximal a posterior probability rule (DMAP) for a multi-input single-output (MISO) uplink communication where the line-of-sight (LOS) link between the base station (BS) and the users are ignored. Furthermore, the BS-IRS links are harnessed as a common-link for decomposing the complex cascaded channels and IRSs are kept always “ON” in the channel estimation protocol. Finally, optimization for the phase configuration of IRSs is constructed to ensure better estimation accuracy. Experimental results show that DMAP significantly reduces pilot overhead and exceeds baseline performance levels.