Chapter 1: The RIS Concept

Learning Objectives

• State the RIS system model and identify the roles of $\mathbf{H}_1$, $\boldsymbol{\Phi}$, and $\mathbf{H}_2$ in the cascaded channel
• Derive the coherent $\mathcal{O}(N^2)$ SNR scaling law and contrast it with the $\mathcal{O}(N)$ scaling of random reflection
• Explain the product path-loss phenomenon and why it makes RIS placement near the BS or near the UE advantageous
• Compare RIS with relays, repeaters, and active antennas along power, spectral, and hardware axes
• State the unit-modulus constraint and explain why it makes passive beamforming optimization non-convex