RIS-Assisted Statistical Channel Shaping for Ultra-High Reliability

We investigate a recently proposed phase hopping scheme for reconfigurable intelligent surfaces (RISs), in which the phases of the RIS elements are varied with each transmitted symbol. It was previously shown that this can significantly improve the reliability of a slow fading channel without the need for exact channel state information (CSI) at the transmitter or RIS. In this work, we will consider an RIS-assisted communication scenario which employs phase hopping. In addition, we take the limitation into account that the phase of each RIS element can only be chosen from a finite set of possible phase values. It is shown that for RIS with a large number of elements, the resulting reliability approaches the one with continuous phases. This implies that phase hopping allows ultra-reliable communications even with quantized phases at the individual RIS elements.