Impact of Pilot Contamination Between Operators With Interfering Reconfigurable Intelligent Surfaces

TL;DR

This paper investigates how pilot contamination occurs between operators in RIS-assisted networks and proposes orthogonal RIS configurations to eliminate it, significantly enhancing channel estimation accuracy and system performance.

Contribution

It introduces a novel analysis of inter-operator pilot contamination in RIS-assisted systems and proposes a practical solution using orthogonal RIS configurations.

Findings

Orthogonal RIS configurations eliminate pilot contamination.

Significant improvement in channel estimation accuracy.

Enhanced system performance and reduced bias.

Abstract

In this paper, we study the impact of pilot contamination in a system where two operators serve their respective users with the assistance of two wide-band reconfigurable intelligent surfaces (RIS), each belonging to a single operator. We consider one active user per operator and they use disjoint narrow frequency bands. Although each RIS is dedicated to a single operator, both users' transmissions are reflected by both RISs. We show that this creates a new kind of pilot contamination effect when pilots are transmitted simultaneously. Since combating inter-operator pilot contamination in RIS-assisted networks would require long pilot signal sequences to maintain orthogonality among the users of different operators, we propose the orthogonal configurations of the RISs. Numerical results show that this approach completely eliminates pilot contamination, and significantly improves the performance in terms of channel estimation and equalization by removing the channel estimation bias.