Pilot Power Allocation for Channel Estimation in a Multi-RIS Aided Communication System

TL;DR

This paper proposes an optimal pilot power allocation strategy for RIS-assisted wireless systems to enhance channel estimation accuracy and ergodic channel gain under practical imperfect CSI conditions.

Contribution

It derives a closed-form expression for ergodic channel gain considering estimation errors and formulates an optimal pilot power allocation method using Lagrange multipliers.

Findings

Allocating more pilot power to weak reflection channels improves ergodic gain.

The proposed allocation method outperforms uniform power allocation.

Simulation results validate the theoretical analysis.

Abstract

Reconfigurable intelligent surface (RIS) is a promising technology that enables the customization of electromagnetic propagation environments in next-generation wireless networks. In this paper, we investigate the optimal pilot power allocation during the channel estimation stage to improve the ergodic channel gain of RIS-assisted systems under practical imperfect channel state information (CSI). Specifically, we commence by deriving an explicit closed-form expression of the ergodic channel gain of a multi-RIS-aided communication system that takes into account channel estimation errors. Then, we formulate the pilot power allocation problem to maximize the ergodic channel gain under imperfect CSI, subject to the average pilot power constraint. Then, the method of Lagrange multipliers is invoked to obtain the optimal pilot power allocation solution, which indicates that allocating more power to the pilots for estimating the weak reflection channels is capable of effectively improving the ergodic channel gain under imperfect CSI. Finally, extensive simulation results corroborate our theoretical analysis.