Channel Estimation By Transmitting Pilots From Reconfigurable Intelligent Surface

TL;DR

This paper introduces a novel RIS-transmitting channel estimation scheme that reduces pilot overhead and overcomes double-fading issues, achieving higher accuracy than traditional cascaded channel methods in wireless systems.

Contribution

The paper proposes a new RIS-transmitting channel estimation method with lower pilot overhead and improved accuracy, along with efficient gradient descent and PDD solutions for pilot design.

Findings

Outperforms DFT-based pilots in accuracy.

Reduces pilot overhead compared to cascaded channel schemes.

Achieves superior estimation accuracy for moderate RIS sizes.

Abstract

Reconfigurable intelligent surface (RIS) is a promising technology for future wireless communication systems. Channel estimation (CE) of RIS device is a critical but also challenging issue for its development. The mainstream of existing CE methods is confined to the so-called cascaded channel (CscdChn) estimation scheme, which treats the multiplicative two-hop RIS channels as an effective one and measures it as a whole. This CscdChn training method suffers from severe double-fading attenuation loss, which significantly degrades the CE accuracy. In this paper, we propose a novel RIS-transmitting (RIS-TX) based CE scheme, which has lower pilot overhead than CscdChn scheme and effectively overcomes the double-fading curse via incorporating only one single transmit radio frequency (RF)-chain into RIS. We develop highly efficient gradient descent (GD) and penalty duality decomposition (PDD)-based solutions to resolve the pilot design task for the RIS-TX CE scheme, which is a difficult quartic optimization problem. Our designed pilot signal outperforms the discrete Fourier transform (DFT) sequence, which is reported to be optimal for CscdChn scheme. Besides, both theoretical analysis and numerical results demonstrate that our proposed RIS-TX scheme exhibits distinct performance characteristics as opposed to its CscdChn counterpart and yields superior accuracy when RIS device is not extremely large.