Plug-in UL-CSI-Assisted Precoder Upsampling Approach in Cellular FDD Systems

TL;DR

This paper proposes a plug-in uplink CSI-assisted precoder upsampling method for FDD massive MIMO systems, enhancing frequency-selective channel performance without altering existing infrastructure.

Contribution

It introduces a novel uplink CSI-assisted module that upsamples subband precoders to resource block level, compatible with current gNodeB systems.

Findings

Improves precoder resolution for frequency-selective channels.

Compatible with existing cellular infrastructure.

Reduces feedback overhead effectively.

Abstract

Acquiring downlink channel state information (CSI) is crucial for optimizing performance in massive Multiple Input Multiple Output (MIMO) systems operating under Frequency-Division Duplexing (FDD). Most cellular wireless communication systems employ codebook-based precoder designs, which offer advantages such as simpler, more efficient feedback mechanisms and reduced feedback overhead. Common codebook-based approaches include Type II and eType II precoding methods defined in the 3GPP standards. Feedback in these systems is typically standardized per subband (SB), allowing user equipment (UE) to select the optimal precoder from the codebook for each SB, thereby reducing feedback overhead. However, this subband-level feedback resolution may not suffice for frequency-selective channels. This paper addresses this issue by introducing an uplink CSI-assisted precoder upsampling module deployed at the gNodeB. This module upsamples SB-level precoders to resource block (RB)-level precoders, acting as a plug-in compatible with existing gNodeB or base stations.