Evolution of UE in Massive MIMO Systems for 6G: From Passive to Active

TL;DR

This paper reviews the evolution of user equipment (UE) in massive MIMO systems from passive to active roles in 6G, highlighting standardization, implementation challenges, and the benefits of UE-initiated beam management and multi-panel architectures.

Contribution

It provides a comprehensive review of UE role evolution from 3GPP Releases 15 to 19, emphasizing architectural innovations and practical implementation challenges for 6G.

Findings

UE-initiated beam reporting improves throughput in mobility scenarios

Multi-panel UE architectures enhance link robustness

AI/ML-based CSI enhancement advances system performance

Abstract

As wireless networks continue to evolve, stringent latency and reliability requirements and highly dynamic channels expose fundamental limitations of gNB-centric massive multiple-input multiple-output (mMIMO) architectures, motivating a rethinking of the user equipment (UE) role. In response, the UE is transitioning from a passive transceiver into an active entity that directly contributes to system-level performance. In this context, this article examines the evolving role of the UE in mMIMO systems during the transition from fifth-generation (5G) to sixth-generation (6G), bridging third generation partnership project (3GPP) standardization, device implementation, and architectural innovation. Through a chronological review of 3GPP Releases 15 to 19, we highlight the progression of UE functionalities from basic channel state information (CSI) reporting to artificial intelligence (AI) and machine learning (ML)-based CSI enhancement and UE-initiated beam management. We further examine key implementation challenges, including multi-panel UE (MPUE) architectures, on-device intelligent processing, and energy-efficient operation, and then discuss corresponding architectural innovations under practical constraints. Using digital-twin-based evaluations, we validate the impact of emerging UE-centric functionalities, illustrating that UE-initiated beam reporting improves throughput in realistic mobility scenarios, while a multi-panel architecture enhances link robustness compared with a single-panel UE.