Technology Category
Search and Optimization: Algorithm ConfigurationPlanning, Routing, and Scheduling: Optimization of Spatio-temporal SystemsIntelligent Robots: Learning & Optimization for ROB
RIS-Assisted XL-MIMO for Near-Field and Far-Field Communications
🤖 AI Summary
This work addresses the coexistence of near-field (NF) and far-field (FF) users in RIS-aided XL-MIMO downlink systems, where FF channels suffer from severe blockage. We propose a joint optimization framework for RIS phase-shift design and base station power allocation to maximize weighted minimum spectral efficiency (WMMSE). To reduce precoding complexity, we introduce a novel visible-region selection algorithm and devise a two-stage optimization scheme. Closed-form statistical expressions for spectral efficiency under CZF, LZF, and MRT precoding are derived analytically, enabling joint RIS phase-shift and power control design. Simulation results demonstrate that, compared to equal-power allocation with random RIS phase shifts, the proposed method improves WMMSE by 31.9%, 37.8%, and 119.2% under CZF, LZF, and MRT, respectively. CZF achieves the best overall performance, while LZF offers a favorable trade-off between low computational complexity and flexible user prioritization.
Technology Category
Application Category
📝 Abstract
We consider a reconfigurable intelligent surface (RIS)-assisted extremely large-scale multiple-input multiple-output (XL-MIMO) downlink system, where an XL-MIMO array serves two groups of single-antennas users, namely near-field users (NFUEs) and far-field users (FFUEs). FFUEs are subject to blockage, and their communication is facilitated through the RIS. We consider three precoding schemes at the XL-MIMO array, namely central zero-forcing (CZF), local zero-forcing (LZF) and maximum ratio transmission (MRT). Closed-form expressions for the spectral efficiency (SE) of all users are derived for MRT precoding, while statistical-form expressions are obtained for CZF and LZF processing. A heuristic visibility region (VR) selection algorithm is also introduced to help reduce the computational complexity of the precoding scheme. Furthermore, we devise a two-stage phase shifts design and power control algorithm to maximize the sum of weighted minimum SE of two groups of users with CZF, LZF and MRT precoding schemes. The simulation results indicate that, when equal priority is given to NFUEs and FFUEs, the proposed design improves the sum of the weighted minimum SE by 31.9%, 37.8%, and 119.2% with CZF, LZF, and MRT, respectively, compared to the case with equal power allocation and random phase shifts design. CZF achieves the best performance, while LZF offers comparable results with lower complexity. When prioritizing NFUEs or FFUEs, LZF achieves strong performance for the prioritized group, whereas CZF ensures balanced performance between NFUEs and FFUEs.
Problem
Research questions and friction points this paper is trying to address.
Optimizing RIS-assisted XL-MIMO for near-field and far-field users
Designing precoding schemes and phase shifts to maximize spectral efficiency
Reducing computational complexity in multi-user XL-MIMO systems
Innovation
Methods, ideas, or system contributions that make the work stand out.
RIS-assisted XL-MIMO for near/far-field communications
Heuristic VR algorithm reduces precoding complexity
Two-stage phase/power control maximizes weighted SE
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