International Journal For Multidisciplinary Research

E-ISSN: 2582-2160   •   Impact Factor: 9.24

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Pilot Assignment in User-Centric Cell-Free Massive MIMO: Techniques, Trade-Offs, and Open Challenges

Author(s) Mr. SYED TARIQ ALI, Dr. Anamika Singh
Country India
Abstract Pilot assignment is a critical design component in cell-free massive MIMO systems, as it directly determines the quality of channel estimation under limited pilot resources. Unlike conventional cellular massive MIMO, pilot contamination in cell-free architectures is governed by local access point–user equipment (AP–UE) coupling rather than cell boundaries, making pilot reuse decisions inherently user-centric. This paper reviews and systematizes pilot assignment techniques proposed for user-centric cell-free massive MIMO systems. Existing approaches are classified into graph-based, clustering, matching, eigenspace-aware, optimization-based, heuristic, and learning-assisted methods. Their operating principles, performance gains, complexity, and scalability are comparatively analyzed with emphasis on spectral efficiency, fairness, and implementation feasibility. The review highlights that locality-aware pilot assignment consistently outperforms network-centric reuse, particularly in dense and massive access scenarios. Key limitations related to fronthaul constraints, mobility, short coherence intervals, and robustness to imperfect statistical knowledge are identified, and promising future research directions are outlined. This work provides a structured reference for researchers and practitioners designing practical pilot assignment mechanisms for scalable cell-free massive MIMO deployments.
Keywords Cell-free massive MIMO; pilot assignment; pilot contamination; user-centric networks; spectral efficiency; access point selection; massive access; fronthaul constraints.
Field Engineering
Published In Volume 7, Issue 6, November-December 2025
Published On 2025-12-26
DOI https://doi.org/10.36948/ijfmr.2025.v07i06.64579
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E-ISSN 2582-2160
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