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Enhancing resilience in cell-free massive MIMO networks via 2D-DOA-based zero-forcing precoding under pilot contamination
Balfaqih, Mohammed Ali, Ehab Alrayes, Mohamed Al-Hazemi, Fawaz Sabri, Fawaz
Balfaqih, Mohammed
Ali, Ehab
Alrayes, Mohamed
Al-Hazemi, Fawaz
Sabri, Fawaz
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Date
2025-09-26
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Abstract
Cell-free massive MIMO networks offer significant advantages in spectral and energy
efficiency due to their macro-diversity and distributed architecture. However, the resil‑
ience of such systems is challenged by pilot contamination and multi-user interference,
particularly in dense deployments where pilot reuse is inevitable. This study proposes
a robust and scalable zero-forcing precoding technique based on two-dimensional
direction-of-arrival (2D-DOA) estimation to improve network reliability and interference
suppression without requiring channel state information (CSI) exchange among access
points (APs) or additional pilot overhead. The zero-forcing precoding is aided with DOA
information to separate between various users by exploiting the spatial diversity
of the correlated channels or allowing spatial multiplexing by antenna weights
adaptation based on the characteristics of the channels. By leveraging 2D-UESPRIT
and 2D-FDLSM algorithms, the proposed approach mitigates both intra- and intercell interference, enhancing system resilience against pilot contamination. A closedform expression for downlink spectral efficiency is derived, accounting for practical
limitations such as imperfect CSI. Simulation results show that the proposed method
achieves near-optimal performance—reaching up to 99.1% of the spectral efficiency
of a deterministic benchmark based on ideal, interference-free conditions—while sig‑
nificantly outperforming conventional systems under pilot contamination. These find‑
ings demonstrate that integrating 2D-DOA-based precoding enhances the robustness
and adaptability of cell-free massive MIMO systems, contributing to the development
of resilient wireless networks capable of sustaining high performance under real-world
constraints.
Keywords: Cell-free Massive-MIMO, Zero forcing precoding, 2D-direction of arrival
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Univeristy of jeddah
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CC0 1.0 Universal