Overloaded Pilot Assignment with Pilot Decontamination for Cell-Free Systems

The pilot contamination in cell-free massive multiple-input-multiple-output (CF-mMIMO) must be addressed for accommodating a large number of users. In previous works, we have investigated a decontamination method called subspace projection (SP). The SP separates interference from co-pilot users by u...

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Bibliographic Details
Published in:arXiv.org 2022-10
Main Authors: Osawa, Noboru, Göttsch, Fabian, Kanno, Issei, Ohseki, Takeo, Amano, Yoshiaki, Yamazaki, Kosuke, Caire, Giuseppe
Format: Article
Language:English
Subjects:
Decontamination
Orthogonality
Overloading
Subspaces
System effectiveness
Online Access:Get full text
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Summary:The pilot contamination in cell-free massive multiple-input-multiple-output (CF-mMIMO) must be addressed for accommodating a large number of users. In previous works, we have investigated a decontamination method called subspace projection (SP). The SP separates interference from co-pilot users by using the orthogonality of the principal components of the users' channel subspaces. Non-overloaded pilot assignment (PA), where each radio unit (RU) does not assign the same pilot to different users, limits the spectral efficiency (SE) of the system, since SP channel estimation is able to deal with co-pilot users that have nearly orthogonal subspaces. Motivated by this limitation, this paper introduces overloaded PA methods adjusted for the decontamination in order to improve the sum SE of CF systems. Numerical simulations show that the overloaded PA methods give higher SE than that of non-overloaded PA at a high user density scenario.
ISSN:2331-8422