Pilot Length Minimization via AP-UE Clustering in Cell-Free Systems

Chowdhury, A and Murthy, CA (2024) Pilot Length Minimization via AP-UE Clustering in Cell-Free Systems. In: 49th IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2024, April 14-19 2024, Seoul, pp. 9216-9220.

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Abstract

The benefits of cell-free multiple-input multiple-output (CF MIMO) systems over traditional cellular systems, viz., a dramatic improvement of spectral efficiency (SE) and uniform quality of service, crucially depend on the quality of the estimated channels at the access points (APs). However, in a CF MIMO system, where a large number of user-equipments (UEs) are served by distributed APs, ensuring pilot contamination-free channel estimates across all the APs requires inordinately high pilot length, which substantially reduces the time available for data transmission. This paper proposes a novel pilot design and allocation algorithm that ensures no pilot contamination among any pair of UEs that are proximal to a common AP, and this is guaranteed at all APs. Further, our algorithm procures the pilot allocation with a minimum number of orthogonal pilots being reused across the UEs. Specifically, we recast the problem as a graph-vertex coloring problem and solve it via a low-complexity algorithm known to be optimal for all bipartite graphs. Unlike existing solutions, our algorithm does not require additional signaling overhead, e.g., signal-to-interference plus noise ratio exchanges, for pilot assignment. Numerical results illustrate the superiority of the proposed technique over existing methods from the literature. © 2024 IEEE.

Item Type:	Conference Paper
Publication:	ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings
Publisher:	Institute of Electrical and Electronics Engineers Inc.
Additional Information:	The copyright for this article belongs to Institute of Electrical and Electronics Engineers Inc.
Keywords:	Channel estimation; Computational complexity; Graph theory; MIMO systems; Numerical methods; Quality of service; Signal to noise ratio, Access points; Cell-free; Cell-free system; Clusterings; Distributed MIMO; Graph colorings; Minimisation; Multiple-Input Multiple- Output systems; Pilot contaminations; User equipments, Spectrum efficiency
Department/Centre:	Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited:	02 Sep 2024 11:10
Last Modified:	02 Sep 2024 11:10
URI:	http://eprints.iisc.ac.in/id/eprint/85982

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