Scalable Cell-Free Massive MIMO Systems with Finite Resolution ADCs/DACs over Spatially Correlated Rician Fading Channels

TL;DR

This paper develops an analytical framework for scalable cell-free massive MIMO systems with finite resolution ADCs/DACs under correlated Rician fading, proposing low complexity detectors and algorithms that improve spectral efficiency and fairness.

Contribution

It introduces scalable low complexity MMSE detectors, a novel partial large-scale fading decoding scheme, and a joint AP clustering, pilot assignment, and power control algorithm for cell-free massive MIMO.

Findings

Proposed detectors achieve near-optimal spectral efficiency.

The new algorithm outperforms traditional pilot assignment methods.

Ensures QoS fairness for all users.

Abstract

In this paper, an analytical framework for evaluating the performance of scalable cell-free massive MIMO (SCF-mMIMO) systems in which all user equipments (UEs) and access points (APs) employ finite resolution digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) and operates under correlated Rician fading, is presented. By using maximal-ratio combining (MRC) detection, generic expressions for the uplink (UL) spectral efficiency (SE) for both distributed and centralized schemes are derived. In order to further reduce the computational complexity (CC) of the original local partial MMSE (LP-MMSE) and partial MMSE (P-MMSE) detectors, two novel scalable low complexity MMSE detectors are proposed for distributed and centralized schemes respectively, which achieves very similar SE performance. Furthermore, for the distributed scheme a novel partial large-scale fading decoding (P-LSFD) weighting vector is introduced and its analytical SE performance is very similar to the performance of an equivalent unscalable LSFD vector. Finally, a scalable algorithm jointly consisting of AP cluster formation, pilot assignment, and power control is proposed, which outperforms the conventional random pilot assignment and user-group based pilot assignment policies and, contrary to an equal power transmit strategy, it guarantees quality of service (QoS) fairness for all accessing UEs.