Scalable cell-free massive MIMO systems with hardware impairments

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This is the accepted manuscript version of a conference paper which has been published in final form at https://doi.org/10.1109/PIMRC48278.2020.9217151Despite the deleterious effect of hardware impairments (HWIs) on wireless systems, most prior works in cell-free (CF) massive multiple-input-multiple-output (mMIMO) systems have not accounted for their impact. In particular, the effect of phase noise (PN) has not been investigated at all in CF systems. Moreover, there is no work investigating HWIs in scalable CF (SCF) mMIMO systems, encountering the prohibitively demanding fronthaul requirements of large networks with many users. Hence, we derive the uplink spectral efficiency (SE) under HWIs with minimum mean-squared error (MMSE) combining in closed-form by means of the deterministic equivalent (DE) analysis. Notably, previous works, accounted for MMSE decoding, studied the corresponding SE only by means of simulations. Numerical results illustrate the performance loss due to HWIs and result in insightful conclusions

Coverage Probability of Cell-Free Massive MIMO Systems

© 2020 IEEE. This is the accepted manuscript version of an article which has been published in final form at 10.1109/BlackSeaCom48709.2020.9235025Despite that ongoing and future networks become denser and increasingly irregular, prior works in the area of cell-free (CF) massive multiple-input-multiple-output (mMIMO) systems relied on the strong assumption of uniformly distributed access points (APs). Actually, this randomness was accounted for only during the simulation and not in the analysis. Consequently, the direction of this paper is towards the application and investigation of a more realistic model for the spatial randomness of the APs in terms of a Poisson point process (PPP). Specifically, we derive the downlink coverage probability (CP) of CF mMIMO systems by means of stochastic geometry and deterministic equivalent tools. Notably, it is the only work having derived the CP for CF mMIMO systems. Among the results, we highlight the outperformance of CF mMIMO systems against small cells (SCs), which increases with the density of the APs due to channel hardening, favorable propagation, and interference suppression. Moreover, we observe the saturation of the CP at high AP density