of RF chains).'
author:
- 'Guillem Femenias,  and Felip Riera-Palou,  [^1]'
bibliography:
- 'Cell\_free\_Hybrid\_precoding.bib'
title: 'Cell-Free Millimeter-Wave Massive MIMO Systems with Limited Fronthaul Capacity'
---

Cell-free, Massive MIMO, Millimeter Wave, Hybrid precoding, Constrained-capacity fronthaul

Introduction
============

Motivation and previous work
----------------------------

by the continuously increasing demands for high system throughput, low latency, ultra reliability, improved fairness and near-instant connectivity, wireless communication networks are being standardized [@Shafi17] while, at the same time, insights and innovations from industry and academia are paving the road for the coming of the [@David18]. As stated by Marzetta *et al.* in [@Marzetta16 Chapter 1], there are three basic pillars at the physical layer that can be used to sustain the spectral and energy efficiencies that these networks are expected to provide: (i) employing massive , (ii) using deployments, and (iii) exploiting new frequency bands.

Massive systems, equipped with a large number of antenna elements, are intended to be used as arrangements in which the number of antenna elements at each is much larger than the number of simultaneously served over the same time/frequency resources. The operation of massive schemes is based on the availability of acquired through operation and the use of pilot signals. Such a 