5G massive MIMO architectures: self-backhauled small cells versus direct access

Abstract

In this paper, we focus on one of the key technologies for the fifth-generation wireless communication networks, massive multiple-input-multiple-output (mMIMO), by investigating two of its most relevant architectures: 1) to provide in-band wireless backhauling to a dense deployment of self-backhauled small cells (SCs) acting as communication relays to end-users, and 2) to provide direct wireless access (DA) to end-users. Through comprehensive 3GPP-based system-level simulations and analytical formulation, we show the end-to-end user rates achievable with these two architectures. Different from the existing work, we provide results for two strategies of self-backhauled SCs deployments, namely random and ad-hoc. Where in the latter SCs are purposely positioned close to UEs to achieve line-ofsight (LoS) access links. We also show the optimal backhaul and access time resource partition due to the in-band self-backhauling operations. For the mMIMO DA, we consider the implication of different pilot reuse schemes for the channel state information (CSI) acquisition, associated overhead and contamination effects. We find that the ad-hoc deployment of self-backhauled SCs closer to the users (UEs) with optimal resource partition and with directive antenna patterns, provides rate improvements for celledge UEs that amount to 30%, and a tenfold gain as compared to mMIMO DA architecture with pilot reuse 3 and reuse 1, respectively. On the other hand, mMIMO s-BH underperforms mMIMO DA above the median of the UE rates when the UEs are in the center of the cell, and the effect of pilot contamination is mitigated.