Toward Ultradense Small Cell Networks: A Brief History on the Theoretical Analysis of Dense Wireless Networks

Abstract

This article dives into the fundamentals of dense and ultradense small cell wireless networks, discussing the reasons why dense and ultradense small cell networks are fundamentally different from sparse ones, and why the well‐known linear capacity scaling law with the base station (BS) density in the latter does not apply to the former. In more detail, we review the impact of the following factors on ultradense networks (UDNs): (i) closed‐access operations and line‐of‐sight conditions, (ii) the near‐field effect, (iii) the antenna height difference between small cell BSs and user equipment (UE), and (iv) the surplus of idle‐mode‐enabled small cell BSs with respect to UEs. Combining all these network characteristics and features, we present a more realistic capacity scaling law for UDNs, which indicates (i) the existence of an optimum BS density to maximize the area spectral efficiency (ASE) for a given finite UE density and (ii) the existence of an optimum density of UEs that can be simultaneously scheduled across the network to maximize the ASE for a given finite BS density.