Ultra-Dense Networks: Is There a Limit to Spatial Spectrum Reuse?

TL;DR

This paper investigates the fundamental limits of spatial spectrum reuse in ultra-dense networks, revealing that capacity saturates due to bounded signal and interference powers, and identifying an optimal SSR density for maximum capacity.

Contribution

It provides the first theoretical analysis showing capacity bounds in UDNs and introduces the concept of an optimal SSR density, guiding future network deployment strategies.

Findings

Signal and interference powers become bounded in practical UDNs.

Capacity reaches a constant limit despite increasing densification.

An optimal SSR density exists to maximize network capacity.

Abstract

The aggressive spatial spectrum reuse (SSR) by network densification using smaller cells has successfully driven the wireless communication industry onward in the past decades. In our future journey toward ultra-dense networks (UDNs), a fundamental question needs to be answered. Is there a limit to SSR? In other words, when we deploy thousands or millions of small cell base stations (BSs) per square kilometer, is activating all BSs on the same time/frequency resource the best strategy? In this paper, we present theoretical analyses to answer such question. In particular, we find that both the signal and interference powers become bounded in practical UDNs with a non-zero BS-to-UE antenna height difference and a finite UE density, which leads to a constant capacity scaling law. As a result, there exists an optimal SSR density that can maximize the network capacity. Hence, the limit to SSR should be considered in the operation of future UDNs.