Optimal Base Station Antenna Downtilt in Downlink Cellular Networks

TL;DR

This paper investigates how optimizing base station antenna downtilt can significantly improve downlink cellular network capacity and delay the ASE crash in ultra-dense networks by deriving analytical and numerical solutions.

Contribution

It introduces a method to determine the optimal antenna downtilt based on base station density to enhance network performance and mitigate the ASE crash.

Findings

Optimal downtilt maximizes coverage probability.

Applying optimal downtilt delays the ASE crash by nearly an order of magnitude.

Theoretical and numerical results confirm performance improvements.

Abstract

From very recent studies, the area spectral efficiency (ASE) performance of downlink (DL) cellular networks will continuously decrease and finally to zero with the network densification in a fully loaded ultra-dense network (UDN) when the absolute height difference between a base station (BS) antenna and a user equipment (UE) antenna is larger than zero, which is referred as the ASE Crash. We revisit this issue by considering the impact of the BS antenna downtilt on the downlink network capacity. In general, there exists a height difference between a BS and a UE in practical networks. It is common to utilize antenna downtilt to adjust the direction of the vertical antenna pattern, and thus increase received signal power or reduce inter-cell interference power to improve network performance. This paper focuses on investigating the relationship between the base station antenna downtilt and the downlink network capacity in terms of the coverage probability and the ASE. The analytical results of the coverage probability and the ASE are derived, and we find that there exists an optimal antenna downtilt to achieve the maximal coverage probability for each base station density. Moreover, we derive numerically solvable expressions for the optimal antenna downtilt, which is a function of the base station density. Our theoretical and numerical results show that after applying the optimal antenna downtilt, the network performance can be improved significantly. Specifically, with the optimal antenna downtilt, the ASE crash can be delayed by nearly one order of magnitude in terms of the base station density.