Coverage Analysis and Load Balancing in HetNets with mmWave Multi-RAT Small Cells

TL;DR

This paper analyzes coverage and load balancing in heterogeneous networks with macro cells and multi-RAT small cells operating in sub-6GHz and mm-wave bands, proposing bias-based mechanisms to optimize performance.

Contribution

It introduces a two-step bias tuning mechanism for tier and RAT selection, optimizing coverage and throughput in dual-band small cell deployments.

Findings

Optimal biases for maximizing SINR coverage and user throughput identified.

Derived upper bounds on cell overloading probabilities.

Provided small cell density requirements to meet system constraints.

Abstract

We characterize a two tier heterogeneous network, consisting of classical sub-6GHz macro cells, and multi Radio Access Technology (RAT) small cells able to operate in sub-6GHz and millimeter-wave (mm-wave) bands. For optimizing coverage and to balance loads, we propose a two-step mechanism based on two biases for tuning the tier and RAT selection, where the sub-6GHz band is used to speed-up the initial access procedure in the mm-wave RAT. First, we investigate the effect of the biases in terms of signal to interference plus noise ratio (SINR) distribution, cell load, and user throughput. More specifically, we obtain the optimal biases that maximize either the SINR coverage or the user downlink throughput. Then, we characterize the cell load using the mean cell approach and derive upper bounds on the overloading probabilities. Finally, for a given traffic density, we provide the small cell density required to satisfy system constraints in terms of overloading and outage probabilities. Our analysis highlights the importance of deploying dual band small cells in particular when small cells are sparsely deployed or in case of heavy traffic.